350 won't heat up

[Huskers]

Hello everyone. My son was recently given an 78 with a 350. This has been a project pickup for us. After sitting in the weeds for 2-3 years, we finally got it running. I'm running across a little problem that I can't figure out though. The engine doesn't seem to heat up. We changed the thermostat and cap so I know that's good and both Heater hoses are hot and it blows hot air so the core ain't plugged. The upper hose gets hot but not hard and the lower hose is rather cold actually. 

 

My three thoughts were fan clutch, plugged radiator and bad water pump.

 

I now don't think it's the fan clutch because it should get up to temp idling even if the clutch was bad.

 

Plugged radiator would make sense except that I would think the engine would over heat if it were actually plugged. 

 

Lastly the water pump. I can't see any movement in the tank as it idles after the thermostat opens up and this might also explain why the upper hose is hot but not the lower?  I would also think that a bad water pump would cause it to over heat.

 

Any thoughts?

[txab]

Maybe temp sending unit is bad or dash gauge is bad..... if that is what you're going by. Fan clutch could be over-cooling. Lower radiator hose should be cold, much cooler than upper. Your heater hoses should leave the intake manifold, go to the core, then return to radiator tank on the passenger side. You should see water movement with the cap off from that alone. Have you driven it at all to try to increase the heat. Those model trucks had big radiators on them and generally supplied plenty of cooling capacity

[Huskers]

Gauge and sender work. Drove it for 30 min, no pressure in radiator and the coolant was only lukewarm.

 

Even with a bad fan clutch, it should warm up at idle.

 

I've drove this thing all over trying to get it hot.

[diyer2]

Thermostat stuck open?

Remove it and check it in a pan of boiling water.

Put in a new one?

:)

 

[txab]

2 hours ago, Huskers said:

Gauge and sender work. Drove it for 30 min, no pressure in radiator and the coolant was only lukewarm.

 

Even with a bad fan clutch, it should warm up at idle.

 

I've drove this thing all over trying to get it hot.

Again, if fan clutch is staying locked up too much of the time (pulling too much air), then you can over cool.

 

I'd double check the operation of thermostat. 195* was the OE temp 'stat. Make sure you have the correct cap for the radiator. By this time the radiator you have is not the original one to the truck. they don't last 42 years. If it has more rows of tubes than OE then it will have extra cooling capacity

 

My 80 model won't get hot idling under the current ambient temps in the morning, nor will it build pressure to the point of the hoses being hard.  If I get on the road it heats up as it should.