1992 525i Touring cooling issue

I bought this car from the insurance as a wright off. 1992 525i Touring wagon M50 B25 automatic, this is a pretty rare car around here it's the only one I have ever actually seen. I belive it has something like 240000 km. The back bumper was damaged and would cost more to fix than the car was worth in their opinion. The front bumper also has damage , however it was not in the claim. I have already got a rear bumper , but not a front. BMW's are hard to find around here. My plan is to flip it to afford to fix another BMW I have , actually I have 5 other BMW's to work on.

Anyway , I replaced the rad as it was leaking when I bought it , coolant level sensor , t-stat and upgraded to aluminum housing , new resivoir cap. I also have , but not installed a new water pump and clutch fan. I would have replaced these as well if I had the wrench to do it (probably going to have to invest in one very soon). The water pump does not leak , however it is probably the original.

I have purchased a Bentley manual and followed the instructions to bleed the coolant system. Once it gets up to running temp and the bubbles stop coming I would put the bleed screw back in and temp would quickley rise causing the RPM to go up and down and stall out the car. The temp never went into the red and does not appear to have a blown head gasket. The upper hose is hot and the lower hose is still very cold. What could possibly be the problem the water pump or a bad t-stat? or could it be something else?

Sounds like the thermostat to me.

OP states he replaced thermostat? could be the waterpump as he says he did not change that yet...

Well I got the problem figured out today and to say the least I feel like an idiot. When I installed the radiator I forgot to remove the cap for the lower rad hose. Took it off put everything back together blead the system and everything works great.

I am also meating a guy in Regina who is coming from Winipeg with a front bumper for me.
Soon another BMW will be back on the road again , well probably another month at my pace.