Having finally gotten a working temp gauge, I was somewhat surprised to see my car UNDER-heating, although it kinda makes sense with how the car runs. 140 was the highest I saw it after driving around town, hitting stop and go traffic, etc. I suspected a failed thermostat and was correct. It had broken into several pieces, so I fished out the parts and replaced it. Now I have the opposite problem! The car overheats pretty bad, maybe 240 or so. Coolant is now coming out of an unknown plug between the heater hose and thermostat housing (see first pic). Can anyone tell me WHAT that is and what it is used for?

I would like to think that the new thermostat could cause this problem, but maybe it isn't. Another part of me is dreading the possibility of a correctly functioning thermostat exposing a weak link in the system.

And before anybody has to ask:

Yes, the air dam is on the car.
Yes, the coolant level is correct.
No electric fans. It has a fan bolted onto the water pump, and it blows air the correct direction.
The car is a 1983.







Also, I have been trying to figure out what this second plug is for on the thermostat housing. Anyone?





As always, thanks in advance!

 

I forget the exact purpose,but the two valves are related to emission control equipment that has been removedThe overheating problem might be "airlocked"heater coolant circuit preventing "bypass"flow around the thermostat-normally coolant from the heater flows around the thermostat wax chamber so it will open when the flow gets to temperature-if this flow blocked,thermostat will remain closed until coolant hot enough to start thermostat opening finds it's way to the thermostat.Revving the engine a little might clear the airlock if that is indeed the problem.

 

You should invest in one of these,beats the heck out of chasing overheating problems.30$ at Harbor freight.

 

It looks like someone tried to blank off that coolant line. I don't know what it's specifically for, but maybe heater related? I would trace it back and plug it correctly, as that's just a bolt that's plugging it on the end of the hose...

 

Here's an update:

I discovered that the thermostat housing itself was cracked. I replaced it, as well as removing and plugging the piece in question in the first picture. With a 195 degree thermostat it still overheated, but not nearly as bad. I have also noticed some white scale around each pipe in the radiator itself. I decided to play it safe and go with a 160 degree thermostat. After putting that thermostat in and reinstalling the little spacer panel between the nose and radiator (oops), it's running cold again. Never above 160. I am hoping that a 180 degree thermostat will give it a good balance.

 

More updates:

Heater core is leaking. I noticed the car running low on water after about a full day and then saw the coolant on the passenger side floor board. I have taken the lines out temporarily. Ends of the heater core capped, pipe plugs inserted into the intake and water pump outlets. I will be testing it out tomorrow on the way to church.

 

Still a no-go. Car heats to 230-240. I noticed I don't see much water flowing through the radiator while the car is running, and it has some white scale on it. Radiator and water pump are next.

 

try it with the heater hose ends connected together instead of blocked-with ends blocked,there is no "bypass"flow around thermostat.

 

Also, I have been trying to figure out what this second plug is for on the thermostat housing. Anyone?





As always, thanks in advance! [/QUOTE]

That's The TVS (Thermal Vacuum Switch)

 

8t2, I will try that this afternoon. Thanks for the tip.

gt4373, I'm sure whatever it used to do, the rest of it has been taken out at some point. I'm not super emissions-savvy.

 

Another update:
Radiator replaced, but it hasn't helped. I initially thought the radiator was the problem when I saw nothing flowing through it while the car was running. There was a lot of hard water buildup in the tubes and I thought that they were clogged. That may have been some of it but now that doubt has been removed entirely. Only thing left is the water pump. It makes sense that it's the pump now. It's not pushing anything at low RPMs. Revving the car once or twice will bring the temp down.

Anybody else have any input?

 

Correctly bypass heatercore instead of just capping. Then replace water pump. They are only around $40

 

RS-Chevy-SS,

I have the heater core bypassed with a short bit of line, and it runs way UNDER temperature. 150-160 MAX. Capping them apparently makes the car overheat, which I don't really understand. I always thought the heater core stuff was an afterthought and had no effect on the operating temp.

One other note: even when the gauge shows 230-240, I can take the radiator cap off. No pressure whatsoever. The cap isn't even hot to the touch. Maybe that can clue someone in?

 

Im gonna say change the pump before we continue. Its relatively inexpensive. Looks like we are going to go process of elimination on this

 

Yeah, I think that's the next step. I'll probably try that before work tomorrow. Thanks for the help!