Engine Running Hot
 

I recently completed the rebuild of my 1983 911sc. The car runs well but seems to be running hot. After about an hour of moderate driving with no traffic and outside air temperatures around 80 F, the oil temperature gage is reading on the 10 o'clock mark (about 245 F from reading other posts). I checked the oil cooler on the engine and the front trombone cooler and they are both hot to the touch. Before reinstalling the thermostat on the engine, I placed it in hot water to check its operation and it worked fine.

I suspected the timing so I rechecked the engine timing. I would expect an advanced timing to lead to overheating. For the 1983 SC, the recommendation in both Bentley Manual and the plackard in the engine compartment is to time the engine at 5 degrees BTDC with both vacuum tubes removed from the distributer and plugged. I did this. After reconnecting the tubes and checking the timing with them connected, the engine is idling with a retarded iginition (about 10 degrees ATDC).

The only other thoughts I have is that the fuel mixture is not right. Maybe lean?

The only other thing worth noting, though I am not sure that it matters, is that the I have not reconnected the heater blower, though I have covered up the duct from the fan shrough to the blower.

Any suggestions are most appreciated.
Rick

Some thoughts:

Could the gage be wrong?
Are the cooling fan pulleys the correct size and is the belt on tight?
Could the engine mounted oil cooler be blocked on the air side?
Something wrong on the rebuild that causes added friction?

I have never investigated why this happened but...

When I first got my SC, it would eventually run up to near the second white line and stay there.

As I was trying different things to bring the temp down, I disconnected the blower hose and capped it (thinking the cap would force more fan air over the engine).

The car ran really, really hot with it disconnected - much hotter than I had ever seen. I hooked the hose back up and it returned to normal hot. I had intended to check to see if somehow the blower was coming on and directing hot air away from the engine. Tomorrow I'll check to see if hot air is blowing out of the valves under the car.

My problem was the engine t-stat - now replaced and it runs around 8 o'clock - but your message reminded me of the heater hose.

Shouldn't have worked that way - but it did.

Good luck with it.

Mitch

Just the opposite. Retarded timing makes it run hot.

Double check your timing and don't assume anything.

Joe

Re: Engine Running Hot
 

My experience was similar. I was doing some testing on reducing oil temps as our Alabama summers get rather hot. Although I had never seen my oil temps get to the 10 o'clock position, well, as a matter of fact I have never gotten to the 9 o'clock position I did see my temps reach an all time high after a simple modification. The modification, as I read about here a couple of years ago, was to disconnect the blower hose and tape off the outlet on the fan shroud. This, in my opinion and my experience, was not a wise move as my oil temps rose higher than I have ever seen - and this was with normal highway driving. I had a new temp gauge / sender as well as verifying the results with a infrared temperature gun.

I have read repeatedly here that this modification has apparently worked out well for others but my experience was exactly the opposite. This is one modification that I would never attempt to do again. I would restore the blower hose to its original configuartion to see if any improvements are noted. This would be the easiest first step in hopefully rectifying your issue.

For the naysayers... my oil / cooling system consists of factory SC fan, 28-row Porsche oil cooler, elephant racing oil lines, an extremely clean internal shroud / fin area, and a on-engine oil cooler that is equally clean. I do not run the AC and my engine oil is Mobil 1 synthetic.

Thanks for the quick replies. As always you all have great advise.

Here's the things that I will be checking tonight:
1) I will recheck the timing again
2) I will reconnect the heater fan and ducts and see if this makes a difference
3) I don't think it is the fan pulley as I put back the original pulley in the original configuration. If anything, the belt might be a bit tight.
4) I don't think there is air blockage on the oil cooler but I will try to check. Not sure how to get there.

I will let you all know what I find.
Rick

Here's a theory on the heater duct. The heater airflow goes through the heat exchangers and appears to be dumped into the rear wheel wells when the heater is not in use. This isn't a large flow but it does cool the exhaust manifolds, which are very hot. So the loss of this flow may upset the engine cooling. Being air cooled, the heat balance is pretty precarious and may be easily upset.

I don't know about the heater ducts situation, mine have been disconnect for quite a while and I run cool after getting the timing right.

You are justified to look into how lean you are running, and do so ASAP.

As bad as an experience as I've had with synthetic, if I had a rebuilt engine I'd be using it. This will lower temps 5-10 degrees (based on my one time experience).

How about spark plugs and heat ranges? I don't know that much about them, will they make a difference?

What's your idle speed?

Look for air leaks around your blocked off discharge heat vents (see arrows).








http://forums.pelicanparts.com/uploa...1156445209.jpg

Hladum,
That seems to be one possibility. I have been thinking about that as well but have drawn no conclusions.

Kach,
When I first start the car cold, it loaps around for about 5-10 seconds, sounds like it is going to stall ramps up and then starts to settle down at 900-950.

Not sure about the spark plugs. What I used was bosch plugs. I don't remember the number but it was the one specified. Maybe W5C or W5DC??

