Help with my heater...... PLEASE!

[Fourtrax]

Can anybody tell me the correct routing for my heater hoses. I know one goes to the intake manifold but Im not sure if the other goes to the radiator or the water pump. The truck heats up ok when driving but as soon as I get to a stop light it starts to blow cooler air.

[Paul72]

I assume you're talking about the hoses to the heater core.

My upper hose goes to the water pump and the lower to the intake.

[Fourtrax]

Yes sir I am, I ran the 3/4 hose to the top of the radiator. So your saying I should go to the top of water pump? Will this allow the heater to blow hot air at an idol? By the way thank you for the response.

[LeftCoast32]

Here is a picture of the proper routing of the hoses to your heater core. Mine was hooked up this way from the factory, I even researched it in the factory assembly manual because I had never set one up like this before. The larger hose goes to the radiator and the smaller hose goes to the water pump. It works like a champ.

[Paul72]

That's interersting..... I don't have a spot on my radiator for the heater hoses. My water pump has 2 outlets and the intake has one inlet. This also was the factory set-up.

I guess GM wasn't consistent on this either....

[da-burb]

If your heater core is installed corectly, it will have the 5/8 line at the bottom and the 3/4 at the top. The 5/8" line will come from your intake manifold. The 3/4" line will go to either your radiator or to a nipple on the water pump.

I had this problem on a winter beater of mine. I never did figure out what it was. I would freeze the moment the truck came to a stop at idle. I would slip it into neutral and run the rpm's up to 2000 and I would get heat.

My best guess was a bad impeller in the water pump. It wasn't making enough flow to push the water to the heater core. I haven't had to fix the problem because I parked the truck. It developed what I think is a bad head gasket, which may or may not be connected to the heat problem. If you figure it out please report back!

[da-burb]

FYI, trucks with automatics usually had the heater hose return built into the radiator. Many replacement radiators do not have the return line so you route it to the water pump instead.

[Fourtrax]

Da burb, That is exactly what mine is diong! Which way is correct?

72blazer, Im not sure if I have a factory air or not because the truck is a 72 and the water pump that aligns correctly with ac pullies is a 70. The outlet on top of my water pump is 3/4 and the one on the lower left off pump is 5/8. Any more suggestions?

[LeftCoast32]

I dont have the assembly manual here, it and the Blazer are in storage. I remember looking it up because I had never had the hoses hook up like this before. Mine has the 3/4 in the radiator and the 5/8 on the water pump. Mine is an automatic and factory A/C, I hope this helps and doesnt confuse you more.

[LeftCoast32]

You will also notice that my alternator is on the passenger side. I am in the process of converting it to the longer style water pump. At the time it was the only alternator mount I could find in a hurry to start it and get it in my storage.

[BobbyK]

If the truck has A/C,one goes to the rad. the other to the water pump.(3/4" hose to the rad.)

No A/C and both go to the pump.

[MJN]

Manual transmission trucks had the hose going to the water pump on the side not the top, but automatic transmission trucks went to the radiator. In the factory shop manuals it shows the routing for each transmission. 5/8" from the intake to the heater and the 3/4" from the heater to either pump or radiator.

[da-burb]

Mine has the 3/4 in the radiator and the 5/8 on the water pump.

1972Blazer, this would not be the most efficient way to supply hot water to the heatercore. The waterpump's job is to pull cooler water from the radiator and pump it through the engine. What you are doing is taking some of that cooler water and using it to supply your heatercore. That would be the slowest way posible to warm up the interior of a truck. I have never seen the hot line(5/8) come from anywhere other than the intake manifold. On Chevy's it has been nearest the thermostat. Your intake probably has a plug screwed in next to the thermostat. That is where your heater hose should go.

[LeftCoast32]

I know which plug you are refering to, It was hooked up this way on my old motor so that is the way I built it on this new one. I am in California and never use my heater. I do believe your assumption on the hotter water at the intake due to the fact that it is the last place in the engine prior to being feed back in the radiator. Thanks!