Odd temp issue

Ok this is going to be a 93 grand 4.0 This is my moms jeep.

She is telling me that when she stops at a light her temp gage goes all the way up and she will turn the heater on and it blows cold air, then when she starts moving again the temp drops where it belongs and heater blows warm again???????? :dunno: She also said it doesn't seem or act like it is over heating, not shooting steam everywhere or anything.

Odd if you ask me and I'm kind of at a lose for this one, could a air pocket cause this to happen? Maybe the temp sensor? I don't see how the temp sensor could or would change the temp of the heater but I could be wrong and just trying to throw a idea or two out there.

Any help would be great here guys, my mom is single so I am the one that needs to work on and fix her rig and I'm the one that got her to get this rig :twak:

Thanks for your help
CJ

sounds like air trapped in the system, probably just needs a good burp

That's what I'm hoping it is, going to take a look at it tomorrow. Just trying to shoot for some other ideas on what it might be in case that isn't it.

Heres a theory.. bad water pump. Impeller does not push enough water. when idling, not enough circulation to cool block.. not enough push to move water though the heater core. Going down the road.. more rpms allows it to push enough water to keep things ok. Your problem sounds odd.. could be just an air pocket - but how did it get there ? Recent hose change, small coolant leak ? been adding coolant ?

Clogged up radiator and coolant passages could also cause this problem. Same theory as stated above, not enough flow at idle. Run a flush through it and burp it properly.

Yeah no new hoses or anything and no lose of coolant so haven't had to add any that is one of the reasons I thought it was odd when she told me what it was doing. Going to talk with her more about it in the morning and start with a flush and good burping (always best to start with the lowest cost and easiest work first) and then go from there. I'm not sure if it is something that is happening at every light and all the time or if it just happened once and she is worried about it lol Find out more in the morning just hope it to be something easy and cheap though, we all know what the grand stands for in Grand Cherokee lol

Keep the ideas coming though the more that I have to go on the better.

CJ

I'm not familiar with the grands.. but if you can get your hand on the radiator and touch it. You can do a test to tell if it is plugged up pretty bad or not.. and it'll save you a flush. After it gets warmed up, put your hand across the radiator and feel if there are any spots that are not warm/hot like other parts of it is. If it is.. then its plugged up. My XJ with the stock rad when I bought it would blow its top in stop and go traffic.. then I did this test and half of the rad was cool to touch. So I got another rad.

Thermostat..


99.9% been there

A fan clutch is a common suspect of temp creep at idle, but you don't normally lose the cab heat when that happens.

Because you lose cab heat WITH the temp increase, my vote is for a failing water pump.