2003 grand cherokee

i have just bought a 2003 grand cherokee 4x4 with a 4.0 and having overheating problems when sitting have already replaced the fan relay and thermostat i read where one guy wired his fan straight to a toggle switch on dash any thing i can try  

the fan controller needs a really good ground...

as does the negative cable to the body... and the engine to the body..

the fan controller controls the amount of current to the fan on the NEGATIVE Side...

if the ground connection is dirty.. and they do get dirty.. the fans will NOT RUN AT FULL speed.. and the engine will overheat if the fan controller does not burn out first..



the back mounting bracket needs to be firmly attached to the bracket/heat sink.. with a layer of dielectric tune up grease or white transistor grease behind it to allow the massive amount of heat build up in it to be dissipated to the moving air flow..


you will want to do the 4 part test on this chart i put together..  you may have other ground connection issues...



do you have a factory service manual to look through???

this is the replacement connector for the radiator fan relay... #861 at AZ duralast /wells...



not cheep at 40 bucks.. but i checked at the wells site.. the 19303 relay uses the 861 connector pigtail..

terminals have been damaged by heat and may not transfer enough current to the fan motor to operate at full speed..

you can also do a voltage drop test.. between the positive battery and the positive wire into the fan motor.. expect less than 0.5 volts    do a similar test between the negative battery post and the negative wire into the fan motor..   both with the electric cooling fans running..

if you cycle the key on 3 times within 10 seconds.. you might be able to make the odometer change from miles to trouble codes.. post any that comes up...  or use a scan tool...

you do not have to start the engine.. just on.. off .. on.. off.. on .. off  on....

if you need more help.. do post.. i only have a 98 gc and a 2005 gc service manual.. the 05 version is over 7000 pages long..  it covers the V6 versions.. not the 4.0..  and the systems are slightly different in the 98 manual..  

there are other reasons for it to overheat at idle..

bad radiator cap.. one that fails to hold pressure..

head gaskets starting to fail..

clogged radiator tubes.. ( Internal )

clogged radiator cooling fins..  (external)


and i am sorry to say... an INCORRECT temp thermostat..

water pump with impeller fins worn off..  once in a while fins broken off..