SureTrack Community Fix: Too Hot at Idle

Real Fixes from the Snap-on SureTrack® expert information resource are documented issues from actual shop repair orders and community discussions. Read on to see how SureTrack can help you correct issues that are not easily diagnosed using OEM information alone. SureTrack is currently available free with the purchase of a current Snap-on® diagnostic software version.

It’s the middle of a record hot summer and your customer’s Jeep is overheating in traffic. They had it repaired at another shop and even tried to fix it themselves. Now it’s your problem. SureTrack community member ProAutoValdosta had a Jeep Cherokee in the shop that would overheat but all the obvious causes are resolved. They posed their question to the community, and with the help of fellow community member DAG1365 and others, they were able to resolve the issue quickly.

The following Community Fix summarizes the interaction between members of the community that led to the solution.

Vehicle
1999 Jeep Cherokee Limited 4.0L

Title
Overheating at idle or slow speeds, replaced head gasket.

Complaint
Customer states that at slow speeds or in traffic, the temperature creeps up slowly to 240+.

Diagnostic Steps Performed/Parts Replaced
The truck came to me after running hot on the interstate. It had a noticeable dead-miss on cylinder 2, the thermostat had been installed wrong, and the radiator had a crack. A shop in Florida had replaced the electric fan and had done a tune up. The customer attempted to replace the thermostat herself and it was installed wrong. The radiator was cracked. We initially replaced the thermostat with an OEM 195 thermostat and replaced the radiator. The temperature hovered around 225-230, even with both fans going. In traffic it very slowly starts to creep up higher. It does not matter if the A/C is on or off. We checked the dead miss on cyl. 2, and considering it had run hot multiple times, we ran three separate block tests and it passed every time. The fuel trims are normal, so it’s not running lean. We ran a compression test and cylinder 2 was low (45 psi). All the other cylinders were 90+ psi. We put a little oil on the #2 piston and the compression came up by about 15-20 psi, to 60-65 psi. The engine has 250,000 miles on it.

This morning we changed the water pump (which had a wobble to it) and swapped in a 160 thermostat. No change, the temp still slowly creeps up past 240 degrees. It has two fans, one electric fan (which is new) and a mechanical fan, which is working just fine. The shroud for the mechanical fan has a chunk missing out of the bottom, but it shouldn’t be enough to matter. The electric fan has an integrated shroud. We have not seen any other coolant leaks, the engine does not smoke and does not have milkshake or any other common signs of a blown head gasket. To recap, it has a new radiator, new radiator cap, new thermostat, new electric fan, and a new water pump and it still wants to run hot at slower speeds and/or in traffic.

Best Answer from Community Member DAG1365
Check with thermal imager/temp gun, check to see same temp readings at sensor, be sure even flow across new radiator, check for combustion (blue fluid), had one would heat up but did not burn any coolant either.

Cause
Because the head & thermostat are mounted higher than the radiator, we jacked up the left front corner of the Jeep until the radiator cap was the highest point in the system, we bled the cooling system, and re-ran the block test, which it failed twice. We ended up replacing the head gasket, which brought the compression up in all cylinders.

Correction
Replaced head gasket. The vehicle no longer misfires and no longer runs hot. The temperature runs around 205 at idle and around 215 going full blast down the interstate.


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About the Author

Nick Taylor

Nick Taylor is the SureTrack Community Administrator and a Senior Applications Specialist at Mitchell 1 with over 25 years of experience with electronic repair data systems. Nick previously worked in the automotive dismantling and engine rebuilding industries.