I did this on my XC60 today, thanks to this excellent video. I would also add, listen to the information regarding applying heat gently for around ten minutes. I discovered how important this is. I also found that mine had the bracket that was mentioned but it had never been bolted in place so I'll be doing that as well with what looks like 7mm bolts. Mine is a late 2011. Great video!😊
I always find your videos very informative and this one is not an exception. Keep up your good work because it helps us Volvo owners. Hope to see more soon!
Absolutely insane, last time I was servicing my Volvo XC60 at the dealership, I asked the tech about the oil leak. He said it was normal and just tightened the nipple bolt. Of course without result :S So perfect video now I can fix it on my car too.
Just did this on my V70 D5. Made a huge difference to the amount of oil dripping down the front of my engine. Easy to do. My nipple had no hose clamp. It's clear that this part of the ductwork gets VERY hot.
Yesterday when I have changing the engine oil on my Volvo XC70 D5 a i found a lot of oil near vent nipple. I was wondering from where the oil leaks out and now i am checking your videos and find another perfect advice. Thank you so much ! You are making a GREAT demonstration how to fix it. Once again thank you.
Been looking like crazy for what this was. Then I found this video and know I know what to do! Awesome video! I don't have the hose clamp, not that it doesn't do much since it's two pieces of hard plastic. My car luckily had the bracket... So I only need to fix the nipple. Thanks again for the video
Oil was spotted on my under-tray when using your transmission flush method. So I found myself here, and it's exactly as your 0:55 example, a completely loose nipple and an oily mess on my 2013 XC70. Plus a small hole had been rubbed in that box thingy. A quick measure suggests I need to buy a 30 mm dia hose clamp in case that helps anyone else. Next job is to buy the missing bracket. Many thanks!
I have the similar setup on my XC70 III with 2.4D. Mine has quite big leak around here. Now I know this is probably it. And even more, the added clamp has started to damage nearby wires. I am glad I noticed that early.
I wonder if you will be able to remove it next time, after adding the rubber sealant! I would use PTFE sealing tape which is both oil and petrol resistant, and also temperature resistant up to 260 'C .
Coming back to this video 6 years later to add an update - a few years after doing the fix shown in the video there is still oil seeping through that nipple. My car is 2011 and it seems it has now developed a leak through the connector of the heated nipple - there is oil iside the connector that has rubber seal to keep moisture coming in from outside. I'm guessing the slots for pins inside the connector are not tight enough and especially after oil change when oil is cleaner and thinner it manages to get through there. My suggestion is that if you are planning the fix shown in video, first unplug then connector and check if there is oil inside - maybe the nipple needs to be replaced as well. It is not so easy to change the nipple after it has been installed with sealant.
Hello and thank you for the time that you spend to help the volvo owners, i had the same problem (as most of us) and i fix it with two "o" ring, since i did that, no more oil ! i'm a plumber... ha ha...that why i decide to fix it with a joint ;-)
Thank you. I did this over the weekend on my new D3 V70. It was so loose it just pulled out with no resistance! I managed to clean and seal it without removing the whole pipe (largely because I couldn't get the intake pipe out and didn't want to break it in the process!). I was getting the occasional code for low boost pressure, and the values for 'requested' vs actual were always out. It *seems* to be better now, so perhaps this was the cause? Have just ordered the bracket, as also missing on mine. Perhaps not so important on a D3 but figured it can't do any harm.
To use a hairdryer are very good tip. Aswell I been working on this on a hot day and after driving so i have spend about 5 min to remove the heater seansor.
Great guides thanks, gotta fix my XC70 MY16, with all of these problems, no bracket, worn plastic/wires, leaking oil even with the clamp there etc. But of curiosity where is this oil coming from? Is it oil in the air from the crankcase, but why is this air fed back info the inlets like this?
Really, I said few days ago, I will say you again: as I bought V70 P3 D5, I wenn to YT and made sub. your channel. Thanky man. I just so few mins ago that leak and saw this on your channel.
Good afternoon. I have followed your videos and they have been very good at doing all the maintenance on my xc60 (2.4 d). I have never had any problem with my car but a few days ago I noticed oil leaks in the crankcase and a drop in the oil level. I suspect it's the PCV valve. Do you have any videos about this? Could you give me some advice? There are also traces of oil in the thick tube that goes to the intercooler. Thank you so much.
