Coolant tank orifice clog caused overheating

[Fuel to Burn]

My coolant tank cracked and the car overheated, shut it off just as I noticed the needle about to peg.
Bought new tank and then had constant overheating and overpressure forcing coolant out of the cap.
Checked thermostat and all the other things but could not solve the problem.

Thought it must be head gasket, bought the testing kit and sure enough the liquid changed color.
Parked the car to fix later as I had an OT project I was working on.

months later I put that new tank on my other e38 (the float was no longer floating) and the overheat / over pressure problems followed it over to the other car.
Turns out the little orifice was clogged and that is a much bigger problem than I would have imagined.

Got another tank and the car is fixed, no head gasket needed, I have been flogging it pretty hard in testing and it is keeping cool, 102C max.
Figured I'd post it up to share my findings. (Red line is the path of the little orifice)

Coolant Tank.JPG

[Majestic7]

Wow weird. So the little tunnel orifice thingy was clogged on a brand new expansion tank? Sounds like it may have been a mfg defect. What brand was it out of curiosity? And that's lucky you have two E38s. That really helped narrow down the variable to being that expansion tank or who knows how much energy you would've spent chasing down the problem.

[Fuel to Burn]

Wow weird. So the little tunnel orifice thingy was clogged on a brand new expansion tank? Sounds like it may have been a mfg defect. What brand was it out of curiosity? And that's lucky you have two E38s. That really helped narrow down the variable to being that expansion tank or who knows how much energy you would've spent chasing down the problem.

Bought the tank from O'Reilly which means made in China. I would have spent a lot of energy, I thought it needed a head gasket because I did that test with the blue liquid and it changed color. Yes, "lucky" I have two e38s and the internet to keep them going. My wife loves them so I am stuck.

[xboss]

Well, if you did the test and it shows you have exhaust gasses in your coolant how are you in the clear?

[Fuel to Burn]

Well, if you did the test and it shows you have exhaust gasses in your coolant how are you in the clear?

Probably not in the clear long term, but in the short time the car has been running with zero issues for the last two weeks, the KTMP reading has been 97-102.
Yesterday I changed the water pump (bad bearing, fan was wiggling but seal was not yet leaking) so I changed the thermostat too.
With the new t-stat it's running 105-108 but no overheating or coolant loss. Another thread says 105-108 is normal, I hope that is true.