Hey guys,

I'm not much of a mechanic so please bear with me. My '01 XJ has about 100k on it and has developed an issue. Runs cold and the check engine light comes on periodically - off for a few days then on again. Also have a weepy seal somewhere as I've got a very slow oil leak. Heater output is tepid most of the time. Seems the heater controls work fine. System maintains coolant level.

If I let the engine warm or if I re-start it after it's been sitting a few minutes the temp gauge shows a "normal" temp - just under 50% of the gauge ~ 190-200 I'd guess. Same holds if I let the system idle after running. As soon as I begin driving I can watch the gauge descend back down to the lower left. I assume running cold will cause the works to gum-up over time due to incomplete combustion.

Based on that my guess is a bad thermostat which has failed in the open position. Does that sound plausible? Should I consider anything else? If I'm correct, is thermostat replacement something a relative novice can handle?

 

well, heater core is an option. they seem to gum up sometimes. you need to flush it forward and backward, and maybe use CLR cleaner on it. the blend door (not technical name) controls the hot to cold airflow. vac. lines are another poss. (if venting to the floor, say, the airflow will partially redirect towards the defrost vents, under acceleration, then return to floor after letting off gas). outside of that... idk... as for the check engine light... mine will (was) coming on like 2-3 days after being flashed. then i went on vacation for a full week and pulled the battery. so far, and this has been since the w/e after turkey day, it hasn't yet come back on... KNOCK ON WOOD!!!

 

T-stat controls min operating temp. If its not warming up or staying warm I would replace the t-stat. They are only $8.

 

8 bucks is nuckin futs! my POSaturn was like 200 for the assembly, mainly cause you couldnt just replace individual parts... but then again, saturn doesnt exist anymore, and jeep does... huh, thats a thinker!

 

....and the CEL code(s) are?

 

Should this be in the Saturn forums?

 

I'm working on getting that info. Is there a way to check them w/out going to a shop to have them read? I thought I read somewhere that you can access that info through the odometer toggle.

 

I'd check your t-stat first, which is most likely the culprit causing the cool engine operating temp.; heater core, vac. lines or blend door wouldn't affect the engine temp....once you get your op temp back up you may find your heat is back to normal.

Oh, and checking/replacing a t-stat is easily done by a novice mechanic - 2 hoses, 2 bolts and 1 electrical connector....15-20 min. job

 

Strategy for troubleshooting a problem that has a check engine light is ALWAYS the same.

Pull the codes. Use the technology provided to you by your Jeep. It is the #1 thing I do when working on a vehicle with a CEL.

You cannot toggle the odometer for yours. That luxury went away sometime in 1997. You will need a code reader, a scantool, or have a place like Autozone read them as they do it for free.

Post the EXACT code numbers here for comment.

 

Clean both surfaces (t-stat housing and head) sterile, apply light coat of RTV sealer to both sides of gasket, install new t-stat in head (pointed side out), make sure it doesn't slip out of groove, install t-stat housing and bolts and DO NOT OVER TIGHTEN, just snug is good.

 

djb383, I cant remeber but do you need to drain the system to swap just the t-stat?

 

no just to slightly lower than the housing tho or when you break the seal you will have a mess

 

Yep, u loose what coolant is in the head. Presuming coolant is still good/clean/green, just top off with 50/50 premix.

 

Thanks guys. I didnt think it would be an issue but only time I swapped t-stats was when I replaced the head gasket so everything was already apart.