WallyP

As Mr Merlin and others have said, this problem is usually air flow.

Do you have the engine pan installed? Do you have the front spoiler installed? If the hot air from behind the radiator can get back to the front of the radiator, the recirculation of hot air leads to overheating.

Make sure that the seal at the radiator touches the hood, that the sides of the radiator are sealed, and that air can't recirculate under the car. Make sure that the face of the radiator isn't plugged with bugs or leaves - it's hard to see between the condensor and the radiator. You can take the condensor loose without disconnecting the hoses well enough the check this.

EdSanders

Thanks Wally for some very insightful comments that I would never have considered. I have visually checked for debris and have pressure flowed water through both cond and rad with a garden water hose and "simple green" cleaner. I will check for recirculating ambient hot .

EdSanders

Greetings Merlin,
I appreciate your comments. I was hesitant to pull and flush the rad as I have read that the internal contaminants are hardened and impossible to flush out. However, it will be done prior to replacement. Your other suggestions i.e heater valve and short hose, coolant cap replaced. I did a C02 combustion blue chemical "uview" test to rule out head gasket.
Thanks,
Ed

76FJ55

I would double check that the fan is wired correctly and moving the air front to back. This wouldn't be the first time I've seen fans installed to combat an overheat problem only to make it worse because it was trying to blow air out the front. I would try jumping the fan switch with out the engine running to verify it is moving air throught the radiator in the correct dorection.

hacker-pschorr

His car has a belt driven fan (unless I missed where he converted to an electric).

EdSanders

Thanks Jim regarding your thermostat tutorial. It has, until now, been a bit of a mystery to me. As other have suggested I will try the chemical radiator flush, following the directions. My 1980 does not have the second thermostat 0 ring. Maybe I will pull the thermostat and check for water pump surge to check for W/P flow. I am up to checking every again twice as usually required for my level DIY diagnostic skills.

EdSanders

Mongo,
My 1980 does not have the second O ring, I did check for correct aux fan airflow and all was blowing correct directions. Does anybody else loose sleep at night, unable to disengage the diagnostic portion of their brain ?

Thanks,
Ed

EdSanders

Dan,
I replaced the silicon oil Toyota 10,000 as described on various posts, I will go back and check rotational characteristics..cold vs hot. When hot, should be greater resistance to manual hand rotation ? I lost the post author, but it was suggested to rev the engine and check for puff of fresh fan air coming from mechanical fan output. Seemed like a good idea. I will be going back and checking everything from square one again after reading all the outstanding diagnostic posts. What a great team on Rennlist !

EdSanders

Fogey,
I have installed a redundant coolant temp guage "Auto meter" with the electrical sensor in the top rad hose. Also have checked Co2 combustion blue chem "uview" test to rule out worst case scenario. It looks like the rad pull & flush is getting quite a few votes.
Thanks for your insights,
Ed

Mrmerlin

your culprit may be the worn fan clutch,
a test as I first posted will answer a few questions

Imo000

I'm willing to bet it's the fan clutch.

dprantl

I remember my former '86 with a good working fan clutch, when I would rev the car up from idle to 3k with the driver's door open and my left hand hanging out under the floor line I would feel a huge blast of air (that car never had any belly pans and never had a hot-running problem). In fact, if the car was standing on some small rocks/sand, I could initiate a sandstorm on someone standing close enough to the sides of the car! A working viscous fan at 3k RPM will flow much more air than even the S4 twin fans on high speed in my experience.

Dan
'91 928GT S/C 475hp/460lb.ft

Fogey1

I stand corrected about what's most likely and educated by a couple of posts. Thanks guys, as usual. But i would have thought that Spal pusher would been a good stand-in for the belt-powered fan.

BTW, Ed, liked your band and loved "The Family." Charlie's a scary guy. Everything has unintended consequences, even the Summer of Love. ;-)

peanut

I remember the trouble I had with the viscous fans on my Datsun Z's .They certainly are an hp hog
You need to identify the problem obviously but if I were you i would fit the twin electric fan arrangement from a 944S2 /turbo if it will fit. A lot cheaper than new head gaskets

Imo000

Better yet. The OEM dual fans from a Ford Contour/Mercury Mystique V6 are pretty much a direct fit and they are dime a dozen at any wrecking yard.