Spittin' Coolant...

[rusty ol ranger]

This issue is driving me insane.

77 F250 400/C6

About the time the t stat pops open, it will blow coolant all over the front of the engine.

But it only does it sometimes, and only till it gets just low enough on coolant it wants to heat up when it idles.

I have replaced the following..
Tstat/gasket
Water pump
Fan clutch
Radiator (3 years old)
Top hose

Its been doing it for a while now. Seems to do it worse in cold weather. I have pressure tested the cooling system, it kept a steady 13lbs (what its rated for), as did the cap.

It dont have a overflow tank, just a vent hose, but after these events its always bone dry.

Any ideas?

 

[RonD]

You have the "original" degas system,

You don't fill radiator to the top, you leave about 2" of air inside.

As coolant warms up it expands into that 2" gap and pressure goes up to, in your case, 13psi any pressure over that should expel air and maybe some coolant if it was over filled, but that should only happen one time, and as long as you don't add more coolant it shouldn't happen again.

Overflow tank system allows coolant to expand into over flow tank and then it is sucked back in to radiator as engine cools down, so this system wouldn't have/need the air gap in radiator for coolant expansion.

Pressure test should have shown any leaks and blown head gasket or cracked head

But from description it reads like you are either getting a hot spot in a head or have a head gasket issue
If you still have the pressure tester install it and pump it up to 13psi
Then disconnect coil wire on distributor, you want a No Start
Crank engine over while watching the pressure gauge
Pressure should stay steady, no up and down movement
If needle bounces then you have a cylinder leaking into cooling system
You can do same test with a Latex glove, Search for Glove Test

Hot spot in engine is hard to fix, usually a restricted passage.
Hot coolant flashes to steam at the hot spot, this increases pressure in the system above the 13psi and since coolant is already expanded it is at the top of radiator so cap opens and blows out coolant.
Flash to steam also creates "air" vapor which is now in the head so less cooling and engine starts to overheat over all.

 

[85_Ranger4x4]

Dad's '80 400 would do that once every two years or so. It would freak out whoever was driving it but nothing ever seemed to be wrong with it aside from that. No bubbles in cooling system and no coolant in oil... just coolant all over everything. Not consistent when it did it... just whenever the mood struck it.

 

[alwaysFlOoReD]

I'll second RonD in that the rad needs to have the fluid down about 1.5-2 inches from the cap.

 

[rusty ol ranger]

All good suggestions guys.

85, yeah, thats exactly what mine does, no real rhyme or reason, just, whenever it feels like it.

Ron, ill do that test though, because it does seem to use some coolant. I have a feeling though it might be the intake gasket because i have a helluva time getting any kind of consistant smooth idle. But i know its not spurting from the intake. Oil is not milky.

Hopefully once i get rusty 2.0 rollin i can put the old 77 up for some much needed freshning. I hate driving my 97 and racking up mileage on it.