Hi All. I'm getting my vRS hopefully on Wednesday.

Should I be letting the engine 'idle down' for a minute or s after a quick-ish drive? The way that people who drive petrol turbos do?

I suppose the priciples are the same?

yup makes them last longer so it seems,

Thought as much!

Not overly necessary, the temp of the exhaust gas is alot less in a Diesel than a petrol, I tend to let it run down for a max of 30 seconds under normal use and about a min under 'intense operation'

All you have to do is make sure the car is idling before shutdown or the turbo will be starved of oil as it's only a fluid bearing after all.

Ben

Like the avatar by the way

Heres the real reason why to idle your engine on a tdi.

The oil inside the turbo starts to burn off if the turbo is really hot. IF the turbo is really hot the oil inside the high pressure feed will also burn off.

This leaves an oily resisdue inside the oil feed pipes. If you do this alot then the residue will build up and clog the oil feed pipe. No oil + turbo = nasty expensive mess

Heres the real reason why to idle your engine on a tdi.

The oil inside the turbo starts to burn off if the turbo is really hot. IF the turbo is really hot the oil inside the high pressure feed will also burn off.

This leaves an oily resisdue inside the oil feed pipes. If you do this alot then the residue will build up and clog the oil feed pipe. No oil + turbo = nasty expensive mess

As I found out

However, the new turbo had nothing to do with the oil, the nut came off the end of the shaft and pop.....new turbo please!!

Cheers guys. Makes sense.

2 days to go..

Was speaking to a mechanic who deals with a lot of turbo engines and he recons its not the heat cooldown you need to wait for so much but the turbo spindown as its spinning for a while after boost, also the temp of the turbo will fry the oil in the lube pipes.

So even if you have taken it easy all journey and only boosted near your house or where your about to stop etc, let the turbo revolutions come to a halt before turning off, as a still spinning turbo will have no oil pumped to the bearings.

Made sense to me when he mentioned it.

Was speaking to a mechanic who deals with a lot of turbo engines and he recons its not the heat cooldown you need to wait for so much but the turbo spindown as its spinning for a while after boost, also the temp of the turbo will fry the oil in the lube pipes.

So even if you have taken it easy all journey and only boosted near your house or where your about to stop etc, let the turbo revolutions come to a halt before turning off, as a still spinning turbo will have no oil pumped to the bearings.

Made sense to me when he mentioned it.

I let mine run down for 30 secs after stopping, just as you say to let the turbo get to a resting speed & just for the temp thing.

IIRC turbos can rotate at anything up to 150,000RPM when running, (obviously less when at rest), so it's best to not kill it straight away.

Ben

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IIRC turbos can rotate at anything up to 150,000RPM when running

not quite as fast as that, i should imagine centrifugal force would bend the impellers at that speed

I would have thought that the turbo would have as little inertia as possible, otherwise it would take an age to spin up. Therefore it will spin down at least as quickly as it spins up, even more so if it is spinning faster than the gas flow speed. You can hear how quickly they do spin down and it doesn’t take very long at all.

"A turbo spins very fast; most peak between 80,000 and 200,000 RPM (using low inertia turbos, 150,000-250,000 RPM) depending on size, weight of the rotating parts, boost pressure developed and compressor design." Wikipedia

If you let the engine idle for 10 seconds on start-up and for 15-30 seconds at the end of the journey, I'm sure that will maximise turbo life.

I also avoid any full acceleration until the temp guage hits its normal spot.

not quite as fast as that, i should imagine centrifugal force would bend the impellers at that speed

They do...

Not sure what the impeller is made of in a Diesel turbo (ceremic??) as the exhaust gasses are not as hot as a petrol but they do go some, probably why they whistle.

You should be able to blow a turbo round with a gentle breath, so it will take a bit to slow down after switch off.

Ben

From an old car magazine:

They do...

You should be able to blow a turbo round with a gentle breath, so it will take a bit to slow down after switch off.

Ben

I’ve seen this blowing demo on the telly, it’s quite cool.

However, I would still be surprised if it took long to slow down as it is in a closed system. Once the engine stops, the gas flow around the turbo stops and if the turbo kept going it would be trying to compress air (whilst creating a vacuum, on the input side I think, unless there are clever valves) without any energy going into to it in order to do so. I think some clever sod called Clausius reckoned this couldn’t happen.

I would let it idle if I'd just come off the motorway and immediately stopped, but driving home normally I trundle through a couple of estate roads at about 20-30mph and reverse in, by which time I guess the turbo has had time to cool enough that I don't need to sit there much longer. Obviously I also would not rev it before turning off either - but that's common sense!

They do...

Not sure what the impeller is made of in a Diesel turbo (ceremic??) as the exhaust gasses are not as hot as a petrol but they do go some, probably why they whistle.

You should be able to blow a turbo round with a gentle breath, so it will take a bit to slow down after switch off.

Ben

Ceramics are associated with low inertia turbos on Skylines etc. They don't take much boost, unless the SOtA has moved on, 0.8, 0.9 bar. These numbers aren't very Turbo Diesel like. Where a remapped PD130 may be hitting 1.5-1.6bar.

As regards a cooldown, after a normal journey, I take it quietly for the last mile or so. @ 30mph, that takes around 2 minutes on low load. Which is enough to take a lot of the heat out of the system.

J.

Actually thinking about this a little laterally. I have a turbo Diesel which has ‘auto stop start’ (loads of companies do them now) and the engine will switch off regardless of the previous running speeds when the vehicle comes to a stop and the clutch is released. So I guess the manufacturers reckon the turbo is OK. I’m betting the clever oils have a lot to be thanked for.

i'll get my coat