hearld500

Well, I've done searches on this forum and left a few posts on JeepForum and have had zero luck trying to get this figured out.

I was still at school three weeks ago and it was -15 out, started my cherokee and let it warm up for awhile. When I went out to go, it was right under the redline and had no heat coming out of the vents. Shut it off and came back the next day, tried it, and it was operating like normal.

When I got home for break I changed out the thermostat, its not overheating anymore, but as soon as it hits 210 it'll drop to (what I'm guessing) is the 140 line. It continually does this and does not even out.

After some research I though that maybe the tstat I had put in was the wrong one since it did not have a little hole with a pin in the top like the one I had take one...so went and got a new one and changed it out, but still doing the same thing.

The heater does not seem to be as warm as it used to be either...maybe it's just my imagination. The gas mileage has also tanked from 22 to 13, I'm guessing thats because of the computer thinking its not warmed up.

Any ideas on how to fix this?
Thanks

fivendime

My cherokee fluctuates as well, but its a little different. I have a 98 wrangler motor in it with I believe a stock t-stat. The heater doesn't blow hot air untill it warms up to about 200 deg. It goes from 230-180 or so. The thermostat is probably not the culprit. If you still have the old t-stat then stick it in a pot of water and turn it to hi and wait for the t-stat to open just around the time that the water boils. If it doesn't its bad. I just did the motor swap in my cherokee and may not have all the air out, but every time I check it its topped off, so I am scratching my head as well. On the gas mileage thing, It could very well be a bad temp. sensor thats telling the comp that its either too cold or too hot, probably too cold. An ohm's test will tell you if the temp sensor is good. I know mine is good because it read fine off the old motor, and shouldn't have changed in 3 days. I will do some more thinking on this.

BuckB91XJ

Sounds like air or a clog in the cooling system somehwere, to me.

fivendime

I also wonder if the valve that controlls the fluid to the heater core is stuck closed or partially closed. I know mine isnt cause its new. This is the reason for the new motor, cause it blew apart on the PO. I still haven't found a good way to bleed the air out. I have a valve I put inline to bleed air, but I still dont know if its all out.

hearld500

I forgot to say I had thought about the sender and had replaced that as well, same results though...there goes $25 down the drain....

Whats the best way to try and get the air out of the system?

farmfuel

The computer will enrichen the mixture if it's cold; you're correct about that. The Radiator cap is above the Thermostat line (as far as height goes), so there's no bleeder screw/valve to bleed pressure/steam out of. There's two sensors for the coolant- one for the gauge, and one for the computer. If you overheat one of these sensors (with steam or otherwise), the possibility exists that it will get damaged. Which one did you replace? The one for the gauge? If so, perhaps it's the sensor for the computer that got damaged.

Also, how is your resivor level? Does is suck in coolant when it's condensing, and blow it out when it gets hot? Bad radiator caps can do weird stuff with pressure in the system.

Last but not least, you should have someone inside command the heat on, while you watch the heater control valve linkage open. If it's -15 outside, my guess is it just takes a while for the coolant to get up to temp? Perhaps a piece of cardboard in front of your grill? Is your electric fan coming on for some reason, like defrost?

XJ Stryker

I doubt it is airlock since he should have the open system.

Do your heater hosed get hot when the engine is warmed up.

Touch them both top and bottom.

hearld500

I had replaced the sender on the front of the engine on the tstat housing. Which one is that? Where is the other sender located? No longer -15 now, warmed up now thankfully...t-shirt weather now (about 40)
I'll have someone run the heater and see what it does.

The reservoir stays about the same level, but it does suck in when condensing. Haven't felt the heater lines, I'll try that today.

Would it help pointing it uphill and running it with the radiator cap off until its warmed up?

fivendime

The front one is the one for the computer. The second one is located on the back of the head on the drivers side, that is for the temp guage. You may not have this if you just have the idiot light. The 98 wrangler motor I put in mine didn't have it since it had an idiot light, so I drilled and tapped it for the sensor.

Pointing it uphill? I have never tried this. I have a cheap bleeder on my heater line since you can pull it up to be the highest point in the system.

farmfuel

Can you elaborate on this? Technically speaking, the heater hoses and control valve are on a higher plain than the cap or t-stat housing, so I do see that the possibility exists for air to get trapped in that area.

I can't remember without looking, but isn't there a CTS sending unit on the intake manifold, aft of the throttle body?

fivendime

Heres my setup to bleed air.

hearld500

Thanks for the pics, that'll be something to add to the list.

I tracked down a scanner yesterday and was watching the engine temp that the computer was seeing. Went between 195 and 206 and moved independent of the gauge. I'm thinking thats the regular range for the tstat to open...does that sound right?

Soooo I guess that narrows it down to bad guage, bad sender, or maybe a bubble in the back of the engine. Still havn't gone long distance yet to see what my mileage does though.

Thanks for the help everybody.

(talk about a clean engine bay fivendime haha)

fatnred

hey buck i am pretty sure it is an air bub in there and i heard that if i loosen the upper rad hose going into my tstat and fill from my overflow it should work butt have tried and it did not work it just back flows back into the res and im figuring if thid keeps happening im going to have to buy another set of bottle and cap which is about 300 at my cost

fatnred

all hoses have pressure in them and warm butt still no clue

prerunner1982

I have a similar problem and had the same "bleeding" set up.. except mine was so melted that it sprung a leak on the way to work this morning. It looked like it was covered in grease, but it was hard. Mine was mounted between the firewall and the heater valve, I didnt know it wasnt factory until today when I looked in my parts book and there wasnt anything like it.

Also, FivenDime...is it just me or do you have the wrong upper radiator hose?