the9-5guy

Hey guys. I'm new.

2004 Jeep Grand Cherokee Laredo with the 4.0 is overheating at idle and in the first 2-3 minutes after idling. Once moving the coolant temp comes down.

Started doing this today. No recent work done to the car or the cooling system. This is the single electric fan set up, and the relays are in the relay box next to the battery. Not underneath the headlight.

I have already tried replacing both relays and it does not seem to make a difference. I can get the fan to come on by turning on the AC system. I cannot seem to get the fan to come on via temperature reading. I cannot and do not see any coolant leaking.

Has anyone else had this problem with this set up? If so what was it?

Thank you.

kjc

I believe the fan should come on when the temp reaches 215 or some such number.. if it's not, you might check the temp sensor. It might have 2, one is for temp gauge and the other for the fan. Also, if you have a clutch fan, you might check that it's functioning properly.

nc527

If you have a single electric fan setup, then you do have the PWM relay under the headlight. In addition to the relay in the fuse block. Most likely either just the relay is bad, OR the relay and fan itself have gone bad. I actually just had this problem with my jeep, and can almost say 100% if you replace the fan and relay, it will work again(unless you have a shorted wire or bad ground). BUT, start off just replacing the relay.

dave1123

He said the fan runs on A/C so I'm assuming the fan and relay are good, however he's not getting a temp signal. These are separate signal sources, both thru the PCM, I believe. My Haynes manual doesn't have that circuit diagram and IDK why, it's got just about everything else! The text on diagnosing the fan says to check the circuit diagram at the end of the chapter, but it's not there. The relay under the right headlight is a pulse-modulated relay controlled by the PCM and I think the other one is used by the A/C system. I'm just winging it here.

Replacing that relay under the headlight is a definite PITA! You might want to rig a jumper wire to the fan until you can replace the relay so you can at least drive it. Put a switch in it so you can control it and make sure it's fused. Electrically, there's no reason that fan can't run all the time the ignition is on.

That's all I've got. Hope it helps. Welcome to CF!

Jeepgirl808

Hi.
I have been having the same problem.
Mine gets hot when in traffic. Running it works great. Trams over temp light comes on.
I've replaced radiator and fan.
Worked wonderful for awhile. Then overheats again.

My a/c does not work. Hasn't since I bought it from the previous owner.

the9-5guy

In an 04 with the two relays in the box, is there a relay under the headlight?

No one on the internet can seem to get this straight...

Does anyone have the illustrations that are a part of this?

Where is the temp sensor?

dave1123

The temp sensor is in the thermostat housing. I believe there are 2 relays that control the fan. One is in the PDC (box) and controlled by the A/C circuit, and the pulse-width relay under the headlight controlled by the PCM (computer).

the9-5guy

There is no PWM relay there. I pulled the headlight out and looked. I can see the 2 holes pre-drilled for the relay but no relay. The 2004's do not have one.

JWheeler

I can't remember what year they quit putting them there but you can't see it by just pulling the headlight. It is on the metal core support, under the plastic headlight/radiator support. A lot of people will just cut a big hole in the plastic to get to it instead of removing everything. Look under the plastic part that holds the headlight.

Jeepgirl808

Seen that on youtube.
Guy easily changing relay

the9-5guy

Yes, it is below the headlight housing. I pulled the housing back and looked down in from where the battery sits. It's not there. 2004s do not have the PWM relay from my experience. Like I said, the holes were drilled, but no relay and no wiring for it.

I replaced the thermostat and the temperature "sender" (Sensor that threads into the thermostat housing). The fan now comes on at temp. Also flushed the system and am currently working on getting all the air out of the system. It was likely only the sender that was bad but I figured while I was there.

Having two temp sensors (One a "sender" and one a "sensor" that controls the gauge) is a terrible design. I would like a word with whoever designed this cooling system.

the9-5guy

Appears as though the issue was either the thermostat or the temperature "Sender" located in the thermostat housing. Issue has been resolved.

dave1123

I believe you are right. In 2004, they eliminated the PWM relay and use a simple relay in the PDC. In my 00' WJ there is one one temp sensor (sender) and it's in the thermostat housing.

The best way to get all the air out of the system is to make sure the heater hose from the thermostat housing goes into the lower of the heater core pipes and to take the temp sensor out, fill the radiator until coolant flows out the sensor hole, reinstall the sensor, and top off the radiator. All the air from the heater will exit the core to the water pump, and the air in the head will leave from the sensor hole. Using this procedure, I've never had to add more than a quart to the overflow resivior after running it.

the9-5guy

So, it's been a week. Things were going great. This afternoon drove it 20 minutes or so down the highway, pulled into the store, went in and shopped for 25 minutes, came out and as we were waiting to get out the mall, we hit just under 260. Got to the last hash mark and I turned the heat on and cranked it as a last resort to increase cooling. It worked, we didn't boil over and as soon as I got on the highway the temp dropped 60 degrees in 2-3 minutes. I am guessing from the airflow at speed.

Got it home, fan was not coming on again. Shut it down for awhile, went out and started it up, got up to running temp and the fan kicked on and stayed on however the temp still rose.

To recap, it has had new relays, new thermostat, new temperature sender. Please remember this is the system with the two relays in the relay box next to the battery.

Seems that the cooling system just cannot keep up. Anyone have any ideas?

the9-5guy

No one has any ideas or thoughts on what is going on here?