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Old 01-23-2013, 11:21 AM
jburke4689 jburke4689 is offline
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Location: Ellicott City, MD
 
Join Date: Apr 2008
Posts: 628
Mein Auto: 2007 335i
Quote:
Originally Posted by 08 335Ci View Post
Oil temp lags water temp by about 50 degrees. So when your oil gauge show 160, your water is already at 210 degrees F.

Coolant only cools the block and head of heat that has traveled THROUGH them. Oil cools the moving parts, pistons, crank, valvetrain, turbos .... where the heat is generated through combustion and friction. Oil temp is a much better indicator of engine condition them water temp. The owner's manual gives a pretty good explaination of this.
Correction, on the N54 at least, coolant cools the turbos. Oil does lubricate them and does carry away some of the heat as a result, but it is the coolant's job to cool the turbos.

The following is right out of the BMW Engine Management Training Document....

The turbine and the compressor can rotate at speeds of up to 200,000 rpm.
The exhaust inlet temperature can reach a maximum of 1050C. Because of these high temperatures, the N54 engine's turbochargers are not only connected with the engine-oil system but also integrated in the engine-coolant circuit.It is possible in conjunction with the N54 engine's electric coolant pump even after the engine has been switched off to dissipate the residual heat from the turbochargers and thus prevent the lube oil in the bearing housing from overheating.
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