Hi, I recently did an oil change on my XC60 D5, and a month or so later I have the warning message, "Engine service system" appeared. After reading about the issue, I wondered if I had over filled the oil (It got 6 litres) and maybe this was the cause of the light coming on. Today I took the bottom engine cover off, and there is oil on the bottom of the turbo and sign of it running down the intake pipe from the top of the engine. Checking the top of the engine, the intake pipe clip where it goes down the back of the engine is oil fouled and dirty. It appears the excess of oil I created at service time has been blown out of that nipple joint. The oil level readout is full, I actually drained out 300ml of oil to lower it slightly, although this made no difference to what the gauge showed me. However I plan to run the car a few more days to check for further leaks and then carry out this modification to the nipple. I doubt I will be able to reset the engine system light ?? Great video and thank you for sharing.
@@bogdanmoga6117 I had the same problem. Oil leaking from the low pressure turbo inlet. Replaced the seal. Almost 100% sure the oild cam from that nipple. Closing it off better and having no leakage will not change the amount of oil getting into the turbo. I wonder if anyone has found the culprit yet. high crank case pressure??
Hello. Thanks for your interesting video! My XC60 D5 is also leaking here. I'm currently looking for a hissing sound when the turbocharger kicks in, which I can't find. There is no oil contamination or damage to the charge air line anywhere. My question: Can such a noise also occur on the suction side of the charge air system? Then the repair you described would be a solution. Thank you very much Eric 
Why does it leak here anyway? Surely there is negative pressure in the charge air hose so what pushes the oil out? Great vid btw sealed mine with ptfe tape round the spigot and nipped up with jubilee clip.
Hi. Great and informative video. I did the same as you, using a silicon gaskdt sealer. However I started worriyng afterwords. What will happen if small pieces of the silicon material falls off and get sucked down into the intake? Has anyone thought of this risk? And if so, where could it potentially end up getting stuck? What are your thoughts about this? Best regards from Sweden
I already did this modification but the oil still leaking. After our investigation with my volvo mechanic who works in an official dealership we found that the source of the oil is the nipple's electrical connector itself. He confirmed that this is a very common issue on these engines and there is nothing to do with it due to the shitty design...
I am 100% sure your leakage from the connector is also just a symptom of oil that should not be there in the first place. My idea is that the crankcase pressure is too high... spitting oil into the turbo inlet... anyone has found the solution
Could you please tell me how to remove safely the air inlet pipe? I mean the brackets and their bolts are really tight. I'm afraid the mounts on the pipe will break during the removing.
Thank you Man! I have '12 d4 awd volvo, and 2 years ago I noticed the problem. I told to the local Volvo dealer and they cleaned it, furthermore, they said, they fix the problem. 2 weeks ago, I checked again, but it is dirty again. I thought it is an induvidual problem, but it seems, it isn't. Thank you for the solution. If I fix it, that will not cause any problem when you need take out the nipple because any reason? Thank you for your videos!
Hi, any plans to instal a oil cach can for the diesel engine? I have a 2.4d from 2008 and i'm wonderrig what kit should i use and where to instal it. It could affect the PCV sistem? Thanks in advance.
Hi, i have an S60 2008 2,4D D5244T5 engine not the same as volvosweden but i do wanna know due there are two tube one going to the rocket cover and one going to the air inlet before the turbo. and i dont whant oil in my turbo and i dont want my valves and or inletmanifold to gunk up.
@@2bias82 this is why we need to find out why the oil is sucked into the turbo inlet in the first place. suction too hard? or just crankcase pressure too high??
Hi, thanks this very usefull video. I had the same problem. I saved 550 euros thanks to you. One question, how did you repair the oil separator? With this same glue?
Firstly…your content is brilliant. Having just purchased a 2013 s60 with D5204T7 engine, your videos are already a massive help. Im needing to do this very leak fix..but I wonder if it is worse due to blocked crankcase ventilation. What would be you check to confirm this? I have zero vacuum on oil filler cap, but unsure if this is a valid test for this engine. If it is blocked can it be cleaned or is a replacement (which include filter housing..) needed.
Great video as always and another job to do on my xc70 . Quick question - i am finding it really hard to locate the part no 30741409 ( securing bracket )on any site . Could you post a link to where you got it please ? Thanks
+Lorcán Sweetman After this video was posted this part got sold all over. Check with the dealer. They could back order it. It's my friends XC70 D4 and he was the one ordering. Good luck.
Mine is doing the exact same, will this result in intake air leakage? I am having an air intake issue which my mechanic can't solve but I've found this issue.
