1995 jeep 4.0 odd heating issue

[humve]

When I drive my jeep it will go over 210 almost to red line then drop back down to 210. I haven't had any issues with it. It has new antifreeze in it spark plugs, cap and rotor. It is a 4.0 5 speed 3.07 gearing and 33 12.50 15. I did read a little bit on it and someone though it mite be a sensor that is bad. That's reading wrong. What do you guys think?

[semnmrc]

Maybe two things.
First, how long ago did you change the coolant? there may be air in the system still?
Second, did you change the thermostat? It may be going bad.

[struhall]

Second vote for air in the system and/or a thermostat. Make sure to burp the system several times once you fill it up. I've done it before and thought I got it all good then checked the next day and it was super low.

[humve]

Just got a thermostat today so will do that and see what happens. I did the antifreeze when I restored. Less than a year ago.

[BigSki]

That tire/gearing combo is the equivalent of a 2.60:1 gear ratio on a stock 28" tire. While probably not the root cause of your current heating issue, the engine is definitely working hard to push the jeep around.

[struhall]

It would take more than just the tires to make it work hard enough to overheat. I'm running 33x12.50 on mine (auto with stock gears) and never had any heat issues because of the tire change.

[87Matchief]

already said but id check thermostat and make sure there is no air in the system.

[humve]

Did the thermostat today and it seamed to be ok but I need to take it a little longer trip so that I know for sure it is fixed.

[thecrusader]

Sounds like an air lock or thermostat. Them jeeps where peices of shit as far as the radiators went. I lost count
of how many i did. They had a crossflow rad with brass headerplates and plastic tanks. Every time
the tabs would snap or the headerplates where cracked.Theyve probably all been fixed now.

Off memory the top housing on the motor had a small outlet for the heater hose. We used to pull this off
when we where filling them to bleed the air out.

Just fill it and check agin when it's cold and top up.

[NTA_Shawn]

Sounds like an airlock. I had it happen to my '01 Ram 4x4 a while back. It happened right after I swapped to a low temp failsafe thermostat and radiator flush. If it was to go bad it goes bad open so the engine wont overheat. The low temp keeps it cooler, yet turns on the check engine light from it being too "cool" for too long. The computer sees the engine too cool and gives it a little more fuel for it to warm up quicker. I have to plug in my Hypertek programmer every now and then to clear the code, but it pops right back up eventually.

[humve]

Took it on a good drive today and it is 85 out. I put a 195 thermostat in it and check for air in the system. It ran cooler on a colder day but today it ran over 210. Is it normal for them to run hotter on a hotter day? Is it possible that being it is 21 years old the gauge is reading wrong?

[semnmrc]

Did you install the thermostat correctly (not upside down)? I know it's been done.

Also, your jeep has both a mechanical fan and an electric fan, correct? If so is it warm enough to make the electric fan come on?

[humve]

No its not upside down (been working on cars since in could walk lol). It has a mechanical fan. One other thing I noticed is when I turn the heat on to try and cool it down the heat will be like hot then cold and hot then cold. Not sure what this means.

[semnmrc]

Originally Posted by humve

No its not upside down (been working on cars since in could walk lol). It has a mechanical fan. One other thing I noticed is when I turn the heat on to try and cool it down the heat will be like hot then cold and hot then cold. Not sure what this means.

Sounds to me like it has an air lock, or pocket.

What I usually do when I have a system that's hard to get the air out of is get a flush kit, the ones with the "T" fitting where one end hooks to a garden hose . Cut one of your heater hoses and install it there, and fill the system from that, making sure to hold the "T" part higher than any other part of the system.
Hope this helps.

[humve]

Sounds interesting. Have to look into it thanks.

[allanon1965]

Originally Posted by humve

No its not upside down (been working on cars since in could walk lol). It has a mechanical fan. One other thing I noticed is when I turn the heat on to try and cool it down the heat will be like hot then cold and hot then cold. Not sure what this means.

this means you have air in the system and its getting coolant when it gets hot, then getting air when it cools down... jeeps can be hard to bleed the system, sometimes jacking the front end up high as the floor jack will go helps along with the tee in the heater hose... keep bleeding it and it will eventually get all the air out.

[humve]

Thanks guys for the help. I think I have it fixed. I took a day and did 180 th, new waterprump, new lower radiator hose, and DIY cooling fan. I also made sure all the air is out. It did take some time to get it it. It seams to running cooler.