My 1990 3VZE just started to rapidly overheat.

Temp gauge goes up and antifreeze spews into overflow tank.

Pulled thermostat and it tested ok. Put a new one in anyway (after testing it).

No heat out of front or rear heater. No leaks that I can see.

When I start it up it takes a normal amount of time for the temp gauge to go to the middle.

Shortly after that, the top of the rad and the upper rad hose fitting on the block gets to 230 - 250 while the lower thermostat housing is only 130. The temp gauge rapidly goes into the red and AF spews into overflow.

Fan works fine.

It's winter here, so overheating is not a normal thing.

Any help would be appreciated. Thanks.

ps please don't say it's the head gasket unless you know it might be, I can guess that too.

 

Sounds like an obstruction in either the radiator lines or in the radiator itself. Are you sure your coolant pump is working?

 

I know you don't want to hear that your head gasket is toast, but at least make the effort to check for it being a possibility. Denial won't fix the problem.

I would pressure test the cooling system and check to see if there are exhaust gases in the coolant. I hate to say it but it does sound like a classic HG failure.

 

x2 on the head gasket -> probable. Do a cylinder compression test.

 

i wouldn't say head gasket yet though. with the temperature differential between the top and lower radiator hose, it sounds like coolant is not flowing.

 

Exactly, that's why you have to do the tests to eliminate it.

 

Quick test to see if there's a headgasket breech between cylinder and water jacket:

Pull radiator cap (do not do this with the engine warm), start the truck, look for bubbles.

 

No, I'm not sure the pump is working. But it seems like it's not circulating.

Going to take it to the shop and have them pressure test it.
Thanks all, will post the results.

 

Marc---You have a clogged radiator.. Get a new one. Hopefully, the heat spikes didn't stress the head gasket too much. Does it overheat at highway speeds also?

 

Yes, it overheated on the highway. That's where it happened.
The temp gauge just spiked and I shut it down right away.
Didn't lose much fluid.

I haven't driven it since then. Just been testing it.

The rad drained ok when I changed the thermostat.

 

The radiator on my '80 wasn't plugged but the layer of corrosion inside reduced the thermal efficiency enough that it eventually started to overheat. I don't think that's the case here but I figured I'd throw it out there.

If your heaters aren't working the heater cores are probably plugged up as well. A good flush *might get everything flowing again. If it hasn't been flushed in a while it would be a good idea to do it anyway.

 

just throughing it in there... but wont a bad radiator cap have the same effects at a bad HG..... Sounds more like a lack of flow though.. just something cheap to check would be your cap

 

OP said coolant was going into the overflow tank, meaning the radiator cap is doing it's job.

 

I don't think the heater cores are plugged.
They were both blowing hot up until the overheat.

 

Cap is definitely working. But thanks.

 

There may still be some air trapped in the system from when you replaced the thermostat. Did you have both heaters on high when you were burping it?

That's what I meant when I said the radiator cap was doing it's job.

 

Maybe a little extra calming hope but I agree with RP. When you flushed your system and did the thermostat you probably just loosened up debris and now its stuck somewhere.

 

rad hoses in okay condition? when the t-stat opens, suction occurs on the cold side of the radiator and if the hose liner has separated from the casing it'll suck shut cutting off flow.

 

I agree this is the MOST likely suspect.

 

You would think so but AF seems to flow freely out of the lower rad hose when I drained it.