Is there any way to check the leanness other than a probe??
Rick

Here's the latest:
I checked the timing to the spec and I am right on.

I installed the heater fan and ductwork this evening. Took the car for an hour long drive. Outdoor air temperatures at the time were about 75 F. The temperature gauge in the car made it up to the 9 o'clock position (about 215 F) and stayed there. This was a slight improvement, though it still sounds high given the temperatures and mild driving.

I will take the car by a local shop tomorrow and see if they can check the mixture.
Rick

I took my car to the local porsche mechanic to have him check the fuel mixture and verify the ignition timing.

He said that I was running lean and adjusted the mixture. He then checked the timing and said that it looked fine. He thought that this would bring the temperatures down.

Unfortunately, it did not. With all of this, I am still running at 9 0'clock on the oil gage after about an hour, with moderate driving, ambient temperatures around 75 F.

Any other suggestion? Or things to look at. Is there any easy way to get to the engine mounted thermostat without dropping the engine? partial drop?
Rick

Are your oil lines severly crimped going up to the oil cooler? Be sure to check at the curves near the wheel well edges.

I ended up going with a full engine drop for my thermostat. I wanted to have the engine mounted cooler checked out to be able to rule that out - as such, the engine came out.

Good luck with it.

That might be part of your problem assuming he fattened the mix to where it now runs hot.

Did they put a new sending unit in with the motor rebuild? Have you checked it with some other type of thermometer dont trust the gauge my gauge reads about 190-200 but the car actually runs cooler about 155-170

The gage theory (inaccurate gage) now sounds most likely to me. However back when I was running hot, if I opened the engine lid up in front of a stranger (off and or runnning) the first thing they would say is "Jee your engine puts off a lot of heat". You could feel the hot air radiate off the engine and feel it like an open oven baking cookies.

Touch the rear bumper. Could you fry an egg on it? Then you are running too hot. It should be warm to the touch not too hot to hold your hand on it for a while.

Good thoughts. I rebuilt the engine myself. Actually checked the cooler thermostat before installing the enging and it opened fine. I did not replace the sending unit and I don't have a feel whether it is good or bad. I also don't know how common this "high temp" condition is with this car as it was December when I bought the car so I had been driving in cold weather only.

When I initially experienced the problems (at 10 o'clock postition) the bumper was very hot. Now after some adjustments, that problem doesn't exist any more but it is still at 9 o'clock.

I will look today and see if there are crimps in the lines and will also check themperature against gage.

One other question:
1) The cooler in the from wheel well is sprayed with undercoating. Not sure if this was original or done some time later. This could have some effect on the heat transfer of the coil. Is this common?? Not sure when they would install the oil lines in the production process?

Thanks for staying wiht me on this.
Rick

If you are running at 215 F...sounds to me like you fixed your problem. That is normal for summer.

Rick,
Just some more information to assist you in getting those temperatures down...

http://forums.pelicanparts.com/porsche-911-technical-forum/176903-checklist-reducing-heat-hot-running-engine.html

congrats
 

on rebuilding yoiur own engine. WIth all the money in parts I would never do it although I have built several other motors. ONE THING NO ONE HAS MENTIONED AND CALL ME SILLY , but you are running a tight engine in the summer. Of course its going to run 10 -20 dgrees warmer. In a few hundred miles this should abate. BTW, it is very easy to check your fuel air mixture yourself. Check out the tune-up dvd sold on this site. Basically you just need a digital volt meter.
I am battling the same thing with my 74 that is a majorly pumped up six weber carb little hummer. I was tired of my bumper always getting black so I leaned the carbs so the plugs were a nice milk chocolate brown instead of charcoal grey and very little soot builds up on the bumper. Now if I drive at 65+ MPH in 90+F weather it will jump up to 235 degrees. A good tech told me this is nothing to be concerned about but I am planning to install an aux cooler just to drop in to 210. IMHO any cooler than 200 and the engine is no longer as efficient. Old Type I VW wanted to be at 186F but that is cause of the poor design regarding the #3 cylinder exhaust valve. ANd even when all dialed in , it was considered routine maintenance to grind valves at 50k miles.

Thanks for all the good thoughts. This temperature may be fine as it is. Actually with today's driving, the temperatures hung around the 8:30 mark. The thermostats seem to be opening like clock work. I have actually been pulling off and feeling the coolers. I can also see the temperature indicator take a slight dip when it hits 8 o'clock position, as the thermostat opens. Not sure if its possible or my imagination but it seems to be gradually running cooler, while the outside temps are staying pretty much the same 75-78 F. Zumwoll may be onto something. I am waiting for a warm day to see for sure.

I too had a local porsche mechanic tell me the other day that the temps were fine but then I have had others say they are high. In any case, I am still looking at a couple of things. In another post, there was the suggestion to spray brake cleaner into the engine mounted cooler by removing the fan and then flush with water. I will give this a try. It may not change anything but can't hurt.

I will let you all know how it works out.
Rick