90 GM LS: Heater Hose and return hose are cool and have no pressure

[Eric_S]

Ok, I have heat again. I replaced the Murray Thermostat with the Superstat one.

The upper radiator hose gets hot, hot enough I cannot hold onto it very long, and the heater hoses get warm.

The air coming through the vents is just warm, which is about as good as it ever was before it stopped.

Many thanks to all you guys. I have learned a lot in this process.

I think I still have issues with the blend door opening and closing properly though.

[Eric_S]

Ok, the blend door is opening and closing just fine. I took apart the whole dash just to make sure.

Today I took the car out for a drive and floored it down a straight stretch for about 5 minutes.

FINALLY, the air started to get warmer. It is now to where I would call it a good heat level. Not really that hot, but good enough.

What could cause this? Did I just not flush out the heater core well enough? Water pump finally pushed some gunk out of it?

My dad says he has some stuff to clean the heater core, but you have to drive sixty miles with it in the radiator. Should I try this stuff? and will it work OK with anti-freeze mixed in?

[88MercWagon]

I bet you do have some air in there. Coolant likes to disappear when there's air in the system. If there isn't any coolant on the ground, I want you to open your radiator cap, and start your car. Put your heat on full on high and let it run. Any air in the system will come out. When it's all gone, the water will start to over flow, at that time, close the cap and add coolant to the resevoir. By then, you should have heat. And everything should be operating as it should.

I'm having a similar issue...where exactly does the coolant dissapear to?

[1987cp]

Two questions:

I took the car out to a mechanic my Dad recommended. When we got there we checked the upper radiator hose and it seemed very hot and had pressure. The heater hose was still slack and cool though. He recommended replacing the coolant temperature sensor.

1) What could an electrical sensor possibly have to do with a system that is entirely mechanical?

I bet you do have some air in there. Coolant likes to disappear when there's air in the system. If there isn't any coolant on the ground, I want you to open your radiator cap, and start your car. Put your heat on full on high and let it run. Any air in the system will come out. When it's all gone, the water will start to over flow, at that time, close the cap and add coolant to the resevoir. By then, you should have heat. And everything should be operating as it should.

2) What does running an electric fan have to do with getting air out of your cooling system?

[gadget73]

The heater instruction is an old thing, mostly for cars that controlled the heat with a valve in the heater line. Ours are full flow through the core all the time.

[mfmagicmike]

I have a problem with my blend door: it doesnīt stay open/closed. When I want cold air, after a while I gets hot, and when I donīt want any air at all, I get hot air.

Anyone, familiar with that issue? Vacuum problem? (interior temperature sensor changed 1 year ago)

[1987cp]

The heater instruction is an old thing, mostly for cars that controlled the heat with a valve in the heater line.

Interesting, never heard of that system. Sounds unreliable. What sort of vehicles did it that way?

[Lincolnmania]

heater core is probably clogged

[gadget73]

Interesting, never heard of that system. Sounds unreliable. What sort of vehicles did it that way?

Lots of stuff, 70s Chryslers come to mind, friend had a 77 Cordoba with a partially seized valve and a broken control cable. It was opened in the fall with vise-grips and closed in the spring. I'm sure others did it.

[Eric_S]

I know this thread is damn near 3 years old at this point, but I'm going through some of my old stuff on the internet relating to this car and trying to add my experiences.

that said:


Well, it wasn't anything in this thread. I did clog up the radiator with stop leak, but that wasn't the root of the problem. Never using any of that shit again. I've learned against magic potions in the last few years. A more thorough flushing and belching of the cooling system improved performance, but it wasn't until later on in the summer that my water pump completely failed that I figured out that was what was causing my heater to not work properly.

After I replaced it the heater works perfectly now.

[mfmagicmike]

In fact I still have the same problem, never had time to look into it. At some point I wanted to change the heater core but it is burried so deeply into the engine compartment and expectably hard to extract that I forgot about it. I have though cleaned chemically the whole cooling circuit with no noticeable change.
As of today, the warm air works for some time (10 min maybe), then the vent door closes audibly and shuts off warm air supply. Maybe the temperature regulator I changed is crap (chinese quality? no offence) or some vacuum line popped off.