Cooling help

[TheGriz]

Ok... perhaps someone can help me figure this out.
The SBC 350 I just put in my buggy wants to overheat. The temp gauge pegs to 250 after 3 or 4 minutes of idling.
I'll post all of the details since this is my first chevy engine build, and there's no detail silly enough that I could have screwed up.
1. The water pump I purchased was intended for a 1995 k1500 5.7L (This is supposed to be a reverse rotation pump)
2. Originally, I had the heater hose coming from the water pump, going into outlet of the heater core. That has since been changed to the setup in the diagram below.
3. The radiator is cool, so I was thinking that either my water pump is turning backward, or the thermostat isn't opening.
Any thoughts?

 

[Black Bear]

there is #4

someone shat in your radiator.

 

[TheGriz]

nice...

I replaced the t-stat, and no better.

Because this overheats so quickly, I'm wondering if it could be a faulty sending unit.

Anyone know how best to verify temperature?

 

[Caver Dave]

1. The water pump I purchased was intended for a 1995 k1500 5.7L (This is supposed to be a reverse rotation pump)

IMO, you should have visually verified the vanes on the WP to insure they were oriented correctly for your rotation... before leaving the parts house! High probability the counter monkeys couldn't correctly find their own @$$ with a map & neon sign!

Also, you might want to eliminate the possibility of air bubbles/blockage in the cooling system. Didn't think SBC are known for that, but... I agree that 4 minutes of idling (even with with the advance pegged) shouldn't get you that kind of heat!

anyone know how best to verify temperature?

Handheld IR temp "gun" is the fastest. It will also show you hot/cool spots in the radiator & on the block to pinpoint the issue...

 

[BoilerTech]

Try squeezing the upper hose while the engine is running. If it doesn't surge full when you let off either the pump is not pumping or the thermostat is not opening. If it does then try a mechanical thermometer in the line to double check your gauge.

 

[houdini]

try purging all of the air out of hte motor wiht the front of the truck lifted up in the air. should help move that air out of the block up to the radiator.