1998 3.8L V6 overheating at idle, gauge doesn’t go up.

Gosintary

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Jun 5, 2020
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Recently I’ve been having an issue with my 1998 3.8L v6 mustang overheating. With the help of my dad, we changed the radiator, and the thermostat. Then we noticed the water pump was faulty so we changed that (thing was like 20 years old). Then we discovered the intake manifold gaskets were leaking, so we replaced the upper and lower intake manifold gaskets, and the head gaskets. We also replaced the fan and fan harness.

We properly drained and filled the cooling system each time.

The car overheats while at an idle, be it traffic, drive thru, just idling to see if it overheats, etc. You have to drive it around to get it up to running temperature. It’s fine driving around. Stop lights, slow moving traffic, the whole 9 yards. When you stop for more than a few minutes the car gets hot. The gauge is normal, it moves around when you drive it, going up as the car gets up to operating temperature, but when you idle and the car overheats it doesn’t move. It will stay where it normally is (right in the center) but the coolent will be boiling hot. The AC fluctuates between hot and cold while it is overheating. We’re kinda stuck with what to do. Any suggestions?

TL;DR

we’ve
- replaced the radiator
- replaces the water pump
- replaces the thermostat
- replaced the head gaskets
- replacer the upper and lower intake manifold gaskets
- replaced the fan
- replaced the fan harness
- had a pressure test done
- flushed the cooling system.

Car is fine will driving, including slow traffic, stop lights, etc. Over heats when idling for more than a few minutes. Gauge moves as engine warms up to normal temperature, but stays normal while coolant is boiling. AC temp fluctuates between really hot and cool when over heating. I’m stuck with what else to try.
 
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7991LXnSHO

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Air is a poor conductor of heat compared to a water mix. I am not familiar with SN 95 V-6 motors specifically, but it is frequent that cars with radiators that are lower than the highest spot in the coolant system to need burped of air pockets when coolant is changed or a hose replaced. The next alternative has to do with wiring, sensors, fan operation (since it cools when air flows). So I hope someone will tell you the best way to burp your baby.
 

tsemmett

Active Member
Jul 2, 2019
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Air is a poor conductor of heat compared to a water mix. I am not familiar with SN 95 V-6 motors specifically, but it is frequent that cars with radiators that are lower than the highest spot in the coolant system to need burped of air pockets when coolant is changed or a hose replaced. The next alternative has to do with wiring, sensors, fan operation (since it cools when air flows). So I hope someone will tell you the best way to burp your baby.
There is definitely a plug on a 3.8 to let air out when filling the coolant system. Front and center on the intake manifold, where the coolant temp sensor is mounted, there's a bolt that needs to be removed.
 
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