Newbie Needs Help: Overheating

KronFox90

Member
Apr 17, 2022
6
2
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36
Tustin, CA
Hi, I have a 90 GT, 5.0 with an AOD. Car has been running great lately until a few days ago when it kept overheating.

Within the last 500 miles I've installed a new 180° thermostat, new hoses, coolant temp sensor, aluminum Radiator and electric fans. I was having zero overheating issues until now.

What's strange is it will overheat and then randomly cool very quickly like nothing was wrong. Then again the temp will spike... then repeat. No rhyme or reason.

I also noticed that the heater doesn't blow hot when it's overheating, but when it begins to cool it blows hot.

Does this sound like a water pump issue or something else? Fyi I've confirmed WP rotation is correct and burped the system.
 
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limp

wrap a little cheese around it and its a done
Oct 4, 2020
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Let it cool down overnite, jack up the front of the car as high as is comfortable, REMOVE the radiator cap and start it... Let it warm up ( water movement in the radiator) and see if you can bleed out the air... WATCH THE COOLANT LEVEL adn add to it when it needs it....
 

KronFox90

Member
Apr 17, 2022
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2
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Tustin, CA
Thinking I might have a bigger/different issue. I tried burping the system again and there were definitely bubbles. Bubbles that never stopped coming. A little acceleration caused even more bubbles. What should I check next?
 

Cheapskate207

The left one hangs a little lower
Jan 12, 2020
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This will tell you if you have combustion gas in the cooling system. I believe it is what’s mentioned above. You can rent it at autozone. 7AF70836-887B-4A22-BB8E-814EC52C5B28.jpeg
 
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KronFox90

Member
Apr 17, 2022
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Tustin, CA
Update: I rented the combustion test tool and bought the fluid. No emissions showed up. Thank goodness! So I tried to burp the system for the 4th time. Tons of bubbles and then suddenly... None. :O_o: must have had a pretty large air pocket.

What's strange is the car was running perfect for 500 miles after I installed the cooling components originally. Is it normal for an air pocket to show its ugly face so long after the fact? If not, what could have caused that air to enter the system if not the head gasket?

The car is now running perfect again, Temp stays nice and cool and the heater works.

Thank you all for your help!!
 
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"...caused me to get the sealed funnel..."
nuttin like it, used everytime = no problems.
Lisle, or Thorstone.
Use it, do it.
Then look @ overflow'n add to proper line there too after a 10, 15 min driveway idle~
"Overheat" to me is 'puke out rad or overflow'. Hi on guage (actual temp reading or needle on lines, idiot light) do not necessarily indicate 'over heat'. They indicate a need to check further & assure 'overheat' does not occur). ie 245, 250* F
 
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manicmechanic007

5 Year Member
Sep 26, 2017
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Bad head gaskets?
A good way if you have access to I/M test equipment is to smell for HC'c in the radiator
The block tests are not inaccurate but difficult to read correctly
I helped read several thousand tests at the dealer back in the day
By the time you get 5 technicians looking at a test liquid or a strip
You are getting sold head gaskets or worse every time!
Best test is from cold
Remove the radiator cap and start the car
Watch the coolant in the radiator (any bubbles = bad)
Old Faithful = very bad
Monitor air above coolant in radiator with I/M probe looking for hydrocarbons ( any = fail )
 

mattys91gt

Active Member
Feb 3, 2022
391
31
38
41
Plymouth Massachusetts
Hi, I have a 90 GT, 5.0 with an AOD. Car has been running great lately until a few days ago when it kept overheating.

Within the last 500 miles I've installed a new 180° thermostat, new hoses, coolant temp sensor, aluminum Radiator and electric fans. I was having zero overheating issues until now.

What's strange is it will overheat and then randomly cool very quickly like nothing was wrong. Then again the temp will spike... then repeat. No rhyme or reason.

I also noticed that the heater doesn't blow hot when it's overheating, but when it begins to cool it blows hot.

Does this sound like a water pump issue or something else? Fyi I've confirmed WP rotation is correct and burped the system.
hey I'm have a 91 gt with the aod my engine bay gets so hot but the gauge isn't at all showing hot
 

mattys91gt

Active Member
Feb 3, 2022
391
31
38
41
Plymouth Massachusetts
The factory gauge isn’t all the accurate. If you’re concerned, throw and aftermarket gauge in accuracy and peace of mind.
the motor just seemed so hot and having the heater core bypassed people on here said the motor would be hotter and I have a 160 thermostat,I have a 195 thermostat coming the car sat since 2014 that was the last inspection sticker and I got it in August it needed alot and still does and me touching the car and never working on a mustang I've messed a few things up I'm trying to take all the info in I can
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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I've never read anyone posting on stangnet that if you by pass the heater core it would run hot, underhood temps are hot, lay a thermometer on the engine (I really don't recommend it) and close the hood the temp can reach 200*+ sitting still. Nothing unusual.
 

mattys91gt

Active Member
Feb 3, 2022
391
31
38
41
Plymouth Massachusetts
I've never read anyone posting on stangnet that if you by pass the heater core it would run hot, underhood temps are hot, lay a thermometer on the engine (I really don't recommend it) and close the hood the temp can reach 200*+ sitting still. Nothing unusual.
someone on here said it lastnight saying that the heater core helps cool the coolant I could have got it wrong what he said I'll look it up but thank you again