Hi. I have DTC's on my 2014 Volvo XC70 D4 50.000km. p023600 and p029900. I have replaced the MAP-sensor 31216308 and I have also resealed the heated crankcase vent nipple. But the code still comes. The engine runs like normal. Is there any normal standard faults on there engines?
@@bogdanmoga6117 Hi Bogdan. The sensor 31216308 that i first replaced is a boost sensor, the MAP sensor(31303974) is located on the left side of the intercooler. When i replaced that the problem went away.
My xc60 has the same problem. My turbo makes a whistle when I accelarate in high gear in low velocity untill reaching higher rpm, then stops the whistle. Is this related?
Comment my Mercedes - Benz Blue TEC diesel has similar problem. The first real issue, in either case, is potential for vacuum leak and creating a code or drivability problems due to that. The second issue is much more serious that is the oil leakage, caused as this from the positive crankcase vent "PCV" for the engine. Now forever all PCV systems have caused oil to enter into the inlet of the engine... any engine where the PCV system causes crankcase gas to be drawn into the inlet of the engine. The the oil leaking from the rod bearings and sprayed on the underside of the pistons in the crankcase becomes entrained as a mist with the crankcase gas by the pumping action in the crankcase. The crankcase gas is from the blow-by caused the piston rings sealing normal leakage, and air vented into the crankcase. When the PCV system draws the gas and oil mist into the intake system this creates first the benefit of the engine burning the resulting toxic gases and oil mist resulting in reduced emissions, approximately 1/2 the total emissions from the engine. But it also creates the problem of contaminating Mass Airflow sensors, with oil either preventing them from working, damaging them or ruining them. And in modern highly emission controlled engines it is made worse because of hot and soot filled Exhaust Gas Recirculation EGR is introduced into the inlet manifold to create the problem of sludge and coking of the oil. The sludge, coking of oil, and grit is formed by the oil from the PCV system; the soot in the exhaust gas in the EGR gases, and; the heat from the EGR gases creating the sludge, coking, abrasive particles, and hard black deposits found in modern car inlet manifolds, and on the inlet port and valve surfaces. From research I was involved in about 30 years ago we found than by removing either any one of the causes prevented these problems... removing either soot [unburned or incompletely burned hydrocarbons], oil [wet hydrocarbon that tends to stick to the soot] or the heat from the exhaust gas solves the problem, the heat must not exceed even the comparatively low temperature of 125 degrees C. The oil is easiest to remove by using a coalescing filter or catch can combination to remove the oil mist. It is hard to remove the heat. Removing the soot is impossible!
I did this on my XC60 today, thanks to this excellent video. I would also add, listen to the information regarding applying heat gently for around ten minutes. I discovered how important this is. I also found that mine had the bracket that was mentioned but it had never been bolted in place so I'll be doing that as well with what looks like 7mm bolts. Mine is a late 2011. Great video!😊
Aver vous des foto svp du support non boulonner
I always find your videos very informative and this one is not an exception. Keep up your good work because it helps us Volvo owners. Hope to see more soon!
Absolutely insane, last time I was servicing my Volvo XC60 at the dealership, I asked the tech about the oil leak. He said it was normal and just tightened the nipple bolt. Of course without result :S So perfect video now I can fix it on my car too.
Mihaly Bak those guys working at car dealerships are all useless. Too stupid to have their own workshops
Just did this on my V70 D5. Made a huge difference to the amount of oil dripping down the front of my engine. Easy to do. My nipple had no hose clamp. It's clear that this part of the ductwork gets VERY hot.
Just bought a 2014 xc60 and noticed afterwards it was leaking oil from the niple. This video helped alot!
Strange coincidence...I did an oil change today on my XC60 and noticed this problem... thank you for this video...
Yesterday when I have changing the engine oil on my Volvo XC70 D5 a i found a lot of oil near vent nipple. I was wondering from where the oil leaks out and now i am checking your videos and find another perfect advice. Thank you so much ! You are making a GREAT demonstration how to fix it. Once again thank you.
My V60 needs this, thank you for the detailed and clear video, this really helps!
Been looking like crazy for what this was. Then I found this video and know I know what to do! Awesome video! I don't have the hose clamp, not that it doesn't do much since it's two pieces of hard plastic. My car luckily had the bracket... So I only need to fix the nipple. Thanks again for the video
Once again thanks! after i followed your front discs video i found an oil leak and this video helped me solve the problem!
