91 3FE Coolant pressure

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Feb 22, 2011
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Has anyone ever experienced excess pressure in their cooling system? (enough to blow an upper radiator hose) I'm at my wits end with this truck and it's driving me crazy. - I bought this truck with a blown head gasket and a cracked head. Bought a new head and had it tested by the machine shop, decked, plugged and complete valve job completed. Bolted it down with OEM head gasket in five upsteps following the sequence until I hit 90lbs consistent. Replaced radiator with a brand new one (all metal), new thermostat (Stant) and new radiator cap OEM. Running green coolant 1/2 and 1/2 mixture with distilled water. Elevated front of truck and ran with heater on until all bubbles were gone. Truck runs normal op. Temps for 15-20 minutes and than starts heating up rapidly when stopped at lights. Cools off once i start moving again. Haven't come close to overheating into the red, but haven't really driven it long enough to heat it up either. New waterpump (Bosch). All new hoses. New fuel pump/screen/ filter. Injectors serviced/balanced, passed emissions flying colors... Runs well... Just has excess pressure in the damn cooling system! Is the only thing that causes it to build pressure the water pump? What would you do in this situation? Is it possible the compression gases are leaking into my coolant passages? I have put on 105miles since it was redone ( very short trips) and the oil and coolant both look clean. (no milky color at all. The overflow bottle doesnt seem to move at all... It always reads full. Considering doing a block test tonight for hydrocarbons in the coolant, but don't know what I could do if they were in there? (torque down the head another ten pounds and pray?) What should I do... I have just over $3000.00 dollars wrapped up into something so close to working correctly, but so far from the mark.... Sigh... Any words of advice much appreciated. Thank you. Brandon 602-448-5852
 

CJF

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No way am I reading all that, but...

The system can't over-pressurize unless the radiator cap's defective.
 
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I would get a NAPA block tester kit. You can check for exhaust gas in the coolant very easily with that.

You can confirm whether or not you have any kind of headgasket/head/etc problems.

Once you narrow that down, you can look at the coolant system itself. I've never been a fan of the Stant thermostats. Are you sure the radiator fan is working correctly? Sure you have all the air burped out of the system?
 
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The overflow bottle doesnt seem to move at all... It always reads full.
This statement jumps out at me. The overflow bottle is supposed to rise and fall with system pressure. As the coolant heats, it expands and the excess, as determined by the pressure release in the radiator cap, runs into the overflow bottle. As the system cools and the coolant contracts, the cap allows coolant to be drawn back into the system from the overflow bottle.

So when the motor is cold the overflow bottle should be lower than when the motor is hot. If it's not as described then the radiator cap is faulty.
 
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Also the 3FE cooling system works very well for the motor when all the parts are there. It sounds like you're not getting proper air flow accross the radiator. Is the fan shroud in place? Have you replaced the fan clutch with a new OEM unit?
 
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Feb 22, 2011
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I will go get a napa block tester kit and check and see if I have hydrocarbons in the coolant. Will report back with pictures and the results of the test.

I don't know if I'm getting proper airflow either. The shroud is on and the fan clutch doesn't show any obvious signs of leakage/seepage. It seems to engage when it's running, but is no means - a wind tunnel of any kind. Maybe it's aged and needs to be replaced?
 
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A good 3FE fan clutch will sound like a DC10 when you first start the truck. If it is of unknown age I would replace it. Be certain you go OEM on this or you'll just be doing it again in a few weeks.
 
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Completed the block test today. The fluid lightened up a little bit during testing, but remained blue... There was no hint of green or yellow. So I'm optimistic there will be some light at the end of the tunnel.

I have a new OEM thermostat and gasket set, so I guess I will throw that on and bleed out the system and see where I'm at.

Hopeful :)
 
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The fan doesn't sound like a DC10 taking off on start up, so I will order a new clutch and see what difference it makes.

Does anyone have Cdans number or know of a place to get a discounted OEM one?
 
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Feb 22, 2011
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Put in the new factory thermostat. Still have to much pressure. Did the block test again and it remains blue. Going to pressurize my cooling system, take the spark plugs out and see if coolant sprays out. Coolant and oil are still clean. Any ideas of further tests that may tell me something?
 
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Have you replaced the radiator cap with OEM? If you're not getting combustion gasses into the water jacket then the only way the system can become over pressurized is if the cap or relief hose off the cap is plugged.

If the overflow bottle still doesn't rise and fall with engine temperature then that has to be an issue. The system needs to dump excess coolant as it heats or hoses and radiator tanks will burst.
 
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You say you replaced all hoses, is it possible you have a kinked hose? Not sure if it would lead to increased overall pressure. I had my upper oil cooler hose collapse from age (where it jumps up over the AC compressor bracket) and it blew the bottom end off the hard line.
 

CJF

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REPLACE THE RADIATOR CAP! :rolleyes:

Plus, how the hell are you determining there's "too much pressure" anyway???
 
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Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.

Well, post # 2, 4, 12, and 14 suggested replacing the radiator cap.

Personally, I'd replace the radiator cap.
Alternatively, you could replace everything related to the cooling system as well, but I'd start with the radiator cap.

The radiator cap regulates pressure in the cooling system so I'd consider replacing the radiator cap.

A faulty radiator cap won't allow the system to properly regulate pressure so the result could be an over or under pressurized system. Both scenarios are bad. Consider replacing the radiator cap.

Either way I'd start with a new OEM radiator cap.

Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
Radiator cap. Radiator cap. Radiator cap.
 
Joined
Feb 22, 2011
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The radiator cap is new OEM. - I'm determining it's over pressurized because the upper hose blows up like a balloon. I've replaced it twice. The coolant doesn't move from radiator to over flow.... The radiator is a new "all metal" after market one. Could it be possible a brand new radiator is defective or undersized in some way? It bolted in perfectly. Going to pressure test the cap Monday and see if it's functioning properly. - just don't understand how I can have so much pressure without combustion gases pressurizing the coolant system? $4500 deep into a $3000.00 truck - wife is loosing patience with me.
 

94SRUNNER

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Is the rad. cap you have the correct pressure rating?

Also, could the rad. cap you have be faulty, if that is in fact the problem?
 
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The coolant doesn't move from radiator to over flow
This is your problem. Have you checked the neck of the radiator to make sure the passage is open?

If you were getting exhaust into the coolant, the radiator would be bubbling without the cap on as soon as you started the motor from cold.

As the motor warms the radiator will start to overflow without the cap on. If you're not seeing bubbles in the radiator and the coolant level rises gradually within the first minute of runnning from a cold motor, then it sure sounds normal to me. The excess coolant MUST bleed out of the system into the overflow to maintain constant pressure in the system.

Without the cap in place you should be able to easily blow through from the overflow tube into the neck of the radiator. This path MUST BE OPEN.
 

CJF

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Jon is correct.

Your piece of crap CSF (I'm guessing here) radiator has a blocked outlet to the overflow.

(Sorry for the early morning grumpiness. :p)
 
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