[Bulanu335d]

Hy guys, I have a problem with my 335d m57 engine from 2011, the coolant temperature wouldn't rise above 85-87 Celsius even after driving hard and after stopping the temp would drop to 65 at idle. I changed the thermostat the main one, I don't have the small one near the EGR. All good and clear, the water stayed at 89-90 at the mechanic's shop, then when I went for a ride to let the coolant circulate everywhere in the pipes the water temp rose to 109 Celsius gradually(but it only stayed there for a few seconds), I had my heat on inside the cabin at max and it blew cold air, after driving another 200 metres it started blowing hot air inside the cabin and the coolant temp started to go down really fast like from 109 to 100 in 5 seconds, then it kept on going down till 71 again and at idle 65-66. Could my problem actually be from the thermostat in my oil cooler?(heat exchanger), I don't know exactly if my oil cooler for the automatic trans has a thermostat inside it or not, if it does, could that be my problem with the low temperature ? my vin is :WBAPN71090A299163 if it helps.

[Tomnavigator]

Try purging the air out of the system and see if that makes a difference. There is an air purge located on the antifreeze surge tank. Open the screw slightly when the engine is running and hot and vent until antifreeze starts coming out. Run vehicle for a few minutes and repeat.

[BB_cuda]

Originally Posted by Tomnavigator

Try purging the air out of the system and see if that makes a difference. There is an air purge located on the antifreeze surge tank. Open the screw slightly when the engine is running and hot and vent until antifreeze starts coming out. Run vehicle for a few minutes and repeat.

Normally, there is already a stream "peeing" back into the coolant reservoir. If stream has bubbles in it, leave reservoir lid off while idling in driveway until stream becomes bubble free. Has worked for me multiple times. I was told to leave that screw Tomnavigator mentioned the F alone. If your reservoir is as old as mine is (original part for 11/2010 build) leave it alone. If you mess with it, be prepared to put another one in. They crack easily and that plastic screw is easily damaged. I have read of brass replacements ones in the aftermarket.

Based on what you explained, I think there is more to it than air in the system though. If I follow the sequence correctly, the cool temp was happening before and after T/S change. Good to rule out air in the system though none the less. Repeat the driving with heater off after bleeding air and report back.

When you run the heater, it pulls heat out of the coolant so seeing temp fall off makes sense but I wouldn't think it would be immediate. I had car overheating sitting on I-10 bridge in Baton Rouge traffic jam and turning on heater pulled me down about 8C/14F.