fireman1600

1994 Cherokee Sport, straight 6, 4.0L, 4x4.
New radiator, full of 50/50 mix, water pump good, thermostat removed, no visible leaks anywhere, tailpipe dry.

Heats up at a normal rate, then just keeps going up. Hovering around 230 at 65mph, heater on high. Can drive about 20 miles, then it starts rising, have to stop, and let it cool off. Under the hood, the overflow tank is full but not overflowing, and is roaring with air coming out of the radiator (not boiling). Release the handle on the radiator cap and air pours out. Then it sucks all the water back in from the overflow tank, and I can drive another 20 miles.

On low speed roads, I can run it normally until it gets hot, then down shift and run about 4000 rpm for a minute and it cools to 190, then starts going back up. Once it cools, I coast in neutral, or otherwise drive as gently as possible, and it works for a little while.

No rhyme or reason. Mayday.

mitch500

What year is your xj? How does your oil look? Any coolant in it?

Also why are you not using a thermostat?

RTorrez1

We need to know the year!
You need to get rid of the lever type of rad cap and get a standard cap set at 16lbs and put in a new t-stat set at 195degs. Is the elect fan working as it should? How is the fan clutch. Those are just guesses since I have no idea what year you are working with.

md21722

Use the normal 16psi radiator cap, check for airflow through the radiator. Are there bugs etc in your A/C condenser? If it's not the cooling system it's probably the head gasket or head itself...

xjmachine

blown headgasket or cracked head

Firestorm500

Yep. Get the wrenches and the money out.

fireman1600

Agh, I knew there was some info I forgot. 1994. Oil is clean, took the thermostat out because we were testing it by removing it, but removing it made no difference, so didn't bother to replace it.

fireman1600

I got the lever type, 13lbs, because standard cap does not fit my radiator; since I replaced the radiator with a generic one, the cap for a 94 Cherokee doesn't fit it anymore; the old regular cap poured all my water and coolant out on the ground, the new lever cap sends my water into the overflow tank, then recovers it. The only thing that comes out the cap is air.

T-stat is not in right now but I have a failsafe set at 165, cause it can't hurt to open too early, but it hurts to open to late, according to my friend, he was who bought the thermostat so......

Electric fan works, fan clutch works too.

fireman1600

Wow, thanks for all the help! Joining this forum is the best thing that ever happened to my Jeep!

djb383

Negative.......it definitely can cause problems when the t-stat opens too early/too low temp. Pass that along to your friend. Fast coolant/engine warm-up is very important to proper engine performance.

Fail Safe stats r a joke.... the stat u want is the one that's guaranteed to open at it's rated temp (and 165 is too low), not one that's guaranteed to fail in the open position.

mitch500

Agreed

The Mick

If you put a 165 failsafe in your Jeep it will lock in the open position as it is designed to before you ever even reach normal operating temp of 195. Thus the same result as not putting it in at all.

Pelican

A standard 16# cap is available for and will fit your radiator. Not sure what you mean by generic but assume an aftermarket OEM style radiator from one of the parts houses.

RTorrez1

For some reason a lot of radiators when changed out the new cap wont fit tight. What I have done on the Jeeps I have owned. Get the correct cap that your year and model calls for and bend the little metal tabs on the cap a little at a time until it seal correctly. I have done this on all of my XJ's that I had to change the rads on and it worked every time.

Firestorm500

It's not the radiator cap.