Does this protect your turbo?

My Dad - who's had a TDi in the past himself - says that you should let the engine run for 30 seconds or so when you stop, before turning it off, so the turbo winds down while there's still oil in there, otherwise it knackers it.

Is this true?

Yes, it is true, and it says to allow for turbo cool down right in my manual.

This should really only be necessary after a long, hard run. The issue is that the oil cools the turbo and the turbo needs some time to cool down via oil cooling before the oil pump switches off. The danger is that the oil that stops in the turbo when the engine is switched off will become overheated and coke up the turbo bearings.

Fortunately, the turbo cools very quickly, and unless you live on the median of a highway or at the crest of a large hill, normal city driving will cool things off enough so that you can shut the car off right away when arriving home. Also, a full synthetic oil will provide additional protection since it takes much higher temps to damage it.

What is even MUCH more important on a TDI engine is to allow the engine to warm up to proper operational temperatures prior to wacking the turboboost on by dipping into heavy fueling with your throttle foot.

It takes a good four or five minutes for a TDI engine to properly warm up from a cold start. DO NOT put it under heavy load until it is properly warmed up, then HAMMER IT!

The need to "cool down" the turbo prior to shut down is ONLY if you have been driving under a constant sustained heavy load for an extended period of time, ie up a steep grade or pulling a trailer. Then a slow shutdown would be prudent.
Other than that though, your turbo boost is never over 3-5 pounds cruising up to 75mph, so there is no need to worry about overheating the turbo and coking the oil, unless of course, you are NOT using a full synthetic oil and are trying to cheap it out with crappy dino oil, then you'll coke it up no matter what you do.

[ May 03, 2002, 05:09: Message edited by: SkyPup ]

Great advice! The TDI does not use a water cooling jacket on the turbo like other cars such as the 1.8T. These use water as well as oil to cool the turbo's bearing housing to prevent oil coking. The fact that the TDI does not have a water cooling jacket is not a major issue however. The TDI even at full load will never approach the temps that a gasoline engine runs at.

On a TDI using a high quality Synthetic meeting the CI-4 ratings such as Delvac 1, issues like coking and sludge due to heat are simply not an issue in a TDI turbo. One good bit of advice is to let the engine idle for a few moments when getting ready to shut the engine down, I usually just let the car run while I unbuckle the seat belt and get my things in order leaving the shutdown to the car as the last step next to opening the car.

When I pull into rest areas on the highway, I use my valet key to lock the car leaving the engine running. The reason is the off-ramp does not really provide enough time to cool the turbo down so to avoid a shutdown and start cycle just let it idle. The valet keys allows you to go inside and not have to worry about somebody stealing your running car.

DB

The heat and therefore temperature in a turbo is not limited to correlation with boost. Even at steady state highway speeds at low (3-5 PSI) boost, there is still high temps in the turbo due to the exhaust volume and energy content. Therefore, the turbine will be hot. When the load is removed, such as going to idle, the heat input to the turbine from the exhaust is dramatically reduced and the turbine temp falls rapidly. This is why if you pull off a hwy into a rest area you must idle for a while to reduce the turbo temps that will otherwise cook the oil that will sit in the hot turbo if the engine is immediately shut down. The circulating oil during the idle cooldown does not allow the oil to stay in the hot turbo long enough to over heat, as would happen if the engine were immediately shut down and the oil stopped circulating.

The mass flow of oil in the TDI turbo is small and is therefore primarily a lube function, not cooling.

Originally posted by Boundless:
The heat and therefore temperature in a turbo is not limited to correlation with boost. Even at steady state highway speeds at low (3-5 PSI) boost, there is still high temps in the turbo due to the exhaust volume and energy content. Therefore, the turbine will be hot. When the load is removed, such as going to idle, the heat input to the turbine from the exhaust is dramatically reduced and the turbine temp falls rapidly. This is why if you pull off a hwy into a rest area you must idle for a while to reduce the turbo temps that will otherwise cook the oil that will sit in the hot turbo if the engine is immediately shut down. The circulating oil during the idle cooldown does not allow the oil to stay in the hot turbo long enough to over heat, as would happen if the engine were immediately shut down and the oil stopped circulating.

The mass flow of oil in the TDI turbo is small and is therefore primarily a lube function, not cooling.

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