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Old 01-23-2013, 12:21 PM
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Originally Posted by jburke4689 View Post
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.
I knew somebody would bring up that feature. And the manufacturers always make a slight improvement into the best thing since sliced bread. I know, I've read my fair share of training materials. But I will admit, water cooling the turbos will lower the stress (heat) on the oil, maintaining the oil's properties longer.

So the N54 is the exception, not the norm. to my statement. My statement applies to ALL cars (even non turbo), motorcycles (Suzuki's SACS especially), medium and heavy duty trucks. Oil does a lot more cooling then people realize.

Don't forget, turbos work by the expansion of exhaust gases. Cool them too much and you'll loose boost. You won't feel it with the N54's stock boost of 8psi but in a big truck or all out racer .... every bit counts.
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