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YOUR RESEARCH996 cooling & engine failures...
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Repair head crack
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We just repaired a head crack that occurred from this and I'll be testing the repair on the track in early August on the track.
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Was out in up to 111F heat today in my 03 Turbo and had A/C on whole time and car ran beautifully.
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Suggestion
Make sure you cooling system if filled properly and pressurized.
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Suggestion
The 996's temperature fluctuates more than some cars, but the ultimate cooling capacity is just fine (I even run AC on track, and still doesn't over heat, I don't have a third radiator either), I don't think it stays hot any more than some other car either.
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Guys I was noticing that the cooling system seems to be somewhat overtaxed on the 996 - is this another 'duhhh....moment??? This morning I noticed that my engine bay was still warm after shutting down the car yesterday at about 5 in the afternoon. (993 or 911 would be cold as a rock by then) If the cooling system can't keep up and cool down significantly after shut down, perhaps the hot soak is contributing to a lot of the engine internal havoc. Engine core temp actually rises for a while when the car is shut down and depending on ambient etc., the hot soak temp elevations could be causing the dissimilar metals to expand and contract beyond design elasticity and contribute to some of our engine failures!?!? I don't know, but just asking.
How about engine failure trends in the C2S and C4S cars - if those cars have a heavier duty cooling system that the pedigree suggests. Or even the turbos - I'm guessing that they and the "S"'s have a larger capacity cooling system as suggested by the huge intakes in front. Can the run-of-the-mill 996's be fitted with larger capacity radiator????
cockpit temp really responds fast when you run the temp up from LO to 60's when the a/c is on:^)
Crazy thoughts I know...I'll be these cars LOVE winter time
to absorb heat from hotter areas of engine and convey this heat away.
Was out in up to 111F heat today in my 03 Turbo and had A/C on whole time and car ran beautifully. Stopped engine several times and when I got back in engine fired right up.
One "trick" I learned a long time ago with my Boxster is if there's a wind try to park with car heading into the wind. This helps remove engine compartment heat.
When I had a garage and would pull very hot car into garage I'd shut engine off and lower garage door and get out and turn a fan on low speed and aim it to blow air under car to help remove heat from engine/drivetrain area to cut down on heat soak.
Not engine parts per se that are affected but wiring/hoses, and fuel injectors which can build up deposits from heat soak temps.
Had my Boxster in 116F heat in southern AZ and engine suffered no harm. That was probably over 100K miles ago. Engine has been run in anywhere from near zero F to well 116F temps over the last 7+ years and for 222+K miles.
I think your car's engine and my Turbo's engine are going to be just fine.
Couple of things: Change that coolant every so often. At least every 4 years. Lifetime coolant is hooey.
Any coolant leak take care of it right away. These engines, any modern engines, do not like to overheat. You have to be careful. A leaking cooling system may not show signs of obvious overheating.
What happens is without pressure hotter parts of cooling system flash coolant into steam. This steam forms pockets that block flow of coolant and very localized hot spots in engine (heads) occur. Bad for engine.
Change that oil/filter. Oil with miles loads up with water and unburned fuel. This lowers viscosity. That 116F experience happened with fresh oil in engine: Less than 1000 miles on oil. Had oil changed in Sacramento and then drove straight down to AZ. I change oil/filter every 5000 miles.
Today in 111F heat Turbo running with fresh oil: Oil has under 1500 miles on it.
Coming in off track -- I never track my cars but for those that do -- or pulling off freeway I'd give engine some easy running to help it shed considerable heat load that builds up from high speed running.
Most of time by the time I get to a gas pump car 's been off freeway for a few minutes and engine's had time to shed heat. If not, I'll circle block or just let engine idle for a minute or so on gas station apron. Also, I try to orient car into the wind so air flowing past helps remove engine heat as I fuel car.
Keep radiator ducts clean of any debris. These can pick quite a load of trash. I've not found any overheating problems but there's a danger of corrosion if you drive car in wet conditions. This debris gets wet and salts will corrode AC condensors and radiators.
Make sure both radiator fans work at low and high speed and the engine compartment fan works.
Sincerely,
Macster.
