DG84S

Have you tried the lower ratio of coolant -vs- water that was suggested in an earlier thread? They claimed that, while coolant provides necessary lubrication, heat transfer ability worsens as coolant concentration increases. That was news to me, but it may be worth trying.
Dave
BTW- Just found out today that I have a schedule conflict that will prevent me from attending the Texas Sharkfest in Blanco. :-(

ErnestSw

Very interesting Jim,
But why do some run cool and some run hot?

ErnestSw

I noticed something interesting today. I'd replaced the temp sender to the gauge and the temp II sensor (I'm clutching at straws) and went for a drive. The ambient temperature was only about 84F, but the needle climbed above the last white mark anyway. I turned on the heater and the needle went down to just below the top white line. I could have sworn it didn't make a difference the last time I tried it, but I may have not left the heater on long enough.
It seems that adding that "extra radiator" makes a significant difference.
What do YOU conclude from this?

T_MaX

Rad fans not operating at full speed?

Hook each one up separately to direct 12Vdc and see if there is a difference in fan speed.

Jim very interesting indeed

Drewster67

Has anyone suggested water wetter?.

reno928s

This is like a soap opera. With all the gurus I can't belive we can't figure this out. Mark and Jim any other suggestions? Reno

Gregg K

I would guess that the air velocity drawn thru the radiator due to the mechanical fan is no more than 60 mph. And that the engine temperature at highway speeds would be the same, with or without the fan. In fact, at some speed the fan actually gets in the way of cooling (altho that may be academic, ie. like 400 mph). Another guess is that they cool adequately even near idle. I doubt the fans are the cause of the observed overheating.
I would not expect a properly cooled engine to run cooler when the heater is turned on. Not unless the engine is undercooled to begin with. I know, I've done that when pulling my backhoe on a trailer behind my truck while going up a grade on a hot day. But this is a sports car with no appreciable load. I still don't know the history. Did this suddenly start one day? And did you boil the block and heads when rebuilding? I mean, it sounds like a hot spot due to an obstruction that causes pinging as well as overheating.
Just my simpleton ranting after a cup of coffee.

ErnestSw

Starting again from scratch, I'm now getting some wonky readings from the fan control unit in the cabin of the car. T_Max is sending me a spare unit and we'll see what happens.

Jim bailey - 928 International

I was wondering about control units / both computer and "amplifyer" the part numbers were used for several years but just what temperature was programmed to be " normal " . The suggestion to hotwire the fans would at least answer the question of if it might be an airflow issue . It does seem interesting that using the heater core cools the car but that is in effect a "larger radiator " and more airflow . It does seem that perhaps the engine is being told to run hotter by the brains . New pump, new radiator , thermostat wide open , thermostat bypass closed , ......no answers here just questions .

Steve J.

Ernest - Even though it runs hot, does it ever exceed the capacity of the cooling system where you are forced to shut it down before something is damaged? Does the temp just keep climbing into the red and off the guage or does it always eventually level off - albeit on the hot side? What happens if you just ignore the "problem"? Does it boil over? Smell burning paint or plastic?

ErnestSw

Steve,
The car never "overheats" to the point where the red light comes on. The car ALWAYS reaches the same equilibrium, ie. above normal. I'm strongly suspecting that the control unit that's responsible for the fan speed is faulty. I'd love to jump the fans to battery voltage, but I'm going to have to build a little harness before I can do that.

Earl Gillstrom

Ernest,

Why don't you try what I suggested several days ago. Remove one of the wires from the AC "frigen" switch? The fans appear to run full speed with one wire removed. Leave the wire off and see what happens.

ErnestSw

Earl,
I tried it and nothing happened, possibly because I have a faulty controller.

reno928s

Ernest, It sounds like your on the right path. I hope it works out for you. Reno

Nicole

Ernest: Here is a little thing that you should also check:

Between the lowest vent in the bumper cover and the front spoiler is a black plastic piece. IT had come out of the groove in my bumper cover, and speed was able to blow it "upwards", so it would block part of the airflow to the radiator. I couldn't figure out how it slipped out, of how exactly it should be mounted, until Bill Ball saw it and fixed it in a few minutes.

I don't know, if this ever had an effect on engine temperatures, but it's easy to check, and there is nothing to lose by doing so.

I hope you figure it out soon! You have a "brother" with the same probmem in Germany, and they can't figure it out either. If they do and I see the solution on the pff (Porsche fan forum), I'll let you know!