how does this even happen (endless overheating)
 

I just can't figure out what is wrong with my car. It overheats in about 20 minutes of driving, city or highway, doesn't matter. The temperature goes up almost to the second bar, then goes back down. It does this a few times typically before it just stops going back down at all. The fans come on (most of the time) but it doesn't help at all and they cut off less than a minute after parking, even when the temp is all the way in the red and the coolant is boiling in the lines. The radiator is also cool to the touch, no matter how hot the engine is. There is no coolant in the oil nor oil in the coolant, and water flows freely through the radiator when poured in one end of it. The thermostat has been taken out, and it did precisely nothing. The waterpump is remanufactured and it has a new thermofan switch.

The only thing I can think of is that the water pump might not be running, either due to the belt slipping or the pump just plain being defective, but there should still be some water flowing through the system even then, right?

Anyway, this is the absolute end of the road for my ownership of this car. It is getting sold in the immediate future, regardless of if we get it running or not.

Any thoughts? Any buyers? (other than this, it needs a clutch and tranny within the next year. everything else is peachy-keen)

well i had air in my coolant system. but to get rid of it, I just elevated the front end of the car and ran all the air out of the system.

I'm pretty sure there's no air in the system. I can't count how many times i've bled it the last month or so.

If water isn't getting to the radiator. Follow the flow (find a flow diagram). Squeeze hoses. Who is getting hot? Could be bad water pump.

Also make sure radiator cap is good (pressure test). I got oscillating temps from that...

You have a block/lazy part, somewhere.

The remanufactured water pump is a prime suspect in my mind. They have been known to have impellers that do not turn at higher rpms and just spin on the shaft.

If you remove both hoses to the radiator and pour water in the top inlet, will it run out the bottom outlet that the hose to the water pump attaches to?

I do not know how much more time and money you want to spend but if you intend to sell and not have the "new" owner come after you you need to find the problem.

Do a compression test and leak down test to eliminate the head gasket. You may have a rotted head gasket.

Remove the radiator and backflush and clean the fins. You may have a blockage.

I know you are tired of hearing this but air in the system heats faster than antifreeze and this will cause your problem.

To continue:
BananaClip-" The fans come on (most of the time) but it doesn't help at all and they cut off less than a minute after parking, even when the temp is all the way in the red and the coolant is boiling in the lines."

Replace your 92/102 thermofan switch with the 75/77 degree and your fans will stay on longer to cool the engine if antifreeze is moving thru radiator.

BC-"The radiator is also cool to the touch, no matter how hot the engine is."

Again, remove the radiator, backflush, clean and test.

BC-"The thermostat has been taken out, and it did precisely nothing. The waterpump is remanufactured and it has a new thermofan switch."

Put in a 160 degree thermostat for the next owner.

BC-"The only thing I can think of is that the water pump might not be running, either due to the belt slipping or the pump just plain being defective, but there should still be some water flowing through the system even then, right?"

Have you tensioned your belts? Loose belts will slip on WP pully and the potential for more damage is huge

BC-"Anyway, this is the absolute end of the road for my ownership of this car. It is getting sold in the immediate future, regardless of if we get it running or not.
Any thoughts? Any buyers? (other than this, it needs a clutch and tranny within the next year. everything else is peachy-keen)"-BananaClip

Lets see...Clutch $1000 for parts, $1200 to $1500 labor. Overheating problem-"Priceless" 1988 944 (purple) value $3500 to $5000 to a "green" buyer who does not do a PPI.

Persistance and Good Luck

John_AZ
1988 924S + 1987 924S

when you say the radiator is cool to the touch, how cool is that? is the thermostat in backwards? is the temp sender bad? do you have a bad ground at the gauge? bad waterpump?

Three reasons (off the top of my head) why lack of coolant flow would result in overheating: Bad thermostat. Bad water pump. Clogged (or otherwise compromised) rad.

I had all your symptoms, and my fix was to replace the rad, replace the head gasket and put in a new water pump while I was at it. Drastic, but I knew the HG was going anyway (there was constantly air in my system, no matter how much bleeding I did). Took me a couple of weeks, moving slowly. Car runs cool now.

Hang in there, and good luck! When these cars are sorted they're the most fun you can have with your pants on.

ok, lets see

radiator cap is new, headgasket is new. water flows through the radiator and pressure builds in the lower waterpump hose (i think this because it tends to back off the water pump after driving around). i know the car is getting hot as the temp sender says because the hoses are too hot to touch and you can hear the water boiling. the radiator stays at room temperature no matter what-- you can leave your hand on it. belts are brand new and we just checked the tension yesterday. the water pump pulley does spin, but i don't know about the impeller.

today the radiator is coming out to be professionally flushed and we'll see what happens.

The hot water from the engine is not getting to the radiator for some reason if it remains relatively cool while the rest of the system is hot. Check the hoses for kinking, blockage, etc., maybe try a new thermostat, and then do a leak down test to see if the head gasket is OK. If none of this fixes it, replace the water pump.

If the radiator was as hot as the rest of the system, i would agree with removal and flushing as the next step. But, it is your time and money. I have spoken with local radiator shops and they cannot remove the plastic tanks and rod/flush them out anymore. They use a garden hose. Figure out why you have no flow first.

Pull the water pump. Sounds like the impeller is off its shaft.

Double post - again!

just a shot in the dark, but any chance you got the wrong head gasket in there and it's blocking a water journal? or maybe it's in backwards? I forget if that's possible.

Why is the radiator getting flushed if water flows through it?

T-stat FTW.

Some say you have to get the front of the vehicle up in the air to purge all the air out. An air blockage will prevent flow completely. It won't cost you anything but 20 minutes of your time to try.
Does the heater work?
These cars are a labor of love. We have all been there.

Jon

i've done it with the front end up and a funnel to elevate the water level above the bleed valve, with the front end down with the funnel, with a water hose, any way you please.

anyway, we got the radiator out and took it to get cleaned and apparently it was pretty badly clogged since when they cleaned it it ate a couple holes in the radiator. lots of greyish grit came out, probably due to the headgasket failure. Tomorrow we'll know if a new t-stat and radiator fix the problem!

Ate a couple of holes in the radiator???

yeah they cleaned it with a rod and it just picked up the grit and wore holes through the tubes in a few spots.

e: i feel silly now because it wasn't the radiator that i found to be cool to the touch, but the AC condenser. haw haw.

Sounds like it's time to replace the radiator then.