SSST

I do the same thing. If I've been driving it hard, I give it an extra minute at idle in the garage.

Macster

Ran this question over and over again through my head and I have come to the conclusion it has to be or should at idle.

I do the same as you, well, not for 2 miles, but I leave the freeway -- and in doing so on the off ramp I coast down on closed throttle to a stop, then off the off ramp and onto surface streets it is 35mph down to 25mph for about a half a mile until I'm home.

This coast down keeps engine rpms up and this means more water gets circulated through the engine's cooling system and more oil through the oiling system (and oil cooler).

If one puts in the clutch/shifts to neutral the engine rpms drop to idle which means of course less water gets circulated through the engine and less oil in the same distance.

Anyhow, what I do, have been doing is letting the engine idle until I see the oil idle oil pressure drop some. It doesn't drop much, the needle settling down just enough to be at a noticeably lower oil pressure. For instance instead of 2 bar the needle drops to just under 2 bar, maybe a needle's width.

The few times I've let the engine idle longer but so far I have never seen the oil pressure increase any.

The coolant temp gage needle is not sensitive enough to really tell if the engine coolant temp is up, down, or steady.

This real but slight drop in oil pressure says to me the oil has heated up which means it has helped remove heat from the engine and some of this heat of course has to be from the turbos which have oil flowing through their bearings. (Aren't the 997.2 turbos water cooled?)

I seldom let the engine idle a full 2 minutes unless I happened to pull off the freeway or highway with no surface street cool down driving between then and when I get to where I'm headed -- almost always a fueling stop -- but I always let the engine idle a minute or so.

Even though the turbos aren't making any boost at those surface street speeds and engine load is not much there is a lot of hot exhaust gas flowing through the turbos which of course heats these up.

They need time to shed this heat to help extend their service life. They can only shed this heat to the engine oil. The exhaust gases passing through the turbos at idle I do not believe carry away much heat. But every little bit helps I guess.

Sincerely,

Macster.

SSST

Macster, you may be right and it certainly doesn't hurt, but I have driven turbo charged vehicles exclusively for the last 11 years and I have never had a turbo failure. This includes a couple of Turbo diesel trucks that pulled a 15K lb 5th wheel all over the place. I had EGT guages (pre and post turbo)and everything.

I really think modern intercooled turbos are less susceptible to heat related failures than their ancestors. Especially when used in normal street driving conditions.

That said, I would be interested in the opinion of an expert like Kevin.

jcb-memphis

Just what I do. Based on what I have been told by my tuner...balance of oil circulation v heat soke. It seems to be the inflection point/sweet spot/yada yada.

Anyway, it is just a formal habbit now.


Jeff

Macster

Apples to oranges in some respects.

Diesel engines run a lower exhaust temperature. This is why variable turbine turbos showed up several years later in gasoline engines vs. diesel engines.

For example, back in 2002 I bought an 02 VW Golf TDi with a variable vane turbo. Porsche otoh didn't offer a variable vane turbo until the 997 Turbo and IIRC Porsche was the first automaker to offer a variable vane turbo in a gasoline engine application.

My info is the hold up was getting the variable vane feature to the point it could withstand the higher exhaust temperature of the gasoline engine.

Also, IIRC the 997 with the variable vane turbo is a water cooled turbo. I can't recall if the TDi engine's turbo was water cooled. I got rid of the car in 2007.

The intercooler removes heat from the incoming charge after it has gone through the compressor side of the turbo. This intercooler does not cool the turbo, and specifically the turbine which is driven by the exhaust gases.

I have been told that under high loads and higher engine speeds exhaust valves can reach a dull red temperature. I would not be surprised if the turbo turbine doesn't get this hot under similar conditions.

The 2 minute idle cool down may be overkill on Porsche's part, too. I can't argue with this if you want to claim it is overkill.

One reason I can't argue is I suspect more than a few Turbo owners do not bother with this cool down business and there doesn't seem to be a large number of turbo's failing and those that do are probably failing due to manufacturing defects and not because the owner failed to give them a 'proper' cool down.

(I remember when I bought the TDi I was touting it to a co-worker. He looked into one but his wife nixed the car one reason was no way she wanted a car that required any cool down of the turbo before shutting the engine off. She argued that she wanted a car that required no special consideration in this regard. She also nixed it because the price premium of the turbo diesel model over that of the 2.0l gasoline engine model meant it would take years of fuel savings driving the diesel to make up the price premium. Did I mention she was an accountant?)

Anyhow, even if there could be some argument this cool down business is not needed, I'm reluctant to risk/gamble with the turbos on my 996 Turbo so I do give the turbos a chance to cool down, just in case Porsche knows what it is talking about when it specifies they need 2 minute idle to cool down.

Sincerely,

Macster.

SSST

In addtion to the trucks, I did have a S80TT and a 335TT. I have no doubt the EGT's are the issue whether diesel or gas. I don't know what the temp limit is on the Porsche, but on my trucks, 1200 F was the point past where extended running would cause the veins in the turbo to get soft and the oil to cook.

