Cooling issue, completely stumped...

mountainbiker42

mountainbiker42

New member
'99 T4R 3.4 with 230k miles. Recently had an overheating issue, the overflow tank was bubbling and coolant in the radiator was low. I topped it off and found that it bubbles every time I drive it when it's hot. No bubbling unless its at operating temp (+/- 200-210) I though it may be a head gasket. Compression tested hot and cold, numbers were all around 180-190. Had the oil and coolant analyzed at our Caterpillar dealership lab, both came back saying no glycol in oil and no combustion gas in the coolant.

So I checked the head gasket off the list...
Replaced the radiator cap and thermostat (jiggle valve up, everyone has a different opinion) with OEM to narrow things down, no changes. Coolant is still boiling into the overflow. I flushed the system really well, it seemed very clean already and no dirty water came out. I stuck a garden hose into the block and ran water through it both directions, same with the radiator. No major blockages.

The upper radiator hose is very hot and pressurized, while the bottom is cool and unpressurized. I first thought my radiator may be plugged. However, it's very very clean inside with no build up. And while flushing the system with no thermostat installed the coolant was flowing very quickly through the radiator (seen by looking into the radiator cap hole). It has no apparent blockages. This is where I was completely stumped.

I pulled the water pump today and it looks almost brand new. Very minimal wear on the impeller blades. No leaks through the seal, and the bearing feels good. The timing belt looks good, and shows no signs of slippage.

I could spend $140 on a radiator to cross that off the list but I don't think it's clogged. I cannot figure this out and need some input from you guys.
 
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If you've been driving in water or mud a bunch, I'd replace the radiator. Seen several people chase mystery cooling issues and then replace radiator last.
 
I'm sure the jiggle valve position is not the issue. I think air can purge easier at 12 o'clock but that's my opinion. The radiator fins look fine. Yes after topping it off it will still loose coolant. The radiator level will drop over time but the coolant overflow usually rises. Classic cracked head or blown HG symptoms but no exhaust gas in the coolant. I boiled both the old and new thermostat, both open at about 200ish degrees.

How can it be normal for the system to bubble constantly going 55+ or in stop/go traffic? The air is coming from somewhere and it causes the system to over pressurize. Whether it's the coolant boiling or exhaust gas pressure, the air is causing the relief to open. If your 4runner does this doesn't it look coolant overtime?
 
frodiesel said:
Sounds like a cracked head.

Sent from my SM-G900P using Tapatalk
Click to expand...

x2 on this. Most of the time when your coolant is bubbling it means that you have air pressure building. This is usually a sign of a blown head gasket, or worse.
 
For what its worth i put head gaskets on a subaru twice before i realized the heads or least one of them....was junk.didnt show it, they can be small.

When the coolant level gets low, and an engine continues to run, the Hotspots inside the head can create pinhole passages for air. Sucks, but least i dont own a subaru anymore.

Sent from my SM-G900P using Tapatalk
 
mountainbiker42 said:
I'm sure the jiggle valve position is not the issue. I think air can purge easier at 12 o'clock but that's my opinion. The radiator fins look fine. Yes after topping it off it will still loose coolant. The radiator level will drop over time but the coolant overflow usually rises. Classic cracked head or blown HG symptoms but no exhaust gas in the coolant. I boiled both the old and new thermostat, both open at about 200ish degrees.

How can it be normal for the system to bubble constantly going 55+ or in stop/go traffic? The air is coming from somewhere and it causes the system to over pressurize. Whether it's the coolant boiling or exhaust gas pressure, the air is causing the relief to open. If your 4runner does this doesn't it look coolant overtime?
Click to expand...

Going steadily at speed it usually means there's a headgasket or cracked head problem, mine had a cracked head and there was no trace of oil contamination, headgasket itself was still good, I had small cracks allowing the exhaust to pressurize the coolant and push it straight out the overflow.

If it's only in stop and go situations that usually points towards a clutch fan that isn't engaging properly and causing the engine to slowly overheat at idle.
 
UnderFire said:
Going steadily at speed it usually means there's a headgasket or cracked head problem, mine had a cracked head and there was no trace of oil contamination, headgasket itself was still good, I had small cracks allowing the exhaust to pressurize the coolant and push it straight out the overflow.

If it's only in stop and go situations that usually points towards a clutch fan that isn't engaging properly and causing the engine to slowly overheat at idle.
Click to expand...

It sure does seem like a head issue. Im going to send in another coolant sample. I was so sure it was the heads that I almost pulled them before I got the results from the first test. But then they came back negative and threw me for a loop. Anyone ever had a radiator get plugged internally? What symptoms did you experience? I cant see how a blown head gasket or head problem would cause the upper radiator hose to be hot and pressurized while the lower is cool to the touch. Maybe ive got two problems at once
 
mountainbiker42 said:
It sure does seem like a head issue. Im going to send in another coolant sample. I was so sure it was the heads that I almost pulled them before I got the results from the first test. But then they came back negative and threw me for a loop. Anyone ever had a radiator get plugged internally? What symptoms did you experience? I cant see how a blown head gasket or head problem would cause the upper radiator hose to be hot and pressurized while the lower is cool to the touch. Maybe ive got two problems at once
Click to expand...

Are you saying the lower hose never gets hot?
 
Every time Ive checked it since this overheating issue started is has not been hot, its only been slightly warm but usually almost cool to the touch
 
UnderFire said:
If it's only in stop and go situations that usually points towards a clutch fan that isn't engaging properly and causing the engine to slowly overheat at idle.
Click to expand...

Only with the AC on would this be the case. My fan clutch is out, and I don't see a rise in temps unless my AC is on while in traffic. The rest of the time while I'm in traffic with no AC the temp doesn't change.
 
mountainbiker42 said:
It sure does seem like a head issue. Im going to send in another coolant sample. I was so sure it was the heads that I almost pulled them before I got the results from the first test. But then they came back negative and threw me for a loop. Anyone ever had a radiator get plugged internally? What symptoms did you experience? I cant see how a blown head gasket or head problem would cause the upper radiator hose to be hot and pressurized while the lower is cool to the touch. Maybe ive got two problems at once
Click to expand...

I've seen rads get 1/2 clogged a few times but in generators. Coolant just gels up sometimes if it gets too old. No way to tell for sure until you tear the rad apart and point the core at the sun and look through it. Only way we could tell something was up beforehand was the air coming through the rad was cooler on one side than the other. That would be hard to test with a 4runner though since you can't stick your hand in there while it's running.
 
MStudt said:
Only with the AC on would this be the case. My fan clutch is out, and I don't see a rise in temps unless my AC is on while in traffic. The rest of the time while I'm in traffic with no AC the temp doesn't change.
Click to expand...

The A/C being on speeds it up immensely for sure, but even with no A/C it would eventually heat up.
 
Update

I decided to pull the heads...I found a steel heater line running from the water pump to the heater control valve had a massive coolant leak. The valley in the block between the heads under the intake was filled with dried coolant (and some fresh). No way it could have leaked onto the ground, I never would have found it without starting to pull the heads...hope this is causing my bubbling issue, I'm thinking without sufficient pressure in the system it would boil.
 
mountainbiker42 said:
Update

I decided to pull the heads...I found a steel heater line running from the water pump to the heater control valve had a massive coolant leak. The valley in the block between the heads under the intake was filled with dried coolant (and some fresh). No way it could have leaked onto the ground, I never would have found it without starting to pull the heads...hope this is causing my bubbling issue, I'm thinking without sufficient pressure in the system it would boil.
Click to expand...

any way you can post a picture of the line your talking about
 
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