let idle before shut down?

[doswell]

I've been told by someone who drives a diesel f250 that you should always let your engine idle for 2 or 3 minutes before shutting it down after a long drive to allow the turbo to cool down or it will not last as long as it should. I have not seen this discussed anywhere and was wondering if anyone could comment on this?

[chittychittybangbang]

That's fine as long as if you just did a drag race. If you watch exhaust gas temperatures after a hard run, they cool down within seconds and the exhaust can cool down within a minute or so. It's cast iron so it does hold some heat but that's why you should use synthetic oil on turbo cars anyways.

During normal driving, these components don't get too hot (relatively speaking) and can cool down as much as they're going to cool down in under 10 seconds. If you're pulling off the highway, the coasting down while decelerating is enough. After all, who is going 60 mph and then shuts the engine off immediately? If you're getting off the highway, you slow down, end at a stop sign, or pull into a parking spot. If you're driving locally, it's not going to get much cooler.

[mr rooney]

Yes it's a god idea to let the engine idle for a few mins after a good thrashing like when your evading the local sheriff ect. This allows the oil to flow around the turbo bearings helping cool and lubricate it.
If your popping down to the local wal mart for the weekly shop i wouldn't worry about it.

[Fluid]

Is his turbo water+oil cooled or just oil cooled? TDI engines are only oil cooled so the only thing running through them to control their temperatures are oil and exhaust gases. If the engine is running hard, the exhaust gases will be hot and the turbo will heat soak. If the engine is idling, it's not too hot and the turbo will cool down if it was hot. Heat > cold.

All the newer VW gas turbo engines also have auxillary electric water pumps so they'll run the coolant through their water cooled turbos after shut down. I wouldn't idle for a few minutes after every drive, it only wastes gas.

[Bug-N-U]

Chitty pretty much nailed it, I also have an F250/7.3 with an EGT guage. With normal normal driving it reads 400deg-F and when I come to a stop it will not read below 400 deg-F no matter how long it idles. Only after I'm hauling a load is when I let idle back down to 400 deg., other wise I just shut it off. Sence I don't haul loads with the Beetle, I just shut it off.