Heat?

[6768chevylover]

For those who have a stock cap on your blazers, How is the heater in yours? I used it for the first time today Since I bought it back in October of last yr.. It seems to push out warm air and not hot air..

[GM man]

No problem with my heater. Mine gets hotter than hell, so much so that I have to disconnect my heater core in the warmer months or my AC can't keep up. Sounds like you may have an issue with the valve that shuts down the coolant flow to your heater core. That's a cheap fix if that's what it is. Could also be your actuator doors aren't opening/closing completely inside your unit or sealing well, causing cooler air to mix with the air going through your heater core. Those are operated with vacuum, so I'd start with the little vacuum hoses and work back from there. It's all very straight forward and easy to work on.

[6768chevylover]

When a heater core goes bad, can it just not produce heat and the truck still operate at its normal temps? I have installed an a/c delete cover to just have the heat. a/c pump and stuff was missing when I bought it. I just don't understand why its warm and not hot.

[GM man]

No. Usually the only way a heater core goes bad is when it springs a leak. Assuming you've got coolant flowing into the core, the only thing I can think that would cause it to not be really warm is if the doors aren't sealing up and it's pulling cool air in and mixing with the warm air. So it could be a vacuum leak preventing those diverter doors from closing all the way, or sometimes crap (leaves and junk) get inside there and prevent those doors from opening and closing all the way. Do you have a heater valve? Looks something like this: https://www.google.com/imgres?imgurl...act=mrc&uact=8

[6768chevylover]

I have a heater valve that only has an on/off switch. Its open because I just installed it last weekend. There are no leaves or junk in the box. I cleaned it all up too last weekend. How different are a/c cabs to non-a/c cabs? Can you put an non- a/c box set up in an a/c cab just by drilling holes or are the hole patterns on the firewall different?

[GM man]

The hole shapes in the firewall are different. But you can make that work if you want to...

[6768chevylover]

Thanks Gmman.. I've been reading other threads about no heat on this forum and others had flushed there cores. Is it just better for me to order a new one and hopefully not have to worry about it again? Or has any one ever flush and forget it type deal?

[6768chevylover]

okay, this might sound weird. I noticed heat at the floor port on the heater box but not at the dash vents and not at the defrost vents. keep in mind I had eliminated the door that's in the air selector box. so its totally open so all vents pass air thru.. tell me if that's something I shouldn't of done..?

[6768chevylover]

Okay, now that the weather is getting colder, my heat seems to be diminishing. When the weather is warmer during the day the truck runs hotter and when its cold it runs colder, so my heat does the same. Can anyone come up with things to check mechanically or anything else Im missing? Heat box is clear, heat valve is new and is open. the hoses come from intake and radiator to my heat core. lines are hot but I guess not hot enough. Only thing I can come up with is the a/c delete box is a piece of crap. Help

[6768chevylover]

also forgot to mention that the stock gauge reads in between the half mark and cold when its cold out and half way when its warm out. thermostat is brand new...

[6768chevylover]

Okay, I hate to bring this back up. I bit the bullet and bought and replaced the heater core and still the same result(barely heat). Specially when its really cold. I don't think I ever mentioned that I have a mechanical fan which constantly runs due to the PO getting rid of the clutch set up on it. My question now is, Would this keep my radiator heat from building up? and that's why I have crap heat?! Could the water pump be an issue?

[jaros44sr]

do you know the degrees of your water? Maybe your coolant system is to efficient, not letting your coolant fluid to get hot. Sorta like diesels, block radiator with cardboard

If your hoses aren't hot, .....

what temp. is you're themostat

[6768chevylover]

well I have one of those laser temp guns and the thermo housing is around 145-155.. the radiator is usually 140 on driver and 95 or so on the passenger.. of course that's not internal degrees.. hoses are hot but I guess not hot enough.. even those are around 140

[jaros44sr]

145 doesn't sound hot enuff, I think these sbc should run 195-205. someone else will post up, if I'm wrong

[ekajkrats]

Originally Posted by jaros44sr

145 doesn't sound hot enuff, I think these sbc should run 195-205. someone else will post up, if I'm wrong

I think Jim is onto something. I agree about the temps he states.

