so my son was driving his jeep last night and the temp gauge shot up in two large steps... once to just before the red lines and then all the way to 260. I replaced the thermostat thinking that might be the issue. I removed it last night and drove it home without overheating, but after replacing it we took it for a ride and all was good for about 4 miles then the temp shot up waited and then went to 260. We turned on the heater, but no heat at all??? Any ideas??
Air in the cooling system would create those symptoms. Make sure the system is free of air pockets by starting it and letting it warm up to normal temp while idling. Shut it off and let the overflow tank suck in what is required to deal with the air pockets (the overflow tank must be full when you do this.)
Repeat a couple of times to insure the proper purging is complete. THEN go for a test drive.
WANTED--MJ Comanche to restore. Must be solid, (relatively) rust free chassis. Send me a PM if you have a line on one that is for sale.
Get cooling system cleaner. first and cheapest step.. next take the thermostat out and run it to see if it over heats.. if it still overheats then its obvious you have a blockage problem.. check the line going from the radiator to the thermostat while its running and if theres no flow then a waterpump could be likely. im accually about to change mine in an hour or so..
Take some of the variables that rely on each other to eliminate the next issue till boom! fixed hahah
First of all, you have an 01, which has the infamous "0331 head" which is susceptible to cracking upon an overheat. You want to fix this RIGHT AWAY, RIGHT AWAY!!!
T-stat can't be installed backwards on these.
What is the history of routine cooling system maintenance? It might be a good idea to replace the radiator, water pump and cap. Overkill? Not so with an 01. These parts are not that expensive and knowing that a single overheat can toast the head and lead to engine damage makes this project more appealing.
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche Without "data", all you have is an opinion!
I had the same problem a few years ago and I did all the regular checks & flushed everything. Ultimately it turned out to be the waterpump had rusted off the individual impeller blades so there was just a flat plate spinning in there not moving any coolant. Kind of a PITA to pull it off to verify. I don't know if you can pull the lower radiator hose from the pump and use a mirror and flashlight and look into the pump but it might be worth a try instead of pulling the pump off for nothing.
Rescued my XJ from neglect the cooling system was totally inoperative! you cannot put the thermostat in backwards. the housing is not deep enough. i found this out by trying a stant thermostat and the head is too big to fit into the aftermarket housing someone had put on this rig. broke down and went to the jeep dealer and got a new housing and factory thermostat.it fit perfectly. I also had the same problem that will1266 had. the impeller rust away so bad it looked like a chinese throwing star. So to conclude i replaced everything in my cooling system....rad,pump,t-stat and housing,all hoses and the heater core.yes i did pull the dash and when i did i replaced the evaporator core because they do leak! and why remove a dashboard twice, but check your heater core for flow first. just simply take the hose off the thermostat housing and the water pump and use a garden hose to flush it out. very simple and easy..if it flows out as fast as it flows in your fine. i use whats called the spill free funnel to fill my cooling systems it has a cap adapter with a hole that the funnel attaches to and i fill it up till its halfway in the funnel and run the engine till it burps all air and thermostat opens usually good to go. the weight of the fluid helps the pump push the air out. good luck!
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