Luis de Prat

Well, it's been a long 215K miles, the last 127K under my ownership over the past 10 years...

Yesterday at a light I noticed the temperature gauge in my 83 944 started to creep abnormally close to the "danger" zone. I pulled over and noticed that somehow the fan harness had made contact with the alternator belt pulley and was practically split. I took the harness plug apart, spliced in new contacts and the fan now works again, but the car is still overheating.

Pulled the spark plugs, and they're all pretty much normal, with none of them being wet or "extra clean."

When the car is at operating temperature, the top hose is very hot, so I assume this means the thermostat is opening normally to let the hot coolant circulate from the engine block when the temperature rises.

I did Charlotte944's test to check if there's air in the cooling system by turning the heater on at idle and revving the engine to see if the air temperature went up, but I didn't notice that it varied much.

I also did Charlotte944's other test, running the car on the highway and downshifting to see whether the temperature gauge dropped. On the highway, the gauge slowly creeps up and when I accelerated it dropped somewhat, but not the way it should.

I also noticed that the needle never enters the "danger" zone, but reaches right before it and sits there. Years ago, it would get stuck between the 3rd mark and the "danger" zone, which turned out to be a stuck thermostat. This time I don't think so, since the top hose is piping hot.

So I'm beginning to suspect the worst, which would be the headgasket, but before I give up I'm willing to try any other ideas.

Thanks!

KuHL 951

Are you running the later 6-blade fans or the older 3-blade type? Converting mine to 6-blade solved all my heating issues on the 83.

Luis de Prat

I think the second fan is the 3 blade, and the 1st fan is the 6 blade. However, this just started happening all of a sudden...

KuHL 951

You didn't mention if you've had to add coolant since the car has been running hotter. A failing HG would drop your coolant level pretty fast I would think. How old is the coolant mix?

83na944

Luis,
Have you looked at the obvious things - waterpump, thermostat, reservoir cap, and radiator? How old are those parts? Any leaks? Did you bleed the system?

My 83 ran hot on and off for years. I upgraded to a turbo water pump, replaced the radiator, all of the hoses. These needed to be replaced, but didn't help much.

I used a lower temp thermoswitch for a while, but it just kept the fans on all of the time. Had to replace the left fan because of that. I used a 6 bladed fan and a stock thermofan switch. That seemed to help a lot. The temperature would rise and fall like it did when it was new.

Hopefully its not the headgasket.

BTW, watch out for Ivan.

Luis de Prat

Thanks guys. The waterpump and complete belt job were done about 27K miles or 2 years ago. The thermostat and fan switch were both replaced. Fan relay was also replaced, and I noticed that the chopped fan harness did blow a fuse yesterday, but replaced that as well.

RE the coolant, I had noticed a slight drop a week ago, but attributed that to at some point having a mechanic put too much straight water in there which would be more likely to evaporate than antifreeze during an extended period when the car sat for a long time in the tropical heat. I topped it off with coolant and the level has stayed the same since then.

RE the thermostat, the top hose feels really hot at operating temperature, so I guess the thermostat must be opening? What bothers me is that it started to run noticeably hotter all of a sudden.

CT944

open the bleeder on the upper radiator hose and crank the heat. let it idle until it gets hot and the fans come on. if coolant starts to pour out of the bleeder valve, the thermostat is opening.

else, make sure you have a good coolant/water mix as it helps things keep cooler. also make sure the mechanic used coolant for aluminum radiaors when he topped it off. if radiator is really old, it may need to be flushed as the internal tubing may be a bit clogged, restricting flow.

83na944

Yea, those sudden changes are scary.

If you have a blown headgasket, you should notice oil in the coolant or coolant in the oil or coolant out of the tailpipe.

As far as I know, the water will not evaporate and leave the antifreeze behid, but I could be wrong.

Did you or your mechanic bleed the system? Its important to open the heater valve when you bleed it. Its really hard to get the air out these cars.

And if the radiator cap is not holding enough pressure. The coolant will actually boil in the engine and you'll end up with low coolant.

Luis de Prat

I think it was 2 years ago when the oil cooler seals went out that the mech (I didn't have the guts to do that fix) filled the system with more water than coolant. It never freezes here in the tropics, so many folks do this. However, the boiling point of coolant is higher, right? So I prefer to have more coolant in the mix.

At any rate, you're right in that perhaps there's still air in the system. I've just been too chicken to let it idle for too long when it gets hot. Coolant does trickle out of the bleeder screw, so I'm not sure how much more air could be trapped in there? I assume it got in there when I added coolant last week and didn't bleed the system afterwards.

KuHL 951

I've always found that the higher ratio of coolant to water makes a car run hotter. It's partly a viscosity thing. The term coolant is a misnomer; water carries off heat far more efficiently than "coolant'. All the coolant does is raise the boiling point, provides corrosion inhibitors, and keep it from freezing. I nearly destroyed a Maxima engine driving home from the shop after they put a 25/75 water/coolant mix; it really ran hot on the freeway; I took it back and changed it to 70/30 and no more problem. If you live in the tropics your old water rich mixture was probably better for the car.

CT944

when i did my radiator replacement, i did exactly that. filled up all fluids, let it idle with the heat blasted, opened the bleeder valve, filled the reservior until it stayed at a constant level, replaced the reservior cap, and when a steady stream of coolant began to emerge from the bleeder valve, i knew it was bled properly. easy job to do.

if you try this and it is obviously about to overheat (going toward the red zone) then halt everything. at that point i would say you have a bad thermostat or weak waterpump. make sure the fans are coming on if you try the above.

bf95cab

I had this problem when my oxygen sensor started to go. Got worse and finally overheated before we found the problem.

Luis de Prat

Hmm, I put in a new oxygen sensor about 2 months ago...

83na944

Was that when the problem started?

I thought a failed O2 sensor would make the car run rich. Overheating sounds like a lean mixture problem.

Anyway, bleeding sounds like the first thing to try. CT944 is right. Leave the reservoir open until the car gets hot enough to pull coolant from the reservoir. Top it up and then put on the cap and open and close the bleeder valve until you get a steady stream of coolant out the bleed valve. Of course, you need to make sure the heater is open.

BTW, the max boiling point and min freezing point is with a 50/50 mixture of water/antifreeze. Check the back of the antifreeze container.