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94 4.0l WP and Thermo Replace Gone Bad...

Steve777

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So I am a little embarrassed to be posting this since this repair is pretty basic, but I am scratching my head as to what might have gone wrong.

94 B4000 4.0l V6 truck is in great shape and engine and drive train were runny well. I noticed the coolant was low after a trip a few weeks ago, so did some investigating. Cleaned the front of the engine and ran it for a few mins then looked for leaks. It was leaking antifreeze from both the water pump and from the thermostat housing. Just to be cautious I did one of those tests for exhaust in the antifreeze (185K miles) and it came out clean.

So I took out the old parts and put in the new ones. Not a big deal or so I thought. The old WP had coolant stains from the weep port, and the thermostat looked like the oring had been crushed or perhaps it got pushed out at the bottom??? Oh one other thing the old thermo was a 180 deg one and the new replacement was a 190, supposedly the correct stock temp.

Anyway filled it back up with new coolant and distilled water and went thru the burping process. It seemed to "burp" quite a bit from the open rad cap, and the upper hose did not seem to be getting warm as I would have expected. Temp gauge settled at 1/2 way idling in my driveway (which I figured was the 190 vs 180 thermo). Stopped, filled up the rad and overflow and took it for a test drive. (Previously the truck ran at about 1/3 on the temp gauge most of the time)

Well under the load of driving, the temp gauge kept going up. I only went about 1/3 mile then turned around and went back home. Engine was warm to hot, but did not smell overheated. Temp gauge never got over 7/8 but when I got back I could hear air (steam) burping into the overflow tank.

So I am trying to figure out what happened here. I put back in almost 2gal of diluted coolant. I captured maybe 1.5g when I drained it, so I think plenty of coolant was in the engine. I suppose the new thermostat may not be opening all the way, and that is causing overheating. Or I suppose the new WP is defective and the impeller is not really turning and moving water (I checked and it turned freely after torquing the WP bolts).

The only thing which seems to have gone right is there no longer are any leaks from the thermo housing or WP, so I suppose that is good.

Seems like from the burping when under load, might be some areas of the engine that did not have sufficient coolant, but there should have been enough in there.

Anyone have any thoughts as to what is going on here, and what to check first?
 


RonD

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Recheck fan belt routing, on some engines fan belt on water pump can be reversed so its spinning in the wrong direction.

Should be a label on rad support or look it up online

Yes could be bad thermostat

Pull off 1 heater hose at the firewall and refill until coolant comes out hose or core, air is all out when it does, put hose back on
 

Steve777

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Thanks RonD.

Double checked the belt routing, and it was fine. Next I pulled out the new thermostat, as that was the next easiest thing. It was seated and positioned correctly, so I tested it in a pot of water on the stove. Did not open, not even a crack at full boil of the water. So I returned that thermo and picked up a new gasket for the old one (old one tested fine on the stove, leak was due to the cracks in its gasket/o ring).

Put it back together and seems to be fine. No leaks, no overheating. Need to do a longer test drive but it is looking good.

Guess I learned my lesson here. Need to test new thermostats before going to the trouble of putting them in.
 

RonD

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Good work

Yes, "new" used to mean "Tested and working"

New now means "You test it and we will replace it if it doesn't work"
 

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