He also earlier asked about what temp thermostat you bought and put in, but you may have read it as, what temp is the housing at. I think he just wanted to make sure you had a thermostat that would stay closed until the engine got up to the desired temp, i.e. 195.

If the thermostat is a higher temp, it should be restricting the flow of the water from the block to the radiator so that the radiator and fan don't cool off the coolant as fast.

I agree about your fan being an issue, since it is always on, especially with the outside temps dropping. It could just be keeping the engine as a whole too cool.

Your lines are hooked up how the '72 service manual says to do it for a v8 w/ 350 transmission. Assuming the intake hose goes to the top, and the radiator to the bottom.

-Jacob

[6768chevylover]

Your right I took it differently. lol.. I have a 180 stat.. Those lines are correct. Intake top and radiator bottom. Is there a benefit to have the bottom ran to the water pump?

[jaros44sr]

Originally Posted by 6768chevylover

Your right I took it differently. lol.. I have a 180 stat.. Those lines are correct. Intake top and radiator bottom. Is there a benefit to have the bottom ran to the water pump?

I don't think they will fit the other way...5/8" and 3/4" hose size, or something like that

Maybe bump your thermostat up to 195 degrees

[ekajkrats]

I don't know if there is a benefit. The service manual shows the pump to top and intake to bottom for a Manual Transmission though.

Also like Jim said, you could try blocking off the radiator with cardboard so the fan can't pull as much air through the radiator and see if you can get up to temp, that would at least point you in the direction of your fan cooling too much by always running. Probably not a permanent solution but something to try for diagnosis.

-Jacob

[jaros44sr]

Originally Posted by 6768chevylover

Your right I took it differently. lol.. I have a 180 stat.. Those lines are correct. Intake top and radiator bottom. Is there a benefit to have the bottom ran to the water pump?

do you have a shroud around your fan?

No pictures, I lose interest?

[6768chevylover]

Okay, dropped the shroud and mechanical fan and put 2 electric fans on with no shroud. Seems worse , heat builds when at idle but seems to lower a normal driving speeds(35-40mph). When I speed up to 50-55 the temp goes up but doesn't seem to be enough heat. Temps always up and down depending on speed and pressure on engine. Is this maybe a pump issue? By the way I do see some small spots on the radiator of old leakage but just small spots.. planning on doing 195 stat but would like to replace pump and radiator if they seem to be an issue as well at same time. but don't want to fork out the money on them if not needed...

[mister.freeze]

in my experience, GM thermostats are typically 195 and 210. I run the 210 and dual electric fans. I have a cutoff for the fans too; the intent was more battery power on startup and faster warmup. Try that. I've turned the fans off at highway speeds and there seems to be enough airflow through the radiator, even in summer, to keep from overheating, but I leave them on anyway. When I did have a heater core, I could actually modulate the heat a bit by turning the fans on and off.

[69-72]

I live in one of the five coldest cities in the world and I have no problem keeping warm so I don't think anyone else would have an issue.

[jaros44sr]

Originally Posted by 6768chevylover

Okay, dropped the shroud and mechanical fan and put 2 electric fans on with no shroud. Seems worse , heat builds when at idle but seems to lower a normal driving speeds(35-40mph). When I speed up to 50-55 the temp goes up but doesn't seem to be enough heat. Temps always up and down depending on speed and pressure on engine. Is this maybe a pump issue? By the way I do see some small spots on the radiator of old leakage but just small spots.. planning on doing 195 stat but would like to replace pump and radiator if they seem to be an issue as well at same time. but don't want to fork out the money on them if not needed...

If you have holes in the rad. you could be letting air in, causing air pockets that the water can't push out

[6768chevylover]

well I bit the bullet and bought a nice new shiny radiator. well see if this solves my issue.
http://shop.championcooling.com/1967...Pickup-SKU-369 Anyone use this company. I had a friend buy one for a different type of vehicle but it looked nice and seems to be working for him..

[paul mora]

Check all you vent lines behind the dash to be sure they are not ripped or disconnected. Next check the cable system to be sure they fully open and close your duct system properly. If you are using a heat gun check the temperature at the inlet and outlet at the firewall in the engine bay to see if there is a temperature differential.