Its.Por-Sha.Not.Porsh

My father swears up and down that his 1977 Porsche Targa was oil cooled and that's why it always was leaking oil and that they were infamous for it. I always thought that as well, until I foudn out they are air cooled and the 996 are water cooled, now this site says air/oil, so hows it work whats the deal explain oil cooling to me.

Bill Verburg

All 911, 964 and 993 are air and oil cooled

JackOlsen

Any engine is cooled by a number of sources. Water-cooled engines rely primarily on radiators and plumbing to do the trick, but they also lose heat to the air around them, as well as out the tail pipe. If you think about it, even the act of releasing mechanical energy through the drivetrail releases (and also generates) some heat.

Pre-996 Porsche flat six motors use a fan that moves huge quantities of air over the cylinders and heads for cooling. This system is supplemented on 911's by an engine-mounted oil cooler which relies on the same main fan. On many 911's, there is also an external oil cooler in either the front passenger-side fender or in the front bumper that uses passing air (sometimes with the help of an electric fan) to cool the oil -- which, in turn, helps cool the engine.

Nothing about either cooling scheme would do anything to cause oil leakage.

The 911 flat six uses a dry sump oil system, which stores oil in a separate tank rather than using the bottom of the case as a reservoir. A 911 will typically take much more oil (10-14 quarts) than a wet-sump car. Leakage, when it occurs, could be attributed to the modular construction of a 911 engine, and also to the fact that it undergoes greater (and more rapid) temperature variations than a typical water-cooled motor does.

Its.Por-Sha.Not.Porsh

Thanx Jack, that helped alot... so not only does it use a fan to blow air and cool the engine, it has an oil cooler that pumps cooled oil into the engine to help internally cool the engine?

Now, my next question is... why did they change that?

JackOlsen

They changed to water cooling because they'd reached the limits on the amount of power they could produce with the same basic powerplant with two-valve heads. They'd already moved to water-cooled four-valve heads on the race motors.

It was pretty much inevitable, if the cars were going to remain competitive with Porsche's rivals.

DGaunt

Another way to think of it is that air cools the cylinders--mostly--and oil cools the heads--mostly. Of course there is some crossover, but if your fan belt goes south, the cylinders fry, if you keep running the engine.

paradisenb

I think it is beneficial to note that full race Porsches engines, even today, have a dry sump oil system and only the heads are cooled with liquid. The 996, on the other hand, is all liquid cooled. The cost to manufacture liquid cooled Porsche engines is about 1/2 to 1/3 of what an oil cooled engine costs. One VERY BIG motivator for a manufacturer. The GT3 has a dry sump oil system.