help me -simple oveheating and now........

I just scored an '87. :guitar: It runs fine, but overheats quickly. :flamemad: The electric fan is mising, but that shouldn't make it do this. It's only about 20 degrees here.
This thing has a brand new radiator, water pump and t-stat. I can't feel the pump working in the top hose, but when it starts to heat up, the system builds up pressure and holds it. Remove the hose from the t-stat, and nothing but hot steamy air comes out. Fire it up with top hose removed and it jets out water erratically. I guess my question is, can a head gasket leak only pressurize the cooling system, and have no mixing or steam???
Thanks guys!!!!

Is there an air pocket?

Some will loosen the temp. sending unit to get the air out. It may be teh absence of the electric cooling fan. Maybe someone else can shed some light on it for you.

Ghost said:

Some will loosen the temp. sending unit to get the air out. It may be teh absence of the electric cooling fan. Maybe someone else can shed some light on it for you.

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I have had all the air out about 10 times, and the electric fan doesn't even get a chance to kick on before shes blowin' water out the top.

you don't have all the air out.

the 87-90 use a closed cooling system that is a ROYAL pain in the arse to do any service to.

if you didn't use an OEM type t-stat with a bleeder hole at the top to allow for the passage of air, you CANNOT get all the air out of the system.

at the back of the head on the driver's side is the temp sending unit, it is a small brass stud with one wire that hooks on to it. with the rear end of the Jeep raised up as high as possible, remove this and start pouring your coolant mix in (you MUST have the oem type t-stat for this to work, if you want, you can make one by cutting a V shaped notch in the outer surface of most aftermarket ones) keep pouring until NO AIR comes out of the small hole where the temp sender bolts in.

close everything back up, then, start it up, (heater on) and let it run and watch the temp gauge. if it still overheats quickly, do this again, and KEEP DOING IT until absolutely NO BUBBLES come out of the temp sender's hole.

if it still overheats, check for blockage in EVERYTHING connected between the block and the firewall (heater hoses, valve, that goofy shaped T-thing, heater core) if there's no blockage, check to make sure your serpentine belt is routed correctly and that the water pump is spinning the correct direction. also, I believe there are two different water pumps (sold based on rotation) verify that you do indeed have the correct one (compare the impeller between the new one and the old one, if the blades are in the opposite direction, you have the wrong pump)


have you changed anything in the cooling system (i.e. converting to the "open" system, using any parts from a 91+ XJ)

CheapXJ said:

you don't have all the air out.

the 87-90 use a closed cooling system that is a ROYAL pain in the arse to do any service to.

if you didn't use an OEM type t-stat with a bleeder hole at the top to allow for the passage of air, you CANNOT get all the air out of the system.

at the back of the head on the driver's side is the temp sending unit, it is a small brass stud with one wire that hooks on to it. with the rear end of the Jeep raised up as high as possible, remove this and start pouring your coolant mix in (you MUST have the oem type t-stat for this to work, if you want, you can make one by cutting a V shaped notch in the outer surface of most aftermarket ones) keep pouring until NO AIR comes out of the small hole where the temp sender bolts in.

close everything back up, then, start it up, (heater on) and let it run and watch the temp gauge. if it still overheats quickly, do this again, and KEEP DOING IT until absolutely NO BUBBLES come out of the temp sender's hole.

if it still overheats, check for blockage in EVERYTHING connected between the block and the firewall (heater hoses, valve, that goofy shaped T-thing, heater core) if there's no blockage, check to make sure your serpentine belt is routed correctly and that the water pump is spinning the correct direction. also, I believe there are two different water pumps (sold based on rotation) verify that you do indeed have the correct one (compare the impeller between the new one and the old one, if the blades are in the opposite direction, you have the wrong pump)


have you changed anything in the cooling system (i.e. converting to the "open" system, using any parts from a 91+ XJ)

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No its a stock 87 system. with new parts.
I did a search and read some old posts (thanks here to Eagle). I may have misunderstood the highest point concept.
I tried this 4 times yesterday, keeps building up pressure. what i may have been doin' wrong was i kept crakin' the top hose free to see if coolant was moving ( i take it I kept putting air back in?). The way coolant came outa the t-stat housing( when running), it is either engine compression or vapor lock. I'm gonna do what you said and post back. Thanks Cheap!!!!!

