cooling problems - what else!!?

My 90' XJ with a 4.0L started out with the typical cooling problems you often hear about. At idle it would start to heat up, but with the ac turned on and the auxillary fan running, it kept the temps down. After going to Camp Jeep back in July, I noticed that it started to force coolant out of the pressure bottle while still running and would just empty the bottle after shutdown. Just prior to Camp Jeep, I had replaced the pressure bottle and cap, the t-stat and the auxillary fan switch in the radiator. When the t-stat opened up, the water flowing into the bottle was boiling violently which led me to believe I may have a blown head gasket allowing CO to add pressure to the system. Well, after spending part of the holiday weekend replacing the head gasket (which did not appear to be blown), the fan clutch, the t-stat again, the water pump and all the hoses, the problem still exists. The radiator had been previously replaced due to a small leak. I started the Jeep up and after about 15 minutes of running at idle and higher revs, just after the t-stat opened up the pressure in the bottle was so great, it blew the cap right off the bottle. The temp had stayed at 210 and started rising to 235 about the time of the explosion. I am starting to think I may possibly have a crack in the head, but was wondering if anyone else had some thoughts on this or maybe experienced a similiar problem with their closed system before. The coolant seemed to be circulating through the system the way it is suppose to with the coolant filling the bottle when warmed up and drawing it back into the system upon cooling. The level in the bottle was where it was suppose to be on the notch, but after warming up, it will fill the bottle until it wasn't capable of holding anymore coolant, thus leading to the explosion of the cap this morning. Anyone have any ideas?

Right up till you said you pulled the head I was leaning towards the mechanical fan clutch. One other question, when you did work on it, before pulling the head, did you at any time remove the serpentine belt ??? And if so what kind of tension gauge did you use to set it to 160LBS ??

Rich - I suspected the fan clutch as the initial problem in the beginning. The temp would start to rise while sitting in traffic at idle, but turning on the ac so the auxillary fan would turn on would return the temp to it's usual position on the temp gauge. The temp would also remain at it's normal temp on the gauge while driving at highway speeds. Gradually the temp started to rise even while driving at highway speeds. The problem only seemed to get worse with time. Prior to removing the head, I had only replaced the t-stat, the auxillary fan switch, and the bottle w/cap because it seemed to be leaking. I actually have not tightened the belt, which I also replaced along with all the other parts I listed. I had just finished putting it all back together and was testing it to see if the problem had been fixed. The problem is the same as it was before removing the head and replacing all the parts. Thanks

How did you retension the belt ??

What you think is 160lbs is in reality closer to about 90lbs. Also the water pump could be shot. I know this might sound really dumb but did you check the fan belt routing, easy to get the water pump spinning the wrong way.
I think I would start from scratch, drain the system, refill with water and flush it with a good flush, then back flush it. Seeing as how you pulled the head without a second thought and put it back on again you might want to pull the pump and take a look at the impeller, see if it's pitted or just plain shot and while you have it off see if it has an "R" on it for reverse.
The only sure way to check for a cracked head is to have the head magnafluxed or have a sniffer check the exhaust and the coolant for combustion byproducts. Hows the oil look ???

Rich - Thanks for your input. The water pump was just replaced along with the head gasket and other cooling system parts. The pump and other system parts all seem to be functioning properly, but as I said, the system seems to be building or getting excessive pressure built up and forcing the coolant into the recovery bottle (pressure bottle) to the point where it is being forced out even to the point of blowing the cap completely off. My next step is to try and determine if there are CO gases in the coolant. The oil is fine and does not show any signs or odor of coolant. The old head gasket was fine and had I not been in such a rush to try and get the problem fixed, I would have had it magnafluxed for cracks while I had the head off. As I said before, I have not tightened the belt other than just making sure it was snug and not slipping because I was just testing the system to see if replacing all those parts would solve my problem. I replaced the head gasket at the advice of a couple mechanics I know who said the symptoms sounded like a blown head gasket.

justjeeps --

You just wrote something that got my attention. You referred to the bottle as a "recovery" bottle, and it sounded like you think coolant flowing into the bottole is a bad thing. Wrong on both counts.

On the Renix-era 4.0Ls, that bottle is an integral part of the pressurized cooling system. It is not a "recovery" bottle -- it is an EXPANSION bottle. If you look inside it, you'll see a post directly under the cap, with a notch cut out of one side. You should be filling to the lower side of the notch when cold, or to the upper end of the post when warm. However, do not attempt to remove the cap when hot, because that cap is your "radiator" cap.

Did you burp the system when you did all that work? This system is difficult to fill correctly. I just went through this after installing a block heater in an '88. I filled it, started the engine, and ran it with the cap loose until the thermostat opened. Then I shut it off and allowed things to cool. When it started sucking down the level in the bottle, I added coolant to keep the bottle half full. When the level stopped dropping, I started the engine and did it again. This went on for four or five cycles, until when I shut off the engine and let it cool the level didn't drop suddenly. (It drops a little due to contraction, but when it's sucking down you can see it and hear it.)

You'll never get the system to cool if you don't purge the air pockets.

