Coolant Boil Over

I have a 98, and yesterday I took it on it's first long trip since replacing the fan clutch. It held 210 for ~50 miles or so, lots of uphill. Got to the first scenic overlook, and shut it off. After 3-5 mins the jeep starts spitting coolant out the passenger side.

I opened the hood, it appeared to have come out the overflow recovery bottle, but it wasn't full. Probably because it was all over the ground. I clicked the key on, the temp guage was reading most of the way to red, well hotter than when I shut it off.

Now from what I understand, the cooling should still occur without the water pump running, it just self cycles slower with the cool fluid sinking, pulling the hot fluid in, etc. If it boiled over after I shut it off, obviously this didn't happen. Would this be a good indication of a plugging radiator? The overflow had what looked like mustard in it from all the old coolant, or maybe stop-leak. I did a quick flush, but it may have been to late for the radiator. :dunno:

I just did mine at a rad shop last week, did chem flush an roded out the radiator.. It was like 108 saturday when i was out testing my u-jjoints, got up to 200.. I flip the fan on and went to 185-190.. Have a shop do it..save some money in long run

Flush was a good idea but if you spilled all your coolant your seal on the radiator cap is more than likely blown. Replace your radiator cap.

It only spilled a cup or so, it's never spilled over after turning it off before :dunno:

I had a similar thing happen and I just replaced the cap to the overflow and it cured my problem. Its a cheap way to eliminate that atleast, I would try that just to see. As said before the seal can be bad on the cap causing it to leak under pressure.

Sean

210 is on the warm side I think? Also any convective movement of the coolant is negligible AFAIK. It very well could be a bad rad cap, get a new one, they're cheap. Your cooling system is a pressure cooker, it uses pressure to raise the boiling point. If it doesn't hold pressure, it boils over at lower temps. Is your electric fan coming on? Another thing you could do is wire the electric fan to stay on for a while after the engine shuts off.

There's lots of general overheating threads you could check out. Beyond the usual stuff, perhaps when the engine is so hot you might let it run for a few minutes after you park to let it cool down? it could be there's a hotspot somewhere in the engine...

IMO you want to open the cooling system as infrequently as possible. Draining and filling it is a PITA. If you're stating to have problems, tear the whole thing apart and do it right the first time. Either get the rad serviced or get a pimp new one, get a failsafe thermostat and test it in hot water against a thermometer, consider a high flow water pump, replace the hoses, etc.

210 is normal operating temp.

So why could it run for over an hour much of it uphill, and not boil over? Ill try the cap just because it's cheap and Im sure this one is original.

The airflow at highway speed keeps temps down, even on a hot day. I had the same thing happen earlier this summer. Had to drive up to Breckenridge and between the big climb and the thinner air up there, she tried to overheat at a stoplight and did once I parked.
No loot for a new rad, so got new t-stat and flushed it. I did the t-stat first because the original tested bad. Flushed it out 'cause the t-stat didn't quite eliminate the problem. There was no e-fan either so I replaced that too. Ran fine for a few days, then I discovered a pinhole leak @ one of the fittings coming off the drivers side fo rad. Broke out the JB Weld and it's all better now. Mine's an '89 4.0 btw.

kujito said:

The airflow at highway speed keeps temps down, even on a hot day. I had the same thing happen earlier this summer. Had to drive up to Breckenridge and between the big climb and the thinner air up there, she tried to overheat at a stoplight and did once I parked.
No loot for a new rad, so got new t-stat and flushed it. I did the t-stat first because the original tested bad. Flushed it out 'cause the t-stat didn't quite eliminate the problem. There was no e-fan either so I replaced that too. Ran fine for a few days, then I discovered a pinhole leak @ one of the fittings coming off the drivers side fo rad. Broke out the JB Weld and it's all better now. Mine's an '89 4.0 btw.

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There are huge differences between a closed system and an open system, however.

98XJSport said:

There are huge differences between a closed system and an open system, however.

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I knew that, just don't really know what they are. I guess I was trying to answer in the affirmative to your earlier question.

Would this be a good indication of a plugging radiator?

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I don't know if it's too late for the rad or not. Have you tried the longer flush? The Prestone (I think) stuff that you leave in for a week? Might be worth a try.
I spent a lot of my free time this summer chasing down problems like this. Super PITA (SPITA?). At least I got to do some jy digging though, fun stuff.

