Marx911TT

Does anyone know whether the 993 TT needs a turbo cool down period before shutting down the engine.Thanks Mark

Anir

I've read that the turbos can spin at as much as 100,000 rpm. After a hard run, you have to give them time to slow down before turning off the engine. Most sources reommend 1 - 2 minutes prior to shutting off the engine after a hard run.

Even after lazy city driving, I wait about 30 seconds just to be safe.

Jeff 993TT

This may help you:

<a href="http://forums.rennlist.com/scripts/rennforums/ultimatebb.cgi?ubb=get_topic&f=7&t=000086" target="_blank">993TT questions</a>

Jeff

SundayDriver

The issue with turbos is that they get VERY hot under high boost conditions. It is not he rpm that is a prblem as they spool down very quickly. What happens is that the stored heat in the turbo transfers to the oil. If the engine is not running, the oil can get too hot and break down. 1-2 minutes after a very hard run keeps oil circulating and avoids the high temps. Even at the track, a single cool off lap should do the job. Frankly, unless you are racing into your driveway, you don't usually need to be concerned about cool off time as a reasonable drive home is enough cool off.

Ran

Yes, while better materials might have contributed to requiring less stringent cool down procedures, there might still be some truth and little harm in letting the cool down take place especially after hard driving. Use it as an opportunity to check your oil level since oil level checking is most accurate only after a long hot run ! As Mark mentioned it is not simply the high spinning rate, it is more a matter of saving the bearings, etc. from high heat.

BESIDES, from what i recall though I could be wrong, my 993TT manual says that it is best to idle for 2 minutes after a hard drive. This is a general recommendation since it is not in turbo section but in the part which applies to both the Carrera and the turbo. Personally, I have to always idle for 2 mins before switch off

ZAMIRZ

The idea behind letting the turbo cool down in addition to all the members contributions is that you need to let the turbo and its associated parts cool down from their thermal expansion under boost and high-load conditions. The turbo and it's associated parts (wastegate, bypass valves etc) are built to super-tight tolerances and if the metals aren't aloud to warm-up and cool-down properly they will destroy themselves. Just make sure you don't go into the boost about 2 minutes prior to shutting it down and you'll be good. If you want to be especially careful go pick up a turbo timer for $90 from a local speed shop and wire it up, that way the engine will idle for an extra preset time (usually set by you or whoever installs or sets it up) and you can take your ignition key out, lock the doors and walk away from the car.

later,

amir

LR993TT

My experience with turbo vehicles, mainly diesels, but a turbo IS a turbo, is to wait until the pre-turbo exhaust gas temp reaches 300*F or less therefore cooling the turbo before shutting down. Oil will coke on the turbo bearings otherwise, unless you are using synthetic oils(such as Mobil 1) which will take a little more abuse. I use 300*F no matter what oil I'm using, better safe than spending $$$.

Les

PramTT

Turbo timer on 993TT?

Has anybody succesfully installed a turbo timer on 993TT? How do you by-pass the drive-block system which supposedly activate when you lock the car when the engine is running??????

Kevin

It is very important to remember that most of the damage that occurs to our turbochargers is a result from a hot shut down. What happens is the heat that is inside of the turbine housine (hot side) need to be cooled down. It is done by two methods, as the engine idles this causes no load and the fuel air mixture cools the exhaust and turbine housing, second the oil temps come down while the car idles and the oil also cools the turbine shaft. The damage is down when one shuts the engine off quickly which causes the heat from the turbine housing to directly transfer through the turbine wheel and shaft. These high temp turn the shaft blue, which burns up the bearings, or scours the bearings. I have enclosed a picture of a KKK 16 (993TT)off of one of my turbo's where the previous owner did not use a proper cool down period. The result was a new cartridge or center section because the damage also knocked out the bearing housing. if you look hard enough you can see the blue in the shaft.

SundayDriver

Let me add one aspect to Kevin's explaination. When the engine is shut down with very hot turbos, the oil flow stops and there is enough heat in the turbo to coke the oil. This creates a build up of solids and reduces the ability to lubricate that area. As his photo shows, this is the turbine shaft where this happens. Eventually you get scoring as there is inadequate lubrication of a part turning 100,000 rpm or more.

mags993tt-home

I seem to remember reading that modern turbo charged cars (Saab's ??) have some kind of system to save turbos from hot shutdowns - I think it keeps the oil circulating even with the engine off. If there is no similar system on the tt why not? I am positive if I take my car in to be serviced no one is going sit idling the car for 2 mins before they switch it off, nor indeed will the average user which makes me wonder why they do not have such a system (it would be very 'Porsche' if they did). I may be wrong here but I am also pretty sure that I have not come across any advice on turbo cool down periods in the manual (and certainly not in big red writing) which seems strange as they even explain how to shut the boot lid without denting it...
M

SundayDriver

Whether they say it or not in the manual, turbos are red hot after a high boost run. They need a couple minutes of easy running to cool. Since this normally happens as you return the car to your driveway, paddock, etc, it is not that big a deal -that is, you usually do the cool off without thinking about it. Actually, the gentle drive is far better than idle time, as you get better oil circulation and air flow for cooling.

As far as service, etc - you probably won't see the high turbo temps in that situation. Even if driven hard I would hope the tech isn't in the boost as he returns to the shop and service bay. I have not heard of the 993TT or 996TT having an automatic circulation system after shutdown, but that does not mean it does not exist.

Greg H.

I was wondering the same thing as Pram - can an aftermarket turbo timer be installed on these cars? I've seen lots of Supras with these things on them. Kind of disconcerting to see a guy get out of his car with the engine running and then lock the door and walk away!

Greg

Rick in Portland

mags993tt-home

Remember, the key here is that it's a good idea to keep the engine running for a couple of minutes AFTER A HARD RUN where you have pushed the engine and was running under boost for a while. As others have noted, the Turbos get VERY hot, in fact, some of the connecting pipes get red hot under boost.

Whether it's in the manual or not, I suggest you listen to these folks or call someone who is an expert like Steve Weiner at Rennsport Systems or Mike Schatz at Schatz motorsports.

Rick
<a href="http://www.993tt.com" target="_blank">www.993tt.com</a>

Kevin

As Mark has mentioned a simple 2 minute idle down will prevent most damage. To answer why a turbo oiler recirculation pump (for cool down) aren't in use for our car, is because the 993TT uses a scavage pump that is driven off the intermediate shaft. Your would have to have the engine run and that would defeat the purpose. Or install a seperate electric scavage pump to evacuate the hot oil to the oil sump, it would be a plumbing nightmare to get everything in. One would have better results with a cool down drive prior to parking the car or using a 2 minute idle period. Also, one or two emergency shutoff's will not kill you turbo's, repeated hot shutdowns will usually cause the damage.