There is a big difference between snug and adjusted, snug won't cut it, when I replaced mine on sunday the old belt with 180,000mi on it only deflected 1/4" near the ps pump, the new belt adjusted to 190lbs deflected less than 1/8" but I used a Krikit II belt tension gauge to adjust it. Eagles burping procedure is one of only two ways of getting the air out and thats provided that you used a thermostat with the weep hole installed at the 12O'clock position in the tstat housing. If the thermostat was an aftermarket one without the hole you will have problems. The other method that some use is to fill the system from the temp sending hole by removing the sender and filling from there. I like eagle method better

I had this same thing happen after replacing the reservoir, cap, and thermostat ( all Mopar parts ) on my '87, it ended up being a faulty cap. It wasn't holding pressure, and after having removed and replaced it a few times, the threads got so they would not keep the cap tight. I've got my original cap on right now and no problems.

Eagle - Thanks for your input as well. I was only referring to the bottle as a recovery so those who may not have as much mechanical knowledge about the closed system, but may have experienced the same symptoms might be able to offer some advice. I also realize the system is suppose to have coolant come and go just as in an "open" type system only under pressure. I did try to burp the system, but not in the manner you described. I will try your method first to see if maybe it could be the cause of my problems. My real concern is the amount of coolant and the pressure that is being put in the "expansion" bottle and is causing the cap to blow off. The cap does not seem to really tighten up, (it gets snug, but any further twist and it will spin like it is stripped) so I will probably go and get another one or two from the dealer again per MJ's thoughts. Also to note ... my t-stat is an aftermarket one and does not have the weep hole in it so I guess I should either drill a hole or purchase a t-stat from Jeep. If I do decide to drill one, what size should the hole be? Thanks

What kind of oil pressure are you running? It seems that you have replaced everything with the cooling system. However the oil is the primary cooling system which most people forget about. If you have low oil pressure you may have a bigger problem.

Also what mix of antifreeze and water are you running?

FatXJ - My engine runs around 40 PSI on the highway and about 20 PSI at idle. I run a 50/50 coolant mixture. The engine has alot of miles on it, but it has been very well maintained and has been using Mobile 1 synthetic most of it's life.

Also to note ... my t-stat is an aftermarket one and does not have the weep hole in it so I guess I should either drill a hole or purchase a t-stat from Jeep. If I do decide to drill one, what size should the hole be? Thanks

Click to expand...

JustJeeps, a 1/8" hole should be about right. Make sure it's installed with the hole in the 12 o'clock position.

I always drill this hole in all of my vehicles' thermostats, if it's not already there. I feel it helps to equalize the pressure/suction a bit during warmups.

I wonder if the lower hose on the suction side of the pump is closing up and restricting flow. There should be a spring inside to hold it open. In regards to burping the system, I have learned from experience to pull the upper hose at the t-stat, hold the loose end as high as possible, and fill the system to overflowing. This fills the system full the first time and eliminates air pockets in the head, etc.

In regards to the hole drilled in the t-stat: My 89 has a machined slot in the recess that the t-stat fits in the head. This slot is effectively a small bypass of the t-stat. It seems this slot serves the purpose of the drilled hole.

XJTripp ..... You are correct about the bypass slot next to the t-stat in the housing and I also thought it would let air pass just as the weep hole would. Also as to the filling of the coolant system, when I refilled my system after changing all of the parts, I removed the upper radiator hose and the heater hose going to the t-stat housing and filled the system through the upper radiator hose until it came back out of the heater hose connection on the t-stat housing. I held the upper radiator hose up above the head and was told this was the way Jeep recommended filling the system to remove any air. I have also done a test to check for combustion gases in the coolant and it came up negative so I guess the head is fine. I am pulling the radiator this weekend to have it checked for any possible blockage. We'll see what happens after I get it checked out. Thanks for your input.

before you pull radiator

Why don't you go through the burping process and consider replacing the pressure bottle cap (again)?
This badly-engineered cooling system is only as strong as its weakest link: the cap.

Good burp instructions here:
http://www.olypen.com/craigh/cooling.htm

It takes very little air in the system to send these trucks into the red zone-- give it a try before you unbolt that radiator.

tension gauge?

Where can I find a serpentine belt tension gauge. I've looked on-line and the parts stores and I can't find them. Seems no one carries them anymore. Thanks, Troy

NAPA

Re: before you pull radiator

DeathByXJ said:

Why don't you go through the burping process and consider replacing the pressure bottle cap (again)?
This badly-engineered cooling system is only as strong as its weakest link: the cap.

Good burp instructions here:
http://www.olypen.com/craigh/cooling.htm

It takes very little air in the system to send these trucks into the red zone-- give it a try before you unbolt that radiator.

Click to expand...

One thing I found on my 87 was that if you overtighten the cap it will distort the gasket and unseat it. There's a fairly fine line between not tight enough and too tight.

Oh man... We just replaced the entire coolant system on my 1987 XJ Wagoneer. It has never been better.

http://www.off-road.com/jeep/cherokee/98/12_dec/radiator/radiator.html

total cost = $300.00

Clean the coolant temp. sensor in the head, too.