kc8esc

ok, I am new to this so please be patient with me. I have a 1998 jeep grand Cherokee that does not warm up as I'm driving on the freeway (65 mph). Driving in stop and go traffic it warms to approximately 200 degrees on the temp gage. Driving 50 mph the temp fluctuates from low 100 to 200 according to the temp gage. The defroster, and heater blow cold air most of the time, and mildly warm air while idling. I put a new radiator in about a year ago. Any ideas what the problem could be

djb383

Does it have a t-stat?....if it does, maybe stuck open? PO's have been known to remove it which just creates other problems like poor heater performance now and hides some other cooling system issues 6 mos from now. Might have better luck over in the Grand Cherokee Forum.

00jeepXJ

Look at your thermostat. Like stated above if it's removed it can cause lots of problems like what your having.

kc8esc

ya, I replaced the thermostat first off, I thought the same thing. I am thinking about replacing the radiator hoses thinking they could collapse at high speeds.

djb383

Why would a hose collapse?......the entire cooling and heater system is internally pressurized......presuming nothing is leaking and the rad cap is holding pressure as designed.

msjacquelinen

I would try bleeding the air out of the cooling system. When the vehicle is cold remove the radiator cap and start vehicle, turn defroster on. Let run until the thermostat opens. Its not a big deal if some coolant overflows out of the radiator, but make sure that you top it off when done.

kc8esc

coolant levels are the same as after I changed radiator last year. Oil level drops 1/2 qt between oil changes, so I don't know of any leaks.
I was thinking as the water pump speeds up it would make a slight pressure on the one line, and a vacume on the other hose, which could collapse the hose, but your right the rad cap should maintain a few lb pressure and prevent any collapse.

djb383

Actual coolant temp dropping down to 100 while driving is virtually impossible......suspect a bad gauge, bad sending unit or bad electrical connection. Might check the heater temp "blend door" operation (under the dash). On Cherokee's, it's cable operated between the temp **** and blend door......don't know about the Grand Cherokee. Also, the a/c compressor is engaged in the defrost vent position and air coming out the defrost vents will not be as warm as air out the floor vent position.