No heat in Roadmaster

I've got ice-cold AC in my 94 RM which is great as I live in Fl and need it every day. However, I don't seem to get any heat, no matter what the temperature is set at. I first noticed it when trying to get some hot air for defrost. Since I've got a couple of road trips to Georgia and NY coming up, I suspect I'll be needing some heat.

Any suggestions? I suppose the heater core could be blocked? What else could it be?

 

Some people put a petcock on the heater hose lines to shut off the flow of heated water - is there anything like that on your hoses? It's a pretty simple setup, so if there isn't a valve shutting off the water, it's probably the heater core clogged up.

 

Besides a manual shut off valve, there are several possibilities, feel the hoses after the car warms up, are both hoses getting warm? If so the problem is probably in the heater controls that open and close the doors that control the heat flow.

If both hoses are not getting hot, there is some sort of restriction to the coolant flow to the heater core, it could be as simple as a stuck automatic shut off valve, and as bad as a clogged heater core.

I have also seen no or little heat be the 1st sign of a water pump going bad. They still produce enough pressure to pump fluid to the engine, but the heater core is usually the highest point in the cooling system and they no longer have enough pressure to pump coolant up to the heater core.

I don't know if you are the original owner or not, but after working on older southern cars in the past, I have seen the previous owner run straight water in the cooling systems before. And that can cause all kinds of corrosion damage to the cooling system.

Sorry I am not more familure with the LT1 Powered cars.

 

No heat in an LTI B body car is common unfortunately. It could be two things, a clogged heater core (likely), or an inop blend door motor. The blend door motor is located behind the glove box, and a bit to the left. Check and see if the motor is turning as you change the temp setting.

I'm going to focus on a clogged core, that is more likely the issue you are having.You will need to flush the entire cooling system thoroughly. Try this link.

http://gmlongroof.4umer.com/t591-heater-core-flush-procedure

The procedure outlined in the link may work for you, but it was always a temporary fix that only lasted a few days for me. I've flushed several different cars, several times, the heat works great for a few days... weeks maybe, but the core gets clogged again pretty quickly soon after. I've had the best luck removing the knock sensors to drain the engine block, then run a lot of water through the engine to flush out all the crap that has collected in the cooling system. Reinstall your knock sensors, fill the system with clean water and a bottle of CLR (Calcium, Lime, and Rust remover). Run the engine for a while, purge the system, and get it hot. Then drain the system, remove the knock sensors again, flush it ALL, REALLY good.... AGAIN. Fill it with clean water, and fresh coolant, purge the system, and get all warm and fuzzy.

You can put in a new heater core, but with out getting all the small pieces of "scale" out of the engine, your just delaying the inevitable.

Mike

 

Both hoses appear to get hot after the engine has run awhile.

Just replaced the water pump.

I've seen a few references to some kind of "air-lock" in the cooling system that can cause the heater to not work. must say I don't understand what exactly that means, or how you could check it, or eliminate it if it were the problem.

I did notice a lot of junk in the overflow and has the system flushed about a month ago.

 

Try connecting a water hose to a heater hose, with both disconnected, to check the flow - no flow = clogged!!

 

Both heater hoses being hot doesn't mean the core is fine, more than likely the core is only partially blocked, and by the way the '94-'96 B body cooling system is designed there will always be heat at both hoses.

Air in the system will cause problems, and needs to be purged out of the cooling system. There is a brass bleeder valve on the top thermostat housing, get the car hot, and crack the valve open, if there is air in the system the valve will spit and spray coolant/air out (bad), if there is no air, there will be a solid steady stream of coolant from the valve (good). Now, the distributor is right below the t-stat/water pump, and if the seals on the distributor are not what they should be you will cause other issues. So take precautions to keep the dist. dry.

Mike

 

If you want to prevent stuff from clogging the heater core a flush is a good idea but to prevent any loose stuff from getting back to the core in the future you can install a coolant filter. They have types that go in the heater hose and better ones that replace a section of the radiator hose and have a cap on top for filter service.

 

Maybe too late now, but one thing I try to do year round on my vehicles is run the heater (at least move the temperature selector to hot) once a week. This circulates the water through heater core rather than letting the same water (coolant) set in core. This prevents separation and sediments from damaging core.

 

I thought there was always coolant going to the heater core, just flaps to direct the airflow.

Regarding air in the system, I picked up a little brass valve that had a nipple on it to replace the bleeder on the top of the block.
You put a small hose on the nipple and run it into a catch can so you don't get coolant all over everything.
I got it from someone on the impalassforum, but I have seen them on ebay as well.

 

http://www.impalassforum.com/vBulletin/showthread.php?t=255705&highlight=coolant+bleeder

 

The bleeders with the nipple are the way to go, I've got them on both my LT1 cars.

Coolant flows through the core all the time on LT1 B bodys, there is no hot water control valve, they use a blend door in the duct work.

Mike

 

I just fixed my no heat condition on my 96. There are numerous things that can cause it, like ppl mentioned before. And the best advice is to thoroughly research the cooling system at impalassforum. It's a reverse flow system and is really amazing! Bc of that there are certain differences like the thermostat - which was my problem. I had ordered a 160* for my car and they gave me a standard Chev SB stat, not the special LT1 stat. So for years my system did not function correctly and i had no idea why!

Finally i pulled the stat (which is super easy) and immediately saw it was incorrect. So i just put in my old one and it's perfect now. My heat works and my system cools properly. It was simply not circulating so the only coolant moving was in the engine itself. On hot days it would quickly climb to the red and freak me out.

But there are other potential issues like blockage from the old orange coolant with clay tablets (if you still have that type flush out well and use green coolant). Also there are 2 plastic pieces (a tee and a restrictor) inline that can get brittle and break apart which will easily clog it. I have heard of the heater having air trapped but seems unlikely bc it's a closed system and you should be able to fully bleed any that will rise up to the high point above the stat.

Hope it helps!

 

I have just over 200,000km on my '96 and it's had orange coolant all it's life. Works perfect.

 

Oh yeah no disrespect there. I know it's good stuff but didn't they have some kind of clay tablet thing to add? I seem to remember hearing that the systems could get clogged with it - prob if the car sits for long periods. I replaced mine with green antifreeze to keep it simple. But they warn to thoroughly flush the old stuff out to avoid mixing the two.