Oil was spotted on my under-tray when using your transmission flush method. So I found myself here, and it's exactly as your 0:55 example, a completely loose nipple and an oily mess on my 2013 XC70. Plus a small hole had been rubbed in that box thingy. A quick measure suggests I need to buy a 30 mm dia hose clamp in case that helps anyone else. Next job is to buy the missing bracket. Many thanks!
I have the similar setup on my XC70 III with 2.4D. Mine has quite big leak around here. Now I know this is probably it. And even more, the added clamp has started to damage nearby wires. I am glad I noticed that early.
I've just buy a XC70 2008's, and I'll check if it has this problem. Thanks a lot for your videos, there are awesome!!!.
Did it have the same problem ? I'm interested.
I wonder if you will be able to remove it next time, after adding the rubber sealant! I would use PTFE sealing tape which is both oil and petrol resistant, and also temperature resistant up to 260 'C .
Coming back to this video 6 years later to add an update - a few years after doing the fix shown in the video there is still oil seeping through that nipple. My car is 2011 and it seems it has now developed a leak through the connector of the heated nipple - there is oil iside the connector that has rubber seal to keep moisture coming in from outside. I'm guessing the slots for pins inside the connector are not tight enough and especially after oil change when oil is cleaner and thinner it manages to get through there.
My suggestion is that if you are planning the fix shown in video, first unplug then connector and check if there is oil inside - maybe the nipple needs to be replaced as well. It is not so easy to change the nipple after it has been installed with sealant.
Mine is a XC70 MY11 D5, will check tomorrow. Mine not made in China, hope I dont have the same issue. Thx for the great video!!
Thanks, I got a lot oil coming out from that spot. Fixed as you told. You tips are very helpful.
Hello and thank you for the time that you spend to help the volvo owners, i had the same problem (as most of us) and i fix it with two "o" ring, since i did that, no more oil ! i'm a plumber... ha ha...that why i decide to fix it with a joint ;-)
Philgyver what o ring did you use?
Thank you. I did this over the weekend on my new D3 V70. It was so loose it just pulled out with no resistance! I managed to clean and seal it without removing the whole pipe (largely because I couldn't get the intake pipe out and didn't want to break it in the process!). I was getting the occasional code for low boost pressure, and the values for 'requested' vs actual were always out. It *seems* to be better now, so perhaps this was the cause?
Have just ordered the bracket, as also missing on mine. Perhaps not so important on a D3 but figured it can't do any harm.
Just a tip is to use a hairdryer instead of a heatgun, smaller risk of messing up. :) Ive gotten into many plastic accidents with heatguns, lol.
To use a hairdryer are very good tip. Aswell I been working on this on a hot day and after driving so i have spend about 5 min to remove the heater seansor.
Same leak con my d3 c30! Will do it when i have some free time, thanks!
I have the same car and same "problem" 😄 Will fix that, thanks for the video.
Great guides thanks, gotta fix my XC70 MY16, with all of these problems, no bracket, worn plastic/wires, leaking oil even with the clamp there etc. But of curiosity where is this oil coming from? Is it oil in the air from the crankcase, but why is this air fed back info the inlets like this?
anyone has a answer for this??
Really, I said few days ago, I will say you again: as I bought V70 P3 D5, I wenn to YT and made sub. your channel. Thanky man. I just so few mins ago that leak and saw this on your channel.
Excellent again sir, thanks very much, very informative and very well presented 👍
Always love the Volvo videos you put up. Best channel! Keep up the good work mate and nice xc70 you own looks really good and clean
Also thx for a driver v70 D4 with the same problem and resolved in the Netherlands
Thank you very much. It's exactly what I was waiting for. Good job.
Thanks for sharing the knowledge finally I can put this leak to rest :)
Good afternoon. I have followed your videos and they have been very good at doing all the maintenance on my xc60 (2.4 d). I have never had any problem with my car but a few days ago I noticed oil leaks in the crankcase and a drop in the oil level. I suspect it's the PCV valve. Do you have any videos about this? Could you give me some advice? There are also traces of oil in the thick tube that goes to the intercooler. Thank you so much.
Hi, I recently did an oil change on my XC60 D5, and a month or so later I have the warning message, "Engine service system" appeared. After reading about the issue, I wondered if I had over filled the oil (It got 6 litres) and maybe this was the cause of the light coming on. Today I took the bottom engine cover off, and there is oil on the bottom of the turbo and sign of it running down the intake pipe from the top of the engine. Checking the top of the engine, the intake pipe clip where it goes down the back of the engine is oil fouled and dirty. It appears the excess of oil I created at service time has been blown out of that nipple joint. The oil level readout is full, I actually drained out 300ml of oil to lower it slightly, although this made no difference to what the gauge showed me. However I plan to run the car a few more days to check for further leaks and then carry out this modification to the nipple. I doubt I will be able to reset the engine system light ?? Great video and thank you for sharing.
