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Old 10-06-2012, 01:53 PM   #98
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Join Date: Feb 2008
Location: Philadelphia
Posts: 6,919
My Ride: M3 & ZHP
Originally Posted by mkodama View Post
Yep, you pretty much answered all your questions. BMW, and just about any current car manufacturer will run as high a coolant pressure as they can, because less chance of cavitation, ability to run hotter engine temperatures, a greater margin of error in case of an overheating situation, and so on. You get a lot of benefits, with no downside other than the cost of slightly higher pressure rated cooling system parts.

Running a hotter coolant temperature does a lot of things as well. Better emissions, better gas mileage, and also increases the efficiency of the radiator as you have a greater temperature difference so heat transfer is faster, which reduce emissions and a gains little bit of power from not having the fans go on as often.
I wouldn't worry about radiator efficiency - S54 has an 82 degree thermostat and cools just fine. In fact, the Z4M has the same radiator as the automatic 330i. The hit to gas mileage could be there, but my gut feeling is it'd be a pretty small hit. I don't really care about emissions.

And I do think there is a downside to higher pressures - the exploding expansion tanks. That's not really an issue on the M3, so I'm not going to consider running lower pressures. But if I still had a 330, I think I'd consider going down to 1.4 bar and a lower temperature thermostat

Last edited by TerraPhantm; 10-06-2012 at 01:55 PM.
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