Engine “Overheating” problems

Hybrid707

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Feb 26, 2020
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I have a 95 GT I just got the motor back into, recently while driving at freeway speeds my temp gauge has started slowly reaching the right end of the normal bracket but will drop back down to the first quarter of the gauge in a matter of a few minutes if I come to a stop and let the car idle. the upper hose and thermostat housing get warm but radiator is still relatively cool, definitely not 220 hot. I have a 3 core rad, 180° thermostat and fan is on a switch and I’ve tried bleeding it a few times. I know the stock gauge sucks but it would never leave the O in normal, any suggestions? I’m puzzled since usually overheating problems happen at idle or low speeds
 
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Hybrid707

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Feb 26, 2020
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do you have the air dam under the radiator support installed? is it in good shape? this is what forces air across the radiator at highway speeds
No air dam, didn’t come with one. It didn’t overheat on the 4 hour drive home when I bought it though which is why it’s weird to me. I did recently pull the motor to do the oil pan gasket if that’s any extra info that might help.
 

General karthief

wonder how much it would cost to ship you a pair
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Aug 25, 2016
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I agree with the air dam, it creates a 'low pressure area' that helps pull the air out of the engine compartment, without it the air 'packs' in the engine compartment and airflow through the radiator slows or stops completely, cooling problems at speed indicates a flow problem, either air or coolant, watch the lower radiator hose as you raise the engine rpms, it may be collapsing.
 
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Chythar

Recently finished repairing my rear
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Aug 26, 2004
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Had that happen on a 95 GT I used to own. I would guess that your coolant system isn't sealed right. Water under pressure can hold more heat per degree of temperature, so if the system isn't holding 19lbs of pressure the temp gauge is going to rise faster than it should. I would recommend renting a coolant pressure tester and test the system. For that 95 GT I mentioned, the pressure tester revealed that several of my hose clamps weren't tight enough and my radiator cap was bad. After fixing those issues, the car ran much cooler.
 
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WhiteCobra95

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May 2, 2006
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Had that happen on a 95 GT I used to own. I would guess that your coolant system isn't sealed right. Water under pressure can hold more heat per degree of temperature, so if the system isn't holding 19lbs of pressure the temp gauge is going to rise faster than it should. I would recommend renting a coolant pressure tester and test the system. For that 95 GT I mentioned, the pressure tester revealed that several of my hose clamps weren't tight enough and my radiator cap was bad. After fixing those issues, the car ran much cooler.
I agree. It sounds like you've got an air or vapor pocket in the system. This can prevent the thermostat from opening and then drive the temp sensor reading abnormally high. The other problem is that you can get an over-heat / boil-over scenario if it's really bad. Hopefully it's just a leak in the cooling system and not a head gasket. A pressure check is in order. Also, are you sure that you bled out all of the air from the coolant system when you refilled it? Sometimes it helps to drill a small hole in the top of your thermostat if it doesn't already have one, and then orient the hole at the 12:00 position.

You need one of these: https://lmr.com/item/LRS-8349C-K/mustang-radiator-air-deflector-kit-94-04
 
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Hybrid707

Member
Feb 26, 2020
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Had that happen on a 95 GT I used to own. I would guess that your coolant system isn't sealed right. Water under pressure can hold more heat per degree of temperature, so if the system isn't holding 19lbs of pressure the temp gauge is going to rise faster than it should. I would recommend renting a coolant pressure tester and test the system. For that 95 GT I mentioned, the pressure tester revealed that several of my hose clamps weren't tight enough and my radiator cap was bad. After fixing those issues, the car ran much cooler.
Sorry for late reply guys I’ve been busy but I actually found out my lower hose is leaking a bit after letting the car sit, I know forsure thermostat has been opening so I’m gonna try and fix the the leak and install an autometer gauge. Check advance timing after that, I appreciate everyone’s suggestions