I am having problems with air in my cooling system and very badly need any advice that anyone can o
ffer!

I own an 89 Cherokee (4.0L) and was having problems with the closed cooling system, I got a brand n
ew radiator for a 92 and also a heater valve and did the conversion to an open system. The overflo
w bottle I have now is less than satisfactory but I am keeping my eyes open for a more suitable one
.

I have air trapped in my system and need a way to get it out. I think most of the air is in my hea
ter core as I get no heat.

Q1: Is there a bleeder valve for the 4.0 cooling system?

When I start the engine, as soon as it starts to get hot I get coolant and air bubbles going into t
he overflow tank. Even before the thermostat opens the tank gets too full and itself overflows. T
he air bubbles continue. If I shut the engine down, as it cools it sucks the coolant back in but s
ome has overflowed onto the ground, so I lose cooland from the system. Also I am betting more air
is going in then.

I have a 190 deg. thermostat so it has to run forever to open and circulate properly. I need to ge
t the air out, mostly in the heater core, so I need the thermostat open so the coolant will flow th
rough the radiator, hopefully releasing all of the bubbles.

Q2: What are the cons of running without a thermostat?

Help! I thank you all!

This is going to sound simple but: Change the radiator cap. These should be 16 pound caps and if you have an old one, it might be releasing too soon.

As far as bleeding the system, go to www.naxja.org and search the OEM Tech Forum. XJs are notorious for cooling probs. Most have switched to a 3 core radiator ($100 from 1-800-RADIATOR). Running without a T-stat will not allow the coolant to stay in the radiator long enough for it to cool down. If you have overheated your engine, you might have damaged the t-stat. Go buy a nice one with a lifetime warranty from AutoZone and they will trade it out for you when you need it.

hope this helps,.

SeanP

Sounds like you have somthing hooked up wrong, or you have a blown head gasket.

Argh. My rad cap is 13# and I can't find a 16# one anywhere :(.

Okay, I found a 16# cap and put it on. The same thing is happening.

I don't think I am getting any flow to my heater core. Both lines to and from the heater valve don't seem to have any pressure while the return hose to the radiator does. Any ideas? I think something may be wacked with the t-stat. It is 190 deg, also I got a 180 deg one that I may put in tomorrow.

Just a thought but have you replaced the water pump lately?? maybe you have the wrong one..the serpentine driven pump runs backwards from the V-belt driven pumps but I do not know whether the 4.0 was even available with V belts

The water pump had crossed my mind, and is has not been replaced. I think it is good because when I run with the rad cap off it forces the coolant out a good deal.

On an older XJ you must bleed the air from the head. This is done by removing the 1/2 inch head coolant temp sensor on the top, rear, drivers side of the head. This sensor will have 1 wire on it. Fill the coolant bottle until coolant comes out from the hole without the engine running. Re-install the temp sensor and wire, and check again for over-heating. Chances are it will use about 2 more quartes of coolant.

Dude, been there many times, changed everything over to new style, if you have problems bleeding the head at the temp switch, spice in a flush mount in the upper heater hose, it works great, hope it's not a head gasket.

Just for shits and giggles, so to say.,..

Drive your truck till it gets hot

then stop the engine, open the hood and try to spin the engine driven fan ((CAUTION !!! WITH ENGINE OFF!!!)), Their should be very little to any movement what so ever, if it spins, ITS DEAD! #1 PROBLEM! FIX IT~!

:)

On a 92+ you bleed the air by squeezing the upper radiator hose with the radiator cap off. You can see bubbles coming up out of the radiator. Since you converted this may or may not apply to you.
If you replace the thermostat check to be sure the new one has a weep hole(92+, I assume its the same for a 89). AZ and NAPA sell one that fits but doesn't have a weep hole. When I was having cooling probs a couple years back this made about 5&deg difference in operating temp. AZ and NAPA might have both kinds, I know the Mopar one has a weep hole. And on the 92s its a 195&deg stat, not 190, maybe this is a difference in model years.
Also, I'm not sure how air can get trapped in the heater core, but you can rule this out if you leave the heater controls in the off position. No coolant circulates through the heater core when the heater control vavle is closed.
And smartass, stop calling it a truck. It's not a truck or a car, it's a jeep. Didn't you just buy one? You better learn how to talk to it or it'll break down on you in no time.

Well, I found out where the air was comming from! My head gasket went the other day. :(

Originally posted by SeanP
Running without a T-stat will not allow the coolant to stay in the radiator long enough for it to cool down. If you have overheated your engine, you might have damaged the t-stat.

Ya know I keep hearing this about running without a t-stat or one stuck open and overheating. Mine was stuck open since I got my XJ 2 years ago and I never overheated when it was a daily driver on the highway or on the trail once it became a trail rig. In fact it ran very cool all the time.

FWIW, I did finally replace the t-stat with a Mopar one this past weekend. Two years later, my heat blows hot air again!