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1991 Explorer boils over after you shut it off -- FIXED

Malchi

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Year, Model & Trim Level
'91 X 4x4
Hi all, I just bought a 91 Explorer, 4X4, 4.0 V6. Got it for dirt cheap cause it is overheating, sorta. Here's the scoop. Fellow that had it thought head gasket was blown. I checked, no water in oil, no oil in water, and let it run for about 10 minutes and did not overheat. Figured can't be blown.



When I went to look at it there was straight water in coolant system, and I noticed that Fan clutch was bad. I drove it for about 3-4 miles and temp stayed normal, about 1/2 way up guage. Drove it another 5 miles to get money from ATM and still seemed fine, until I shut it down to do the paperwork. Then, about 2-3 minutes after I shut it off I could hear it boiling over at the resevoir. Started it up and checked guage, was only 2/3 way up guage, still well within the 'Normal' brackets. Hmmmmm.... figured it was due to just water in system since water boils at 212 deg. So, I bought it anyways. Hey, 125K miles and got it for $400, figured can't go wrong.



So, I drove it about 10 miles to a friends house and drained radiator and added 1 1/2 gallons antifreeze and topped off with water. Then, drove it about 25 miles to my house. About 1/2 way still was staying less than 1/2 way up guage, so turned on A/C, still never got much over 1/2 way up guage all the way home. Got home, parked it and was not boiling over, so shut it off. Well, within a minute or two it started boiling over. Started it and temp guage was still just over 1/2 way or so. What gives?



Today I got a Block Tester. Checked it quite a bit and blue liquid never turned yellow. Used an infrared thermometer to check temp at the sending unit located where the upper hose goes into the engine, was reading just under 200 deg, guage was reading just under 1/2 way. Seems about right, no?



FWIW, I do have a freeze plug, located just above LH motor mount near front of engine, that is leaking. Any relevence?



This thing has me stumped. Any ideas? I havent' replaced thermostat or fan clutch yet cause I don't think those are the problem and don't wanna put any extra money in it unless I can figure this out first.
 


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willindsay

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I have a 94 that does the same thing from time to time I hope someone can help you out. I had my Thermostat replaced and it didn't fix the problem.
 




97 EB Mike

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I'd suggest a new radiator cap. No pressure = lower boiling point. Just a guess, but that's where I'd start.
 




willindsay

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I'd suggest a new radiator cap. No pressure = lower boiling point. Just a guess, but that's where I'd start.

IIRC Rad caps have different Lbs. ratings so what is the correct rating for a 94 Auto??
 




97 EB Mike

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Assuming napaonline is correct, 16 lbs. That's a pretty common pressure for automotive applications.
 




willindsay

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Alright well thats what mine is rated at and it was replaced at the same time as the T-stat at the beginning of June. Any other suggestions??

Malchi Sry for hijacking your thread.
 




Malchi

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Alright well thats what mine is rated at and it was replaced at the same time as the T-stat at the beginning of June. Any other suggestions??

Malchi Sry for hijacking your thread.

No problem.

I was actually thinking of the Rad cap. Right now it has a 13lb cap on it. Maybe get a 16lb one tomorrow and try that out.
 




Maniak

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Factory was 16 but most books list the 13 for replacements. Get the 16. Also if you have any leaks in the cooling system you may boil over since the pressure is really what gives you boil protection.

~Mark
 




unclemeat

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I would check and oe replace the thermostat and make sure it is istalled properly. They have a air release valve that need to be on top.
 




Malchi

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Factory was 16 but most books list the 13 for replacements. Get the 16. Also if you have any leaks in the cooling system you may boil over since the pressure is really what gives you boil protection.

~Mark

Ok, gonna do that today. Will get back and post results as soon as I get a chance to test it.
 




willindsay

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Alright guys I tackled my truck today I got a new Rad Cap and then decided I to straighten out some of the bent fins on the Rad. While I was doing this I noticed a huge clump of black stuff that looked like Lint or a bunch of asphalt. I took it to the local car wash and cleaned it all then put it all back together so far it has been running cooler and no boiling over.
 




Malchi

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ok, replaced the Cap and all seems fine, except for the 2 freeze plugs that are leaking. Gonna work on those today.

Thanks to all for the help. I would never have figured this out without you.
 




92ebxplorer

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since you guys are talking about overheating, do you think you can shoot some advice this way? i'd really apreciate it!!

here it goes i have a 92 explorer automatic i drove it about 150 miles and the temp gauge stayed on the o on the gauge, but when i drive to walmart down the street in city drving condition it overheats real quick never getting too far past the L on the gauge but overheats!

what could be the cause? how should a fan clutch feel?

it has a new fan, water pump, t-stat, freeze plugs, and radiator,
the previous owner was throwing parts at it! lol with out an idea on what it was!


any advice would be greatly appreciated!! thanx!
 




jungleryan00

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Make sure there is nothing blocking the airflow in front of the radiator.
 




willindsay

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X2 on the blocked airfood that was my issue plus the rad cap. Now mind barely gets past the or in normal.
 




JOEZ33

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A lot of times it's the radiator cap and it's completely overlooked. People pull the cap and sit it on the bench, but NEVER look at it. The spring ALWAYS fails on them. There's a spring loaded metal plate under the cap, and it is supposed to hold is shut. When the radiator cools off, and the water that had expanded and pushed itself into the overflow tank starts to cool off, that spring loaded little metal disk will allow the water to reverse flow from the overflow tank back into the radiator.

If the little spring is broken it will just hang open with gravity and pressure will never build up. Water will then boil at 212 degrees instead of like 260. So when you shut the engine off the water in the block gets extremely hot, and when it hits 212 it boils into the radiator, and begins overflowing instead of just holding pressure.
 




92ebxplorer

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no blocked air flow but a radiator cap?! i will get a new one tommorrow =]!

any advice on the fan clutch is it supposed to spin kinda freely or be tough to spin?

thanx!

Im trying to get it ready for a long trail ride and it is all desert out here so it cant be heating up!
 




doonze

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I know all about overheating, see my sticky up top!! LOL

Anyway, when it was my Radiator not moving enough water I overheated on the highway, but short in town trips where fine.....

Logic and experience tells me if you do fine on the highway, but not in the city you have an air flow issue somewhere.

Plenty of airflow when on the highway due to your speed.

Not enough in the city due to lower speed and sitting....

So Fan clutch would be my number 1 priority

Search on here for fan clutch test...I know there are a lot of threads about it, that would be better for you then me trying to explain, plus there is more then one test and more then one school of thought on it.
;)
 




92ebxplorer

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thanx alot =] this is probably the most useful thing i have used INTERNET for in a while!! lmao but i appreciate all the help!


do you know about a rough idle? I read somewhere on here it was due to my spark plugs? could this happen i have platinum+2 bosch
 


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general x

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If your fan clutch and rad cap checks out alright then it could still be your coolant that is causing the problem, if the previous owner happened to put in too much antifreeze or simply antifreeze and no water then your cooling systems would not work very well. Antifreeze by itself does not have a very good rate of heat transfer compared to water alone, but with mearly water in your cooling system you miss out on freeze protection as well as a raised boiling point and corrosion additives. I believe coolant alone can also gel at cold conditions I don't know how you would check for an overly antifreeze rich coolant mixture but if all else fails it's something else to try for not much money
 




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