Today I pulled the primary cooling fan, cleaned it up, and filled the coupler with 10000CST silicon. It accepted only two ounces or so. I also added one bottle of Red Line Water Wetter to the coolant.

Today is about 10degF lower than yesterday, so it's not an apples-to-apples comparison. The car may be running somewhat cooler, but at a steady 30mph on city streets OR at 80mph on the freeway the needle hovers just above the uppermost white mark - not close to that beautiful red one with which it was snuggling yesterday.

I think the problem needs more work, and higher level thinking is welcome. This week I will pull and check the radiator (which looks new and does not appear to need cleaning!), and despite warnings might remove the thermostat or at least replace it. I examined the cooling system, which is typical of all modern cars, and see no reason why the absence of a thermostat will elevate temperatures.

When nothing else is left, I will do the water pump (and Tbelt). Ugh.

Looks like this car MIGHT make it to Sharktoberfest!

Not a guru

 

Maybe this will help:

https://rennlist.com/forums/928-foru...ml#post2213147

http://www.rennlist.org/techarticles...%20Thermostat?

 

clearly not a guru..... you do NOT UNDERSTAND how a 928 thermostat works.... but what do I know

 

[QUOTE=notaguru;12663331]Today I pulled the primary cooling fan, cleaned it up, and filled the coupler with 10000CST silicon. It accepted only two ounces or so.[quote]

That seems low..only 2oz? How long did it take to do 2oz?

You're missing some huge fundamental ways in which the 928 cooling system works.

I've only worked on -1- other car that SEALED the bottom of the thermostat as part of it's operation.

It was a 12b rotary engine.

Not typical at all.



Learn from the engine disasters of others.

This is why the 928 has the myth of "a bitch to work on"..because too many people attempt to apply conventional shade-tree wisdom to it, and it goes downhill on them for some weird reason.

 

If the thermostat checks out, then water pump? Also, are the front flaps/vents (might not have the verbiage correct there.) open? Mine were not functioning properly (relay), and for a long time I ended up disconnecting and just zip tying them open.

 

no flaps on pre 1987....

 

No magic. It's the standard Behr part from our trusted vendors here.

When I first got the car back on 1997, I went through everything to baseline all the services. Parts order was split between 928 International and a fledgeling business called "928 Specialists". The 75ºC thermostat came from them, and lived in the car for 75k miles before it started acting erratically. It's, um, well out of warranty at this point.

So back to the OP's symptom, that is insufficient cooling when the car is at speed. Things that cause that are too much heat generated, or not enough heat dissipated. To the first possibility, how well does the car run at speed? Services all up to date?

To the second possibility, inspect the lower tubes in the radiator via an inspection mirror through the lower nozzle, and/or a borescope or similar mini camera. Looking for mineral deposits that limit flow in the bottom. It's possible to use thermography to see the heat profile at the radiator, except that the AC condenser blocks the view. Meanwhile, when you remove the radiator for cleaning and inspection, be sure to clear out all the dirt, leaves, mud, bugs etc that accumulate inthe condenser and the radiator, and note the amount built up between those components. In some cars there's a substantila amount of airflow blockage.

Looking for waterpump flow problems is a chore unless you happen to be removing and replacing the pump for some other reason. Use childs modeling clay to determine the clearnces between the impellor and the volute section in the front of the block. I'd have to scrounge up notes on when I looked at mine a couple years ago during a TB replacement, but something like 0.020" sits in my head for the three point something inch impellor diameter, with allowance for expansion. Don't want to have interference, while more clearance means more internal recirculation and less flow through the system. A yardstick test for pump function vs radiator blockage as a caus is to turn the heater on full with full fan when you see the heating at speed. If the temp comes dow noticeably after a few minutes of this, look at the radiator. If no significant change, it may be the pump or some other restriction to coolant flow.

 

I have an 87, and have experienced a similar "slow burn" on the coolant temps when driving at freeway speeds and under load (uphill) when ambient temps are 90-100+ degrees F. Pretty much everything on the car has been done, wp. tb, intake refresh, thermostat, fans running properly, etc, etc, etc. Scratched my head over this last summer, and finally after much thought figured it was down to radiator. Mind you, I never got into red zone but the gauge would happily climb above that last white line under a load. Made me nervous. Being lazy, and hating to drain that damn cooling system, I finally got around to pulling the radiator and found quite a blockage consisting of leaves and road crap between the radiator and ac condenser. A good 4-5 inches of blockage up the vertical face of the radiator, and not easily visible without pulling radiator. Seems that this arrangement acts as a natural vortex to pull crap into the space between the radiator and condenser. Cleaned all of it up, and I can say that I have significantly slowed the progress of that temp needle, and it has stayed a needle width below the upper white line.

Of course, I need to wait until it gets damn hot again around here, which might be next May, but I feel like it has really helped. Take a penlight and look between the radiator and condenser, just a thought... you might see a load of gunk in there.

 

Chalk:

Did you have the lower engine cover(s) when you found this debris?

 

Turning my car's heat on brings the engine temp down (slowly) and gets it udner control again - but installing the CSF radiator did not affect the problem/symptoms at all, so the old radiator cannot be to blame.

After reading through the threads that SMTCapeCod linked to, I'm very confused - how do the fans work in my '89? Do I have a "fan clutch" or is it a simple electrical on-off fan?

Here are some questions and ideas that popped into my head - please comment:
1) I have no debris between A/C condenser and rad, but could the condesner fins be bent or impacted enough with crud to restrict air flow to the rad?
2) Could something operating incorrectly in the A/C system be putting so much heat out through the condenser that the air flowing over the rad is too hot for it to dissipate the engine heat effecctively?
3) Blown head gasket seems unlikely without any sign of coolant-oil mixing, ever
4) If I have deposits coating the cooling channels in my engine, is there a coolant additive product that can help clear it out? I saw the citric acid cleaner discussed in the FAQ link but using it is a big project.
5) Do I need to drain the coolant to add Water Wetter, or can I just pour it into the overflow tank/reservoir and it will circulate through on its own?

Thanks!

 

Yeah they have always been on.

 

Sounds like you worked on the viscous clutch fan. Are you now happy with the feel of it?
Does the auxilliary electric fan in front of the radiator come on? Is it wired correctly to push air through the radiator? I once wired one wrong and the car overheated until I figured it out.
You could inspect the thermostat, and even replace if unknown.
Also pull and service radiator, since you mention it, certainly could not hurt, and would cross one more potential problem off your list.
Good luck,
Dave

 

for all who are reading this thread i would suggest to use a IR gun to get running temps at the inlet and return to the radiator the cars temp gauge is a trend unit and unless you have calibrated it with the IR gun you really dont have all the info you need

GAZ after reading your info I would suggest that you get IR readings,
if they are high then you should consider swapping in a new water pump ,
if no joy then swap the head gaskets

 

Stan is right, as usual. That IR gun can be very helpful, here and elsewhere.
Dave

 

Will do Stan. I will even try to video myself taking the readings so it's clear where and how I'm doing it, but something is definitely building heat in my engine, since the temp gage needle will sit right on the money once the car heats up, and heat will only build under high load and high ambient conditions.

That said, I don't know if I'll be able to replicate the behavior as it's fairly cool here in CT these days - but I'll crank the AC and drop it down a couple of gears and tear up the back roads to the very best of my ability! In the name of science, of course...