Wierd Overheating

backtobirds

Registered User
My 90 has been overheating. Not what typically happens, oh no, that would be too easy. It runs a little on the high side of the "normal" (sometimes), or goes to the top of the guage. But then it will drop down. Then go back up. Then back down. Then back up. It got real hot one day, and was boiling out of the overflow. Out of coolant. So I filled it back up later, and noticed it was pretty eager to push out the overflow. So I replaced the radiator cap. Also, it has had a mystery coolant leak. Runs too good to be a head gasket, also doesn't blow white smoke. No leaks with a pressure tester. So ok, it has been pushing out the overflow, even back when it wasn't overheating. So is my overheating causing my coolant loss, or coolant loss causing my overheating. got real hot today after I replaced the cap, but the coolant wasn't boiling over. BTW, I recently did a coolant flush. HMMM, maybe I dislodged some crud that is now blocking the thermostat. The upper hose is hot and has good pressure, though, not like it is blocked. I'll try a thermostat tomorrow, but wonder if anyone else has any input. The car is acting different than any other overheat I have diagnosed. Driving me crazy. Thanks.
 
Fluctuation in temperature indicates that you are low on coolant. If you just did a flush it's possible you have air pockets in the cooling system. Did you open the bleeder screw when you refilled the system?
 
Yup. I have a lot of experience with these cars, and I've had my LX for six years. Let me rephrase that. After I did the flush, I am positive I got all the air out. When it was acting up real bad yesterday, it had boiled over and pushed all the coolant out. Added some coolant, all good. Today when I changed the rad cap, I went ahead and bled the system just to be sure. I have a funnel that locks onto the radiator fill. I usually fill it 1/3 to 1/2 and add as I need to. It was pushing out the top before it got hot. Maybe a blockage, hadn't considered that yet. Hope not. I'll check for that later this evening when I go out.
 
Head gasket.

Change out the t-stat, and look at the weep hole on the bottom of the water pump.

You can get a pressure tester and test and look for leaks. You can compression test the engine and that'd tell you where your gasket blew out. I have even seen stuff you put in the coolant and it tells you if it has combustion gases in it (blown hg).
 
I'm changing the thermostat tomorrow. I already pressure tested it, no leaks. And I will do a block test tomorrow also. I was looking through the Ford service manual and it said to leave the vent cap off while bleeding the system, with the engine running. You know anything about that? I thought it had to be replaced before engine start, like it says right on it.
 
Yeah, I already checked that out. I have to be overlooking something. I've checked all the obvious things. Like I said, it's not like any other overheat I have diagnosed. I'll put a T-stat in tomorrow and see what happens.
 
I pop the vent screw out till the bleed hole is visible, and then start the car, once it starts dribbling coolant out I shut it.

Now mine is stuck in and I don't want to break the t-stat housing again, so I can't get it out. (twisted one vent tube right off on my last housing). So the last two times I have changed coolant I fill it almost but not 100% full in the radiator and let it run with the cap off for a few minutes till it starts to come up on its own, then put the cap on it and add to the overflow res. Once the car cools back down I check the radiator and if I have to I'll top it off.
 
So I changed the thermostat today, put a 180 in. I also did a block test and didn't find any combustion gases in the coolant. Bled the air out, and at around 225 degrees the coolant was violently sloshing out, but I got it done. Drove the car home, it never overheated but did get hotter than it should. Checked the coolant when I got home and it hadn't boiled over, but was bubbling into the overflow. I've never seen this, my LX never gives me this kind of trouble. Oh yeah, I also pulled the lower hose off and there seemed to be good flow through the block and radiator. And it gets hotter sitting still, but the fan does work. I'm more worried about the bubbles. They have to be related to the overheating, especially since it has been boiling over. And they should not have been residual air, I bled it pretty good.
 
my 91

my 91 had the same thing going on. i tryed evrything that you have tryed. i got sick of messing around with everything, so i went and bought a new radiator and it was all good. i dont know what was going on but it work so? try that, it cost 300 for a brand new one with 1 year warrenty from autozone.
 
I've thought about that. If I knocked something loose and plugged some passages in the radiator that would explain the temperature fluctuations. But the bubbling is what really bothers me. After I bled the system and drove it home, it should not still have air in it, especially not enough to produce a steady stream of air. There is no way even old coolant should boil around 220 degrees, not to mention brand new 50/50 mix. And the only place I can think of that would put positive pressure on the cooling system would be a blown head gasket, but there is not a single indicator of that. Did yours have the mysterious bubbling like mine? I'll go warm it up later and take temp readings across the radiator to see if this the right track.
 
Something else you may want to check. Get the car up to operating temp then rev the motor from under the hood while watching the lower radiator hose. It may be collapsing and causing a loss of circulation.

David
 
Alright. I was talking to my dad about it, and he said my LX was acting the same way when the hg's went on it (he babysat it for me when I was gone doing some Air Force training, after that he quit driving Toyotas and got himself a Bird). No constant bubbling out the radiator, but the temp would jump around and it had a mystery coolant leak, but no white smoke, still ran great, and passed a block test. So what kind of gaskets are recommended. I'd probably just get a Fel-Pro set over at NAPA, unless there is something else that works better.
 
The tempature fluctuated on my 94 and then next thing I know there goes a headgasket. The guage would go crazy, it almost looked like it was turning off then on then off then on and so on....
 
I called a guy I know at NAPA looking for a head gasket sealer to temporarily patch mine since I don't have time to do the gaskets now, and he said all they carry is this stuff that is $60 per quart. I didn't think to ask the name of it, but he said it is supposed to be the best in the world, he sells a lot of it and has never had a complaint. Anyone have thoughts on this?
 
well i started cheap and started replacing everything. The stat, gauge senders, fan sender and such. when i got to the ragiator i found out it was 60% clogged with segement from sitting. 90k in 16 years will do that. I took it to a radiator shop and 70 bucks latter he hot tanked it. pulled off the endtank and rodded it out and even gave me a warrenty. i didnt mind spending the cash because it was alot cheaper than a new brass or griffin for that matter. id say start witht he radiator. Mine was acting exactly like yours sounds.
 
I was about to do the radiator, but it has since started running bad. Missing, bleeding off boost, falling on its face under acceleration. Also it quit boiling over but the coolant is still going somewhere. I think it must be a HG and is getting worse now that I flushed the cooling system and cleaned out all the junk.
 
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