The truth about Ford Ranger Mazda BT 50 10min oil change time limit | Auto Expert John Cadogan

It’s absolutely true that the Ford Ranger and Mazda BT-50 oil pump risks losing its prime if you drain the oil for more than 10 minutes. This is one of those Donald Rumsfeld-style ‘unknown unknowns’ - something you don’t know that you don’t know - because you think you know how to change the oil.
These are always the things that bite you on the arse. Just like changing the battery. If you disconnect the battery on a modern car, it can make the infotainment system think it’s been stolen - and generate a whole bunch of other ECU-initialisation kinds of issues.
Which is why people who change batteries for a living use small auxiliary batteries - often connected to the 12-volt outlet in the cabin - to power up the CAN bus while the main battery is disconnected for the changeover.
I guess it’s a similar thing with many modern diesels and oil changes. There’s an engine control ECU setting for oil dilution. Often you need to go in an reset that with a laptop after an oil change, so the engine can make the right set of decisions about regenerating the DPF.
It’s complex - but the complexity is excusable, because it’s a tradeoff against delivering greater benefits thanks to the technology, which demands that complexity. There’s no valid argument against this - although there’s obviously a balance between those two things.
So why did Ford do this with the 3.2 in the Ranger and the BT-50? Because it seems superficially stupid, and many mechanics will tell you it is.
But really it’s not. They had their reasons. The benefit is that the oil pump varies the oil delivery in response to revs - in other words it's a variable-flow pump rather than fixed flow.
This optimises the oil delivery across a range of operating revs and minimises the parasitic fuel consumption related to driving the oil pump. Maybe additional oil flow at high revs doesn't have to be bled off through a relief valve. I don’t know the specifics at that detailed level. But that’s why they did it.
But I do know that ancillaries - alternators, water pumps, oil pumps - they’re all essential, but you can derive a direct fuel economy benefit by minimising their power consumption. Which is clearly the objective here.
Servicing professionals simply manage to get the new oil back in, within the 10-minute window. And here’s the bit where Evan and I disagree.
Modern oil is quite thin, so there’s no problem draining it, whipping the new filter on, and re-filling in under 10 minutes. There’s no practical benefit to the engine in letting the last 12 drops of old oil fall out over the next three hours (or something), which is what anally retentive DIY oil changers often do.
Which is, of course, nuts. Even if there’s 50 CCs of drainable old oil still in there, and there’s probably not - five minutes is a long time to sit there draining…
...but even if there is, 50 CCs diluted against five litres of new oil is only one per cent by volume, which is nothing.
And even those contaminated (probably not) 50 CCs of old oil … it’s probably 10 per cent contaminants and 90 per cent viable oil.
So that’s like one part per thousand of contaminants once the new oil goes in. Which is nothing. In the context of long-term reliable engine operation, it’s insignificant.
To me, this oil change time limit is absolutely not a reason not to buy a Ranger or a BT-50. It’s just a procedure that you need to follow if you own one.
I would drain the sump soon after shutdown, just because the contaminants are more likely to be evenly mixed through the oil, and it’s at its thinnest while it’s still hot.
Don’t presume procedures you learned several decades ago still apply to modern cars today. Cars evolve - and therefore servicing does too.