Overheating issue

Karl

Karl

TJ Enthusiast
Joined
Mar 4, 2019
Messages
168
Location
Vancouver Canada
My turn for some overheating issues. I’ve never had any before.

Essentially as long as I’m going under 80kmph I never have an issue. When I hit the highway, it goes up to about 230/235. One time it randomly popped up into the red zone. I pulled over, checked everything, got back in and it was back down to 230/235 for the rest of my driving.
The second I’m off the highway, the temps start to come back down. So it doesn’t overheat at idle or driving under 100, and after being high it comes back down.

I’m thinking maybe thermostat since it doesn’t hesitate at the 195 point at all, where the thermostat should open up? And below that I’m fine, below the rating of the thermostat opening.
My coolant and oil are full and not leaking.

I’ve got a Robert Shaw 330-195 coming in the mail. Any other thoughts?
 
For me, overheating only in idle is usually thermostat or fan clutch.

Overheating only on the highway has been a failing or blocked-up radiator.

Edit: confirm you don’t have any leaves etc. blocking the front of the radiator. You can also flush and back-flush the radiator to hopefully remove any internal blockage.

You can also use prestone cooling system flush, followed by thermocure flush, and then distilled water if your system has corrosion inside (which should largely be dissolved by doing these items).

If the radiator is bad, I recommend replacing with a Mopar unit. I don’t recommend running a cheaper unit if you value longevity (peace of mind).

You can boil your current thermostat in water to see if it opens. Are you running an 18 psi cap? Maybe try a new cap as well just to eliminate it. Keep as a spare if it doesn’t fix it (same for the thermostat).

Fwiw, my guess is that it’s radiator related if you are only having issues at highway speeds.
 
Last edited:
Mikee024 said:
For me, overheating only in idle is usually thermostat or fan clutch.

Overheating only on the highway has been a failing or blocked-up radiator.

Edit: confirm you don’t have any leaves etc. blocking the front of the radiator. You can also flush and back-flush the radiator to hopefully remove any internal blockage.

You can also use prestone cooling system flush, followed by thermocure flush, and then distilled water if your system has corrosion inside (which should largely be dissolved by doing these items).

If the radiator is bad, I recommend replacing with a Mopar unit. I don’t recommend running a cheaper unit if you value longevity (peace of mind).

You can boil your current thermostat in water to see if it opens. Are you running an 18 psi cap? Maybe try a new cap as well just to eliminate it. Keep as a spare if it doesn’t fix it (same for the thermostat).

Fwiw, my guess is that it’s radiator related if you are only having issues at highway speeds.
Click to expand...

Thanks for taking the time. It was flushed 3/4 times this summer and there was no apparent blockage. I have a new pump and thermostat on the way with some gel pro gaskets. Even if that’s not the issue I have them as back up. I will try the new cap but it’s not leaking through the cap? Could it still be the issue?
 
A bad cap doesn't allow the proper pressure to build up, which results in a lower boiling point for the coolant. A bad cap usually results in the coolant boiling over into the overflow.
 
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Mikee024 said:
For me, overheating only in idle is usually thermostat or fan clutch.

Overheating only on the highway has been a failing or blocked-up radiator.

Edit: confirm you don’t have any leaves etc. blocking the front of the radiator. You can also flush and back-flush the radiator to hopefully remove any internal blockage.

...

Fwiw, my guess is that it’s radiator related if you are only having issues at highway speeds.
Click to expand...
I would also look for an air flow issue.

A while back a coworker had overheating issues coming back from a camping / fishing trip; vehicle overheated only at highway speeds, and was fine at lower speeds. He found a mouse had built a nest between the radiator and AC condenser, which blocked about 1/4 of the air flow across the radiator. After removing the nest, no more overheating.
 
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