1998 Jeep Cherokee Sport
Running warm, even at speed, around 212-215. In stop and go traffic, it runs up over 222. With the air on, it runs up over 222. If I leave the air on in stop and go traffic, or am in traffic for an extended amount of time with the air off, it will all of the sudden jump from 222 to 248 in less than a second. It will sit there around 250 for a minute or two, and then drop just as quickly back down to 222.
New Radiator cap
New mechanical fan clutch
New electric fan
New temperature sending unit
Flushed the Radiator when replacing the t-stat
Lower hose has the spring in it, so it doesn’t appear to be collapsing
Upper hose is hot to the touch, so coolant is flowing at least part of the time
No leaks anywhere visible
Any additional suggestions would be greatly appreciated at this point. Only thing I can think of is the water pump.
It could be the pump working intermittently, but that seems unlikely. Can you hear the pump squeeking or making any noises?
When the other repairs where done, did you drain the coolant and replace it? It’s almost sounds like you have pockets of steam shooting by the thermostat.
Are you sure all the air was purged from the cooling system after the repairs? To make sure, do the following.
Get the engine up to operating temperature. With the engine idling, loosen the upper radiator hose clamp. Take a small flat bladed screwdriver and insert it between the upper radiator hose and the radiator hose neck. Allow the engine to continue to idle until all the air is purged and nothing but coolant comes out. Remove the screwdriver and tighten the hose clamp.
I would start with a compression test and a new water pump.