Diagnostic help!
 

The problem:
I noticed I had intermittent heat (climate control) and so I thought I might have low coolant or a bubble in the system. I did have low coolant so I topped it off and that helped at first. Then it happened again so I looked into more. After some of the initial repairs I still had the same problem with the heat but noticed a bigger problem, the coolant had constant bubbles coming up through the coolant bleeder funnel I was using.

Things I’ve done so far:
-changed water pump
-changed thermostat
-flushed radiator, block, and heater core
-head gasket leak tester

None of these things have fixed the issue and with the head gasket leak test coming back negative it has left me stumped. I did do some research on here before posting and I found a post to where the guy had bubbling coolant but also had coolant sitting on top of the block (I do not have that issue) and it ended up being a seal on the intake. Idk if that would fix my issue. I really don’t want to waste more time replacing things that aren’t the issue. Hopefully this issue is very obvious to someone else, any help would be greatly appreciated. If any more information is needed let me know.

You need to keep bleeding until it stops bubbling. How long did you bleed it for?

I bled it for well over thirty minutes and numerous times. The problem is that with the bubbles the coolant level never drops, only gets higher as the fluid heats up

You put the heat on without the ac? Perhaps heater core maybe has some air in it?

Coolant bleeder funnel? Have you cracked the high-point bleed valve? It's that right-angled fitting near the firewall.

I did. I had the heat on high every time I bled the coolant system. The bubbles are endless so I’m highly confident that some form of gas is getting into the system somehow.

Yeah it’s like a high walled funnel that you can over fill and should, in theory, allow for all the air to come out. And yes I also cracked the bleeder valve up near the fire wall on the heater core line.

Bubbles even with a cold engine? A hot engine will simmer at atmospheric pressure (cap off)

I’m pretty sure yes, even cold. But it’s been a couple weeks since I have done anything with the car. I’ll test it tomorrow and post results.

Why do people insist on running engines with the rad cap off? The system needs to be pressurized or you will always be creating bubbles.

If you have no way of doing a proper vacuum fill, engine off, fill it up with your funnel and crack the bleeder valve. Once it's full and you've got no bubbles on either end, seal it back up and give it a steady 1000-1500 rpms to warm it up until the thermostat open (keeping an eye on the temp of course). Shut her down and let cool. Reinstall funnel, open bleeder and top off system.

Yeah even when cold and with the cap on it was sending bubbles into the over flow tank. I also noticed a little bit of moisture dripping out at the slip joint for my headers to the over pipe.

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

Most people don't have a real understanding of those details. Even if someone is experienced with pressure cookers, it can be quite a leap from those to engine cooling systems.

Oh and since we're going on about that...

Even if the rad cap is installed, it means nothing if it's defective. A bad rad cap is a common issue that shows up as low coolant/no leaks. In my youngers days as a mechanic I had an experienced coworker who was adamant that my old and busted high KM 4Runner had a bad head gasket. It held pressure, had no leaks but was losing coolant long-term. I decided to test the rad cap, it failed, was replaced and the issue was resolved.

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

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 http://youtu.be/okEy0VkVQ3o 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.

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.

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.

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!

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.

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.

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.

Did you check for cracks around the plastic filler neck.