Hello all recently our 2001 540i has at random started blowing out cold air when the heater is on, I've replaced all cooling system parts radiator, fan clutch, water pump, thermostat, belt. This morning in was driving and I looked down and the temp guage was pegged to red so I promptly pulled over. Checked the coolant level completely full the engine wasn't quite warm het I had just left the house. Grabbed my temp guage from tool bag definetly wasn't overheating. Now when I turn the key 2 clicks so all the dash starts working the twno guage immediately goes To Red even now as it's completely cool. The question I cannot find the answer to is which of the 2 sensors is the sender to guage and which is sensor for fan there s a 4 prong in the top of the water pump round and a square I believe 2 prong in the end of the lower hose. I've been searching for over and hour and cannot find a definitive a seer so I know which one to order. Any help appreciated tha is on advance
Last edited by Tact1c1an; 10-17-2017 at 03:29 PM.
When were the repairs made. Sounds like a short to ground or poor connection if the gauge is pegged at dead cold. Try and reconnect sensors, and make sure completely bleed system.
HTH
John
PS - have the same car
2001 540i/6 - 144k
1997 328 ic - 67k
hardtop
2008 328i 6spd 88k
2008 328i 84k auto
1998 328i sedan 5 speed - 190k RIP
1995 325i sedan - Hellrot - 124k RIP
Tact1, welcome to the forum.
The dual temp sensor in the waterpump housing goes to the DME and the cluster gauge.
If you disconnect the temp sensor connector when the key is on the temp needle will peg.
To fix this you need to disconnect the battery (after the trunk light goes out, 16 min) for a few minutes.
Blowing cold air after the engine is warmed up is a different problem.....there is air trapped in the heater core. You need to bleed the system. You could also disconnect the top radiator hose and pour more coolant into it until it won't take any more, then quickly reconnect it to the radiator.
The sensor in the lower hose controls the aux cooling fan speed.
Last edited by JimLev; 10-17-2017 at 10:51 AM.
Thank you yes that's the info I needed I bled it a while back and that quit it's been starting again gonna have to find where the air is coming in at gonna bleed itbwhrn inger back home. I tried the battery unhook for 10 mins and that worked once I get back home going to rebleed check all grounds and battery voltage I normally figure things out myself but For their I'd me I couldn't find which of those 2 sensors down what again ty
Bookmarks