Boiling in to overflow tank

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Nick91
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Posts: 8
Joined: Sat Oct 16, 2021 5:56 pm
Location: 59034
Isuzu vehicle(s): 1991 pickup

Boiling in to overflow tank

Post by Nick91 »

Hi all,

I picked up a 1991 pickup from a junkyard and it's pretty clean, some dings and dents but no rust and complete. I got it running again and it was building pressure in the cooling system and causing it to boil over into the overflow tank. It never got in to the red on temp guage and no coolant in the oil. I have since replaced head gasket and placed a shim(head was warped and machine shop milled it and did not detect any cracks, I believe it's a later head as it was a 5? Something number on the back), placed new head bolts, new water pump, new timing belt and tensioner, new radiator cap, and it ran good for about 30 miles. Then it started getting warmer and bubbling again. I retorqued the head bolts and the #1 bolt to start the torquing sequence was just a tiny bit loose (about 1/2 turn to retorque) to 70lbs, all others were tight. Then it ran good without issues about another 30-40 miles. Then the boiling started, so I'm assuming it's loosened up again and allowing air to be forced in to the cooling system. Once it cools I'll double check this theory. If that is the case, has anyone seen this? Is head bad? Would locktite on the one stud be a possible solution? Block cracked where bolt threads in to it? Any other possibilities you can think of? Thanks for reading, sorry such a long first post. It's a cool little truck, so Id like to get her back on the road!



Nick
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Red Truck
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Location: Vader, WA

Re: Boiling in to overflow tank

Post by Red Truck »

I believe it's a pretty sure assumption there's a crack in either the cylinder head or a cylinder. Don't know if you have access to the equipment, but a Leakdown Test would point you to which one(s) are bad. A decent automotive repair shop will do the test, as well. As far as repairing a crack, I can't help ya. Additionally, I didn't know they made head shims for these engines.....and the shim must be installed next to the block, under a new stock head gasket. R/
'87 Isuzu p'up 4ZD1/2.3 gas, carb'd, 5spd, 4WD, base model, Fed spec
Nick91
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Posts: 8
Joined: Sat Oct 16, 2021 5:56 pm
Location: 59034
Isuzu vehicle(s): 1991 pickup

Re: Boiling in to overflow tank

Post by Nick91 »

Thanks, I will take it to local shop and have them do the leak down test. It's so strange that it will run fine for a while, then do it over again? Now I'm finding out why it was in junkyard, but I'm in too deep to give up now lol. They only make one size shim, I got it off of Rockauto. The only reason I knew is because there was one on there when I pulled the head. I sprayed block side with copper spray and left gasket side and gasket dry. Thank you for the help! I'll let you know what I find out!

Nick
dorf
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Location: N. Central Arkansas 81 LUV 4x4

Re: Boiling in to overflow tank

Post by dorf »

Could it be just a bad or weak radiator cap....or too low a pressure cap

Just my 2 cents
Nick91
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Posts: 8
Joined: Sat Oct 16, 2021 5:56 pm
Location: 59034
Isuzu vehicle(s): 1991 pickup

Re: Boiling in to overflow tank

Post by Nick91 »

Hi, I was hoping that too. I tried 2 different new 16lbs caps with no luck unfortunately. I'm assuming head is shot, hoping not the block Any other places something else could be allowing air in to system. Strangely myself and a shop tested coolant for exhaust gases and neither myself or them detected any? Oil stays clean too. Could a clogged radiator or heater core possibly cause this? I'm going to try and get a leak down test next week as Red Truck suggested. I'm almost ready to just order a reman long block at this point lol
gruff54
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Location: Central NC

Re: Boiling in to overflow tank

Post by gruff54 »

I'm not saying it's the head yet, but it's more likely the head than the block given these engine's history of bad heads. My latest Trooper w/2.6 was doing similar when I got it, a new head fixed it. I do remember Squatch chasing a similar problem in his Spacecab. Turned out to be a crack in the cylinder wall. I'd still bet on the head.

Mike
'89 Trooper 2.6L-5 spd
'87 Trooper 2.6gas to 4jb1-t swap(in progress)
Nick91
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Posts: 8
Joined: Sat Oct 16, 2021 5:56 pm
Location: 59034
Isuzu vehicle(s): 1991 pickup

Re: Boiling in to overflow tank

Post by Nick91 »

What places would you recommend getting a new head from? Anyone sell complete new heads? I've never put one together and don't want to screw up a new one if I get one.
Nick91
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Posts: 8
Joined: Sat Oct 16, 2021 5:56 pm
Location: 59034
Isuzu vehicle(s): 1991 pickup

Re: Boiling in to overflow tank

Post by Nick91 »

Update:
I was driving truck short distances of a few miles on the highway and several miles on some dirt roads around my house and the temp stayed cool several different times. Then I tried running it down the the highway, and as soon as I hit about the 5 mile mark it would start creeping up again until it would boil. So I checked head bolts again. The head bolts had stayed tight, so I was wondering if maybe the radiator was just not flowing enough or possibly getting intermittently clogged????? So I ordered a new one before I took it in for a leak down on the hopes of not having to tear in to motor again lol. I put it in and so far so good. It's stayed really cool, no boiling or bubbling on a 100+ mile round trip to Billings on the interstate running 65-75 mph. About 5 miles from home it was barely above the C on temp guage so now I'm having the opposite problem of being too cold :? Hope it's just the thermostat sticking now! Thank you for all your help and hope this will help someone if they are having similar issues. It's probably the trucks first trip out of the county in 15-20 years. I can't believe it was in the crusher line! Thanks again!

Nick
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Red Truck
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Re: Boiling in to overflow tank

Post by Red Truck »

That's great news! As I was reading over this entire subject, I'm kicking myself now: Nowhere do I see mention of replacing the thermostat!
For what it's worth, if this symptom occurs again, a faulty t-stat might very well be the culprit. R/
'87 Isuzu p'up 4ZD1/2.3 gas, carb'd, 5spd, 4WD, base model, Fed spec
gruff54
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Joined: Sun Oct 21, 2012 6:00 am
Location: Central NC

Re: Boiling in to overflow tank

Post by gruff54 »

I've read to be careful if you use a t'stat other than OEM. Something about a bleed hole, I think, but there may be something else.

Mike
'89 Trooper 2.6L-5 spd
'87 Trooper 2.6gas to 4jb1-t swap(in progress)
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