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Arench, Master Technician
Category: Jeep
Satisfied Customers: 1490
Experience:  30-years experience auto and truck repair.
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I have a 2008 Jeep Grand Cherokee Limited with a 4.7L

Customer Question

Hello, I have a 2008 Jeep Grand Cherokee Limited with a 4.7L V8. I have recently been having overheating issues ONLY when the vehicle is sitting at idle, such as at a drive-thru or sitting for 10-15 minutes waiting to pick someone up. As soon as I start
driving/moving, the temp returns to normal. A/C air also turns warmer when running at idle and parked. I have checked electric fan by pulling relay from fuse panel. Fans comes back on when relay is replaced. Coolant level in overflow tank is at correct level
when cool. Have not see any signs of leaks. Wanted to get some advice before I started replacing unnecessary parts.
Submitted: 2 years ago.
Category: Jeep
Expert:  Arench replied 2 years ago.
Hello this is Mike and I will help you with this issue. There are no pattern failures for overheat on this vehicle. Some occurrences involving things you have already touched on like low coolant from a leaking radiator. Sometimes the water pump impeller becomes loose and doesn't pump good. The result is intermittent high temps and loss of heat in the winter. This would not affect the A/C. Some issues with fan belt slipping due to bad tensioner. This usually comes with a burning smell, squeeking noise and eventually the belt pops off. Operate the tensioner loose/tight see if it is working normally. If the tensioner locks when you loosen it, then replace the tensioner and belt. I don't know if you have a lot of trees where you live but here in the northeast we have a problem with tree fuzz blocking up the air flow through the radiator and condenser. Open the hood and blast the condenser and radiator with high pressure water like a garden hose nozzle or self-serve car wash. Occasionally you will encounter a bad head gasket. This often comes with mysteriously disappearing coolant and misfire fault codes.I am happy to discuss this with you further if you have any more questions. Start at the bottom of the list here and clean the condenser first and retest. If no joy have a look at the fan belt and tensioner.
Customer: replied 2 years ago.
I will try the things you have mentioned. We have plenty of trees but when looking around the other day I did look at the front of the radiator and saw nothing that looked like it would be clogged or have impaired air flow. I considered the thermostat, but don't believe that would cause overheating only when the vehicle is sitting still. My thought is that it is something to do with the electric fan since that is the only source of cooling when the vehicle is not moving.
When checking this I started the vehicle while it was still warm and the fan was running. As mentioned I pulled the relays out and the fan stopped then started again when I replaced the relays. There are two relays, so I do not know if one could be bad. I read on a Jeep forum that this could be a two speed fan. If so, is it possible it is not running at the correct speed? I believe it is temp controlled, because I bought this vehicle totaled out and rebuilt it. There is some kind of coil like thing near the bottom of the fan housing that plugs into the fan motor. Also, the vehicle has almost 100K miles (except the motor which I had to replace when I rebuilt vehicle) the motor has approximately 50K on it.
I'm sorry for providing so much info, just trying to cover everything. Thanks, Steve
Expert:  Arench replied 2 years ago.
There is no such thing as too much information. People like me eat this stuff up like ice cream and cookies.
This is a two speed fan. The coil thingy is the resistor for the slow speed.
Under most conditions the fan runs at low speed. If you idle with the A/C on max and the interior fan on high you should be able to wait a few minutes and hear a change in the fan speed to high. There is an experiment for you.
If your temp gauge is climbing and you did not hear the change to high speed then you may have a faulty fan.
Diagnosis of the two speed fan requires a scan tool capable of two-way communication to command the fan on low and hi.
Another thing to remember if the Jeep has had body work in the nose it may be missing parts like air control shrouds and gap fillers.
Find a way to look at another one the same model as yours and compare for missing pieces around the radiator core support area.
Customer: replied 2 years ago.
Thanks. Should I take it to a dealer and have them run a scan on the fan? I do remember putting the gap fillers back in. Don't really know what the air control shrouds, unless you're referring to the actual fan shrouds. All of that would have been replaced. Also, I have had this vehicle for nearly 5 years and this issue has just become a problem recently, now that the temps here are in the 90s. Although it happened last night and it was around 75 at the time.
My daughter has it now and is at work so it will be tomorrow before I can get under the hood and look at the belt and tensioner. I did notice that on the top of the coolant reservoir it looked like something had been spilled on it. Could it have overflowed for any reason? Any possibility of there being an air pocket in the system? I remember having to bleed the air out when I was completing the engine swap.
One other thing that happened was that when I had it idling in the driveway and checking the fan, the a/c was running but then the compressor disengaged. I got in the car and that is when the cool air started to become warmer, but the temp gauge was at normal.
Expert:  Arench replied 2 years ago.
I would not rush over to the dealer yet. You know they are going to hit you 200 dollars to see if the fan is working. An entire new fan assy is only 93 bucks on
Clean the front, check coolant level (not bottle) with cold engine, check belt tensioner, check if the fan has audible high speed. Then see where you are at.
Customer: replied 2 years ago.
I will do that tomorrow. Thank you for all the time and information. If I need additional help after checking the things you have mentioned, will I need to start a new conversation tomorrow or can this one be continued? I'm more than happy to include a tip when finishing. You've been a great help.
Expert:  Arench replied 2 years ago.
This can be left open and I will be around this weekend. Hopefully we will have plenty of fun, pool and beer.
Customer: replied 2 years ago.
Okay great. Thanks for your time, I'll try your suggestions with the Jeep and hopefully that will lead me to the cause. Have a great weekend and I will reconnect with you shortly. Steve
Expert:  Arench replied 2 years ago.
Thanks Steve, see you later.