I've been on this one all day and between both my and a friends automtive knowledge we can't figure this one out. Hoping someone here has the easy obvious answer we are missing!

Mid 90s BMW 2.5l Straight 6 engine. Radiator began seeping a few months back and got noticeably worse to the point that I was topping it off daily. So last week I parked it, drained it, took the radiator out and ordered an OEM replacement. Replacement came yesterday and I installed it today. Prior to installing I filled it with water to see of there were any obvious leaks then drained it again. When I drained it last week 8 quarts came out (10.5 quart total in the system) so it stands to reason I would need 8 quarts collant mix to refill it. After everything was put back together I filled the block by disconnecting the upper radiator hose at the radiator and pouring coolant into the hose. It took 2 quarts before it filled up. I then filled the radiator via the attached expansion bottle (this is the only way on these cars) and that too just about 2 quarts as well. There is a bleed screw on the radiator so per the instructions I cracked it and started the engine. THe idea is to close the bleed screw when coolant comes out.

So here's the problem - coolant has yet to come out of the bleed screw. Remember that I only got 4 quarts of new coolant in the system. After the engine got to op temp I noticed:

1. The block and upper radiator hose were very hot to the touch yet the coolant in the radiator is still cold.
2. I get no heat from the heater even on at full blast with the engine temp guage showng straight up (normal temp)
3. And most puzzling is that even though the coolant in the radiator is still cold it starts to backfill the reservoir spewing the coolant out of the vent!

I've already looked at the obvious, the thermostat is not the culprit and the water pump IS spinning. Someone suggested a huge air bubble is preventing coolant from reaching the pump, how would I fix that? I've changed my share of radiators before but this one is new to me.

Any help appreciated. I'd drive my truck to work (see signature) but its...um... too big for the dinky parking garage I have to use.

 

I have experienced similar, and after having run it, you may be able to get more in once it cools. I have had many vehicles seem full, but after letting it cool down, I can add plenty more coolant. Can't really answer why, just that I have obseved such.

 

What fellro said.
Sometimes the air bubble can be pressurised because of the heat...

Can you fill the radiator by disconnecting the top tank hose, and filling it through there?

 

BigF350, I did fill the radiator that way to make sure it was full. I am letting it sit tonight with the bleed screw open - can't hurt. Also had a thought, anyone know if this would work: leave the bleed screw open and force the system to pressurize like they do in a leak test? Good idea? Bad idea that might cost me a lot of $$$?

 

Drill a 1/8" hole in the thermostat and reinstall.

Remove the heater hose from the heater core. The one that goes to the water pump. Leave the bleed screw open. Using a large funnel, pour coolant into the heater hose. Be sure the heater valve is turned on. Rig up something to catch coolant coming out of the heater core. The weight of the coolant in the big funnel will help to displace the air. Be patient, it will take a while.

 

There comes a time in every man's life when he realizes he's an idiot (although this has got to be my third or fourth time now )

My driveway is a somewhat steep downhill slope as shown in my sig picture. Anyone care to guess which way I parked the car? I turned it around so that the radiator is now the high point and no more problem.... I must be getting old to have missed that.

Thanks for the suggestions

 

Duoh!! Just plain hurts doesn't?

 

I don;t know which hurt more, realizing I missed it or admitting it

 

Dont feel bad. Those BMWs have a very borderline cooling system. My '92 is out of service again for cooling system problems. This time the overflow tank exploded. Im replacing the tstat and hoses while I'm at it. I love how the car drives, but Germany is a lot cooler climate than here. Its almost 100 down the hill today. When something goes wrong with the cooling system, you only have about one mile from perfectly normal to the gauge all the way off scale and the red light on.

The six cylinder cars have a 2bar (29psi) cap and 92C (198F) thermostat. I decided to install the four cylinder parts, 1.4bar cap and 88C thermostat. I also notice that replacement thermostats do not have the tiny bleed hole at the top like the original, so I drilled one. BTW, the original water pumps have a plastic impeller that separates from the metal shaft. Many aftermarket replacements are all metal. Another point, do not use "Dexcool" orange or regular green coolant, it will leave crud. Blue dealer stuff or the yellow G-05 for late model Ford and Chrysler has the right chemistry. I also use distilled water.

Jim

 

Wow thanks for the advice. I only use the blue dealer coolant but it is expensive... I am defintely keeping an eye on the cooloing system as August and Septembers here get into the 110 degree range. Didn;t know th 1.8l had a cooler thermostat, I may replace with one of those to be on the safe side.

 

I didn't realise they took a 2 bar cap
Lowering the cap to a 1.4 should make it more likely to boil... shouldn't it???

I know you mentioned you can only run certain types of coolants - a 50:50 glycol mix I have found to be the best - requiring at least 135C (275farenheight) before overheating...

 

ask this on bimmerforums.com

they will tell you that the water pump had plastic impeller, which failed and destroyed the rest of the cooling system.

replace the radiator and the water pump.
It's a well known bug in bmw circles, do a search on the forum above