Diagnostic help!

[Ultramaroon]

If I had a nickel for every time I've mentioned that here, I'd have a bunch of nickels.

[Essentials]

Originally Posted by Ultramaroon

Uh oh. Does your exhaust have that characteristic sweet smell? Any sheen on top of the coolant?

It does not, also no smoke from the exhaust. The coolant I can drain after trying what RZNT4R mentioned. If his suggestions don’t fix the issue. Also, how would I test my radiator cap? If with the car running and the radiator cap on, there is still bubbles coming up through the fluid in the expansion tank. Does that mean the radiator cap is not working correctly?

I tested my coolant with the combustion gas engine leak tester

and the results told me it shouldn’t be a blown head gasket.

So I was thinking it may be air, not combustion gases, getting into my coolant somehow.

[RZNT4R]

How to test the cap? You know those pumps you install in place of the cap to pump up the cooling system and check for leaks? there are adaptors to put the cap straight onto the pump to test it.

Alternatively, if the cap has been on it from cold and the engine is now warm and upon squeezing the upper rad hose you find that it is not hard, you know your cap isn't holding pressure.

Alternatively alternatively, a rad cap is considered a maintenance item and is pretty cheap, so it's not a waste to just change it. it's considered appropriate to change it any time you do mainenance on the cooling syste, like changing coolant, thermostat, water pump, rad, etc, because by the time the car is old enough to need those maintenance items, the rad cap is probably done too.

[Ultramaroon]

Originally Posted by Essentials

If with the car running and the radiator cap on, there is still bubbles coming up through the fluid in the expansion tank. Does that mean the radiator cap is not working correctly?

That is the exact symptom of a leaking radiator cap IF there is no air in the system. Bubbles come out continuously with a hot engine, and coolant is sucked in to replace the vapor gap when it cools. When a system slowly loses coolant, a pinhole leak in the cap is by far the most likely culprit.

Bubbles are to be expected from a recently-filled system that hasn't been completely bled. Less careful folks just add coolant to the reservoir until it stabilizes.

Normally, the reservoir is actually an expansion tank. Hot liquid water squeezes out of the system under pressure, and then is sucked back in as it cools.

[Ultramaroon]

No! I just realized that I've been wrong all these years!!!

The only symptom for a leaky radiator cap is gradual loss of coolant!

Why?

Because with a full system the only escaping gas would be STEAM, which immediately condenses back to liquid water - before it even reaches the overflow tube!

Damn!

[RZNT4R]

Not quite.

With a good radiator cap, steam should not escape, the cap is there to prevent steam. As the coolant heats up and expands, the caps holds it in until the set pressure. As it continues to expand, it escapes to the overflow tank as a liquid (because it's at the radiator, definitely not the hottest part of the engine, where the heat from the heads and all the cast interior passages provide lots of nucleation sites for bubbles to form). As the engine cools it gets sucked back in.

That is why the fluid level in the overflow tank varies between a hold and cold engine.

With a failed rad cap, the engine will produce a steady stream of steam bubbles and that is what will escape into the overflow tank. As there is now a constant flow of steam into it heating it up, the coolant will eventually evaporate from that because it's not pressurized.

[Ultramaroon]

That has been my misconception until just now.

I am saying with confidence that, with a full cooling system, all the way down to the reservoir, only liquid will ever exchange between radiator and reservoir.

[Essentials]

The new radiator cap did not help with the bubbles in the expansion tank. So, I’m back to leaning towards head gasket or somehow air getting in somewhere without a leak.

[blsfrs]

Did you check for cracks around the plastic filler neck.