Cat3TRD

I have a 94 3.0 pickup. Let me give you a summary of the history of this issue:

I had a remanufactured engine put in about 2000 miles ago. The mechanic damaged the metal radiator it had and replaced it with a thinner plastic one. The engine would overheat at idle but would cool down on the highway. I bought a new CSF metal radiator and put it in and burped the system and it would idle seemingly all day, but would overheat if I drove over 60mph. I have since replaced the water pump, fan clutch, upper and lower radiator hoses, radiator cap, thermostat, heater hoses, TB bypass hose, and the antifreeze. I’ve also replaced some stuff that could tangentially be related thinking maybe it’s a fuel/air ratio issue.

Yesterday I removed the new metal radiator and reinstalled the plastic radiator, to see if maybe now that I’ve replaced the entire cooling system, it would work. I was thinking maybe the CSF is defective or something. So, I’m trying to burp the system and it gets up to temp, then I start to hear some pops coming from the radiator so I turn off the engine. It immediately starts geysering steaming coolant all over the place. The heater didn’t blow hot air and the bottom of the radiator and lower hose were cold to the touch. I looked into it and most opinions said it’s a clogged radiator, faulty thermostat or failed water pump. Today I bought a new thermostat and pulled that plastic radiator out. I flushed it and it flowed really great so I ruled out clogged radiator. I also flushed the metal CSF radiator and it also had no clogs. I removed the old (recently installed) thermostat and put it and the new one in a pot on the stove and they both opened and closed correctly. So, it doesn’t seem to be the radiators or thermostats. Only thing left should be the water pump. Before I get into that project though, I wanted to put the CSF radiator back in with the new thermostat and see what happens. In that test, the temp gauge gets up to “normal,” the heater blows hot, the coolant doesn’t geyser out, but the bottom of the radiator and the lower hose are cold. The top hose is really hot. Now, if I had not had that geyser/popping issue with the plastic radiator, I would say this one is working and would start driving it. I don’t know if the bottom hose should be warm/hot or if the radiator cools so well that it’s like cool tap water coming out of the bottom.

My theory is that there’s no circulation. I don’t know why the temp gauge doesn’t climb higher than normal though. Maybe I’m just dumb and it’s working correctly. I’m afraid to drive it. I don’t want to destroy the new engine. What do you think? If the water pump wasn’t working this whole time, could that have been causing my overheating at highway speed issue? Do you think it was maybe working at a defective level, and now doesn’t work at all?

RAD4Runner

How do you know it overheats if the temp gage does not climb higher than normal?
Need to VERIFY if there really is a problem. I suggest you get an infrared thermometer and measure and record temp at thermostat housing when cold, when in normal operating condition and when gage reads high.
BTW, I get about 50degrees difference in temp between top radiator hose and bottom one when it reaches operating temp.

Cat3TRD

Before this Labor Day weekend, I knew it was overheating because the fan clutch would kick into overdrive when the needle got just a hair over halfway. The fan would start roaring and the gauge would climb all the way up until it was almost in the red if I didn’t slow down to below 60mph. Once the temp gauge got back to about halfway the fan would go back to normal.

Right now, my main concern is that the coolant doesn’t seem to be circulating. So, you’re saying the bottom hose on yours is 50 degrees cooler than the top hose. It should be warm to the touch then. I can touch roughly the bottom 2/3 - 3/4 of the radiator with my bare hands right now while the needle on the temp gauge is almost to halfway and it’s cool to the touch. Not less hot, actually cool/cold. The top of the radiator and upper radiator hose is so hot you can barely touch it without feeling like it’s going to burn you. If the coolant isn’t circulating, I’m concerned that the coolant in the temp sensor housing is taking longer to warm up than the coolant in the engine.

I’ve been searching and searching this forum and others for months looking for stories similar to mine that actually list a resolution and haven’t found any so far that actually worked for me. But when I posted this last night, the forum suggested a few posts with similar content and one of them sounded extremely similar to mine. The guy ended up removing his water pump to inspect it and decided it was fine, so he reinstalled it and when he got everything back together, it started working. Coolant started circulating and his overheating on the highway issues went away. He suspected that the belts weren’t tensioned correctly by the mechanic that installed them. I’m going to check my belts today. I went out last night and felt them, and the alternator belt seems a tiny bit loose, and I get about 1-2 seconds of squeal when I first start the truck. If that doesn’t fix it, next weekend I guess I’ll be pulling the water pump for an inspection.

RJR

If the coolant is not circulating you will be boiling off water/losing coolant. There's no way for the coolant not to boil in the block if it is not circulating. So one thing to check is, are you losing coolant.

Cat3TRD

I have an IR thermometer on order. Should receive tomorrow.

RAD4Runner

Yes, bottom hose is warm but not as hot as top hose. So many variables to a cooling system issue.
That's why we really should take good care of it. One simple and basic thing to do is regular flushing.