Intake manifold carb heater line - surprises

[Stanley]

Got some rubber caps to temporarily plug the pipes, pulled the short hose off the lower thermostat housing. Now, my coolant is new and green, but what came out was a few drops of brownish corrosion. The 1/2" hose barb was corroded. Pulled the other end of the hose off at the intake manifold. That hose barb was totally plugged with some grey-green gunk. Looks like no water flowed through there for a long time. I'm guessing the gunk is stop leak put in by the PO (flushed the engine three times when I got the car a few years ago, to get rid of the gunk) , plus coolant residue and rust.

Then I cut the short rubber hose that connects the rear of the intake manifold to the steel water tube that runs around the back of the motor. Plenty of corrosion there also, and some green coolant.

So where's the coolant come from that keeps dripping down on the exhaust manifold? For sure it's not coming from the thermostat housing (like the arrows in the FSM). So it's being pushed up into that deadhead tube from the other side of the engine somehow. Coolant's not supposed to flow that direction. A puzzler.

[Captain Obvious]

So where's the coolant come from that keeps dripping down on the exhaust manifold? For sure it's not coming from the thermostat housing (like the arrows in the FSM). So it's being pushed up into that deadhead tube from the other side of the engine somehow. Coolant's not supposed to flow that direction.

It's not deadheaded. It's got a hole out to atmosphere at the end, right? That's the whole reason it leaks!

With a small almost deadheaded leak like that, the "normal" flow direction doesn't really matter... Remember you've got both absolute and differential pressure in that system. Thermal expansion provides the absolute and the water pump provides the differential. Either one of those pressures is capable of forcing coolant out a leak hole. In your case, I suspect that the absolute is forcing water "backwards" up that tube and out the leak hole.

And BTW, I found lots of gunk in those tubes when I was messing with that stuff on my 74.

[Stanley]

Right. Also, since the tube is lower than the coolant level in the radiator, when the engine is shut off I guess the coolant just gurgles it's way up there, by the principle of water seeking it's own level.

Anyway, plugged the lower thermostat outlet with some caps from pep boys. The 1/2" cap fit it but looked flimsy so I put a 5/8" cap over it. Also capped the pipe that goes behind the motor. Have a hose and some BSPT stuff on order - at least it's not leaking and I can drive it for now. Also put a restrictor on the heater loop (a hose clamp with a piece cut from radiator hose to cushion it) that should cut down the recycled hot coolant by about half. Later I'll put the "real" restrictor - a washer.

Here's a few corrosion shots...