Closed coolant system problem

I have a 90 4.0 with the awesome closed system coolant system.:banghead: it overheated a few weeks ago. i ended up getting a new coolant tank and thermostat. filled it up, and good to go. went out the following week and had no issues. well, i hit the road on the way to the park today, and the temp gauge starts climbing. gets to about 220 or so and i pulled over and shut it down. the tank was boiling and pissing fluid out through the cap. so i let it cool, filled it back up and headed to the store to get some water just in case. it ran about 210 all the way there, and when i parked it, i heard the boiling again. let it cool, took the thermostat out and filled it back up. it ran about 170-180 all day today. no overheating. then on the way home, the gauge started climbing again. WTF? get home, yup, the tank is boiling again and the tank is leaking again. flushed the radiator and took the AC condenser out just to let more air into the radiator. i havent taken it out since then.

so, whats the damn deal? should i just look for a used radiator and tank from an open system rig and convert or is there a solution for my problem??

It sounds like it may not have burped good after you re-filled it from the repairs.

xjtrailrider said:

It sounds like it may not have burped good after you re-filled it from the repairs.

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Agreed
Jack the rear up, fill tank, unscrew temp sender unitl no air is left in sys.
Next chance you replace T-stat drill small (1/8th in) @ 12 & 6 o' clock for auto burp
:repair:

He said it boiled over with no thermostat. I agree though, if it's got air in the system it will boil over easy. The problem might be the cap on the plastic tank has gone bad (btdt), but I suspect the radiator is plugged, especially if its the original. I had good luck and pricing at radiatorbarn.com and many folks recommend dpgoffroad as well. Both sell all-metal CSF brand. If you want to switch to the later "open" cooling setup, order a 1992 radiator and get rid of the plastic surge tank. A quick search on the forums will give you plenty of info.

I was thinking radiator too, but he should check both the mechanical cooling fan clutch and the especially the electric cooling fan as well to see if the temperature switch or wiring to it is bad. That electric fan should come on and stay on before it boils over.

I had alot of problems with my closed cooling system earlier this year in the summer when temps got hot. The 17 year old coolant bottle cracked, a few hoses burst but luckily didn't cause any drama (this all happened in my driveway after I had driven for 2 hours..luckily). I replaced the coolant bottle, a bunch of hoses and flushed the system. Now that it's operating properly the closed system works pretty well.

When I replaced the parts I didn't burp the system properly, and got similiar problems. Burped the system and all is well now, it stays within spec's all the time.

clunk said:

I had alot of problems with my closed cooling system earlier this year in the summer when temps got hot. The 17 year old coolant bottle cracked, a few hoses burst but luckily didn't cause any drama (this all happened in my driveway after I had driven for 2 hours..luckily). I replaced the coolant bottle, a bunch of hoses and flushed the system. Now that it's operating properly the closed system works pretty well.

When I replaced the parts I didn't burp the system properly, and got similiar problems. Burped the system and all is well now, it stays within spec's all the time.

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I've said it time and time again - taken care of properly, there is NOTHING wrong with the closed cooling system.

If it overheated without the thermostat, my first suspects would be the radiator and the thermal fan clutch for the mechanical fan (I've posted extensively on both of those.)

As far as purging air from the system, I've also detailed how you can modify the thermostat (you drill two holes - and it takes about a minute and a half...) to make the system purge itself of air without help from you at all.

The service life of the OEM RENIX radiator is 150-180Kmiles, and I've not heard of one going past 200K. Get a quality aftermarket replacement (CSF or Modine) and put it in - then forget about it. Keep on your flushes every other year or so as well.

Reading back, you mentioned replacing the bottle. Did you replace the cap too?

A few years back, the day before a planned off-road excursion (when I still had the 4.0), I replaced a cracked expansion bottle with a new one from Chrysler, along with a new cap. I was told to be careful installing the cap, that they had a tendency to strip when over tightened.
With new bottle and cap in place, I got ~150 miles, when I had to do a "potty" stop (I'm "aging:looney: ). Coming back to the Jeep, I notice coolant under neath--WTF!!.
The new cap was spewing coolant! I re-tightened, but had the same problem two or three additional times during my trip.
Re-installed my old, original cap, and never had another problem.
The new caps are sh*t.
And an "open" system does not cool any better than the closed system; but the plastic bottles are problematic. Swap it out for a metal one, and all your problems will be solved, given that every thing else in your cooling system works correcly.

yes, the cap was replaced with the tank. i also flushed the radiator out last night and it seems unclogged. the water came out at a pretty good pressure from the drain XXXX. i suspect i never got all the air out. so the best way to purge a closed system is to drill the holes in the thermostat?

XJBeater said:

yes, the cap was replaced with the tank. i also flushed the radiator out last night and it seems unclogged. the water came out at a pretty good pressure from the drain XXXX. i suspect i never got all the air out. so the best way to purge a closed system is to drill the holes in the thermostat?

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yes.