The intercoolers on the trucks cooled the oil coming out of the turbos as well as the air charge. I traced the lines in the Porsche and it appears that they also go through a cooler (I could be mistaken, but that's how the plumbing looked to me). I've always been under the impression that the purpose of the cooldown period is to keep residual oil in the turbos from cooking and gumming them up.

Normal, low RPM driving of an intercooled (perhaps I should say oil-cooled) turbo car would accomplish the same thing as idling for a couple of minutes.

I could be wrong. That's just the way I understand it.

mdkelly1

No issue at all for the Turbo as a daily driver. It's contented to roll along at low speed limits and through intersections with all the other traffic, and if the need or inclination arises to mildly put your foot in it, you'll find all the performance you need or want without stressing anything on the car, or with yourself for that matter.

If there is a track day in the future, the Turbo will reward you there without any complaint as well.

Do the regular maintenance, and drive it like it was designed to be driven.

threesacharm

Hey everyone. I use my 996 TT Tip every 4-5 days for a 7 mile commute to work, 14 miles round trip, all city driving, with a top speed of 60 mph for about 5 minutes in the middle of my travel. No mods on the TT other than a Speedtech exhaust and 20-inch rims. It has 108k on the odometer. Any advice, if my goal is to preserve my dream car? In what manner and frequency should I use the original turbos so that they can last for awhile? I'm aware of the factory recommended maintenance schedule. Any advice for extending the life of my Tip tranny? It's never been opened and it seems to still shift smoothly (maybe sluggishly even, but definitely not abruptly or jerky, whether in auto or manual mode). I don't ever plan to part with my TT. Thanks in advance, guys!

wross996tt

Do a search....Kevin recommends a 1-2 minute cool down at idle in all cases (even to fill up with gas). He has recorded temperature drops with and without cool downs....since the oil stops flowing when you shut down (and it is the major cooling for a turbo)...

911Königin

Love this thread

Dans996tt

Years ago I owned several Kenworths and the cool down was required because the oil would coke in a hot turbo. Now we have synthetic oil that doesn't coke so is a cool down necessary? 2 of my kids drive turbo Volvos that run synthetic oil and have never had a cool down in 200k with no ill effects. I think we have a bit of ancester worship, I haven't bought a tt yet and was wondering what the owners manual says?

Dan

Kevinmacd

The issue is the high heat that is transferred from the driven wheel to the spinning shaft bearing. By idling for 1 to 2 minutes it allows the oil a chance to cool down the shaft bearing when the turbo is not seeing it's highest exhaust temps. Porsche states cooldown necessary when driven hard.

jcb-memphis

Some volvo's just circulate water for 30s or so after you shut the car down...our 996tt's don't have this feature.

Wish they did.

Just a thought....apples to oranges.

jeff

Dans996tt

Neither our 850 turbo or C70 turbo circulate after shutdown. So the owners manual says to allow cooldown time when running hard but none required for normal driving?

Dan

Macster

Briefly, all you can do is give the car reasonable servicing, take care of any little problems before they become big ones, and avoid accidents.

Reasonable servicing consists of regular oil/filter changes, and I prefer to do this at 5K miles. Also, every 4 or so years I have the coolant drained and replaced.

Now for both of my cars, unfortunately, this time interval coincided with in the case of my 02 Boxster a busted radiator (hit a tire carcass at night) (~100K miles), a failed water pump (172K miles), and a bad coolant tank (~220K miles), while the Turbo had a busted radiator (from a deer hit) (~12K miles).

My advice would be to avoid forcing the service by avoiding hitting stuff.

Every 2 years have the brake system flushed/bled.

Change the intake air filter, fuel filter, and cabin air filters at reasonable intervals.

I have the manual transmission fluid changed in my cars around every 50K to 60K miles, though I did let the Boxster go past 90K miles before I had the fluid changed the 1st time.

Oh, and plug changes. Different models require this at different miles or even after different elapsed times.

Use a name brand gasoline of the proper octane grade, and buy gasoline from a busy station.

I would add if at all possible you should try to get the car out for a longer drive once in a while. I'm still surprised by how a 50+ mile drive at freeway speeds (with an occasional hard acceleration to pass a slower vehicle) really perks up the engine of my cars. And I drive my cars 60 miles (mostly freeway) a day for my work commute, so it is not like they see short trips in between the longer drives.

In your car's case, the Tip probably should have had a fluid change by now.

However, if it hasn't it may not be the best thing to try to 'catch it up'.

The risk as I've been told is if the fluid is ignored too long that it seems to be more likely the Tip will act up and seriously act up after a fluid change. Better to let sleeping dogs (Tips) lie.

However, if it were my car, I would probably -- probably -- change the fluid.

My thinking such as it is is if the Tip was sick enough the fluid change would push it over the edge, I'd prefer this happen on my timetable, sooner rather than later.

Since I'm often out and about in my car and sometimes hundreds of miles from the nearest dealer (nearest large town in fact) a transmission problem/failure could be a real bother so I would change the fluid and treat the car/Tip to a considerable shakedown period by using the car around town, for work commuting, short but high speed road trips, etc., before I headed out on a couple thousand mile road trip.

Lastly, keep the car clean and looking nice. Be sure to keep the water drains free of plant trash and the radiator ducts clear of plant trash, road litter, or even road kill.

Sincerely,

Macster.