Hi Iban. I have the same error. How did you solve it? Thanks
@@bogdanmoga6117 I had the same problem. Oil leaking from the low pressure turbo inlet. Replaced the seal. Almost 100% sure the oild cam from that nipple. Closing it off better and having no leakage will not change the amount of oil getting into the turbo. I wonder if anyone has found the culprit yet. high crank case pressure??
Hello. Thanks for your interesting video! My XC60 D5 is also leaking here. I'm currently looking for a hissing sound when the turbocharger kicks in, which I can't find. There is no oil contamination or damage to the charge air line anywhere. My question: Can such a noise also occur on the suction side of the charge air system? Then the repair you described would be a solution. Thank you very much Eric

Thank you for your helpful information, see you next time1
Thanks a lot! Had this exact issue and you helped me resolve it 👍🏻
Why does it leak here anyway? Surely there is negative pressure in the charge air hose so what pushes the oil out? Great vid btw sealed mine with ptfe tape round the spigot and nipped up with jubilee clip.
Hi. Great and informative video. I did the same as you, using a silicon gaskdt sealer. However I started worriyng afterwords. What will happen if small pieces of the silicon material falls off and get sucked down into the intake? Has anyone thought of this risk? And if so, where could it potentially end up getting stuck? What are your thoughts about this? Best regards from Sweden
I already did this modification but the oil still leaking. After our investigation with my volvo mechanic who works in an official dealership we found that the source of the oil is the nipple's electrical connector itself. He confirmed that this is a very common issue on these engines and there is nothing to do with it due to the shitty design...
Correct! The oil is leaking through the sensor connector. I'm planning to drop few droplets of super glue in there.. its broken anyway..
Bonjour comment aver vous résolu le problème? Svp
I am 100% sure your leakage from the connector is also just a symptom of oil that should not be there in the first place. My idea is that the crankcase pressure is too high... spitting oil into the turbo inlet... anyone has found the solution
Could you please tell me how to remove safely the air inlet pipe? I mean the brackets and their bolts are really tight. I'm afraid the mounts on the pipe will break during the removing.
Alors apres avoir fait cest démarche. Es ce que le mamelon ne fait plus de fuite dhuile ?
Thank you Man! I have '12 d4 awd volvo, and 2 years ago I noticed the problem. I told to the local Volvo dealer and they cleaned it, furthermore, they said, they fix the problem. 2 weeks ago, I checked again, but it is dirty again. I thought it is an induvidual problem, but it seems, it isn't.
Thank you for the solution. If I fix it, that will not cause any problem when you need take out the nipple because any reason?
Thank you for your videos!
Can you fix the earlier euro 4 one like this ? D5244t4
Why the hell vapor oil has to go into fresh air pipe?
Would you use one of those ports to spray an intake cleaner? EGR, intake valve, turbo cleaner?
Could a faulty pcv heater nipple cause a misfire and p0100 code ?
Can someone tell me what the box is for on this pipe? Many thanks
On my s60 the entire plastic is cracked. It's like the clamp was way too tight or something.
Hi, any plans to instal a oil cach can for the diesel engine? I have a 2.4d from 2008 and i'm wonderrig what kit should i use and where to instal it. It could affect the PCV sistem? Thanks in advance.
Hi, i have an S60 2008 2,4D D5244T5 engine not the same as volvosweden but i do wanna know due there are two tube one going to the rocket cover and one going to the air inlet before the turbo. and i dont whant oil in my turbo and i dont want my valves and or inletmanifold to gunk up.
@@2bias82 this is why we need to find out why the oil is sucked into the turbo inlet in the first place. suction too hard? or just crankcase pressure too high??
is this problem for 2004 D5 also'?
The charge pipe leaks too.
Hi, thanks this very usefull video. I had the same problem. I saved 550 euros thanks to you. One question, how did you repair the oil separator? With this same glue?
I would have been even better for the turbo/intercooler to install a oil catch can there. Otherwise Good video!
