Heater Hose Tube on Radiator

[jec]

Getting ready to install new heater hoses on my Longhorn 402 big-block. Truck has no A/C correct factory heater box on firewall with 3/4" core tube on top and 5/8" core tube on bottom.

I have the normal 5/8" fitting on top of engine manifold near thermostat housing. This supplies hot water into the bottom of heater core.

I have the normal 3/4" fitting for a return from the top of the heater core to the side of the water pump.

Any ideas why my radiator has 3/4" Male Heater Hose Tube about an inch below filler neck pointing straight out toward engine?

Maybe it's for an auxiliary heater return or something?? I can't think of any purpose for it. Maybe somebody knows or has seen it on other trucks.

[Stocker]

IIRC, the preferred routing for the 3/4" return hose is to the port on the radiator -- not to the water pump.

[7dee2]

Take a look at this thread http://67-72chevytrucks.com/vboard/s...d.php?t=188679

Here is another pic from the 1972 Chevrolet Truck Chassis Service Manual 10 to 30 (1A-3). I have the same HD Rad in one of my C30's it's non-A/C with Turbo 400. Hope that helps.

[jec]

O.K., thanks alot.

Found the pictures in my Factory Service Manual Section 1A.

I'm going with the 3/4" return to the radiator.

[7dee2]

No problem, I have not had any issues running my truck this way.

[FirstOwner69]

Just to clarify the hose routing...

Based on my observations, the earlier model year trucks had the 5/8" hose from the heater core to the intake and the 3/4" hose to the side of the water pump. There was no 3/4" fitting on the radiator. I'm not sure when the change actually occurred. My 69 with a 350, A/C and 4 row radiator is routed this way. All, or most, of the later year trucks (71/72?) I've seen had the 3/4" hose to the radiator.

[davepl]

I've been working on GM cars and trucks for along time and I've NEVER seen a heater hose go directly to the radiator. I almost looked to see if it was April 1.

You learn something every day. Why only with automatic trans?

It looks like hot water comes out of the engine, goes to the heater core, and dumps back into the radiator. I would think this would really slow down engine warmup...

[LSUMurse]

Originally Posted by davepl

I've been working on GM cars and trucks for along time and I've NEVER seen a heater hose go directly to the radiator. I almost looked to see if it was April 1.

You learn something every day. Why only with automatic trans?

It looks like hot water comes out of the engine, goes to the heater core, and dumps back into the radiator. I would think this would really slow down engine warmup...

Wouldn't it only slow down warm up if you had the heater on? If the heater is not actively pulling heat from the core, there would be only a slight amount of heat escape from the hoses, etc. OOOOOORRRR, I could be completely wrong. Which, tends to happen more so than the other option.

[Stocker]

Originally Posted by davepl

I've been working on GM cars and trucks for along time and I've NEVER seen a heater hose go directly to the radiator.

All I know is I bought my '72 K20 (with factory A/C) when it was just 5 years old and by all appearances, it was 100% original at the time. The heater return hose went to the radiator. Still does, though the radiator has been replaced once (and the heater hose more than once).

[kaycee]

OK got a ? for you all ,it seems to me that it would cool down the system better if it went to the radiator.Is there any logic to this ,I have a/c cab(someday I'll hook it all up) but man does it get heat from the heater core.Even when I just try and get outside vent air

[Andy4639]

Here is the heater hoses in the factory manual for AC.

I agree if the hose on the water pump pumps water through the heater core and dumps straight back to the radiator it would take longer to heat up the truck to correct temp. The hot engine water going through the heater want cool it down much and dumping back straight to the radiator will not let the engine water temp get hot very quickly because it's cooling off with out building heat up in the system.
How long does it take for the truck heater to warm up the truck on cold days? That would be the test to perform and see if there is enough differance in the heat to change it.

[Legolas894]

This is the same issue I'm having so instead of posting another thread, I'll just add on. I had the 3/4" line on the rad capped with a rubber end cap and hose clamp. My setup was 5/8" line from intake to bottom of heater core, 3/4" line from top of heater core to fitting on water pump.

Yesterday, my rubber rad cap failed, spewing coolant in the parking lot so I started to look to see if I could fix this setup. What do people think about capping off the water pump inlet and letting the heater core go to the rad fitting? The 3/4" hose fitting on the water pump doesn't look like it will come off easy so putting the plug on it may mean taking the water pump off.

Is there any advantage having the heater return to the rad instead of the pump?

I have a 283 with no A/C and manual trans.

Thanks!

[Fitz]

Originally Posted by Andy4639

Here is the heater hoses in the factory manual for AC.

I agree if the hose on the water pump pumps water through the heater core and dumps straight back to the radiator it would take longer to heat up the truck to correct temp. The hot engine water going through the heater want cool it down much and dumping back straight to the radiator will not let the engine water temp get hot very quickly because it's cooling off with out building heat up in the system.
How long does it take for the truck heater to warm up the truck on cold days? That would be the test to perform and see if there is enough differance in the heat to change it.

Unless you live in a place that can get really hot in the summer you can not appreciate the wisdom of routing your heater this way. When you are pulling a load up a steep grade on a 115 degree day in the desert and the engine temp is climbing fast you will appreciate that heater return to the rad. Turning your heater on when it's really hot outside might not seem to be a good idea but if it prevents a boilover 100 miles from the nearest water you will be glad that the engineers at the General did it this way.

[davepl]

I wasn't thinking of heat loss through the heater core as much as the fact that it would be continually cycling its warm coolant through the core and back out to the rad rather than keeping it in the engine. So I see it as not having a thermostat but with a smaller rad hose, in a way.

A "normal" configuration would send it through the heater core and back to the engine for further warming (or re-warming). Once the thermostat is open and all the coolant is at operating temp, shouldn't make a diff.

[davepl]

The LMC rad I bought for my '70 had this port. The factory one didn't so its another case of a 'halfway universal' reproduction part.

Mine leaked badly. I wound up having to pull the rad out, put a metal plug in, and solder it up.