Make sure the cap on the reservoir(sp) bottle is the correct one. This can lead to problems on a closed system.

Have you moved your temp gauge around while the heep is on? ( Vent, Heat ect...)

Cracked bottle?

Ok... I filled the top hose and bottle. Then I let it run until it was hot. All the fluid comes back into the bottle. With flats up front and ramps + 31's under the rear, I bled the system at the sensor. Added fluid, let run, and bled again. All the fluid stays in the bottle until you crack the sensor. I bled it, and couldn't add fluid 8 more times. Every time I would get air, and when it was running the fluid all goes to the bottle when it gets hot. I can not get the top hose to fill, the radiator stays cold. When I open the sensor hole up, i get some air, then straight fluid, and then the level in the bottle goes back down.Fire it up, the level goes right back up. (then boils over) What am I missing? :dunno: Could a tiny crack in bottle cause this? I just saw a tiny, and I mean small, hairline split in the plastic. I just noticed it as I was packing up tonight. Everything else is new.(heater core is also old, but works fine)

All my non-jeep friends are saying head gasket......what do they know.... :twak:

In the '89 "closed" style cooling system, the plastic bottle on the firewall is part of the pressurized system. If it is cracked, even a hairline, the system will not hold pressure and will overheat.

Here's what I suggest: Do an initial fill the way CheapXJ suggested, through the temp sender orifice in the head. Then button that up. The bottle is higher than that, so every time you remove the temp sender, you drain down the system and let air in. The bottle should be filled to the halfway mark when cold.

Now start the engine and let it idle, with the cap on the bottle but not screwed down tight. After a few minutes, the coolant in the bottle will start to boil. Shut the engine off immediately. Allow the system to cool down. As soon as you can do so without scalding yourself, remove the cap from the bottle. After a few (5 to 10) minutes, all of a sudden the system will start to pull the coolant out of the bottle. As the level goes down, add fresh coolant to keep the level at about the halfway mark.

When the system stops sucking, put the cap on loosely, start the engine, and repeat. And then again, and then again, until when it cools down it no longer sucks coolant out of the bottle to fill the system. The last time I did my '88 I think I went through 5 cycles before it was mostly done. After that, you should be good to drive but you may still have to add a bit every day for a few days.

If that doesn't do it, I would suspect what CheapXJ referred to: the incorrect water pump. The skinny is that the 4.0L and the older YJ 4.2L engines are the same block, and the water pumps interchange. However, some of the 4.2L engines were equipped with conventional 'V' belts rather than a single serpentine belt. The belt arrangement was such that the pump for the 'V' belts rotates the opposite direction from the one for the serpentine belt. The one for a 4.0L with serpemtine belt should have a big letter 'R' cast into it somewhere, but it's possible that not all brands do this. If you have a 4.2L pump, it won't push coolant through the system because the impeller blades are backwards for the direction of rotation.

gupandme said:

Could a tiny crack in bottle cause this? I just saw a tiny, and I mean small, hairline split in the plastic. I just noticed it as I was packing up tonight. Everything else is new.(heater core is also old, but works fine)

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It's the bottle!

My MJ has been overheating on the highway since I swapped the 4.0L into it. I've been screwing around with it to try and lessen the problem, but if I really push it, it'll overheat at high speeds.

two days ago, my pressure bottle just exploded while idling in a parking lot. no warning. just a muffled pop and a giant cloud of steam. didn't have any parts to fix it with, so I ended up plugging up the hoses that go to the bottle and I used my recently installed flush connector as the fill point.