Oh and one other thing - the engine is blanketed on three sides by significant heat sources: two big mufflers and a couple catalytic converters. AND on the fourth side by the tranny - while not as significant as a heat generator, it certainly helps holds in heat during shutdown hot soak as well. Maybe this is the optimum engine for those big huge Artic-Cat snow machines???
+1 yes just go drive it.
FYI there was never a 996 C2S. The factory did have an option for a 3rd radiator which I think the tip already has. As long as you are not overheating you are fine. Make sure you cooling system if filled properly and pressurized. Also clean out those darn front radiator grills. They get packed with leaves, plastic bags, you name it.
we have noted several trends in the failures, which cars they come from and what they are... Certain cylinders and areas of the heads fail in different cars as well. The differences in Boxster and 996 failures also have trends and are quite repeatable.
It will take a few more years to gather enough trend data to make the forecasts that everyone wants to hear...
That said, the cooling system is adequate, but there are ways that it can be optimized. The issues we have seen with cracked heads primarily stem from casting flash within the heads that keep coolant from flowing to certain areas of some heads..
I know of several failures that have stemmed from inadequate bleeding of the cooling system and air pockets that occur in some areas of the engine that end up being "Hot spots"... We just repaired a head crack that occurred from this and I'll be testing the repair on the track in early August on the track.
Heat soak and cool down is critical and I have noted that these engines do not cool well at all when being shut down in higher ambient temps... We have a resolution for that, we just have to perfect it.
Marlon, I'm glad you brought this up. My new-to-me C4 stays hot for a surprisingly long time after I shut down. I'm talking hours! This had been bothering me, but I feel better about it now.
All the cars are slow to cool... Without coolant circulating through the engine and cooling system the heat soak issue creates a spike just after the engine is shut down.
We have a way to combat this and it isn't that expensive, finding a place to mount it in a street car is a challenge, but we are working on it.
When I datalog these engines I find they can still have coolant temps over 180F for 3 hours after being shut down with hotter ambient temps. The oil can stay hotter than that for longer.
The Boxster is the worst as the heat can't escape from the engine bay very well at all, but we have a solution for those as well, thats a bit more simple and uses a turbo timer from a Diesel truck..
My thought is that an automatic circulator motor that comes on kind of like a post-shutdown oil circulator for a turbo engine would work great. I just don't know enough about the coolant flow and temp activated/actuated valve arrangement in the 996 to draw it in my mind. The odd thing is that the Tip cars come with the 'third' radiator and it still stays hot. My .02 cts worth for now...
A post circulation system is what I have been referring to. One of our test cars already has one installed, but the killer is where to mount it and the fact that it can kill the battery in less than 7 minutes of run time.. Ultimately the engine needs to run to help keep the battery charged while the post cooling occurs, as the the stock water pump won't move enough volume by it's self.
The solution is to keep your engine from getting so hot to begin with, which is easily accomplished. Cool down after a run is very quick if you run your engine compartment and radiator fans for a few minutes while pulling the car into the garage.
The 996's temperature fluctuates more than some cars, but the ultimate cooling capacity is just fine (I even run AC on track, and still doesn't over heat, I don't have a third radiator either), I don't think it stays hot any more than some other car either. I've very seldom had the engine compartment fan come on when it's a 90+ degree day and just got off track with a short cool down lap.
You want an engine compartment that stays warm for a while, try an iron block M3... You're not only worrying too much, you're worrying about the wrong thing for "engine" longevity, engine compartment temp is not going to effect bearings or other internal engine parts, that's strictly a function of oil temperatures. Again, from what I've seen a 996 is just fine in this regard also, again unlike a lot of other cars...
Your engine would last far longer if it always stayed at operating temp, then the parts wouldnt go through cycles of expansion/normalizing.
I think the longer the parts stay hot and slowly cool, the better.
Of course spikes create rapid expansion which isnt good.
This of course is nothing to leave sleep over, ALL engines suffer from heat soak to some degree.
I agree that slower changes in engine temperature at cool down is optimum. What I do not like is the fact that the engines can rise in temperature after shut down as much as 30 degrees.
There is absolutely no risk to the engine of cooling down too fast even in sub zero temperatures. The only way you could cool it down too fast is to submerge it in a cool liquid,. Although there are a few areas of a water cooled engine that MAY increase in temperature after shutdown, these are few and experience minimal increase in temperature which is very short lived. These componants are primarily external to the engine or do not put your engine at risk.
Hm. I guess you've never heard of temperature coefficient of materials and delta Temp.
Try pulling a spark plug out of a hot motor and see what happens to the motor.
On the other opposite extreme example, put a very hot cup of coffee/tea in the freezer and see what happens.
Material change is directly proportional to delta temp and temp. coefficient of material.
My guess is that there is no one on this board that had the years of experience in thermal testing as I have.
BTW. No damage will occur to a hot cup of coffee or tea that is placed into a freezer that has a temperature of ZERO.
Like I said, air temperature in areas that cars can be driven cannot cool down an engine fast enough to cause any damage due to thermal contraction or expansion of any componant.
My guess is that there are few people on this board that has years of education and experience; including those who claim having multiple years of experience in "thermal testing."
That's not what you said. You said: "There is absolutely no risk to the engine of cooling down too fast even in sub zero temperatures."
Again, I urge you to try pulling a spark plug when the motor is hot and see what happens and WHY it happens.
Nevertheless, that is that. Enough pissing match for me.
Have a good day!
It would be optimal if the motor stayed at operating temperature indefinitely.
Our jet engines are simply measured in hot/cold cycles the parts go through.
You could relate this to the reciprocating engine too.
What in the world does removing a spark plug from a hot engine have to do with engine cool down? Seems to me you are changing the debate into something you might be able to defend. What a text book teaches you is most often absent of any real world truth.
Please name just one componant that can be damaged by turning off a hot engine in sub zero climate.
Text book? Ambient temperature is lower than internal temperature. When you pull a plug when motor is hot, it will cause stress cracks on the head. Why? You figure it out, you seem to have everything figured out already.
A text book makes one understand WHY instead of empirical results from "years of experience."
Enjoy your long weekend. Do they have 3-day courses on physics? Maybe you can get one over the long weekend.
/out
WHY are you still talking about spark plugs?
I didn't expect you would answer my question about what component would be damaged by shutting diwn an engine in cold climates. And if you did provide an answer, it probably would not have anything to do with the subject of this thread.
As far as your spark plug fetish. Can you tell me what material a spark plug thread can be coated with to eliminate any possible damage to both the plug and the head? HINT: Virtually all plugs have this coating.
Don't be afraid to continue your education using GOOGLE.
I have had my fair share of schooling from Engineers who cant even change plugs in their cars.
Engineering gives you knowledge that cannot be learned through tinkering.
Yup, text book knowledge is the way to go. You don't need the experience on top of it. Just memorize the pages and you're good to go. I guess that's why medical, engineering and physics books have not had any revisions in the past 200 years. The academics had it right all along.
Book learning is only the beginning of knowledge. Experience is needed to prove or disprove the theories that have been crammed into your head. Theory often does not work in application.
This is an interesting and timely discussion. This weekend we had some very hot temps. here in the Bay Area. My thermometer in the car showed up to 100F while I was on 280 doing about 80mph. I had the AC on the whole time and engine temp was fine, well within normal. Even in stop and go, after getting off the freeway the temp. never changed much at all. The next morning the car, in garage overnight and a warm evening, the car was pretty close to stone cold. These are only my observations.
Anytime you rapidly cool anything, metals included you run the risk of problems. This is especially true in air cooled airplane engines were you try to avoid shock cooling at all costs. We have seen many cracked heads, usually around the spark plug holes in airplanes, especially in training aircraft where the pilot is asked to perform tasks that require rapid reductions in power outputs.
My .02 cents.
Tony C
I have my A&P but only have experience around jet engines - recips, only in cars and tech school.
When a jet engine cools off, the rotor will expand on top from the rising heat and shrink on the bottom causing "rotor bow".
Excuse me...um, do all these theories only apply in physics? Do they apply in biology as well??
Um...um...is it all right to pull it out when it's still hot from peak temp and exhaustion? Will it damage my piston or its related components??
I've kinda been doing that all my life, and am a little concerned.....
manual says to let the car idle for a bit before shutdown after hard driving. When autocrossing I don't shut down between runs as the temp drops faster with the fluids circulating.
duuuuhhhh! - of course not! You don't sit in your car for hours with it not running matey - the only time the car dies - is when you are in it. So yes - you are correct
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