Odd radiator/expansion tank issue

[89GMCK5]

Okay, over the past several weeks I had noticed that after I shut it down there was some gurgling at the expansion tank. Small air bubbles. After some searching I noticed the nipple from the radiator fill neck for the hose to the expansion tank was cracked completely all the way around. Replaced the radiator, thermostat, hoses, and new hose to the expansion tank.

Also, when this was happening, coolant wasin't flowing into the expansion tank as it should. The hoses would just gain more pressure, get harder and harder, and the coolant level in the expansion tank would stay about the cold fill line level. Once I found the crack at the expansion tank nipple, that was acting as a pressure relief, and not causing the cap spring to compress and send coolant over to the expansion tank.

After replacing the radiator, hoses, thermostat, and small hose over to the expansion tank, and burping the system I fired it up.

Sitting at idle in the drive way, coolant flows as it should over to the expansion tank. Good to go?????

Not so. If I drive off after the temp gauge needle just starts to move (normal), the coolant doesn't seem to be pushing over to the expansion tank. I drove about 15 - 20 miles, stopped to check it out, and the expansion tank level is just about at the cold fill line, hoses very hard.

The cap I have is one of the safety vent style, when I relieve the pressure it pushes into the expansion tank pretty forcefully.

Temps running as normal, no overheating, 190-200 degrees, I can feel the thermostat cycling as the temp fluctuates in the drive way. No smoke, no water/coolant in oil, no leaks, not loosing coolant, it's just not expanding into the expansion tank.

Bad cap? That would be my first guess, cheap too, but same symptoms I had previously.

Think I should drop to a 14lb or 12 lb cap? Any other ideas?

P.S.> I did a search and the gurggling seemed to get the consensus that it is fairly normal.

Thanks guys.

 

[4xcrazy]

You can FEEL the thermostat cycling as the temp changes?

wow.. very sensitive sense of touch there..

especially since they are a slow moving valve.

 

[British Slave]

I don't think you have any issues, it sounds like it's operating normal.

 

[K85 Octane]

drive it and keep an eye on it. Sounds fine to me. If the radiator cap is old, replace it, otherwise keep on thumpin'. I wouldn't change cap strength either, 16lb is what it's supposed to be, if that doesn't work, something else is wrong.

 

[hillbilly deluxe]

My rad/cap are both new-ish. I put some antifreeze in the resivoir because it seemed like the right thing to do, but in all these years I have never really seen any fluid transfer. Never really heard it make any noise either, though. Increased pressure from thermal expansion causes the hoses to get hard (up to 16 psi, correct?). Gurgling was probably due to it sucking in air through the crack when cooling and expelling after heated. I don't think it necessarily has to expel fluid each time it warms up, if there is enough air in the top of the rad to accomodate the glycol expansion then there is no reason to vent to the expansion tank. The fill line on my Suburban's radiator is a few inches below the neck.

 

[cybrfire]

I doubt you'll see anything in the tank unless it overheats.