///alpinepower

Any recommended makes? Which one were you using?

Ruf-Dan-Ruf

Last one I had was a blitz which I had on a Subaru STi Version 5 2 door coupe. The factory turbo in this car produced 18# or 1.25 bar of boost so it could run very hot. As the turbo is mounted above the engine block and it is a sumped oil system as soon as the engine stopped all oil dropped from the turbo. So critical to run the engine long enough for the turbo to slow spinning to idle speeds.

The models have changed but all these seem to have the functions I had and more. http://www.blitz-na.com/turbotimer.html

AA993TT

After cool down of about 2 minutes there is a fan that runs while the car is turned off, is this normal and how long should the fan run? Thanks

Kevin

The heater/engine fan will kick on and cool the heat exchangers, if the temp is high enough.. I think its 170.. It is nice to have the air being moved through the hot ducts..

docjackson1

i have a 996 tt-i don't remember anything in the handbook about letting the turbos cool down after regular street use. is there anything in the 993tt handbook that directs you to let them cool down before engine shutdown? i fly a turbocharged twin engine airplane with older technology, and there is a necessity to let those cool down, but i am unaware of the need to do that after regular use in a modern car.

Kevin

doc;

On your plane you use higher leaded octane, a prop cooling the engine, and you aren't landing at full power, and we know that you have to let the engine idle down.. The 993TT and 996TT share the same turbochargers, they aren't water cooled..

If you don't cool then down you will be rebuilding the turbo's before 25K.. The proof is on the burnt shafts and slobbering seals on the turbine side. If you don't cool the turbine housings down with the idle circuit, the heat will soak right thru the shafts..

docjackson1

kevin-what you say sounds reasonable-you are correct, i let my engines in my airplane idle for 3-4 minutes before i shut down. but, if that's the case in the tt, why doesn't porsche tell us to do the same? i have owned several turbo charged cars, and never had a problem, despite not letting them idle. as porsche has to replace the turbos during the first 4 years, you would think that if that was the issue, they would make a big deal about telling us to idle the car before shutdown.

Kevin

I have posted many pictures showing the results. I don't know why Porsche doesn't suggest it in the 996TT manual. I do have a email from KKK saying that the heat shields around the turbine housings don't help the matter. The only reason as to why they are there is for shielding the tire from the heat.. I have said this before, when you pull your car up to fill the gas tank, do you stage your car or do you just pull up to the pump and shut the engine off? As far as many turbocharged cars? 911's because the majority of turbocharged cars are water-cooled.. I'm going to start a new thread posting some pictures of failed 993-996 turbo's.. All of them are heat related..

Stummel

Porsche does not suggest it, because in germany there is a law that it is not allowed to let the engine run if not driving.
at least it is not allowed to let the engine warm up before driving.
people used to do this a lot here, especially at colder days to save the engine

Thats all to save the environment and so on.

Porsche made a big deal that the 993tt was the cleanest production car in the world because of the 2 cats and obdII. So the cool down thing didnt fit into the marketing campaign i think.

just a thought

///alpinepower

Just a side note about an experience with a turbocharged car. My father has a W124 Turbo Mercedes and the first turbo lasted him 50k miles before it exploded....he drives pretty hard to work. Since then, he tries coasting in the last few miles and idles for a moment before shutdown.

hatchy

Kevin, how else would a turbo fail if it wasn't heat (lubication) related? Obviously, aside from FOD.

Kevin

Well, if one wastegate actuator hose blows off, or if it get a crack. Your engine will try to open up the other turbo to keep the boost in check, however, the uncontrolled turbo will be running in an overspeed condition. This will knock the thrust out along with accelerated bearing wear..

Next is oil starvation, typically we don't have to deal with this problem with our cars, however, many people will try to run 10k without an oil change! Not good, this will lead to bearing/shaft wear.

Overfilling engine oil, compressing a liquid (oil recirculated through the intake that is filled with oil) will cause coke build up and will put stres on the thrust bearings.. and this also leads to drowning the turbochargers from lack of scavenging.. Oil must me removed out of the turbochargers. If it isn't, oil coming in will be blocked and heat will build up/ along with oil being burnt on the turbine side. Bad situation for the health of your turbo's..

hatchy

Thanks. Won't all of the failures above show up as heat related failure? In other words, how can you tell that the failure is a result of lack of cool down vs poor maintenance?

I have 1 blown turbo (Garrett GT30 based) that has been sitting in the corner of my garage, and another turbo (Mitsu 18G) that has a blown seal on the hot side but still builds boost and still on a car. I am going to take these things apart when time permits and would like to understand why it failed, and what to look for...

Ruf-Dan-Ruf

Kevin, when the engine is switched off does the oil pressure go from the turbos on 993's?
With most Japanese Turbo vehicles this is the case.

Turbos spinning in excess of 100,000 rpm that loose oil pressure puts huge stress on the bearings and main shaft.

A two minute cool down allows for the turbo spin speed to come down to idle speeds thus when oil pressure is lost no damage.

On my 944 turbo the oil/water pump kept working for a period after enigine shut off to keep water/oil circulating through the turbo. I am wondering if the 993's keep the oil pump circulating oil after shutoff as well?

Kevin

Oil stops flowing when the flywheel/crankshaft stops