Random overheating after coolant drain and refill

92 4.0L, 220k.

I decided I was going to flush my cooling system today. Didn't get past the first step. To start with, I drained the system at the petcock and refilled with straight distiller water. I only got maybe a little over a gallon out, and refilled it with the about the same amount. I let it idle with the cap off to burp it, and while lots of air bubbles came out, the water level never dropped noticeably like I've seen before- I only had to add a few splashes to keep the level up. Once the motor got up to temp, the bubbles started getting more violent and started spewing steaming water, so I turned the engine off and replaced the cap. I thought that was unusual; the water at the radiator neck went from cold to steaming almost instantly.

Anyways, I drove to the nearest burger place to get some grub and let the distilled water circulate some, so I could drain it again and fill with the 5 hour flush chemical. It's about a 5 minute drive, and on the way it started to run a little hot (215-220) and as I pulled into the parking lot, it spiked up to maybe 240 before I shut it off. Leaving the burger place, it acted normal for a minute, then at speed it started creeping quickly towards the red. I pulled over and shut it off for 15 minutes, started it up and drove the rest of the way. It held a steady 215 right until I pulled onto my street, and by the time I pulled into the garage it was nearly at the red again.

Before this, the only cooling trouble this jeep has ever given me is a consistent creep while idling, and as soon as you hit 20+ mph it cools right back down to 210. I know that is probably the fan clutch, it will be replaced eventually. But that short trip tonight was unlike anything it's ever done before; it overheated at high and low speeds sometimes, and then ran cool sometimes at both speeds, all on a 3 mile trip.

To me it acted like the thermostat was sticking, and since I have no idea how old my stat is I'll go ahead and replace it tomorrow, though it's never acted funny before. The other thing that comes to mind is trapped air, or possibly a clog, since the stuff I drained was filthy and who knows how old.

Any of you had this sort of random overheating after a drain and fill? Got any clues or anecdotes that may help?

I'd appreciate your thoughts. Thanks!

I had this same problem back a few years ago with my first vehicle, a 1986 toyota 2X4 22-RE. This was when I thought I could make my 20 mile commute on a blown head gasket. Any ways for the ideas I have read below.

When you added in the water was the engine warm or Hot? If it was hot and if you didnt have the enginge running while you put in the cold water you could have either blown your head gasket or maybe even cracked your block.

As for the air bubbles more frequently that sounds like a blown head gasket.

Also the thermostate would be a good place to start then I would check the water pump. Also see if water flows freely thru the radiator.

I went thru all of this stuff with my Yota and finally wised up and decided to go MOPAR.

If you didn't have symptoms before this, I would do the following:

1. Thermostat change for absolute sure!!! 195 degree. I buy my stats from Jeep and also like the Stant SuperStat

2. See how things work with the cooling system flush, new rad cap and stat

3. Still problematic, I would consider swapping in a new water pump and if that radiator is old, get it out of there at the same time. Also would be the time to install that new fan clutch, which we know is bad. Then you know your cooling system has been overhauled. Don't forget about hoses. They are often overlooked and when one goes, it can leave you on the side of the road and worse yet, a major overheat.

this is abnormal?

Capacity of the system is about 12 quarts or three gallons.

It concerns me that you were only able to get one gallon out, that would seem to indicate severe blockage.

You could try and drain enough of the distilled water to add the radiator cleaner and drive it the requisite 3-6 hours.

The temp creep at idle indicates a weak/failing fan clutch.

joe_peters said:

Capacity of the system is about 12 quarts or three gallons.

It concerns me that you were only able to get one gallon out, that would seem to indicate severe blockage.

You could try and drain enough of the distilled water to add the radiator cleaner and drive it the requisite 3-6 hours.

The temp creep at idle indicates a weak/failing fan clutch.

Click to expand...

I agree that the 1 gallon drain is concerning, but if there was blockage that severe you would think I would have had problems beyond temp creep at idle.

When you drain the system, how does the block/head drain if the thermostat is closed? It seems like it needs to vent somehow, otherwise you're just going to drain the radiator and the hoses, in which case 1 gallon seems about right.

I'm going out now to change the thermostat, so when I pull the old one off it should be able to vent and drain. But I don't think you should have to pull the thermostat just to drain the system. Is there some other way it vents, or am I just not thinking about this right?

Other question, if you are running the heater and shut the engine off, is there usually enough residual vacuum in the system to keep the valve open, or would it shut into bypass mode with the motor off?

Thanks for the responses guys.