Once you shut off an engine, it will heat up a bit. No fans, no coolant flow, no air flow. How the heck it's supposed to keep cooling is beyond me.

Sounds to me like it's doing normal, I woudln't sweat it too much.

I vote cap too.

Dang. Skwerly beat me to it.

I know it's normal for it to heat up a bit. Hence the injector issues with newer jeeps. But it's not normal for that much to come dumping out the overflow, unless the cap let the pressure drop after I shut the engine off, causing the coolant to boil a bit. :dunno: But I will try a cap before messing with the radiator. What is the OEM cap pressure? Is there any benefit to increasing said pressure?

98XJSport said:

I know it's normal for it to heat up a bit. Hence the injector issues with newer jeeps. But it's not normal for that much to come dumping out the overflow, unless the cap let the pressure drop after I shut the engine off, causing the coolant to boil a bit. :dunno: But I will try a cap before messing with the radiator. What is the OEM cap pressure? Is there any benefit to increasing said pressure?

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It's generally recommended to replace the cap whenever you replace the coolant which IMO you should do annually. I'm pretty sure it's 15 PSI. Vato zone has a pressure tool that you can use to test the cap as well as the system. I know for a fact mine holds 30psi But there's no benefit to running that high pressure; just because your coolant doesn't boil doesn't mean you aren't destroying the engine.

Another possiblity is an air bubble, if you didnt' burp the system properly. I vaguely recall having a coolant barf after shutdown episode, and burping seemed to fix it, but I might be imagining things.

I heard...to burp it, you run the engine, pull off the heater hose by the t-stat...until you see coolant, then put the hose back on.

have any of you done this?

BOB

X3 for the Pressure Cap.

The water pump circulating the fluid is what keeps the temperature down, when you shut the motor off, the water pump stops and conduction from the radiator is NOT going to overcome the heat soak from the hot steel engine block. Its normal for the temp to climb up some after shutting off the motor.

The higher the pressure, the higher the temperature that the fluid will boil and vice-a-versa. A weak pressure cap will maintain a lower pressure and the sooner the fluid will boil. If the fluid boils over, i.e. forces past the pressure cap, you get a sudden drop of pressure even more and it creates steam pockets and the engine temp can spike up even more.

If your seeing goop in the coolant, then you still need to flush more. Get one of those reverse flow flush kits, the little "T" that connect to the water hose and splices into the heater hose. Except I don't cut my heater hose, I get a 1/2" hose connector and remove the heater hose valve and replace it with the "T" for one line and the connector for the other. I open the water jacket drain on the block and the stop XXXX on the radiator and turn the hose on full blast. Then I close them one at a time and let the water back flow up through the engine and radiator and out the pressure cap mount. Wait for the water to run clear and let it continue to run for a few more minutes.

I run some of the chemical flush for 10 minutes. Then repeat the flush with the hose and all the ports open (let it cool down first, don't pump cold water into hot engine).

Then fully drain everything, including pulling the water jacket drain, and shooting some compressed air into a heater hose to force the trapped water out of the heater core. Fill with DISTILLED WATER and run the motor till its warmed up plus 10 minutes again.

Fully drain, like before and then fill with new coolant, 50/50 mix anti-freeze and DISTILLED WATER.

Keep checking the anti-freeze after this, there may still be scale and deposits working themselves free. If the anti-freeze is getting dirty, then change it early and do the thorough flush all over again.

IMHO, changing anti-freeze every year is overkill, every 2 years is a good interval, definitely do NOT go longer than that. If you want to change anti-freeze less often, then thoroughly flush it like I describe above and fill it with Zerex G-05 that can go 5 years between changes. From my research, seems the best experts are recommending G-05 as retrofit for vehicles that used the Original Green Anti-Freeze, if the owner wants to go to long life anti-freeze. DO NOT USE DEX-COOL, that stuff can mess up your cooling system bad.

BOB said:

I heard...to burp it, you run the engine, pull off the heater hose by the t-stat...until you see coolant, then put the hose back on.

have any of you done this?

BOB

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thats pretty much the procedure i use on renix's.... but i plumbed in a fitting i can open and close.
putting that hose back on the fitting with coolant gushing out of it will leave your feet covered in coolant splatter, which is VERY bad. i would rather be covered in oil than coolant