1975 911 Carrera Overheating

[sceaf3]

I bought my '75 Carrera (42,000 miles) in the spring of '09, and drove it all through the spring, which can be a very warm season here in Florida. The car was equipped with the trombone front oil cooler and I did not experience any significant overheating problems (220 in traffic). While it was in the shop for a clutch, I installed a Mocal unit to replace the trombone, as well as a front bumper scoop (no fans). Spring is here again and the temperatures are in the high 70s, low 80s; I have suddenly begun to see temperatures higher than with the old trombone. I have seen 250 in only moderate traffic on an 80 degree day. Yestereday, after seeing 250, I immediately pulled onto the interstate to get her cooled down. After cruising over 8 miles the temp was only down to 230 degrees. The oil cooler seems to be working as it gets warm as soon as the thermostat begins sending oil forward.
I feel like something is not working properly, but I don't know what it could be. I need help and advice.
Thanks,
Jack Skelding (sceaf3)

[carrera turbo]

Hello

I had a similar problem it ended up being a temp sending unit after alot of diagnostic. another thing double check the belt tension if you already havent. another thing the new system maybe opening at a higher temp allowing a higher engine temp.


im sure others will chime in with better info.

cheers ed

[Steve@Rennsport]

Jack,

230 degrees, much less 250, is FAR too hot for a magnesium-case engine and I'd not drive it until you find the source of the problem.

You may have a thermostat (there are two) thats not opening all the way, an obstructed engine-mounted cooler, a stuck distributor thats not advancing or retarding properly, excessively lean fuel mixture, leaking spark plug boots,...any number of things.

I would install a fan on that cooler, given your climate.

Hopefully, the Mocal cooler has a LEAST -12 fittings.

[sceaf3]

Carrera Turbo, Steve@Rennsport;

Thank you both for taking the time to reply. I immediately checked belt tension, it is ok; also checked timing, it too is ok. My CSI system seems to be rich, at least on initial start up. I will have it checked. The spark plug boots are brand new. I thought of the thermotstat possiblity, and thanks to your confirmation, I am taking the car to the shop immediately to have the thermostats checked; I am also having two 6" fans installed on the oil cooler.
I can't remember....does the engine have to be removed to get to the interal oil cooer and thermostat?
BTW. what is max safe temp for summer driving? 220?
Again, thank you.
Jack Skelding (sceaf3)

[sceaf3]

It seems that it would be relatively easy to diagnose the failure of the external oil thermostat: the front oil cooler would not heat up along with the engine. Does any one know how to diagnose the failure of the internal thermostat? Is it just a matter of elimination? If the external thermostat is ok.....then it must be the internal thermostat.....or is it more complicated than that? I guess it could also be a sheared pin on the interal cooler, but I really don't want to talk about that.
Jack (sceaf3)

[86 911 Targa]

Originally Posted by sceaf3

It seems that it would be relatively easy to diagnose the failure of the external oil thermostat: the front oil cooler would not heat up along with the engine. Does any one know how to diagnose the failure of the internal thermostat? Is it just a matter of elimination? If the external thermostat is ok.....then it must be the internal thermostat.....or is it more complicated than that? I guess it could also be a sheared pin on the interal cooler, but I really don't want to talk about that.
Jack (sceaf3)

Jack,

Before you perform any intrusive analysis:

The internal thermostat is a 100% mechanical device, without any indicators.

If your front (top) oil cooler line feels very hot with the engine fully warmed up,
then the oil is flowing to the front oil cooler, thereby elimenating the engine
mounted oil cooler issue.

If the lower line is cooler, then the front oil cooler thermostat is not open.

Remember, that once the engine mounted oil thermostat opens,
the oil is always at the front oil cooler, and is circulated through
the front oil cooler, and back to the motor when the front oil cooler thermostat opens.

A fan is the answer.

Along with a 200F fan thermoswitch.

The optimum temps for any 911 is 185F (when the engine mounted thermostat is fully open),
and 210F.

We have the '86 Turbo oil cooler configuration as per the attached jpeg,
but with a 200F front oil cooler fan thermostat, not the factory 248F.

Our '86 (dry motor) rarely exceeds 210F in 90F weather and only in traffic
where the temp may increase to 220F for a short time.

Oil consumption is about one quart/1K miles with 104K miles on the motor.

You may pm me.

Good luck,

Gerry

[86 911 Targa]

Engine Oil flow diagram.

[sceaf3]

86 911 Targa;
First, thank you. This is a lot of information; I will study what you have sent and be back in touch with you.
Sceaf3

[red 2.7]

Also make sure your oil lines to the front cooler are not squeezed by incorrect jack placement. It happens a lot.

[sceaf3]

Red 2.7
Thanks, I have checked the lines for crimps; they are ok, but I believe the problem is flow related. The intake and exhaust lines to/from the front cooler are both very hot, one is not cooler than the other. I think that indicates restricted flow. However, since the lines are not crimped, I belive that the culprit is the regulator valve. I have been told that it is prone to failure after many years. I have ordered one that should be installed by next week. I will post the results.
Thanks for the help.
Jack (sceaf3)

[boyt911sc]

Originally Posted by 86 911 Targa

Engine Oil flow diagram.

Based from the attached diagram, the fan will only run when the thermo switch is closed and optional switch closed too. When the thermo switch is OPEN, the optional switch could not activate the auxiliary fan to run. So you can not run the fan at any temperature as indicated in the flow diagram. The optional switch should be connected to the ground lug for it to work. Please advise on this comment. Thanks.

Tony

[sceaf3]

Boy911SC;
I don't have a fan on my front oil cooler. I removed the trombone unit and installed a Mocal unit. It worked fine until recently. I have the fans but have not installed them yet. I plan to use a manual swithch. The only time I have overheating problems, absent my current flow problem, is in moderate to heavy traffic, so I can turn on the fan when needed.
Thanks for your help.
Jack (sceaf3)