Rob

birchlakeXJ said:

If you didn't have symptoms before this, I would do the following:

1. Thermostat change for absolute sure!!! 195 degree. I buy my stats from Jeep and also like the Stant SuperStat

2. See how things work with the cooling system flush, new rad cap and stat

3. Still problematic, I would consider swapping in a new water pump and if that radiator is old, get it out of there at the same time. Also would be the time to install that new fan clutch, which we know is bad. Then you know your cooling system has been overhauled. Don't forget about hoses. They are often overlooked and when one goes, it can leave you on the side of the road and worse yet, a major overheat.

Click to expand...

Add to that, make sure the new thermostat has a small hole at 12 o'clock for air to pass through. You can drill one if the replacement doesn't - this helps burp out a lot of the bubbles that work their way through the system as it is running.

Edited to add:
Check out http://naxja.org/forum/showpost.php?p=245111207&postcount=12 to see what I mean about the hole.

Robs92XJ said:

When you drain the system, how does the block/head drain if the thermostat is closed? It seems like it needs to vent somehow, otherwise you're just going to drain the radiator and the hoses, in which case 1 gallon seems about right.

Click to expand...

The radiator drain is one of the lower parts of the system. Fluid is going to drain down from the radiator, for sure, but it's also coming into the bottom of the radiator from the block by way of the lower radiator hose.

You talked about draining your radiator today, but I just want to clarify - you topped off the radiator as well, right? Not just the overflow bottle?

Jim www.yuccaman.com/jeep

So I replaced the thermostat and flushed the system today. The thermostat I took out must have been an OEM one (hopefully not the original) since it had a hole with a BB in it, to make a sort of crude check valve. I replaced it with a 195 deg Stant, modified by drilling a 3/32" hole at the 12 o clock position on the flange. 3/32 seemed closest to the original hole size.

I back-flushed the radiator, block/head, and heater core separately with two garden hoses (one supply from the hose bibb on the patio, one a return to a drain or bucket) and random barbed fittings and vinyl tubing. Man, either that was the original coolant from '92, or it was filled with swamp water at some point. It took 15 or 20 gallons to get clear water from the block. Heater and radiator were pretty nasty, too. There is still a red mud colored residue on all of the metal parts, like the filler neck. Hopefully the flush chemical will help with that.

Anyways, I filled it back up with distilled water and started the engine. It burped for a while, but when the thermostat opened it didn't start puking steaming water. The water level dipped a bit and I added some more. I wasn't able to get too much more into it. It took probably 2 gallons total, including what I put in the overflow tank.

On the test drive it did great. My idle creep seems to be gone- I sat in a slow Arbys drive-thru for 10 minutes and it never got past 210. Granted, its a cool night, but two days ago it would have creeped up to 230 or more. I got on the main drag and made a quick run at 50 mph, no trouble.

So, I guess it was mostly a wonky thermostat causing the randomness last night, and perhaps my idle creep had more to do with dirty coolant than a fan clutch. My fan clutch always seemed to pass the hand-spin test, anyways, and seems to move plenty of air. I'll have to wait until next spring/summer to tell for sure, probably.

It still seems like I should be able to get another gallon or so in the system. Next weekend I'll run the chemical flush and hopefully that cleans up any blocked passages, if there are any. The other possibility is that there is a gallons worth of water trapped in various low spots of the system. With the motor as old as it is, if it stays running well and doesn't overheat I'm not going to worry about it.

Thanks for the responses.

-Rob

98XJLongBuild said:

I had this same problem back a few years ago with my first vehicle, a 1986 toyota 2X4 22-RE. This was when I thought I could make my 20 mile commute on a blown head gasket. Any ways for the ideas I have read below.

When you added in the water was the engine warm or Hot? If it was hot and if you didnt have the enginge running while you put in the cold water you could have either blown your head gasket or maybe even cracked your block.

As for the air bubbles more frequently that sounds like a blown head gasket.

Also the thermostate would be a good place to start then I would check the water pump. Also see if water flows freely thru the radiator.

I went thru all of this stuff with my Yota and finally wised up and decided to go MOPAR.

Click to expand...

please explain? sounds like bs...

Fill a glass with cold water and ice. Let it set for ten minutes. The quickly poor out the water and ice and replace it with hot water. What happens? The glass cracks or breaks.

An engine and cooling system works the same way the engine block is hot and you put in cold tap water and so it is to much of a quick change from Hot to cold and it can sometimes crack the block.