Rebuilt 400 SBC Overheating Issue

[72k20Farmtruck]

I just rebuilt the 400 in my 77 C10. Here’s the specs: Bored .060 over, stock bottom end bearings, trick flow 195 aluminum heads with 3 out of the 6 steam holes drilled, comp 292 cam with .501” lift, I verfied headgaskets are indeed correct. Ran the motor today and it kept overheating. We tried two different t-stats, a 195° and a 180°, still overheating, then ran without the t stat, overheated again. Checked the oil no water in the oil, no oil in the water either. What else could it be? My dad thinks the parts guys gave me the wrong water pump, maybe i have a pump for a serpentine setup and it’s pumping backwards. I don’t know what else to think and I’m pulling my hair out trying to figure it out. It’s the second motor I’ve built, first one without any guidance so if anyone can think of something that i may have overlooked during assembly please chime in. Thanks!!

[jkk]

Try purging the air out of the system that will make a big difference

[Dead Parrot]

What is your sign it is overheating? 41 year old gauges with aftermarket senders rarely read correctly. Double check temps with a laser temp reader.

Run it without the radiator cap in place and check your water flow. Without a t-stat, should get lots of flow. Easier to see if the radiator is a couple of inches below full. If your heater return hose empties into the radiator, it should have good flow as well even with a closed t-stat. No or weak flow, your dad might be right or it could be a correct but bad pump.

[Mattchu60]

Is the internal bypass blocked? I used the wrong head gasket on my SBC build - didnt have the hole for the internal bypass - and it would overheat on startup until the T-stat fully opened. I fixed it by putting an external bypass in between the intake and water pump.

Gauge would go to like 240ish and then finally fall back to 190 or every time I ran it.

[geezer#99]

Originally Posted by 72k20Farmtruck

I just rebuilt the 400 in my 77 C10. Here’s the specs: Bored .060 over, stock bottom end bearings, trick flow 195 aluminum heads with 3 out of the 6 steam holes drilled, comp 292 cam with .501” lift, I verfied headgaskets are indeed correct. Ran the motor today and it kept overheating. We tried two different t-stats, a 195° and a 180°, still overheating, then ran without the t stat, overheated again. Checked the oil no water in the oil, no oil in the water either. What else could it be? My dad thinks the parts guys gave me the wrong water pump, maybe i have a pump for a serpentine setup and it’s pumping backwards. I don’t know what else to think and I’m pulling my hair out trying to figure it out. It’s the second motor I’ve built, first one without any guidance so if anyone can think of something that i may have overlooked during assembly please chime in. Thanks!!

Why only 3 of the six holes?
Retarded timing builds heat too.
What’s your timing curve like?

[72k20Farmtruck]

We haven’t set timing yet, just got it to the point where it would run, acts like it’s advanced. Basically my sign of overheating is coolant blowing out of my radiator all over the shop floor haha. And on the trick flow heads, the steam holes are pre-drilled only on the intake side i believe because that’s the way those heads were designed with a return to the water jacket.

[72k20Farmtruck]

Originally Posted by Mattchu60

Is the internal bypass blocked? I used the wrong head gasket on my SBC build - didnt have the hole for the internal bypass - and it would overheat on startup until the T-stat fully opened. I fixed it by putting an external bypass in between the intake and water pump.

Gauge would go to like 240ish and then finally fall back to 190 or every time I ran it.

Never heard of an internal bypass! What does that look like? I ran without the stat however and it still overheated so i don’t think this is the case but I am interested in what the bypass might be.

[Mattchu60]

internal water pump bypass in the block. If you took the T-Stat out and still have the problem then I would say that is not your issue.

[geezer#99]

The holes you drilled, where they on the intake or exhaust side of the head?

[72k20Farmtruck]

Originally Posted by geezer#99

The holes you drilled, where they on the intake or exhaust side of the head?

I didn’t drill them, they came pre-drilled from the trick flow factory. Pretty sure they are on the intake side.

[72k20Farmtruck]

Ok i just looked up a picture of them, they are actually on the exhaust side.

[geezer#99]

Originally Posted by 72k20Farmtruck

I didn’t drill them, they came pre-drilled from the trick flow factory. Pretty sure they are on the intake side.

But where they the right size!

They need to be 9/64 th’s.

[72k20Farmtruck]

Originally Posted by geezer#99

But where they the right size!

They need to be 9/64 th’s.

Most likely haha. They’re little dudes.

[geezer#99]

Likely your problem then.
Do you have the heater hoses hooked up so you have water flow from the intakeback to the water pump or rad?

[kwmech]

I'd be more concerned about the 60 over bore an a 400 block. Did they sonic test? Out of the 1/2 dozen 400s I've built, I always had an issue with a 60 over block. If I have a factory block... standard bore.. I always try to go 20 over the first time around.

[72k20Farmtruck]

Originally Posted by geezer#99

Likely your problem then.
Do you have the heater hoses hooked up so you have water flow from the intakeback to the water pump or rad?

Heater hoses go from intake to radiator

[72k20Farmtruck]

Originally Posted by kwmech

I'd be more concerned about the 60 over bore an a 400 block. Did they sonic test? Out of the 1/2 dozen 400s I've built, I always had an issue with a 60 over block. If I have a factory block... standard bore.. I always try to go 20 over the first time around.

Yeah my machinist told me I had plenty of meat left on the block to go 60 over, he checked it. The block was already bored 30 over. All of the early 400’s, from what I’ve heard, had more to work with, some people even bore them 80 over. This block came out of an early 70’s caprice.

[truckin 79]

Like someone else mentioned, did you burp the coolant system? You probably have air in the system

[72k20Farmtruck]

Originally Posted by truckin 79

Like someone else mentioned, did you burp the coolant system? You probably have air in the system

Yeah i filled it directly through the thermostat port.

[cadillac_al]

No temp gauge?

[72k20Farmtruck]

Originally Posted by cadillac_al

No temp gauge?

I do have a temp gauge

[72k20Farmtruck]

UPDATE:

Ran the truck today, no water flow at all at idle. Going to change out the pump tomorrow. Thanks for all the input, I’ll post the results tomorrow.

[72k20Farmtruck]

Changed the pump and it all works perfectly now. What a relief!! Thanks again everybody! Hopefully someone in the future can use this thread for help.