1999 Jeep Laredo car overheating

More than likely it is your water pump, they are about $20-$40 at the auto parts store and you should buy one at carquest, they are the more reliable ones that I have found. The 4.0 engine is known for water pumps.

I would frist replace the Thermostat here is a good one for $13.54 there is a link to a place you can get a good part from
I as well want to say I agree with the person that posted water pump I would check the thermostat frist as it sounds like it is locked closed if you replace bolth and still have a problem it could be a hole in a hose, bad radater cap, cloged radater. I hope I was of help and it's a cheep fix.
Thomas

http://www.autopartswarehouse.com/search/?refType=Sort+By&refValue=&N=0&Nr=AND%28universal%3A0%29&Ntk=Main&Ntx=mode+matchall&Nty=1&Ntt=jeep+grand+cherokee+thermostat&D=jeep+grand+cherokee+thermostat&Dx=mode+matchall&Npp=50&Ns=

Stant Thermostat
Part Number: ST13008Manufacturer Number: 13008
List Price:$15.98
Our Price: $13.54
You Save: $2.44
Quantity:
STANT THERMOSTAT -- 180%XB0 F, A Direct Fit OE Replacement Engine Coolant Thermostat, Made Of High Strength Stainless Steel Assembly, Offers Engineered Springs For Smooth Performance, Comes With Self-Cleaning And Self-Aligning Thermostat Valve
Fit Note: Alternate Temperature
Fits the following 1999 Jeep Grand Cherokee submodels:

1999:Laredo; 6 Cyl 4.0L; "GAS, FI, VIN S"