mestoned

Hi Folks

Hoping someone out there might know what is going on with my cooling system. I replaced the water pump, thermostat, expansion tank and about 2/3rds of the the hoses connected to them. I refilled the coolant and warmed up the car but I keep getting a low coolant warning every time I start or turn off the car. I have driven the car a bit but I don't feel comfortable driving it more than a few miles to test the system because of the warning. When I check the hoses while the car is running the upper hose on the right gets smoking hot while the lower running into the thermostat is cold. I've never gotten a temp warning on the dash but it does not seem like the system is working properly. I know it's cold up here in the North East but the fan has yet to turn on since I completed the repairs. The only thing I reused on the assembly is the coolant temp sensor, would this keep the thermostat closed, could it just be a air bubble in the system, did I miss a step in the bleeding process?

Almost forgot its a 05 545i 6sp man with about 150K
thanks for your help

turboawd

did you bleed the air out of the cooling system? if so, how?
did you check the coolant level afterwards?

mestoned

I followed the procedure here although now that I read it again I realize that I forgot to turn the seat heater on I'll give that a try this morning and see if it makes a difference. I waited a day to check the level and it pops right up and indicates it is at the max level.

e6t.lab.rat

If your fan is not turning on then the problem is likely to be a bad sensor on the lower radiator hose. The lower radiator hose is hot coolant from the engine returning to the radiator for cool down by the fan. This sensor triggers the fan to turn on when the coolant from the engine is hotter than normal. The upper sensor located above the thermostat will usually warn of a bad thermostat. Good luck

mestoned

I had replaced that lower sensor when I replaced the hose, old one leaked like crazy when I put in the new hose. When I went thru the whole fill procedure with the seat heaters on I let the car get up to temp and that lower hose never gets warm it stays stone cold the entire time. Would the sensor on the water pump itself trigger the thermostat to open?

mestoned

Thought I'd give the site an update. I finally brought the car into the dealership and they determined that it was air in the system. When I asked the SA how they bled the system he said they use a pressurized system to bleed the car. By far the cheapest repair I've ever had at the dealer $65. Unfortunately while they were going over the car they let me know the upper timing chain cover gasket needed to be replaced, not the cheapest repair ever

540i

I always wondered about this, are you sure this is the case? My lower radiator hose (left side when looking straight at the car) is always cold and the upper hose (driver's side) is always hot. I always assumed the upper hose is the coolant that comes from the engine and the lower is the cold coolant going into the engine...

540i

And just to confirm, my coolant temperature never exceeds 96 degrees during normal operation - measured by the Torque app and OBD2 adapter which takes the information straight from the car's ECU. My fan always comes on as soon as it hits 96 degrees so everything seems to be functioning properly. Can someone confirm which way the coolant circulates?

540i

Ok, i know I'm talking to myself, but this diagram (although not for the N62 engine) seems to confirm what I thought. I thought I was going crazy.

BimmerFan52

Discussion of cooling system for N62B44 engine in 545i starts on page 40.