Thread: N54 water pump
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      11-20-2012, 11:10 AM   #11
Stupid Idiot
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Drives: E90 335i & C6 Grand Sport
Join Date: May 2009
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Originally Posted by GOTMH8N View Post
I have a question. The other day I was on the highway where I did some hard pulls and as I was coming up to my exit I noticed the water temp had dropped down to around 180. Then as I came to a stop at the street light it came back up to 210 like normal. Could this be a sign the water pump is on its way out? Since the early water pump codes say fan speed below normal, I always thought that would cause an increase in water temp though.

I have yet to see the water temp fluctuate like that, but I've done mostly city driving lately and this was the first time I've driven the car hard on the highway in a while.

Yes, it is very normal for the coolant temp to drop after making a full throttle burst. One of the great things about the N54 platform is that the DME has a lot of control over coolant temps in the cylinder head. Between the electric water pump, the MAP thermostat (controlled by a heated wax core) and electric fan.

There are several operating modes the DME will choose for cooling strategy. When you got WOT, it will open the thermostat and crank up the water pump speed. Normal coolant temp for the N54 is targeted around 104 C. It runs warmer when cruising for better fuel economy, reduced friction, etc. , but when putting a heavy load on the engine, it will try to reduce temps to 90 C (which is about 194 degrees).

This is actually how the MAP thermostats have worked for years, even on the E46. Now with the electric water pump, BMW has made it that much more effective. Hope that helps.