Is my Jeep overheating on idle ? -
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post #1 of 5 Old 06-14-2021, 05:51 PM Thread Starter
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Is my Jeep overheating on idle ?

Hi, I have a 2003 Jeep Grand Cherokee 4.7 HO. Recently the weather has been getting hot where I live with the temperature today hitting slightly over 100F. I was looking at my coolant temperature while driving and it was around 203F - 210 F in the city. When I Idle my temperature starts to slowly rise. I decided to stop for a while while idling to see the coolant temperature and it went up to 221F before it kept on fluctuating between 219F and 221F but not any hotter than that. I was wondering if this was normal since this is hot outside and if it isn't normal then what could be causing this ?

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post #2 of 5 Old 06-14-2021, 06:39 PM
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sounds about right - 220deg is ok, where the system will command fan to on.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 5 Old 06-14-2021, 07:21 PM
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That sounds fine.

Mine is a 4.0 but I think the electric fan, fan relay and maybe the mechanical fan clutch might be bad because mine will overheat with the AC on at a stop, 230° and climbing. So no AC for me. I have started shifting to neutral when I stop to remove as much load and heat from the car when it doesn't have enough air flowing through the radiator. That seems to be working but with temperatures over 100°, I want my AC back!

I'm planning a complete cooling overhaul soon, radiator, hoses, water pump, fan clutch, thermostat, housing, serpentine belt and tensioner. I'm not sure what I should do about the electric fan. The replacements for the fan and relay don't seem to have a great track record for long service. If I can upgrade my fan and the radiator enough to work without the electric, I would probably just take it off.

I know the 4.7 has it's own cooling issues and weird stuff like a fan driven by the power steering pump but if my car had your temps, I would be rolling with AC and not worried.
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post #4 of 5 Old 06-15-2021, 07:33 AM
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About what mine was doing when it was between 70 & 75F here the other day.
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post #5 of 5 Old 06-15-2021, 12:17 PM
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When your car is moving air flows through your rad because of a force known as inertia.
That flow of air through your rad keeps your engine at the thermostat level, 203F - 210 F.

When you stop, the air stops flowing through your rad.
When the air stops flowing through your rad, the coolant temperature rises until the fan thermostat switches your fan on, at about 219F.
When the thermostat cuts in your fan sucks air through the rad cooling the coolant down.

That's the way things are organized.

If your car rad cap is in good condition, when you are at sea level, and you use water in your rad, it won't boil until it reaches around 260F.

If your thermostat is in poor condition, and you are in the mountains, then your water will boil at a bit lower temperature than 260F.

Hence it's wise to check your rad cap every now and then.
Your local auto parts store would probably test your cap for you.

The coolant you use in your rad will have higher boiling points than water.
Since I don't know the coolant you use, I used water as an example.

Last edited by Delta0; 06-15-2021 at 12:30 PM.
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