**cooling system issue**
 

So I have a 1966 C10 that I've been restoring for a little while. Winter hit and I had to stop but now I'm back at it.

I finally got the 4.1 250 back together after blowing a head gasket. I replaced all gaskets and seals along the way. Also got a new upgrade to an electric choke from the factory manual choke.

It turned over, let it idle some to see how it would run then turned it off. Today, I filled the antifreeze to in the radiator normal height, replaced some rubber hoses and fuel line that attach to the new carb. New PCV valve line as well.

The truck wouldn't turn over so I went to check that I didn't unhook something. The radiator was bubbling and overflowing down the overflow tube. I knew it would explode if I took the cap off.

What could make this truck cooling system build up so much pressure in the radiator? It never started (battery needs jumped again). Just turned the engine about 15 seconds but no attempt to start up. Also, I'm replacing the heater core in a few days when that part comes in.

Re: **cooling system issue**
 

I've replaced thermostat, thermostat sensor, radiator is an aftermarket large 3 row radiator, new radiator hoses. Heater hoses and heater core are this week.

New head gasket, seated valves and timed engine to the best of my ability until I can get it tuned the right way when it's ready. Trying to finish the valve work but need the truck to run safely before I can keep going.

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Pressure only comes from the combustion chamber.
Cracked head, cracked block or bad head gasket.

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And I just replaced that and all the other gaskets -__-:waah:

The coolant bubbles. I can feel and hear it in the radiator hoses. Even minutes later I can still feel and hear it until I open the radiator cap.

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"Exhaust gasses getting into the coolant, possibly due to a leaking head gasket."

I found this. So my new head gasket isn't sealing or broke..?

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Or the head is warped.
Did you put a straight edge on the head to check for flatness?

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Yep. Everything looked great. Torqued everything down to spec so this wouldn't happen. Any chance it just has air in the system? I never ran the radiator even though it's been installed for a year.

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It might just need burping but what you describe is a lot of air.

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The heater core is now leaking out of the box. Maybe it's getting stopped there and can't circulate?

Or maybe a clogged line somewhere? I'm in denial of the broken head gasket lol.

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I thought de Nial was a river in North Africa! Lol!
You could pressure check each cylinder with a little pumped air. Make an adaptor from an old spark plug, hook a small compressor to it, put the cylinder at tdc and listen/watch for air or bubbles in the rad.

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I'll have to do that. Going to check the plugs for antifreeze. I hope it's just something I missed and not the head. I'll probably just save and upgrade to a 350 or something.

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You could bypass the heater to eliminate that. Sometimes they trap air and are hard to burp. May narrow down the problem.

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If the engine didn't start up and run, there were NOT any exhaust gasses.

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If the engine never started, the coolant never got hot (so no boiling, no thermal expansion) and no exhaust gasses to leak into the coolant even if you did have a defective head gasket. It would therefore be impossible to have pressure in your radiator. Any bubbling and overflowing would just be air pockets working their way to the highest point of the system.

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I'm wondering if your radiator is plugged with a wasp's nest or something. IF your engine never fired, the only way to build pressure in the system is if the water pump is pumping (when you were turning the engine over with the starter) but the radiator is plugged tight.

I'd check the heater core and radiator both for being plugged.

But I'm trying to think this through - when the engine is cool and the thermostat is closed, coolant circulates without ever going through the radiator - I just can't imagine how you are building pressure if the engine doesn't fire.

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If you’ve got a path for the unburned air/fuel to flow into when both valves are closed then that air/fuel will pressure up the coolant system.
If you keep cranking it over trying to start it you’ll get some air/fuel in the coolant passages and the majority will exit when the exhaust valve opens.
It’ll only be a small amount at each revolution but it’ll definetly flow there. Cranking compression could be 150 psi exiting into a near zero pressure.
Air is just like electricity. It will follow the path of least resistance.
Do you catch my drift on this.

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agree with geezer, do a cylinder leak down and compression test on all cylinders and report back

otherwise you're just chasing your tail

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For the guys saying if the engine never fired, there's no exhaust gases so it couldn't get into the coolant system through a crack, etc. etc.
No, but there IS compression in the cylinders, and if there's a cracked or warped head, or blown head gasket, that compression wold absolutely still get into the coolant passages, exhaust gas or no.

Check your oil and see if there's any coolant in it.
Quicker than a compression test, do a leak-down test. This pressurizes the coolant system, and it'll tell you if there's any coolant going into the cylinders (which is the problem you have, but the other direction)

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Leak down test is to determine leakage inside the combustion chamber and not used to pressurize the coolant system.
Two different systems. Two different tests.

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UPDATE**

So I got the truck running again and starts right away. FINALLY

Now... it still smokes like a freight train. I'm hoping maybe it's just burning off oil and everything from when the engine blew but I have a feeling something else has happened.

Stupid question but I'm asking anyway.... the intake manifold gasket has a small leak around the 2 and 3 piston. Would this cause the smoking? I don't think I tightened down the manifold bolts enough because I was afraid of doing too much to start. Going to run a compression test on the pistons this weekend and try to fix the manifold in hopes this is the cause and not something worse.

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A leak between the intake manifold and cylinder head will definitely cause heavy smoke. Oil is sucked into the combustion chambers.

Re: **cooling system issue**
 

Not on the six banger he has.

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What color is the smoke?
Light gray/white is coolant, blue and black is oil.

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It's antifreeze color. White/ grey like it was when the gasket was blown. The intake/exhaust gasket wouldn't cause that with the leak it has?

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If it is running smoothly and not overheating, it just may be coolant in the exhaust. Run it until it clears up. That may take awhile. I had it happen on a car of mine and I drove it about 30 miles before the water vapor calmed down.

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I might try to do that and see what happens. Just afraid something is wrong and running it like that hurting it worse. I'll check compression tomorrow and see what that says. If ys all good I might just run it for a while

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Smart move!

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I found that compression should be about 150psi in a 250 chevy.

Mine is: 130/120/150/120/120/120

I did see antifreeze on the 1st and 2nd plugs and unfortunately a little discoloration on the oil dipstick. I'm not sure why there is such a variation in the compression PSI if it's all suppose to be 150 like I've read.

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Could bad timing or setting the valves cause the compression to be off? I'm doing as much as I can on my own but starting to look like I need someone to take a look and diagnose this thing before I waste time on a warped head or something unfixable.

Timing and setting the valves are the only other things that I'm not 100% I've done right. Or maybe not close enough to perfect to make everything relatively smooth for now.

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I just found another forum saying that the compression should about 130 from the manual. So why is the 3rd piston at 150? clog? valves too tight and can't escape the cylinder? just bad timing?

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Could be carbon buildup. Your compression numbers aren't the greatest, but about what I'd expect to see in an old engine. I'd expect to see something like 150 psi on a new/rebuilt engine. It looks like at least the head is going to have to come off for either a gasket replacement or possibly a valve job, plus draining the contaminated oil.

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well... I've had the truck 2 years and hasn't seen the road for more than about 30 minutes. I'll look into getting a new gasket and probably intake while i'm at it. Valves are terrible to set. Not sure I've even done that right yet. I'll drop the oil out this weekend and start the gasket replacement all over again.

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Did you bring the head to a machine shop to have it checked?
If you pull it back off, you should have it checked before you re-install it.

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My dad is an engineer with all that stuff. Said the head checked out. Maybe the block has some issues. Torqued the head bolts to specific but maybe I missed something? Hard to believe it's broke before running it.