Turbo Cool Down? and Synthetic

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Mar 16, 2004
I just purchased a 2004 WRX Wagon. I love the combo of utility/fun to drive. I drive it realitively easy but let it spool up on occasion. Anyway my father-in-law mentioned turbo cool down (letting car idle minute or two after driving) to cool oil in the turbo. From what I read the turbo is cooled by water and convention causes flow after you shut off. His experience is being service manager at Isuzu dealer and having many blown Impluse turbo's but this was years ago. I plan on using Mobil 1 every 5k. I don't drive like a nut. I plan on keeping the car a while. Do I really need to do this?
Just let the engine idle a short while to let the turbo spool down. If you shut it down right after higher rpm, the turbo could still be spinning for a while, even after you get out and walk away. Letting it spool down a little will help your turbo live a little longer, although they are normally a pretty robust item.
Yes. But no need to go more than 60 seconds unless you do some real spirited driving...if you put-put into your neighborhood (wise) and just ease into your driveway the need for idle down is minimal.
Long story short, yes you do. I'd suggest getting an electronic turbo timer (HKS, Greddy, etc...). Select your desired cool down time, put it in park/neutral, set the e-brake, remove your key from the ignition (it'll keep running),lock it up and walk away. I had one on my 88' Supra.
What they said. If you park the car immediately after a hard run with lots of boost, the turbo is going to be really, really hot. Even though there is some convection cooling going on after shut down, it's still a good idea to idle the engine for a minute or so right after a hard run. But if the last mile or so to your destination is driven gently, there is no need to idle at all before shutting down. You could probably ignore doing any of this and still get by, but taking a few precautions will undoubtedly add to the lifespan of the turbo unit.
Does the car have a coolant after-run pump? Audi turbos used to (and still do I think). This will keep the coolant flowing in order to cool the bearing down further even after the car is turned off. It shouldn't take the turbo but a few seconds to actually spool down to its idle state. I would still probably err on safety after long extended/hard drives and let it run for a minute. I think the after-run pump and synthetic oil have helped turbos come a long way.
There is no pump involved in turbo except when engine is on (water pump), when the engine is shut off natural convection causes cooler coolant to flow in.
I used to have an Audi S4 and it did have a the coolant pump that you mention. It also had a seperate oil line that fed oil directly to the turbo bearings from the sump. This meant the oil was cooler and there was almost no cchance of the turbo bearings being starved for oil. Most turbo engines, including the WRX, don't have either of these features.
Originally posted by Jay: Does your owners manual recommend a cool-down period?
The manual states not a thing about cool down period.
Originally posted by harrydog: . Most turbo engines, including the WRX, don't have either of these features.
Well, we know at least Audi learned something from the 80's turbo era. Apparently no one else did. [Wink] I'd definitely let it sit for a minute after running, or better, buy a turbo timer.
I thought I heard that there is something special in the WRX turbo (cooling or oiling) that does not require a turbo timer. I would do some research on a WRX forum if I were you.
Subaru turbos are much the same as most modern turbos. They have water cooling and oil cooling/ lubrication lines for the turbo. The water lines reduce the need for cooling down & turbo timers. Not sure that there are turbos without oil lines. You really only ned to cool the turbo down after a hard run and this is best down by driving slower before turn-off rather than using a turbo timer. However, if you must there are automatic units that determine the cool down time, rather than a fixed time period. OT The other issue with TT's is that many alarms (including the standard alram fitted here) do not arm until the TT has stopped the engine.
And let us not forget the real reason for cooling down the turbo is that oil can get cooked in the oil lines. This is called coking and causes the oil lines to gradually block and reduce/ stop oil flow to the turbo bearings. Bad! This is much less likely to happen with a water cooled turbo and the use of good synthetics. Nissan had a strict service interval of 5,000km on pre-watercooled turbos. This is now 10,000km.
Even my '89 Dodge Shadow had a liquid-cooled turbo. Unless you were hammering on it before you parked it, I wouldn't worry about idling it to let it cool down - that's what the coolant is there for. Add in the protection of a good synthetic and you're on your way.
Originally posted by rjundi: Do I really need to do this?
I've been around a turbo or two and I'll say this: If you're just driving around normal, then no. Just shut 'er off. On the other hand, if you've been going hard on it, idle for thirty seconds MAX after coming to a stop...
I think the place where the oil coking tends to take place is in the turbo bearings, not in the oil lines. It's a cumulative thing. Each time it happens, there is residue (coking - burned oil) left behind. Eventually it will destroy the ability of the bearings to do their job and the turbo impeller shaft will seize up. I had a 1986 Saab 9000 Turbo which surprisingly wasn't water cooled. I know the old Porsche Turbos weren't water cooled either. They tended not to have a real long lifespan. But these days I think all turbos are water cooled. This makes a huge difference, but I still think that there is a need to cool the turbo down after a hard run before shutting down. In my opinion, the convection action in the WRX isn't enough to completely prevent coking if you continually shut down immediately after driving really hard. The old Audi S4 engine was really bullet proof and way over engineered. Nodular cast iron block (stronger than the normal block material). All forged internals. Sodium filled exhaust valves. Oil jets that cooled the underside of the pistons. A seperate oil circuit to feed the turbo bearings. A secondary electric water pump that continued to circulate water through the turbo housing after shut down, until the temps were safely low enough. And guess what...The owners manual still mentioned that you should drive gently or idle briefly before shutting down after driving extremely hard. I can't remember the exact wording, but it was there. Audi really did (and still does I think) want their vehicles to last a long time as is evidenced by their effort at rustproofing. They're second to none in that area, along with Porshe and VW. It always disappoints me when I see how car manufacturers cut corners with their designs to keep costs down. Having said all that, Subaru seems to be one of the better manufacturers at being more engineering driven than accountant driven and their cars seem to hold up well over the long run.
Whilst the bearings may be the main area of the coke forming it is well known to deposit in the oil lines, these being fairly narrow, and reduce the oil flow to the turbo.
My understanding was when the oil flow stopped on the hot bearing it took the heat of the metal and was cooked on to the surface. If the oil was flowing it removed the heat but did not stay long enough to cook. Water cooled maybe better by being cooler but when the oil flow stops the result will be the same. I would try to let it have a little cool down time. Coasting and easy drive time counts as well as idle time. Trucks with exhaust temp gauges will usually try to get the temp to below 300 before shutting down. This seems to take from a few seconds to several minutes. It has to have good effects on the valves and other metal parts to eliminate the hot spots and heat build up.
Thanks guys for the replys. Someone send me this and also Subaru themselves gave a techincal answer from customer care that its not necessary as the car was designed to avoid this: http://www.spdusa.com/turbo_timer.htm I'll just use Mobil 1 and if I drive really hard let it idle otherwise not worry. Thanks again.
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