Firstly…your content is brilliant. Having just purchased a 2013 s60 with D5204T7 engine, your videos are already a massive help. Im needing to do this very leak fix..but I wonder if it is worse due to blocked crankcase ventilation. What would be you check to confirm this? I have zero vacuum on oil filler cap, but unsure if this is a valid test for this engine. If it is blocked can it be cleaned or is a replacement (which include filter housing..) needed.
After doing this fix, there is a lot more oil coming from inlet manifold gasket….could this mean PCV blocked, or just need new inlet gasket?
Great video as always and another job to do on my xc70 . Quick question - i am finding it really hard to locate the part no 30741409 ( securing bracket )on any site . Could you post a link to where you got it please ? Thanks
+Lorcán Sweetman After this video was posted this part got sold all over. Check with the dealer. They could back order it. It's my friends XC70 D4 and he was the one ordering. Good luck.
Having the same thing on Volvo V60 2012 D3.
Mine didn't come with a hose clamp, anyone got any idea what size is needed?
Such a small detail but gives volvo a bad name.
Do you have the Volvo part number for this? Mine had snapped in half.
for the T10 30750911 is the heater itself the problem???
What is the box on/under the inlet pipe for?
I believe it is a sound/noise resonator.
@@nocountrymembers5852 thanks, but i figured it out. And yes your thoughts are correct.
Mine is doing the exact same, will this result in intake air leakage? I am having an air intake issue which my mechanic can't solve but I've found this issue.
No if you have low boost issues your air leak is elsewhere.
Hi.
I have DTC's on my 2014 Volvo XC70 D4 50.000km. p023600 and p029900. I have replaced the MAP-sensor 31216308 and I have also resealed the heated crankcase vent nipple. But the code still comes.
The engine runs like normal.
Is there any normal standard faults on there engines?
To days after i did this fix the DTC's deleted itself and i have not had any DTS's since. I also replaced the MAP-sensor.
The DTC is back again after 1.5 week :(
Hi Simon. I have the same problem now. How did you manage it? Thanks
@@bogdanmoga6117 Hi Bogdan.
The sensor 31216308 that i first replaced is a boost sensor, the MAP sensor(31303974) is located on the left side of the intercooler. When i replaced that the problem went away.
I stick with P2 😃
Mine is becoming loose
Can this problem cause engine light to come up ?
My xc60 has the same problem. My turbo makes a whistle when I accelarate in high gear in low velocity untill reaching higher rpm, then stops the whistle. Is this related?
Here's the link to the airpipe modification.
th-cam.com/video/ZTS6uVG_mEU/w-d-xo.html
The Chinese just don't make'em like they used to....
holidayhouse03 blame Ford not the Chinese :)
Comment my Mercedes - Benz Blue TEC diesel has similar problem.
The first real issue, in either case, is potential for vacuum leak and creating a code or drivability problems due to that.
The second issue is much more serious that is the oil leakage, caused as this from the positive crankcase vent "PCV" for the engine. Now forever all PCV systems have caused oil to enter into the inlet of the engine... any engine where the PCV system causes crankcase gas to be drawn into the inlet of the engine. The the oil leaking from the rod bearings and sprayed on the underside of the pistons in the crankcase becomes entrained as a mist with the crankcase gas by the pumping action in the crankcase. The crankcase gas is from the blow-by caused the piston rings sealing normal leakage, and air vented into the crankcase. When the PCV system draws the gas and oil mist into the intake system this creates first the benefit of the engine burning the resulting toxic gases and oil mist resulting in reduced emissions, approximately 1/2 the total emissions from the engine. But it also creates the problem of contaminating Mass Airflow sensors, with oil either preventing them from working, damaging them or ruining them. And in modern highly emission controlled engines it is made worse because of hot and soot filled Exhaust Gas Recirculation EGR is introduced into the inlet manifold to create the problem of sludge and coking of the oil. The sludge, coking of oil, and grit is formed by the oil from the PCV system; the soot in the exhaust gas in the EGR gases, and; the heat from the EGR gases creating the sludge, coking, abrasive particles, and hard black deposits found in modern car inlet manifolds, and on the inlet port and valve surfaces.
From research I was involved in about 30 years ago we found than by removing either any one of the causes prevented these problems... removing either soot [unburned or incompletely burned hydrocarbons], oil [wet hydrocarbon that tends to stick to the soot] or the heat from the exhaust gas solves the problem, the heat must not exceed even the comparatively low temperature of 125 degrees C. The oil is easiest to remove by using a coalescing filter or catch can combination to remove the oil mist. It is hard to remove the heat. Removing the soot is impossible!
finally, someone understands this issue!