Kubcat

Please help a very frustrated 1974 2.7 911 cab owner.

Basically the engine overheats at anything below 3000rpm and is fine at over 3000rpm. It just started to do this one day for no apparent reason.

I have had the car (ex California now in Sydney Australia) for about 3 years. I have rebuilt the engine and added J

Kubcat

Sorry, lost most of my post, is there an issue with the spell checker?

Basically rebuilt the engine about 6 months ago with Nikasil coated cylinders, J & E pistons and SC cams. Rebuilt the fuel head, new injectors, new fuel damper and new oil cooler.

One day it broke the air cleaner mounts and started running rough and overheating. Porsche dealer has gone through it a number of times and says there is nothing wrong after rebuilding the distributor, changing the fuel pressure regulator, rebuilding the alternator, reshimmming the 11 blade fan and changing the muffler.

When the ambient temeperature is about 40 and the engine gets to 250 after about half an hour of idling or stop go traffic, I think there is something wrong, especially when I had no problem in summer.

The car is fine when running hard and even after half an hour of chasing and bieing chased at the last Porsche Club run the temperature never exceeded 220.

Short of running flat out everywhere, does anyonme have any other suggestions.

Jim

74 911
71 Jeep
56 Chev Truck

Steve Weiner-Rennsport Systems

Hi Jim:

A few questions,.........

Did the engine start this overheating in traffic AFTER you did the rebuild?

What exactly, do you have for a front oil cooler? Does it have a fan?

Where is the CO set at?

Where is the ignition timing set at?

Kubcat

Thanks for the response.
Engine was rebuilt 6 months ago and ran well through our summer with not much overheating.

No front oil cooler or lines for that matter, but as I said, it did not have this probelm through summer.

CO level is set at 1.6. Apparently according to my Porsche dealer they are set differently here due to emmissions. Having said that, inside the exhaust pipe looks quite black and sooty (rich?).

Timing is 5 btdc at idle and 35 at 4000rpm.

Don't know if this helps but the car will not hold 1500rpm, it bucks wildly. It will pull from idle without a problem, just will not stay at that speed while driving.

Thanks

Jim

Steve Weiner-Rennsport Systems

Hi Jim:

Your CO sounds lean to me,........ I like 2.0 to 2.5 % MUCH better.

Due to the fuel additives, never make any mixture judgements based on tail pipe color. If you want to determine that without a 4-Gas tester, do a few plug cuts and read the spark plugs. I'll be happy to e-mail instructions about how to do that if you send me a direct message.

Timing sounds OK.

From your description, I'd say that its bloody lean and you have a vacuum leak somewhere that is making the engine run lean enough to cause that bucking. Get a can of carb cleaner and carefully spray a little bit around where the manifold legs meet the heads, around the injectors, around the rubber boots that join the alumium manfold legs to the airbox and around the the throttle area.

If you have a vacuum leak of any kind, the idle speed will pick up.

Kubcat

Increased CO to 2% then 2.5%. Made no difference to temperature although throttle response has decreased.
Carb spray made no difference, although I suspect as it only happens sometimes, their is a leak, just haven't found it yet.

Although the old thermostat seems to work fine in a pot of hot oil, I have ordered a new thermostat just in case. I will keep you posted on results.

Kubcat

Latest update.

Changed fan as the old one was knocking and had worn aroung the pulley shaft.

The new fan has a smaller pulley and therefore spins faster.

All overheaing problems seem to have been solved although I have not had a good really long fdrive to be sure the problem is not just delayed.

The new fan is noticably louder and throttle response dropped again as I guess it is sucking more horsepower.

Not sure if the old fan was slipping and we just didn't notice or the extra airflow is masking the real problem.

I guess I should just be happy with no overheating.

Thanks for the help...