Coolant bubbles, can't get them out. Exhaust gas test negative
 

2002 R53

Keep having air in top hose. Combustion gas block test is negative (the blue liquid through the coolant reservoir test)

Blead numerous times - pipe bleed bolt and top hose.

Starting cold, air bubbles come up the coolant reservoir lower hose as it warms up.

Keep spurting air from top hose bleeder while bleeding hot.

Stage 1 fan turns of at 105.

Infrequently overheats at stop light - stop car, start to drive temp normal while driving.

Sometimes Stage 2 (3?) runs after car is parked. (the louder fan).

Ideas?

I had the relatively the same problem but mine never over heated. I relaced the thermostat and housing first and then the cap. Pretty much ended the bubbling and coolant filling the overflow tank. I replaced the water pump and radiator with hoses next but mainly as a precaution than an issue. Coolant now if perfect with no issues. I believe the cap was sucking air into the system but it never leaked coolant.

I realize this is rather fundamental: Have you pressure-tested the cooling system? I use my MOTIVE pressure bleeder since the threads on the cap of the bleeder match those on the reservoir. Pump it up to 15 lb. and see if it bleeds off pressure. If so, look for the leak.

This!
I would also try bleeding the system while under pressure - preferably cold, with pressure bleeder.

In addition to checking your system for leaks using a pressure bleeder, you can opt to buy a refiller. It will pressure test and refill your system.

I have this tool: Instead of putting your cooling system under pressure (what the motive does), it does it under vacuum.
This may come off as a sale's pitch, but it's really good.
You do need an air source, but it has been absolutely the best tool for checking and refilling cooling systems. It'll put the system under vacuum, if it holds, then great... you're cooling system doesn't have any leaks. It can then refill the system if connected to a coolant source (distilled water, coolant, etc).
Works incredibly well.

I recently replaced my radiator, and used the refiller. Once everything was buttoned up, it took maybe 3 minutes to refill the system and call it complete. That's installing the refill, pulling vacuum, refilling, and uninstalling, and closing the hood for the test drive.

That vacuum refiller looks cool. Agree, pressure test (and now vacuum test) could bring insight.

BTW, AutoZone has that tool for less than Amazon link. Unfortunately it doesn't look like it's in the loan a tool program at AZ.

I found a free loaner tool at autozone. Did the trick

https://www.autozone.com/tools-and-e...RA:LAT-Cooling
I see the pressure tester but I don't see the vacuum filler... Did you find the vacuum filler at AZ?

This is the vacuum filler

https://www.autozone.com/heating-and...artNumber=true

Did not pull vacuum on mine, but pressurized only

had the same issue twice , if new thermostat housing gasket and water pump , and your overflow tank isn’t leaking then to be honest and straight up you’re gonna need to replace the head gasket it’s just signs of it going out

​​​​​Update (though more work to do too solve)... Pressurized system to 15psi. Overnight dropped to 10 (and to 7 over two days)... Did that several times over a few days wondering if the tester may have a leak in it (it is just a pump after all)... Was busy on other things and after a few days noticed a drips under one side of the front bleeder fitting and one under the Xs that connect to the heater core. So have to find better clamps for those and the uncomfortable process of replacing them. Currently an using the OEM spring clamps throughout and it looks like I have to go to worm/mechanical clamps to get tighter compression forces.

Update
found a couple leaks at 15psi overnight went to 10psi. Cracked bleeder in front house and T in heater hose connection. Fixed them.

Not losing coolant. Not overheating. Still air in front hose when open the bleeder. When cold, if I have bleeder open and open reservoir cap, to hose fills and, interestingly, when I call reservoir, upped hose empties again.... Haven't figured that one out yet.

So far so good. Will be keeping an eye on it.

Replce your cap: https://www.ebay.com/itm/113764814404

My money is a leak somewhere (likely near the top of radiator) or a bad cap. I had serious overheating problems due to a bad head. I replaced the head gasket, had the head reworked, replaced all the hoses, t-stat and radiator, and couldn't get all of the air out. I bled mine ad nauseum and it ended up being an aftermarket tank that didn't have the same thread as the OE cap (even though it was 200+ dollar top of the line aluminum tank). Got a new PLASTIC tank and new OE cap, that did the trick. When the system is correct, literally all you have to do is fill it up in the reservoir tank, crack the bleeder on the hose and let it run until fluid comes out and it stop sputtering and spewing air, close the bleeder and your are done. Good luck, I know how frustrating it is.

Edit, Oh, see you found it! Good deal!

I typically fill from the bleeder screw hole. Should prob check it again to make sure there's no air...