I do that, and I've also put a T fitting in the upper heater core hose. One with the screw on top.
That let's me fill the coolant bottle and wait for the upper heater core hose to be full. I've not had a problem with air in the system since I started doing that.

xjbubba said:

And an "open" system does not cool any better than the closed system; but the plastic bottles are problematic. Swap it out for a metal one, and all your problems will be solved, given that every thing else in your cooling system works correcly.

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I disagree on the metal bottle. I have found that if you fix the real problem(s), the plastic bottle and cap works fine, and after 3 to 4 years its are only 26.95 to replace them before they give me trouble. I like being able to see the coolant level in the plastic bottle!:eyes:

When I bought my first renix (87) jeep I had problems too. One day I put my hand on various parts of the radiator when it was overheating, and found sections of the core, tubes in the middle of the core that were room temperature, but the radiator had good flow! Problem was 1/2 the tubes were blocked in the middle of the core with no water / coolant flow. I had already replaced the fan clutch and thermostat, bottle, cap and hoses. Turned out my real problem was the radiator.

Most cooling problems, IMHO, are more often the radiator, or a small leak at a hose connection, and worn out or poor quality fan clutches.

so, even if i have good flow when flushing the radiator, the heater core could be plugged? doesnt seem right to me.

XJBeater said:

so, even if i have good flow when flushing the radiator, the heater core could be plugged? doesnt seem right to me.

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I am assuming you meant the radiator core, as the "heater core" is a different part, but yes, all it takes is to have 15 to 25% of the tubes blocked off at the entrance of the tubes, and those openings are real small, like 1/16 of an inch wide. With 20% of the tubes getting no flow the water flows through the other tubes faster, and so the heat slowly builds up until it boils over. Flushig a radiator will not clean the blocked tubes. Pulling the radiator and having the core roded out will sometimes work, but now days you can buy a new all brass/copper radiator for about $125, and a radiator shop charges about $75 just to rod out a radiator if you pull the radiator yourself.

Just turn the engine off once its hot, and check the temperature at various places, top, center and bottom, of the middle of the core (tubes) between the two side tanks to look for cold spots. If you find any areas that are not hot then that's your problem, or at least one of them. Also if the middle of the radiator is cold, the fan clutch does not get hot enough to lock up at idle, thus adding to the problem, which of course assumes the clutch is not also bad.

Oh, and if you like MUD, the radiator outside surface and AC condensor may need a good washing!

Ecomike said:

I disagree on the metal bottle. I have found that if you fix the real problem(s), the plastic bottle and cap works fine, and after 3 to 4 years its are only 26.95 to replace them before they give me trouble. I like being able to see the coolant level in the plastic bottle!:eyes:

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I've seen aluminum with sight glass.($155) Not cheap but Final fix & forget

Also if you look at many newer vehicles I've noticed they are starting to go to a pressurized system. That has to be for a reason.

when my 89, with no ac or electric fan, was new, it used to overheat in stop in go traffic in the summer. replaced the stock radiator with a 3 row and never had the problem again. every 3-4 years i do replace the pressure bottle and cap along with thermostat. most times it under cools, which tells me its time for new thermstat. i also fill the system by pulling top hose off the thermo housing and pour down the tube, start and run till gets worm, sut down and fill to top of rod in pressure bottle, repeat until system doesnt go below the rod.

My wife's Windstar has the closed system and a really nice well made and re-enforced bottle. Some day I'm going to try this swap on my 90, but my system doesn't give me any issues as of now.

Here is a pic of the bottle and I think it will fit.

Sorry for the "Huuuge" pic!

Harlee&Tahoe said:

Agreed
Jack the rear up, fill tank, unscrew temp sender unitl no air is left in sys.
Next chance you replace T-stat drill small (1/8th in) @ 12 & 6 o' clock for auto burp
:repair:

Click to expand...

When doing this, how close to the edge to you drill? I'm changing my t-stat this weekend and would like to do this if it makes my life easier!
TIA

cykaaro said:

When doing this, how close to the edge to you drill? I'm changing my t-stat this weekend and would like to do this if it makes my life easier!
TIA

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About a quarter-inch in will usually do.

The key thing is to drill two holes, 180* apart, and install the thermostat with one hole fully above the "poppet" and the other below.

I usually drill holes a sixteenth of an inch, but there is no reason and eight-inch should not work.

Thanks. Hopefully it'll allow me to get all the air out. Been fighting no heat since it's been cold last few days. Seems to be intake on the heat core seems hot, but the output isn't. Had the system flushed but guess the core needs to be done seperately as it's probably cruded up. I'm just hoping I don't have to replace it. We'll see. For some reason with the warmer temps today it decided to overheat. Not sure why but t-state may be shot, so will be replacing it. Hopefully all will go smoothly for a change and it'll get back to where it should be. Just need to figure out why the damn electric fan doesn't turn itself on when it needs it. Sensor in rad was replaced, but still doing it. Not sure why. maybe bad relay somewhere?
So how's things going your end?