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Join Date: Jul 2018
Location: Portland Oregon
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1981 911sc running hot.....

Hi
New owner of a 1981 sc...seems to run hot especially in traffic/city. Typically on the highway the needle is just below mid mark and then in slower traffic creeps up to 10/11 ...and in heavier traffic went into the red. I of course shut it down but wondered what is causing the issue?
I felt the oil return lines under the front right fender...both are hot...so it seems it is getting to the cooler....any thoughts or suggestions very w, but I know my O2 sensor is not working....idle is between 950 and 1000 rpm.
Thanks for any suggestions
Old 06-16-2019, 05:24 PM
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You say both lines are hot, but there should only be one running to the radiator and one running back to the engine. Are the temperatures between the two lines the same or different? I'd probably check to see if something is blocking the radiator from allowing air to pass through.

Do you have enough oil in the engine? Considering air and oil cool these motors a lack of oil would mean less fluid to carry heat.

Is your engine fan running reasonable to your engine speed? I think a simple test would be to observe the fan speed while you rev the engine by hand.

A faulty o2 sensor would probably cause the engine to run richer as a fall back. The by product of that would just be increased fuel usage, but I can't imagine that causing the engine to overheat...
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Old 06-16-2019, 07:28 PM
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Do you have a trombone cooler in the front wheel well on the passenger side?
My experience was even though my thermostat in the rear passenger side wheel well was stuck closed it still go the trombone warm to the touch.
What i wound up doing was replacing the thermostat pill in the external thermostat and that solved my issue, well that an i added a carrera cooler.
however that was a much more involved process
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Old 06-16-2019, 07:40 PM
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new to you 911 take a strong flashlight and look behind the fan on top of the cylinder fins and see if there is any accumulation of debris, mouse nest, etc blocking airflow.
Old 06-16-2019, 07:54 PM
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bennysc1
 
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I have seen if the car is running a lean mixture that will cause the temp to climb in traffic.
Old 06-16-2019, 07:58 PM
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Hi All,
First thank you for the suggestions.
Yes I have a trombone cooler.....going to check the the thermostat valves tomorrow...though when I touch the trombone today after a drive it was relatively hot.....
Do not think there is debris but will look in daylight tomorrow....
I think it is not running lean but again hope to check that tomorrow....i did have a hot start issue recently and that has cleared up nicely.....I love the car and driving it....and want to do so almost everyday....and since I am in a city need to sort out the issue...on the highway all seems fine.
I want to thank the many people here whose experience is so helpful....a wonderful community!!!
Old 06-16-2019, 08:40 PM
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SO today I took a 50 minute drive , partially on the highway where the temperature was steady at 8'0clock. As soon as I had to come in on "city" roads temperature started to rise to 10-11 .....I felt under the front wheel and trombone was hot, both lines...and then checked in the rear wheel and again both lines hot going in and out of the thermostat......so not sure ...ambient temperature is 69-71 today.....any idea what to check next? Even with trombone cooler it should not get this hot in this climate should it? thanks for any input.....
Old 06-19-2019, 03:22 PM
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How do the oil lines that run from the rear thermostat to the trombone look? Check especially under the rockers front and rear. They are often crushed when the car is put on a lift. They could allow enough oil to get to the trombone so it feels hot, but the flow isn’t enough to cool the engine.

Mark
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Old 06-19-2019, 04:28 PM
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I went through years of having an overheating Kombi.
I had about 20 pages of advice on a VW Kombi forum, suggestions ranged from timing, carbs were running lean, fan shroud was dirty, tappets needed adjusting, air vents blocked... after following everybody's suggestions, I decided to partially dismantle my engine down to the oil cooler. It ended up being caked with grease, dust, dirt and mud. As soon as I cleaned it up, it ran 20-30 degrees cooler. Most of the above would also be relevant to an A/C porsche. Check fan belt is tight enough too and isn't slipping. All tinware is in place, no gaps in fan shroud letting cool air out. If oil has leaked onto top of heads/cylinder fins this can contribute to overheating. If you pull the dipstick out when it's hot, can you hold it or is it too hot to touch?
Definitely check cooler, tappets, fuel mixture and timing. I'd say they are the main culprits.


