overheating....but no heat?

[als70chevy4x4]

My 3/4 Ton has a problem i havent seen on here yet.When I bought it the heater core leaked and didnt throw barely any heat when fully warmed up.I changed it out and still no heat.Then thinking the rad wasnt up to snuff (green color around the sides) grabbed a rebuilt one out of my parts truck(2 core instead of 3)same problem.When I've got my camper on or a load of wood climbing hills I can watch the temp rise steadily.Talking with some different mechanics they have mentioned air lock???I've flushed the system twice and still no luck.Anyone out there had this problem and corrected it?Help!

[dubie]

mabe you have a bum thermostat and it could be stuck open??

[jmanz69]

You have an air lock. It needs to be vacuum pumped to get the bubble out. It won't come out with just flushing it. It's probably in the block or heads. You could pull the plugs in the sides of the block and pull the temp fitting out of both heads and see if that will release it. A radiator shop will be able to get it out for you for a few bucks. Time to dust off the wallet maybe... I hate having to pay for services, but it's necessary at times.

[da-burb]

Have your anti-freeze checked for hydrocarbons. This could be caused by a cracked head or a bad head gasket.

[Longhorn Man]

Is the cable completely moving the door in the heater box?

[flip66]

Does it have a heater control valve if so did you check it? I had a car that would run hot and I changed the 2 core to 3 core and solved the problem. If it had a 3 core I would put that back in it especially if you are pulling a load.

[als70chevy4x4]

dubie..... forgot to mention swapped in 2 different thermostats Longhorn man......yes the cable moves the door completely closed and open.jmanz69......I'm pretty sure you hit the nail on the head,I was just hoping I could tackle it myself.Anyone out there get this done?cost?

[Longhorn Man]

Is this an A/C truck?

[crazy longhorn]

My vote would be airlock also.....altho, i have not seen that be a big issue on the trucks. Pull the rad cap when the eng is cold, & leave it off for the first 20 minutes of running time(or till the stat opens up)....then top the rad off....end of that problem on the newer cars that mount the rad well below the heads (due to slope nose), that is a very big issue with air lock. on my 69, when the stat is out, i fill the block through the intake, then stick the stat in , & top the rad....run till the stat opens, then top her off again. That seems to work fine....save your cash crazyL

[als70chevy4x4]

Longhorn Man.....no its not a/c.Crazy Longhorn....it's worth a shot,I've tried just about everything it justs seems too simple....so I'm hoping it works because in my experience simple usually works lol

[Russell]

I drilled a small hole in the t-stat so air could get out of it, just kept adding coolant until the coolant level stopped going down.

[67_SS396]

I had a similar problem with my '67. Make sure nothing sits higher than your radiator cap, ie; the upper hose or thermostat housing. If the upper hose sits higher than the cap, that's where the air pocket could be. The '67 had/has that problem because I used a later set of engine mounts and it set the engine up just a tad higher than the radiator cap, therefore there was an air pocket in the upper hose causing the engine to run hotter than it should. Just a thought anyways.

[gonebad2]

Sounds like a stupid question.....But.....Here goes, How are your heater hoses plumbed? One out of the upper right hand side of the intake manifold (5/8") and one out of the waterpump (3/4") ?

[jlmtrout]

The heater core is just a small radiator. Hot water goes in one side, a fan blows across the core and the water goes out the other side as it passes through the core. Doesn't matter about the routing. That has been my experience with the old 250 w/and w/out the a/c. Just a matter of hot water going in the top, or in the bottom(reverse flow through the core). Good luck and keep on truckin'.................Jerry

[mrein3]

EVERY time I do something to an engine where I have to remove the coolant I "burp the radiator" when I'm done.

Start the cold engine with the radiator cap off and a catch pan underneath it if you don't want to clean up a mess. The coolant will slowly rise in the radiator. After a while, when the t-stat opens up, the level will drop and you'll notice coolant flowing in the radiator. Keep adding 50/50 until it is topped off. Remember when you pour cold coolant/water in the radiator it will close the t-stat and stop the flow. It will then take a couple of minutes to warm up and open the t-stat again.

The process will take about 20-30 minutes.

When you can't add any more put the cap on and you're done.