56 truck heater hose routing - overheating

[BS Stuff]

Trying to figure out why this truck gets hot and spits out before circulating / thermostat opens. Wondering if heater hose routing can make a difference?? Heater hose off manifold versus off water pump to special side of core ??? Drained block, all coolant flushed out and all hoses off / flushed. Was new engine and radiator 10 years ago but never put in or ran. Did not find hidden nests, etc.
56 Chevy Panel Truck
Targetmaster 350
Stock style 3 core radiator
Deluxe heater with new valve and recon core. Valve worked properly before installing.
195 Degree thermostat.
14" Electric fan with temp sensor kit - note - it kicked on fan right as spitting / puking started. Engine was ran long enough before capping so should have been no air in system.
Thanks !!

[1project2many]

Heater hoses should be connected to top of manifold and to water pump. Doing this creates a path from near the thermostat back to the water pump which allows hot water to enter the top front of the manifold where the 'stat is located Without that path, or with it blocked, the thermostat may not "see" enough hot water to open. Many of the old trucks like ours have a shutoff device to prevent water from circulating through the heater. If you drill a small hole, about 1/16", in the thermostat it will allow some coolant to circulate through the radiator even when the 'stat is closed regardless of flow through the heater. This will bring hot water to the sensing element of the 'stat.

I have seen a number of the Stant Superstats that act as you describe even with proper flow through the heater. I now opt for the regular Stant or more often, for another brand.

A question for you: Are you filling the radiator right to the top? If you are then you have no room in the system for coolant expansion. This will cause coolant to be pushed out the overflow line no matter how well the cooling system works. The radiator should be filled to about 1 1/2" below the filler neck. Fill to the top works if you have a recovery bottle and a cap designed for a recovery system.

[BS Stuff]

Originally Posted by 1project2many

Heater hoses should be connected to top of manifold and to water pump. Doing this creates a path from near the thermostat back to the water pump which allows hot water to enter the top front of the manifold where the 'stat is located Without that path, or with it blocked, the thermostat may not "see" enough hot water to open. Many of the old trucks like ours have a shutoff device to prevent water from circulating through the heater. If you drill a small hole, about 1/16", in the thermostat it will allow some coolant to circulate through the radiator even when the 'stat is closed regardless of flow through the heater. This will bring hot water to the sensing element of the 'stat.

I have seen a number of the Stant Superstats that act as you describe even with proper flow through the heater. I now opt for the regular Stant or more often, for another brand.

A question for you: Are you filling the radiator right to the top? If you are then you have no room in the system for coolant expansion. This will cause coolant to be pushed out the overflow line no matter how well the cooling system works. The radiator should be filled to about 1 1/2" below the filler neck. Fill to the top works is if you have a recovery bottle and a cap for a recovery system.

Actually thought about drilling the hole !! What about the sides of the heater core versus the block?? Was currently off pump to drivers side of core and off manifold to pass side of core.

[BS Stuff]

Originally Posted by BS Stuff

Actually thought about drilling the hole !! What about the sides of the heater core versus the block?? Was currently off pump to drivers side of core and off manifold to pass side of core.

Also - don't think I filled it to top - was below - but I am also building an overflow bottle anyways - just to catch small amounts. Thanks !!

[mr48chev]

Originally Posted by 1project2many

A question for you: Are you filling the radiator right to the top? If you are then you have no room in the system for coolant expansion. This will cause coolant to be pushed out the overflow line no matter how well the cooling system works. The radiator should be filled to about 1 1/2" below the filler neck. Fill to the top works if you have a recovery bottle and a cap designed for a recovery system.

Right there is the reason a lot of guys new to AD or TF trucks or Old vehicles in general have problems. On a stock style tank on top radiator you absolutely have to leave that expansion room/

Usually the heater hose off the manifold runs to the fitting on the heater core that goes in at the top and the one going to the water pump goes to the one exiting at the bottom. Same setup as the radiator, Hot in at the top cooler out at the bottom.

Drilling the small hole in the body of the thermostat is to let any trapped air bleed out before the thermostat opens so it isn't trapped there. Too big a hole lets a bit too much coolant get by and slows the thermostat opening down. No need to know why I know that but you can assume that----- and be pretty correct.

When I was towing a lot in warm/hot weather I would take an old thermostat and remove the guts and just put the washer/shell back. That slowed the coolant down to just above the point where a wide open thermostat would let it flow. Not worth much in cold weather because the engine never warms up enough to get heat out of the heater but great in hot weather.

[BS Stuff]

Thanks man !! Not new to old trucks - just have been away too long !! All the things you said make perfect sense - I just need to make sure heater hoses are on correct sides just to be extra safe. Will look at older heater core tomorrow to see which is actually feeding top of core - hard to tell outside the box. They are side by side - not up and down. Tjanks again man !!

[roger55]

It sounds to me like the bypass holes where the water pump mounts to the engine are blocked. You didn't happen to make your own gaskets for those and not put in the holes did you?

Another possibility:
Is this a Vortec engine? The L31 truck small block is a Vortec.
If so, those need another bypass because they don't have the built in as all the older small blocks do. Vortecs use a bypass hose just like all big blocks do.

Not having a bypass would cause an issue just like you describe.

[1project2many]

You have the connections reversed according to the factory instructions but I wouldn't expect that to make a difference. If you wanted to check that the core is the problem you could bypass it completely.

Instructions for the deluxe heater insallation are here and the recirculating heater is here.

[BS Stuff]

Thanks !! Was trying to find picture of 55 - 59 routing where both inlet and outlet appear to be at same level. Also fools you a little that the cable pushed in actually opens the valve too !! Thanks again !!

[_Ogre]

i run my 58 truk just 1/2'' over the core, almost 2'' below the neck
the level self regulates if i overfill the radiator, i think your overfilling the radiator

[BS Stuff]

Most likely !! And thanks for the tips !! I also swapped the heater hoses around to make sure going in correct side. Should have all set tomorrow or Wednesday.
Thanks again !!
Bob

[mr48chev]

Ogre is one of our half dozen TF gurus on here. What he suggested is just where I ran the coolant level on my old 57 Panel with the 327 and do on my 48. You can play with the level some but these trucks really do like to have expansion room in the expansion tank.

[BS Stuff]

Thank you to everyone that gave advice on this. Ran for quite and fan kicked on, etc but no signs of issues. Next week it may take voyage down road so we will see !!! Thanks again !!!