Last edited by Adrock; 06-20-2019 at 12:12 AM..
Old 06-20-2019, 12:10 AM
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Lines all look good.....wondering if it might be a bad sensor....I have reached under both the front and back wheels to feel the pipes and they are hot....which I assume means oil is going thru them fine, so could it be something else? back sensor to gauge or something???? thank you all for your continued help....will sort it out eventually.
Old 06-20-2019, 12:43 PM
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i doubt its the sensor if it is indicating normal then going up with stop and go driving.
i would be looking at replacing both thermostats both internal and external as a start . ( obviously just the pill in the external. ) it may not be opening completely.
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Old 06-20-2019, 12:55 PM
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I too have similar issues which I noticed last week going to Italy. 9 o'clock at moderate loads (3500 rpm and less) but goes into the red in stop and go traffic and continues to climb. About ten o'clock after prolonged 4000 rpm + in 5th. Trombone is hot no doubt. Some loss of oil pressure with temperature, as expected but not to bad with the Motul 300V15w-50. I run conservative ignition timing at 3degress at idle and 20 + at 4000, with twin spark. Not running lean either according to AEM gauge
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Last edited by trond; 06-20-2019 at 01:35 PM..
Old 06-20-2019, 01:03 PM
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trombone lines are both hot, then look for limited airflow around the engine mounted oil cooler. It does the largest amount of cooling anyways, what with that big ass fan on the alternator always trying to push air thru it.

Remove the big fan. Remove the alternator. Have a lookie lou inside and see what you can. Use your smartphone video recorder with the flash on to get a good look.

I wouldn't suspect the temp sensor as it seems to be accurate on the interstate and back road.
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Old 06-20-2019, 01:55 PM
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Quote:
Originally Posted by ralfoto View Post
.....wondering if it might be a bad sensor....
No, as stated by other members. Your car will run fine in Lambda open loop with a dead sensor. In fact, some prefer it. There is no reason to not have a functioning Lambda system on a stock car, though. I am assuming this is the sensor you are talking about.

Your air/fuel mixture screw may be set too lean, though, as stated. Rich is a b***h but lean is mean. Lean will cook things.

Lots of good suggestions here.

Here are my thoughts after reading all posts:

Oil level

Fan belt

Physical air obstructions (mouse nest(s) or shredded paper towel or the like in forward passenger side of engine - that's where the big air exits downward through the rear oil cooler). Baked on gunk defeating cooling.

Engine timing

Air/Fuel ratio - pay a pro to check it if you are still a pup as to Porsche maintenance. Another way to say it is don't eff with it until you know what you are doing.

Thermostat replacement

An easy to harder list, I think?

Do yourself a big favor and spring for the front cooler. Read, read, read on this beforehand. It will $$ sting but man, what a difference. Kill the snake causing the problem then buy some peace of mind.
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Last edited by Bob Kontak; 06-20-2019 at 01:59 PM..
Old 06-20-2019, 01:57 PM
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Did this hot condition just start happening or has it been gradually getting hotter?

Make sure the sump plate drain plug is oriented on the 1-2-3 engine side or driver side if USA delivery. If not it will impede the oil flow.

What plugs are you running? No fancy ones. Just copper.

Also, if your 81 is USA delivery your frequency valve should be operating too.

Dave
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Old 06-20-2019, 03:34 PM
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I need to ask....

How do you know the O2 sensor is not working?
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Old 06-20-2019, 03:53 PM
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Porsche decided to deal with the cool highway, hot in traffic, issue for the 3.2 Carrera by, eventually, installing both a better front cooler and an electric fan. You can do both.

Suggestions: Send your temp gauge to a speedometer shop to have real temperature numbers. Much better way to know what is going on. Hollywood Speedometer? A common procedure.

Buy an aftermarket cooler, or at least the latest 3.2 cooler (they got better during the model run). One with fins at a minimum.

I've not retrofitted a fan (and its housing and so on), but it shouldn't be hard to do. Maybe get one from a Porsche junkyard from a 3.2, along with all the trimmings?

Porsche operated the fan from a thermostatic switch in the front cooler. Some install a dashboard switch so they can turn the fan on before the thermostat does that.

Here is a picture from the '87-89 catalog (which you can download from the Porsche North America site):

Old 06-20-2019, 04:48 PM
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Can someone recommend an aftermarket oil cooler?
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Old 06-20-2019, 06:25 PM
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Ok thank you all...O2 sensor is not working as Lambda was just rebuilt , re-installed and three good Porsche mechanics checked and told me O2 is not working. We looked for mouse nests etc today by the back shrouding and found nothing.....and yes I am a newbie and therefore not doing this all myself....a very kind and knowledgeable Porsche Person locally has helped me and so far we ruled out running too lean (he checked that ) so a bit stumped. Granted his expertise is with earlier Porsche cars but be is very well informed on the SC cars as well......I am going to run it the next few days and keep close attention......again I thank all , a great community to have the honor of being part of.......
Old 06-20-2019, 07:35 PM
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I had a friend with a similar issue, car ran very hot and low on power in the upper RPM range. Turned out to be mis-set cam timing, retarded too much. Was the correct spec for a Porsche engine, just not his 1975 2.7L engine. Builder will remain nameless...

Maybe not so likely if you know the car has run properly some time before you took it over, but don't rule it out if all other possibilities are eliminated. My friend spent much time and money trying to get his car running properly before this was discovered.

Good luck and hope you get it figured out.
Bill
Old 06-20-2019, 08:18 PM
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