Since the elimination of the bottle, my temp. needle has not gone over 210* once. At the time, I was hauling at least 1500lbs of stuff in the bed, highway speeds, uphill, all that good stuff that would have made the temp needle shoot up like nobody's business.

the next day, I drove it from central PA to providence, RI and I was actually able to exceed the speed limit for extended periods of time without overheating (actually, I was able to drive as fast as the MJ would go without any problems, and this was the FIRST time I've been able to do this since I've put it on the road back in august)

I used to think that a properly bled and serviced closed cooling system would be reliable, but to be honest, that goddamn bottle is never going back under my hood. NEVER.

I'm going to try using one from a volkswagen (plastic is about 3x as thick) and see how that works out, if not. I'll be ripping all the closed cooling system garbage from all my Jeeps and I'll replace it with something that actually works.

that makes sense to me. i'm gonna give it another go tonight and see if i can get this crapbag to cool itself.

Thanks guys--for real....check back , i'll keep you posted.

It has to be the head gasket letting compression into the system. It is the only thing that makes sense. :gonnablow: :

gupandme said:

It has to be the head gasket letting compression into the system. It is the only thing that makes sense. :gonnablow: :

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What leads you to that conclusion? My '88 is at 247,000 miles and no problems with the head gasket. They do go bad, but rarely on the 4.0. The cooling pressure bottle, however, is a frequent problem.

Have you run a compression test? If the head gasket is bad, a compression test should show either one cylider lower than the others, or two adjacent cylinders lower than the other four.

Quadratec sells the bottle with cap for $19.95. Direct replacement. It's more money, but I don't trust the plastic and I replaced the bottle with an aluminum racing surge tank made by Moroso. They are available from Summit Racing.

head gasket?

I agree, the tank with its worthless cap is the weakest link in this cooling system. Couple of years ago, a mechanic told me my head gasket was fried.. thank gawd I didn't listen. I slapped on a new cap and have had NO problems since. It's amazing how such a seemingly tiny leak in the plastic setup can turn the XJ into a boiling freakshow..

Eagle said:

What leads you to that conclusion?

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a few things....

1. when both the block and radiator are full, and i disconnect the top hose from the t-stat, engine running, the coolant jets out...not a thick stream or flow, but a small amount at VERY high pressure. (sends it about 15 feet.) and then nothing. then it does it again. then nothing. It just looks like engine compression.

2. neither of the 2 previous owners planned on keeping this vehicle. i know both personally, they beat the shit outta this thing. (It has no gas pedal.)

3. I never saw it run before this problem. I did, however see it being driven with steam blowing out from under the hood around town a few times.

I haven't run a compression check yet, but i will tonight.

i can't get water to flow through the radiator or top hose with the engine running, and can't keep water in the block. I'm lost.

Everything you describe points to a defective pressure bottle, and air trapped in the system.

Eagle said:

Everything you describe points to a defective pressure bottle, and air trapped in the system.

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I know from homework that you are the man when it comes to these systems.
This thing is sitting in a friends garage, and he's not thrilled. So if you believe this is in the cooling system, I'm gonna take your word, and tell him to chill...I'll drive it away in a few days. I really need to get one of my junks running to keep my jobs, so $$$ is tight. (just blew tranny in my Caprice).

I really appriciate all the help and will let you know what works or doesn't.

Thanks for being patient with my newbie ass. :anon:

You should still do the compression test as part of your dignostic routine, but the symptoms are those of a system that won't hold pressure.

have you checked to make sure the rad is not blocked

massxj said:

have you checked to make sure the rad is not blocked

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yeah- it's brand new...I unpacked it, and took the shipping caps off

Eagle said:

You should still do the compression test as part of your dignostic routine, but the symptoms are those of a system that won't hold pressure.

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So I'm gonna order a new bottle today...and while I'm waiting for that I'm gonna borrow a cylinder leak down tester. My compression gauge sucks. :banghead: