1999 grand cherokee laredo overheating when idling for 15 min. or so. Not when driving, everything ok. radiator replaced about 8-9 months ago, water pump pretty new, and extra electric fan worked on about 4 months ago. Just replaced radiator cap 2 days ago. I do not think I hear the fan coming on. Not sure. What do you think could be causing car to overheat when idling to long?

SOURCE: 1999 jeep grand cherokee laredo

Try these troubleshooting tips before replacing anything else.

SOURCE: 5.2 1994 Jeep Grand Cherokee overheats at idle

I don't remember ever seeing a Jeep that did not have an electric fan as a supplement to the mechanical one. The electric one should come on when the A/C is engaged. Jeep radiators are far smaller than they should be due to ground clearance issues. The only way to make them work is to enhance air flow through them by using electric fans. (or adding an extra row of cooling cores such as in the special tow package). When the vehicle is moving there is enough air flow created by that to eliminate the need for fans altogether, but you have to stop sometime!
Your a/c compressor adds to engine loading (why it pulls rpm down) When at idle with a/c on, the engine "thinks" it's going up-hill and produces more heat. The heat needs to be scrubbed from the system or it can and will overheat.
Make sure that the clutch fan is engaging. It spins free when cold but should lock up after it gets hot. Add an electric fan to the system...check with several scrapyards and see of any Jeeps like yours have one and take it.(some electric fans are on the drivers side and some are directly in front of the mechanical one) If equipped, there is wiring for it in the car. If necessary you can add one either inside or outside the radiator and operate it by way of a switch and relay or just a switch. (there are aftermarket ones that are "slim line) and are designed to fit between the radiator and the front grille) You could also add an external transmission cooler...in doing that, it will take some of the heat load off the radiator. Also make sure that the new radiator has the same number of core rows as the old one did....some shops mistakenly put ones with less cores in when replacing due to cost. In a system with a marginal design this can become critical. (most radiators come with one two three and even four rows)
Once the problem has been solved, don't forget to put the 195 t stat back in or the engine controls won't work properly.

SOURCE: 1999 jeep grand cherokee laredo 4.0 litre

OK here we go you will need a test light for the following tests, i will try to be as descriptive as possible so lets get started

fist start the engine and turn on the a/c that should command the fan on.
right front engine compartment next to the battery is the power distribution center pop off the top, ground your test light to the negative battery terminal and find fuse number 10 it is a 40 amp fuse check both sides of this fuse with your test light, if you have power on both sides of the fuse than we shall go further.

unplug the connector from the cooling fan, there should be two wires in the plug one is dark green and the other is black with a pink tracer, with your test lite grounded to the negative battery terminal check the dark green wire for power, if there is power there than move your test light ground clamp to the battery positive terminal and test the black wire for ground,
if testing the black wire made the test light shine than the ground circuit is good, if it did not than check you ground connection behind the right headlight.
when testing the dark green wire, if the dark green wire made the test light shine and the ground circuit is good than you simply have a bad coolant fan motor.

I suspect you were not getting power to the fan motor so you will need to take a look at the radiator fan relay, this is a special solid state relay mounted to the inside of radiator core support on the right side down behind the bumper.

here you will find a single plug with 4 wires in it

black = ground
dark blue / pink = relay controll from pcm
dark green = output to radiator cooling fan
gray = battery power from fuse # 10 in pdc

unplug the relay ground your test light to the battery negative terminal, with the engine running and a/c turned on check the gray wire the test light, it should turn on if not recheck fuses.

move your test light to the battery posistive terminal and test the dark blue / pink wire, if the test light turns on than you have a bad radiator fan relay, you can pick one up at your local parts store for about $85.00 just make sure you get a high quality one the cheap ones have a hard time with the amprege consumption of that fan.

good luck

wesley [email protected]

SOURCE: 1999 Jeep Grand Cherokee : Replaced Water Pump and Drive Belt now Jeep won't start?

When you replaced the Water Pump, did you replace the Timing Belt? Any time you replace a Water Pump you have to replace the timing belt because it stretches out. If you did not then most likely your Engine is out of time and there for will not start, but it will turn over. hope this helps, good luck.

SOURCE: Intermittent overheating on 96 Jeep Grand Cherokee

I had this same problem on a taurus and did all the things you did and found out after that the coolant reserviour bottle had a crack in the bottom of it