rj7630

First post here. I have an 84 us stock auto that runs hot. The temp gauge usually sits at or just below the last red mark before the hot area. I've checked temps with an IR gun and hooked up a temporary manual gauge. They both show temps in the 200 -210 range when idling and pretty much stay there if I rev it up.
I've read the posts here about over heating and have completed the following:
I1. Replaced the water pump
2. Replaced thermostat and thermostat seal
3. Changed out radiator with a brand new aluminum one (beautiful work on the welding BTW).
4. The fan pulls very good as far as I can tell. IR gun shows 130 -140 coming out of radiator
None of this has changed the temperature issues. Still pretty much as before. About the only thing left I can think of is the some type of blockage in the heads. Is this something that is an occasional issue w/ 928's or is this one of those "I’ve never seen that before" things? I'm not too excited about pulling the heads if I'm likely off on a wild goose case, but will dig into it if there is a need.
Also, can the heads on a US 16v come off w/o pulling the engine?
Thanks.

76FJ55

Is the temp stable at 200-210 or will it continue to rise? you mention you checked it at idle, what do temps do out on the open road? The fan clutch is another area to look it is a known cause of high temps if the thermotatic clutch isn't functioning correctly. There are write-ups on replacing the silicone fluid in the fan hub if you search for them, they use Toyota fluid as it is readily available from Toyota dealers. If the temp is high in trafic or while idleing but drops once your moving this is likely the cause.

rj7630

It runs about the same temp out on the road. Cool 60 degree day, 65-70mph, really no change. Maybe a littel cooler if you are on a downgrade, but nothing much.

SQLGuy

Might want to check with a shop to run a hydrocarbon sniffer on the coolant, just in case you have a leaking head gasket... although head gasket problems, AFAIK, are not common on these engines.

Lizard928

You have not stated what year you have.

On the later engines behind the thermostat there is a seal with a rubber surface.
This needs to be replaced with the thermostat and can/will cause your problems.

Also what temp of thermostat did you put in? I recommend a 83 C one.

Last and final thing is that the fan uses a viscous clutch. if the fluid has leaked out the manual fan will not be up to the task of moving the air.
To test, when hot can you move the fan easily?

rj7630

I did mention the year in the first post, but a little hidden I guess. Its an US spec. 84S auto.
I have replaced the thermostat and the seal behind it along with the water pump and radiator.
The outlet from the radiator to the water pump runs about 130-140 at idle absed on my IR gun.
If I rev it while sationary, the temps stays about the same both coming to the water pump and on the engine temp guage. It just acts like either the thermostat doesn't fully open even though I had the same issue with the original thermostat and a new lower temperature thermostat. So as three different thermostats all give the same results I'm pretty much ruling that out.
Or the flow through the engine is restricted for some reason.

76FJ55

It seems I recall reading somewhere that the seal behind the thermostat was installed backward and gave a similar result. Having recently replaced mine I'm not sure how one could install it backwards but I guess it is a possibility.

Lizard928

Try removing the thermostat and get a rubber plumbers plug and prevent any recirc through the engine.
If the temps are lower it is a problem with the thermostat, if they arent then you have ruled that out.

rj7630

So if the thermostat opening is fully blocked off, all coolant goes to the radiator? That would be good way to check it. And I agree, I can't see how you could put the seal in backwards, but I've done some interesting things at times when working on my cars.

Jascd

That does not sound so hot, its 93-98 degrees C. I think the normal operating temp is low 90s but I can't find the reference for that so I am trusting my memory. The 83 degree thermostat is only fully open at 98 c according to the manual (page 19-2b). On my car there is a two stage high temp warning, the first one at about 118 C and the next at 120 so that give you an idea dangerous temps. I regulary see temps on the waterbridge at a bit over 100 c after a hard drive and then idle but it quickly comes down to early 90s. My temp alarm has never gone off and I have replaced radiator, hoses, thermostat, seals, header tank and flushed the block so I know my cooling system is in good shape. You may be running a little warm but there seems to be some variation between cars anyway. I suggest you double check the thermostat and maybe the expansion tank cap and if they are OK then there may actually not be a problem?. The stable temp is a good sign and the needles are well known for not being very accurate so the IR will be more reliable but again your temps may not be as out of range as you think.

Jason

89s4

rj7630

Jason, I tend to lean your direction on the issue. The temp is stable regarless of whether it is idling in my driveway or cruising down the freeway. That would tend ti indicate that the flow is keeping up with cooling demands. It is just unsettling to see the temp needle pushing up toward to danger area all the time.