Yams

Got my daughter a 96 for her 14th.

Soooo..
Temp goes into the red when driving. Will settle down when at a stop.
215,000 miles on engine.
Thermostat opens on the stove pan. Even tried a new one.
Heater works like a champ, Can use it to bring the temp down if it gets too high.
Engine fan runs constantly, won't spin freely with engine off. Can get maybe half a turn/spin by hand. Wondering if fan clutch is close to locking up?
Even with the fan constantly running it would seem to make it cooler, not overheat.
AC comes on and the AC pump cycles, however not on defrost. Work on that later.
Top plastic on radiator, and upper hose gets super hot. No heat anywhere on radiator or bottom hose. Thermostat housing gets hot to the touch(enough to open thermostat?, maybe)

Last night I removed the thermostat and used the rubber o ring to reinstall the housing. Ran cold on an entire 15 minute drive(climbing 2 mile grade and all). Put the thermostat back in, 6 o'clock position on the jiggle valve
Goes right back to red on the gauge. I even drilled two smaller holes at 120 degrees apart from the jiggle valve. nothing!!!

Not getting any gas bubbles, not losing water..

Haven't done a compression test yet. and don't know the real temperature of the upper hose when gauge is in the red.
Heater core must be flowing water because heater is working; so some action is coming from the pump.

Questions:
Can the water pump impellers be so "gone" that not enough water is circulating to draw water though radiator?

What water flow causes the thermostat to actuate? The oil cooler return line only?

Can the oil cooler channel get blocked? Hard to imagine.

Totally stumped, runs cold without a thermostat, over heats with the thermostat.

skypilot

iTrader: (1)

On the cheap side its a bad thermostat that does not fully open, you can test it in a pot of boiling water. Your test is not valid, one job of the thermostat is to slow down the water flow so it can be cooled. If your lower radiator is questionable it may be collapsing at high RPM.
Or you have a plugged or moth eaten radiator. Here in NY I use the V6 radiator with the I4 engines due heat. That said you should probably run a radiator flush before you take the radiator to a shop to be boiled out.

For the oil cooler I like race car tech, a dedicated oil cooler w/ fan and AN lines / fittings. Yes its a costly way to do things but it saves money in the long run.

Yams

I kinda mentioned that I heated the thermostat in water. nothing wrong there.

As for the radiator, I dumped water into the top hose inlet, and it poured out the bottom hose outlet just as fast as it would go in. Not suspecting a bad radiator. nice and clean, almost like new.

maachine

probably a bad water pump. at that range of mileage i'd say thats a good bet. probably not flowing coolant like it should.

my reasoning is that if you pull the thermostat out, itll flow just fine, but once you put the thermostat in, it restricts the flow enough that the water pump cant push enough coolant through it.

rworegon

Is the radiator the original? Even though it flows well, the small channels throughout may have build up on them that reduces the efficiency. Is there dirt in the radiator fins? And, as already mentioned the WP is suspect too.

habanero

Colorado is where I go when I want to see if my radiator cap is working or not.....it's a cheap thought. I'll recommend a Toyota cap after having an aftermarket version fail me (in Colorado- again!) within a year. Though I do lose some coolant through the overflow when it is a bad cap...otherwise the symptoms are similar. It's prolly something you've already ruled out.
For that other question, my fan spins by hand with a little resistance when engine off.



PS. Dang, that is one lucky daughter you have!!

Yams

My first car was a 70 chevelle. Dang I miss those days.

I figured I would have two years to get this truck running right for when she gets her license. Looks like it might take all two years. We do live out here in the country, so she might get to drive a little sooner

I guess I'm stuck waiting for the weekend to do a compression test. If I'm gonna tear into it, I wanna do it all at once.

Yams

Update: pulled the front end apart. The tensioner was flopping around because the bolt hole was wallered out. Had to heli-coil the hole. Guessing the belt was slipping at higher engine speeds causing the overheating. got a new kit in it, and will put back together this weekend.