Losing coolant and foaming at radiator filler neck!?

Question

I posted about my coolant not getting back to radiator after engine cools down a few weeks back. I tried putting a new cap and observed for 2 weeks. Now I still loss coolant. There were things I failed to mention or maybe didn't notice then when I first popped the question.
1. If I let the engine run without the cap, i can see fine bubbles (foam) building up on the filler neck.
2. After turning off the engine and letting it sit overnight, the radiator is still pressurized. Turning the rad cap a quarter(loose but still locked on), a huge pressure is released on the sides of the cap and some goes and displaces the water in the reservoir.

Is this a sign of a huge head gasket failure coming?

I posted about my coolant not getting back to radiator after engine cools down a few weeks back. I tried putting a new cap and observed for 2 weeks. Now I still loss coolant. There were things I failed to mention or maybe didn't notice then when I first popped the question.
1. If I let the engine run without the cap, i can see fine bubbles (foam) building up on the filler neck.
2. After turning off the engine and letting it sit overnight, the radiator is still pressurized. Turning the rad cap a quarter(loose but still locked on), a huge pressure is released on the sides of the cap and some goes and displaces the water in the reservoir.

Is this a sign of a huge head gasket failure coming?

Added Details: I already took out the thermostat since i noticed the coolant not returning to the radiator a few weeks back.

Answer 1

Three things to check or address for sure... in this order...

1.) Coolant maintaining pressure after cooling down overnight... most likely indicates an incorrect cap... A.) the pressure lift-off valve should be of the correct calibration... B.) a 2nd centered coolant recovery valve whch equalizes the pressure during overnight cooldown... Fix is to buy another new cap, either from a dealer or an auto-parts store with the CORRECT application information.

2.) Install a brand new correct thermostat... do not run without one... You havn't mentioned the brand, but some engines have a lower coolant flow resistance thru the internal block bypass vs. the 'stat open pass to the radiator... these require a thermostat with a bypass blocking baffle to direct ALL the coolant to the radiator, rather than partially thru the bypass... Proper flow is designed to run with a thermostat , never without one... Best to have a good working thermostat rather than none at all...

3.) Bubbles in the running coolant... usually bad news... compression and combustion pressures are the usual cause... To diagnose, run the engine to full operating temperature... shut down... quickly remove the spark plugs and do a compression test at each cylinder while still hot... If one or more cylinders is low... that indicates a leaking cylinder via a blown head gasket, poorly seated or worn valves, or even possoble a cracked head casting... if the head is removed for low compression, don't just assume a head gasket... Have the head pressure checked and magnafluxed for cracks, and the valves ground at a good rebuild shop... If indeed it is found cylinder pressure is entering the coolant while running, the explanation for the coolant pressure not bleeding off overnight back thru the cylinder leak(s),.. It is not uncommon for the cylinder gas leaks to occur one-way into the coolant at operating temp only... at shutdown the coolant often will NOT leak back in the reverse direction to the cylinder(s) because compression leaks tend to close when cool, and the coolant pressure is lower than the operation cylinder gases...

In summary... Install a brand new correct cap and thermostat and perform an all cylinder compression test at operating temp... you'll likely know more than you know now...

Answer 2

Coolant Filler Neck

Answer 3

May only be the thermostat.. have you tried replacing (or just removing and testing) it to see if this still happens?

I traded an old stereo for a nice looking Oldsmobile a few years back that "had a blown head gasket". First thing I did was pull the gooseneck and saw a serverly plugged thermostat.. got a new one and drove it for a year (ran the **** out of it, then sold it for $350). Check the ez stuff 1st!

Answer 4

Have you ever overheated your car?

I just had a prob with my car, leaking coolant, then it wouldn't start. Turns out it was a burned up wire. It could be a number of things, you might have to give in and have it looked at by a professional.

Or you could try replacing the head gasket and see if that works... My car is really ghetto, thats the problem... putting money into cars and hoping it fixes the problem, or spend more money fixing everything else. Story of my life lmao

Answer 5

It sounds like you (or someone) used two incompatible anti-corrosives in the radiator, and they have set like a jelly and clogged the system. Try reverse flushing the cooling system with high pressure water, but don't forget to temporarily remove the thermostat first. It's happened to me once or twice, so try this before pulling the motor down. You could save lots of $$$$s. Also, new thermostats only cost peanuts, so replace it while your on the job.

Answer 6

Probably the thermostat is jammed and needs replacing. Unless there's a milky substance in the water or in the oil it's not likely to be head gasket.

Answer 7

the bubbles are from engine compression getting into cooling system,look for oil in coolant or coolant in oil.Its either a head gasket leaking or a cracked head.when you get it fixed put the thermostat back in.good luck.

Answer 8

I had a cracked reservoir in my car that was causing it to overheat. At first, I thought it was the thermostat and I also thought it was the head gasket (what a nightmare that would have been! Ford would have had to replace my $12k engine as it's easier to replace than fix).