best oil for 1980 Porsche 911 SC?

Status
Not open for further replies.
Z

zoomzoom

Joined
Aug 20, 2003
Messages
799
Location
Washington, DC
Friend of mine has this air cooled 911 that he uses as a track and fun weekend car.

Currently he runs Castrol gtx 20w-50. He has been experiencing some overheating issues lately.

Would switching to syn oil help him out with lowering his engine temperatures. I was thinking he should try redline 10w-40.

Any other considerations or oil recommendations for air cooled Porsche?

Doug?
 
Synthetic oil doesn't have any more heat capacity than dino, so it won't lower the temp.

The fact that he's had overheating issues lately and not historically makes me think there is another problem with the engine that you're trying to get a quick fix for by buying expensive oil.

I would buy syn, as it's less likely to fail at the overheated temp. But I doubt it will fix the cause of the overheating.
 
Valvoline VR1 20W50, it has extra ZDDP. Good stuff for that car and can be bought at most any parts store. Brad Penn is good stuff as well, but it has to be ordered. Used to use the GTX 20W50 myself, but it doesn't have enough ZDDP after the SM rating. That Porsche needs at least 1300-1400 PPM of ZDDP....
 
Last edited:
Redline 10w40 would me my choice.

In either case, I would only use a synthetic. That thing makes a lot of heat. Synthetic will be better in a high heat application. Redline would be great.
 
Hi,
zoomzoom - Not all Porsche 911SCs (engines) are the same. The first question is does the engine have an oil cooler(s) fitted and if so what type is (are) they?

Did the "overheating" suddenly occur?

What is the maximum oil temperature recorded and for how long - and what was the ambient?

What is the oil pressure normal & lowest recorded) and has the oil pressure light ever come on or flashed?

This may help a bit - GTX20W-50 is a fairly robust lubricant!
 
If he does have an oil cooler, maybe it has gotten clogged with some debris.

How many quarts of oil does this engine hold, I am thinking since it is air cooled, it probably holds between 10 too 12 quarts.
 
Originally Posted By: Doug Hillary
Hi,
zoomzoom - Not all Porsche 911SCs (engines) are the same. The first question is does the engine have an oil cooler(s) fitted and if so what type is (are) they?

Did the "overheating" suddenly occur?

What is the maximum oil temperature recorded and for how long - and what was the ambient?

What is the oil pressure normal & lowest recorded) and has the oil pressure light ever come on or flashed?

This may help a bit - GTX20W-50 is a fairly robust lubricant!


I will pass on the question to him, I do know that he has oil cooler on the car.
 
If it's like my '85 there are two thermostats.

One is for a small oil cooler on the right side of engine. It's is located on top of the engine, remove air box to access. No need to drop engine.

The other is located in the right rear wheel well and controls the oil cooler under front right wheel well.

I have had overheating due to the first thermostat in summer stop/go traffic.

Oil won't solve this problem. See rennlist or pelicanparts forums for more details.

The factory rated oil consumption is 600 miles/qt. This should be considered if you are paying full price for oil.

I studied the ZDDP issue awhile ago and believe it is not an issue for stock cam/springs. I now have about 20K miles on 700-800ppm oils. It is an issue on during break-in on rebuilt and aggressive cam/springs. If frequent teardown is an issue this should be considered.

In the past I used GTX 20W50 year around in N. Cal. After study/experimenting oil for several years I have concluded 10W40 is best in the winter and _W50 in summer. I think the _W50 is too thick in winter and the scavenger pump has a hard time getting the oil out of the dry sump. Winter oil consumption dropped somewhat when going to 10W40 from 20W50.

There is a list of Porsche approved oils,such as M1 0W40 Euro, but these really need to be used with the factory OCI (12K miles or more)
 
How were the overheating temperatures measured?
Or, what were the symptoms of overheating?

Oil temps generally will be about 10-15 deg hotter with thicker oil. This is my empirical and vicarious experience.
 
I do not believe that a front oil cooler was standard on a 911 until 1984, so your friend probably doesn't have one. But with nearly 12 quart oil capacity and a sizable oil to air heat exchanger built into the engine shrouding, this engine is actually "oil cooled." Porsches of that vintage destined for the US got an oil temperature gauge that has no numbers while the European models had a gauge with numbers. Your friend might consider buying a Euro gauge/sender; they did not used to be too expensive, <$100. Then he'll know if he actually has a problem. On my 1988 Carrera summer oil temps would occasionally approach 260°F. Shutting off the air conditioner would drop it to about 230° which I think is about normal for 911s. Incidentally, I used to run Syntec 15-50 when I lived in St Louis. I switched to GTX 20-50 when I moved to Tampa. I noticed little difference in oil temperatures between the two.
 
Originally Posted By: bepperb
Synthetic oil doesn't have any more heat capacity than dino, so it won't lower the temp.


Where did you get that brilliant piece of information?

PAO and Ester compounds routinely demonstrated higher specific heat capacity and higher heat transfer coefficients than conventional base stocks. Also consider that they ever so slightly reduce friction over a conventional, then you have less heat to begin with.

A synthetic is also going to cope better with the increased oil temperatures associated with air cooled engines, thus maintaining viscosity and film strength better.

A large part of the cooling system for these air cooled boxer engines is the oil. Maybe it's overheating because of the craddy conventional developing deposits in the lines for the oil coolers.

PAO evaporates when it reaches extra high temperatures, versus conventional leaving a thick sludge-like film behind.
 
Actually Pao leaves behind harder deposits than dino oils deposits when it starts to leave deposits . Syn oil will not cure the problem.
 
The Mobil 1 0w40 I heated on a hot plate almost completely evaporated. The same can't be said of the 10w40 GTX that slimed my iron skillet. I threw it out because of how caked on it was.

A couple of hard deposits are better than a thick slime that restricts oil passage flow, drys out seals, and prevents the good oil from extracting heat from the interior surfaces.

Steve, if you want to want to try and convince me that a PAO is going to leave as many or more deposits than a conventional oil, you are sadly mistaken.
 
"PAO and Ester compounds routinely demonstrated higher specific heat capacity and higher heat transfer coefficients than conventional base stocks."

I would love to see that. I don't believe it.

Edit: I stand corrected, they do have up to 10% more heat capacity per a book from Leslie Rudnick.


they [synthetics] ever so slightly reduce friction over a conventional

New to me too.

I think this is a perfect application for synthetic oil, but I don't think that will solve the problem. I think something is wrong in the exchange of heat from the oil to the air... ie... closed thermostat, clogged cooler, maybe even oil deposits in the cooler or elsewhere.
 
Last edited:
Status
Not open for further replies.

Similar threads

B
Engine oil for Porsche 996 Turbo 0w40 or 5w50
Replies
8
Views
2K
bcnr33v
Tals975
Best performing oil for track use - Camaro SS
Replies
18
Views
2K
Snagglefoot
9
Best oil for a 3rd gen 4Rnr w/261k on it?
2 3
Replies
42
Views
6K
rainman49
I
Corvette Oil Question--Flavors of Mobil 1
Replies
17
Views
2K
The Critic
W
Is there a "best" oil for timing parts longevity in Ford's 2nd Gen Coyote?
2
Replies
23
Views
4K
zray1
Back
Top