Switching off a turbo engine

[Cedric]

I was wondering if it's right to let a turbo engine run idle for a moment before switching it off. Why is that exactly?

[Revo]

If you turn the engine off immediately after parking, the oil pump will stop pumping oil around the turbo. But it takes time for the turbo to slow down from as high as 100,000 rpm. Hence the bearings will have inadequate lubrication and it will shorten the life of turbo.

Ideally, you should let the turbocharged car idle for a minute before switching off the engine.

[Cyco]

It depends on how hard it has been driven up to that point too - the harder the drive, the longer it should stand.

If driven slowly for atleast 5 mins after hard use then there should be very little need for it to stand

[Ferrer]

Does that also happen with supercharged engines, or only with turbo ones?

[Matra et Alpine]

ONly turbo.
It's not because of speed - a turbo drops to idle speed almost immediately after the engine
It's the latent heat in the Turbo. It will boil off oil unless it's being replenished.
SCs don't get that hot ( no exhaust gasses ) just "normal" mechanical "hot" !!

[Cyco]

Not really a problem with superchargers as they (normally) run at much lower speeds. The supercharger also doesn't have the same operating temp as a turbo due to it not being on the end of a (sometimes) glowing exhaust manifold.

[Cedric]

So, it's not rotating speed, but excessive heat due to a lack of fresh oil that causes damage in the long run?

Besides, how long would it actually take for a turbo to go from 100,000 rpm to a complete standstill?

[Dino Scuderia]

Think of it as a pump, a pump impeller doesn't free-wheel on it's on, it's either suction or force that moves the impeller. So if the engine is at idle so is the turbo's impeller at idle speed whatever rpm that may be. No?

[Waugh-terfall]

I thought it was only for larger turbos, eg. We never let the 1.8T run idle for a while before switching of, nor the Discovery TDI and most of my friends Mum's that drive TurboDiesels turn their cars off straight away, although there was that one with the Laguna 1.9dCi that had it's Turbo blow itsself apart... But it was running at the time.

Another friends Dad drives a 97 Impreza WRX with a HUUUGE Turbo, when he parks up he removes the key, locks up and can walk away with the engine runing at idle, it turns itsself off after about 2minutes to keep the oil running around until the Turbo cools off enough.

[TheOne]

Another friends Dad drives a 97 Impreza WRX with a HUUUGE Turbo, when he parks up he removes the key, locks up and can walk away with the engine runing at idle, it turns itsself off after about 2minutes to keep the oil running around until the Turbo cools off enough.

thats because he more than likely has a turbo timer.

the heat from the turbo will burn the oil if ran too hard, oil can sludge inside the turbo and also run out of oil to lubricate, so a turbocharged engine should be let to idle for 1-2mins after a hard run before shuttin it down.

it doesn't take long for a turbo to slow down from a 100k rpm run.(friends mk3 supra, the charge pipe blew while riding, we could hear the turbo spin up and down pretty fast, and this was a newly rebuilt turbo)

[my porsche]

FWIW with our RS6 you can switch it off immediately and it has an automated fan system that sucks out the heat. But our old A6 2.7T you needed to leave running. With both though during hard driving we tried to cool it down a little bit before parking. I.e. out in the hill country when we go to lunch or something on back roads for about a mile before stopping no hard acceleration etc.

[NSXType-R]

Wow, thanks for asking this question. I never knew about this before.

Back to Waught, a reason why those turbo engines aren't dead is because in a passenger car it could be running relatively low boost, especially when it's a Volkswagen. I could be wrong though.

A high performance car would need the extra time because it's putting out a lot more power and is strained.

Correct me if I'm wrong.

[AndrewD]

Your all wrong.

Its true that the oil coaks up inside the bearing housing of the turbocharger if it is not cooled. Most turbochargers are not watercooled and hence the oil serves a dual purpose, cooling as well as lubrication. Because all oil pumps are mechanically driven from the engine the engine needs to idle for a small period of time to remove the heat from the bearing housing. If some of the manufacturers have become tricky and adapted a watercooled turbocharger then you can turn off the car immediately, alot of VWs have this. These can be either driven by an electrical pump or by syphon.

As far as turbo speed acceleration and deceleration it is dependant mainly on the inertia of the shaft and wheels (which changes with size of turbo), exhaust gas enthalpy and a few other parameters. However i have seen a Garrett GT 15V which is one of the smallest commercially available turbochargers accelerate at over 200,000 rpm per second2!

We have also measured the speed at a peak of 245,000 rpm right at the end of the map

Hope this helps