I have a trans cooler, Also have a SPAL fan and shroud.

I have noticed that on very hot days here in SW Florida (95 plus) that when driving on the highway (over 70mph) that my engine temp will come up to almost 3/4.

I was having a problem with the factory fan (reason for the SPAL) with my low speed driving and having the temp go to and over 3/4. The SPAL fan has fixed the low speed overheating. Didn't notice the high speed overheating issues before.

Now, my problem is when driving on the highway at the higher speeds. I notice the temp gauge going up and the A/C not functioning like it should. Now, if I slow down to around 60 the temp gauge drops and the A/C gets cold again.

The question(s):

What is causing the temp gauge to raise when driving high speed?

Will adding a trans cooler fan help?

 

If you have done some water fording, check for debris in the radiator. To keep things cool, water wetter, heat relief hood.

 

Is there anything sitting in front of the grill; winch, lights, etc.?
Is your JK lifted?
Bigger tires?
Is the air dam still on?
Is the JK old enough to suspect the thermostat is bad?
How much radiator area is covered by the tran cooler?
As mentioned above, are all your radiators' fins absolutely clean?

Individually, these things will not cause a problem.
Added up, they could.

 

Lifted 4"
Tires 35"
No air dam
2008 with 24K miles could be thermostat
Trans cooler covers 60% of radiator
Radiator is clean

Would a trans cooler fan help?

 

Is there anything in front of the grill, such as lights, or winch?

What is your axle gear ratio? If you didn't regear for the bigger tires, your engine and transmission are producing more heat.

The first thing I would do is change the thermostat. It's easy and cheap, if you do it yourself.
It could be the cause, so eliminate that possibility.

If your radiator is clean, and a new thermostat gives no improvement, you may be seeing the accumulative effects of inadequate air flow through the radiator.
Lifted allows more air under the Jeep.
No air dam (and no front skid in its place?) allows more air into the engine bay from below, reducing flow through the radiator.

You already have a fan behind the radiator, so I wouldn't expect another one in front to give any improvement. It is the last thing I would try, after trying to improve natural air flow through the radiator.

Another thought is the coolant temperature sensor could be bad.
Get an infrared temperature gun and point it at the thermostat housing next time the gauge shows overheat.
The gauge normally stays straight up when the temp is between 185°F and 220°F.
If the temp gun reads well within that range, I would suspect the sensor is reading too high.

 

THis sounds almost the same as what is happening to mine lately. Currenly mine is in the shop as it is at the point that it goes right to completely overheating to the max on highway.

I removed my tsat completely (put back in with no guts) to diagnose this problem, but that made no change at all.

I have noticed for a long time that my cooling fan never shuts off, most of the time it runs on high, even sitting in a parking lot idle.

dealer is diagnosing as we speak and has had it for 3 full days now.

I suspect either the cooling pump is not working, not operating to full spec, the interior of the rad is somehow plugged or........... a messed up head gasket allowing exhaust gasses into the cooling fluid.

I suspect the exhausts pressure is higher than the cooling pressure (18 PSI rad cap) and hence the exhaust goes into the cooling fluid and heats it up in excess of what the cooling system was intended to overcome. as the pressure in exhaust is greater than the cooling system you DON'T find milky oil or oil in the cooling system.

The jeep takes the normal amount of time to warm up to normal running temp, and then usually sits just above the half mark (all other jeeps sit just below half mark) then at times it will rise to 3/4 and with driving usually comes back down. But over the weekend it went haywire and now overheats to the red when driven.

I will post here the results from the dealer

 

Im just throwing this out there but has anyone check to see if the fan is a pusher or puller? Maybe just maybe its pushing and fighting against the wind driving. I know the fan shouldn't come on that much driving at highways speeds, but one guy said his runs all the time on high. This is just a thought.

 

FANS ARE FOR LOW SPEEDS ONLY. I don't care what kind of rad fan you have it will never produce 70mph winds.

as stated above is it a pusher or puller.

 

Both jonboy and JEEP THRILLS beat me to it, as I too was going to recommend that you verify direction of flow from the fan, and also the run status of it at speed. Like has been said, the fan shouldn't be on at highway speeds, or really much over 45mph even (not that I know that to be the exact number for these Jeeps, but for other vehicles I have dealt with over the years 45mph was a good, general guideline). Good luck.

Tom

 

That's a good point about the fan direction. But, jeepers, I hope he didn't miss that when he installed it.