Engine Temperature Spikes

[wichitaguy57]

Stock 1983 911SC

I’ve had five temperature spike episodes since April including my testing today. I live in a fairly rural area so I don’t often drive with much traffic. What I found today is this. If I closely follow a behind a car (not tailgating) in the 45 – 55 mph range, shifting between 3rd and 4th as they slow for turns in the road; after three or four miles my temperature gauge starts to climb from the 205/210 range up and beyond 250 depending upon when I pull over. I then turn the motor off, raise the lid, wait ten minutes while I talk with my troubleshooting friend before continuing on my way. Back on the road running by myself, the gauge will go back down to 210 and stay there running approx. 3200 rpms (60mph +/-) in 4th gear. I was able to test and verify this twice today. The second time I turned off onto a side road and keep driving without any other traffic in 3rd then 4th gear and the temperature did not go down, but continued to climb. I finally shut down waited as before. The temperature went down as I drove on.

The original gauge and sender where replaced with the numeric gauge after episode two. The external thermostat seemed to be working, but I replaced it after episode three. I do have a small dent in one of the brass lines behind the front wheel. I do have a Mocal cooler without a fan which I cleaned by blowing compressed from the inside out. Cleaned the outside of the thermostat and oil brass lines. Oil level is good. Oil pressure went down as the engine became hotter (240F+). When coasting into a parking area the engine ran rougher, but returned to normal when I would start again. The temperature during the first episode was 55F and between 65F and 80F for the others. I’ve run by myself on 90F without any problems.

The cooling system can’t dissipate the heat load, but is it a heat problem or a cooling problem ? Not sure what to look at next… Pull the fan?

Thanks,
Guy

[RoninLB]

I have oil temp issues in mountain areas at lower rpms.

for instance if i keep the rpms down in 5th gear the cylinder head temps may start to rise. When this happens I downshift and keep rpms between 3.5-4k

before the cylinder head temp gage [CHT] install the only indication was that oil temps would rise. By the time the oil temp rise it's almost too late as it takes a long time to bring the oil temps down. The CHT gauge reflects engine heat immediately and gives me plenty of time to prevent oil temp rise.

my car has a front fender cooler without a fan. Oil temps are fine 99% of the time but for a 180 hp engine there isn't much room for rare events as the oil cooling is on the edge

hope that helps

[kach22i]

I don't know how warm it is outside when you are starting out in the 205/210 range, but that is high unless it is about 90 degrees outside.

Going from 210-250, a 40 degree range is a bit high, but okay.

If you were to start at 170-180 (where I am at on 70 degree days) then a 40 degree raise gets you to 220, not bad.

I once lowered my operating temperatures over 30 degrees by getting the ignition timing right (stupid shop messed it up). In my case I had to reindex the distributor, most likely you will not have to.

Check your ignition timing.

[Grady Clay]

Guy,

First,
Welcome to the Forum
You will find a lot of help here.


You are getting good advice above.
Make sure all the engine running ‘tuning’ has been addressed.
Those include ignition timing,
mixture settings
and vacuum leaks.
I recommend you know the basic condition (cranking compression, cylinder leak, valve adjustment and cam timing) – all baseline ‘important to know stuff’ about your engine.

Engine ‘cleanliness’ has an effect on cooling.
Is the engine oil cooler clean?
Can there be a rodent nest under the fan shroud?
You have the front cooler and oil pipes relatively clean.


All that said, our 911s are somewhat ‘thermally challenged’ in hot weather and original (stock) configuration.
The two common ‘fixes’ are:
Replace the OE cooler with a later (or aftermarket like yours) version with far more cooling capacity, an electric fan and improved air ducting. (I’m not sure how large your Mocal is)
The other is to change the engine fan ratio from your 1.62:1 to the 1.82:1 used on the 930 Turbo. This reduces the heal load on the oil cooling system by improved cooling of the heads and cylinders.

Are you using you’re A/C during these ‘spikes’?

If the heat off the leading car is the cause, you are driving too close for the street.
I can tell you first hand that effect from being in a 935K3, 6” off the rear of Bob Akin’s (and other’s) 935K3s for hours at a time. One 650 hp furnace chasing another 650 hp furnace.

Best,
Grady

[wichitaguy57]

All,

Thanks for the feedback.

Not running A/C when the problem occurs.

Pulled the fan so I could get a look at the top of the cylinders. Oil/dirt crude on top of #3 and #6. Crude by #5 intake port. No mice nest or such. I didn't realize the fiber glass shroud had a channel going to the right that must be sending air to the top of the oil cooler. That channel had a film of oil and dirt although I couldn't see the top of the cooler. Sprayed de-greaser, wiped and brushed away as much of the crude as possible. Liquid crude dripped down and under the engine, but I never saw any liquid run out the bottom of the oil cooler. Not sure what that means. Dirty yes, but no smoking gun either.

When I purchased the car last fall, it had oil leaks in the cam oil lines, oil tank sending unit seal, and oil return tubes. These have been repaired and the engine area top and bottom cleaned.

The PPI showed good numbers for compression and leak down although I don't know them off the top of my head. This past winter I replaced the plugs with Bosch WR-5-DC+, ignition wires with Magnecor KV85 (Red) wires, new cap and rotor, timing set to Bentley numbers for an 83, O2 sensor replaced, new fuel injectors / seals and adjusted the fuel mixture using the dwell meter technique as described on this site. I have a rough idle at start up that will go away so I went through the CIS analysis looking for a problem. Found a low resistance reading in the WUR. No vac leaks, but I'm not totally convinced. Planned to drop the engine this winter to fix some other common oil leaks and to take a closer look at the CIS.

Current Mocal is the 6x12.

What type of results have people had with the addition of the side light air scoop?

Thanks again,
Guy

[RoninLB]

Originally Posted by wichitaguy57

What type of results have people had with the addition of the side light air scoop?

some guys say the side light scoop is worth 10F. Track guys would have harder info

some guys say the C2 electric rear spoiler is worth 10F when raised



a wild guess is that you may have an engine operation related issue and that a scoop is always a good idea but it may only be a band-aid

if this ends in a happy outcome please come back here and post the info

good luck

[kach22i]

Originally Posted by wichitaguy57

timing set to Bentley numbers for an 83

There is not a Bentley covering my year (1977), so I don't know what's in it.

Do they tell you to check the advance while revving at 6,000 rpm as well as at idle?

Lots of threads on this topic.