And yet another over heating issue

SMOKEDYA

15 Year Member
Jul 13, 2003
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95 cobra motor. Car only blows hot air from heater getting hot and overheating. Stock gauge reads fine sometimes sometimes it pegs on red. A few times it blew hot air from the heater vents now after replacing with the new stock 195 t stat with a 180 T stat it blows cold. The top radiator hose is always hard, then after it cools off it becomes soft and almost collapses, and all the coolant it in the over flow tank. I also have noticed i keep going threw coolant with no leaks.I feel i have the air bubbles out of the system as well? I have replaced the T stat with the same results. It dont always over heats but it does more so then not. Fans wok as they should. Tonight ,I double checked the burping of the system, when i took the cap off the radiator. I never really seen the coolant flowing to speak, but more less bubbling like air. Once this slowed down i added more coolant then it really started to bubble over then became violent boiling over like hot boiling water. Also when it gets hot it don't matter, if it's idleing, stop and go traffic, or freeway driving. Also when it gets hot sometimes it cools back off (on the stock gauge and everything is fine,. Then i can shut it down go out the next day and it's a hole new ordeal. Could over heat, or it might not? Hard to say... almost like theres a blockage then it frees itself up? Any ideas? Also any way to do a good flush on these systems?
 
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96pushrod

I think they're a little easier to get off
May 15, 2018
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If you’re losing coolant with no leaks, then it could be getting burned due to a head gasket having gone out.
 

GT4Lyfe

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Cobra should have coolant bled through crossover, very important. Air bubbles cause alot of problems on this engine.
 

General karthief

wonder how much it would cost to ship you a pair
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Pull the thermostat out and pan test it on the stove with a thermometer to see when it opens, even new ones don't always operate correctly, I jack up the front of the car as far as I can when refilling the coolant or use one of those burbing funnels.
Also make sure the t stat is oriented correctly.
There is the possibility of a blown head gasket. Compression test it.
 
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jozsefsz

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@GT4Lyfe just noting the 4.6 didn't appear until 1996.

They also have those combustion-gas tester things to check if you have a blown head-gasket, at least the kind of leak that's pushing exhaust into your cooling system which it kind of sounds like yours might be. The compression test or leakdown test would determine what's going on too. The bubbling typically isn't a great sign unfortunately, but the General has good suggestions for what to check first. Aside from the thermostat, I'd also suspect a clogged radiator or worn-out water pump if coolant isn't moving.
 
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GT4Lyfe

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@GT4Lyfe just noting the 4.6 didn't appear until 1996.

They also have those combustion-gas tester things to check if you have a blown head-gasket, at least the kind of leak that's pushing exhaust into your cooling system which it kind of sounds like yours might be. The compression test or leakdown test would determine what's going on too. The bubbling typically isn't a great sign unfortunately, but the General has good suggestions for what to check first. Aside from the thermostat, I'd also suspect a clogged radiator or worn-out water pump if coolant isn't moving.


In my old car I got major bubbling in the res with a bad thermostat. Just depends on how it is, also with water pumps.
 

SMOKEDYA

15 Year Member
Jul 13, 2003
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Pull the thermostat out and pan test it on the stove with a thermometer to see when it opens, even new ones don't always operate correctly, I jack up the front of the car as far as I can when refilling the coolant or use one of those burbing funnels.
Also make sure the t stat is oriented correctly.
There is the possibility of a blown head gasket. Compression test it.
I checked the t stat when it was new before i put it in and it opened at 185ish
 

SMOKEDYA

15 Year Member
Jul 13, 2003
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Tucson AZ
Drove a few miles tonight (roughly about 10 miles) to a show. On the way there about 2 miles away from home it got hot, then the temp dropped like a rock to the mid way on the gauge (assumed the t stat opened) Let the car cool and the level was low in the radiator. On the way home the Temp got hot again, but never really cooled off on the gauge, the heat was only luke warm then cold (usually the heat is so hot at times it will melt the windows) get home and the upper hose was hot and hard, cracked the pressure release lever on the radiator cap and filled the over flow tank. Tonight it was roughly about 50* outside. Drove it about 20 miles today when it was almost 80* outside and never heated up.
 

SMOKEDYA

15 Year Member
Jul 13, 2003
3,627
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Tucson AZ
@GT4Lyfe just noting the 4.6 didn't appear until 1996.

They also have those combustion-gas tester things to check if you have a blown head-gasket, at least the kind of leak that's pushing exhaust into your cooling system which it kind of sounds like yours might be. The compression test or leakdown test would determine what's going on too. The bubbling typically isn't a great sign unfortunately, but the General has good suggestions for what to check first. Aside from the thermostat, I'd also suspect a clogged radiator or worn-out water pump if coolant isn't moving.
The radiator is from my other 94 gt and is a aluminum radiator and worked flawless even if the hot 112* days we had last summer. I did a compression test and all cylinders were 140-155 on all cylinders.
 

SMOKEDYA

15 Year Member
Jul 13, 2003
3,627
8
79
Tucson AZ
@GT4Lyfe just noting the 4.6 didn't appear until 1996.

They also have those combustion-gas tester things to check if you have a blown head-gasket, at least the kind of leak that's pushing exhaust into your cooling system which it kind of sounds like yours might be. The compression test or leakdown test would determine what's going on too. The bubbling typically isn't a great sign unfortunately, but the General has good suggestions for what to check first. Aside from the thermostat, I'd also suspect a clogged radiator or worn-out water pump if coolant isn't moving.
I did suspect a blown head gasket on the passenger side since one cylinder on that side was shooting out a small amount of coolant when i did the compression test
 

jozsefsz

5 Year Member
Aug 11, 2013
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Well shoot, that's not good. Still a small possibility it's something else - leaking lower intake manifold gasket. So I'd leakdown test that particular cylinder for a final confirmation. Basically rotate engine to where both of the valves on that cylinder are closed (TDC), and hit it with compressed air through the spark plug hole. If you get the radiator bubbling, the head gasket is confirmed. If you don't, then you might be lucky and have a lower intake problem.

Here's a link that describes the process (you probably know how, for anyone else not familiar with leakdown tests): https://www.mobil.com/en/lubricants...vehicle-maintenance/how-to-do-a-leakdown-test
 

SMOKEDYA

15 Year Member
Jul 13, 2003
3,627
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79
Tucson AZ
Well shoot, that's not good. Still a small possibility it's something else - leaking lower intake manifold gasket. So I'd leakdown test that particular cylinder for a final confirmation. Basically rotate engine to where both of the valves on that cylinder are closed (TDC), and hit it with compressed air through the spark plug hole. If you get the radiator bubbling, the head gasket is confirmed. If you don't, then you might be lucky and have a lower intake problem.

Here's a link that describes the process (you probably know how, for anyone else not familiar with leakdown tests): https://www.mobil.com/en/lubricants...vehicle-maintenance/how-to-do-a-leakdown-test
The coolant coming out of the spark plug hole, was before i changed the gasket. I changed it and never rechecked it....