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Discussion Starter #1
I wifes 5.0L 1995 GT cooling system isn't working right. When started up from being cold, the temperature gauge will go almost to the red, and then drop back down to about Nominal. It gets hot enough that it is pushing coolant and steam out in the engine compartment. I think it is coming out at the radiator cap, but every time I go to lift the hood, it's not, but there is coolant around that area. I replaced the radiator a couple of months ago because it was leaking(cracked at the return hose). I am checking the fluid level in both the radiator and the overflow it it is good. Last week I replaced the thermostat, thinking it was not opening like it should, because the temp gauge would go so high before it opened. While the temp is going high, I am only getting cold air from the heater vent, when the temp finally comes back down, then I get hot air from the heater vent. I was thinking this was also an indicator of a bad thermostat. What else could be causing this over temp condition and the steam/coolant getting out of the system?:grinroll:
 

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It almost sounds like you don't have enough coolant in the system. When you replaced everything as you described, did you run the engine after it was hot and continue to fill the radiator and overflow tank to the proper location?

Low coolant will cause hot/cold readings with the engine, as well as intermittent heat and cold air from the vents.
 

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Did you replace the radiator cap when you did the radiator? A bad cap will cause overheating issues.
 

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Yes radiator cap is a good culprit.

You also mention the needle shooting to the red.....the stock gauge is notorious for not being accurate.

Is you fan working correctly?

Any codes?

Any other leaks anywhere?
 

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Discussion Starter #5
I did replace the radiator cap, but it doesn't seem to fit real tight. I will take a closer look at it.

When I replaced the radiator, I filled it up and ran it with the cap off until it started flowing. When it did, it started backing up out the radiator cap spout, so I put the cap back on. I just checked it before I would drive it and I had to add a little coolant the first couple of times.

How can I know for sure the system is full? I suspect maybe it isn't.
 

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I think that may be your problem....once the thermostat opens, your radiator will drain pretty quickly. I would say if you looked at it now, it would be pretty empty.

It may have backed up a bit as it heated up, but once the t-stat opens it'll drain...then fill up your radiator, and you should be good to go.
 

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Sometimes it helps to lift up the front of the car while you burp it.

Jack it up, start it with cap off, let it warm up - in theory, the air will rise toward the cap which since you jacked it up is the highest point in the system. Sometimes this will work if you have an air bubble trapped in there.
 

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Discussion Starter #8
So i bought a new radiator cap, jacked up the front end, took off the cap and warned up the engine, a the engine warmed fluid started backing up out the spout, lost about a pint. Then the thermostat opened up and the level dropped. Added about 3/4 gallon, the temp gage never went above nominal. Put the cap back on. After a few more minutes, the fan turned on. Took it for test drive and the temp gage stayed at just under nominal. So the high temp issue was low fluid, even the the fluid levels looked good when the engine was cold.

Now i just have to figure out how the fluid is leaking out. There is nothing obvious.
 

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Pressure tester will help find a leak.
 
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