BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > NA Engine (non-turbo) / Drivetrain / Exhaust Modifications > Engine overheat when AC is on?

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      10-19-2012, 02:06 PM   #1
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Engine overheat when AC is on?

Can someone help me figure this out? I don't have a great mechanic that I always go to. So, I'd like some assistance in figuring this out. I like to understand things to make the most efficient decision I guess.

When driving long distances at speeds over 60mph with out my AC on, I'm fine.

When I'm driving almost any variable distance with AC on, the engine seems to get hot. I pull over and coolant is pumping.

History: I have has AC issues in the past.

Do you guys think I just need a new thermostat? Or a water pump?

I was told last year I needed a new water pump.

How can I determine?

Any help is appreciated!
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      10-19-2012, 02:23 PM   #2
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Who told you the t-stat needed replacement? If it was a reputable shop, then chances are you need it. If you're going to replace the t-stat then do the pump @ the same time. You'll experience symptoms such as your car is displaying. It was also log codes as well. Someone w a scanner can read them for you and let you know. These cars are notorious for the said parts failing and its usually at the most inconvenient times. Do a little research on the forums and you'll see the posts about this exact same issue. There's a lot of them too. If you're fairly handy at diy tasks this is more than doable if you have a lift. Good luck.

Edit: didn't even realize it was you delon. How you been man?

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      10-19-2012, 08:47 PM   #3
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This from E12 and E39 experience: failure of the aux fan in front of the radiator. When not at highway speeds, warm weather and a/c load will overpower rad + fan alone.

With electric water pump, it either does or doesn't. WP failure will cause overheat under all circumstances. T-stat stuck closed will result in the same result.
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      10-19-2012, 10:08 PM   #4
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This occurred to me before I had to replace both Water Pump and Thermostat. I suggest that you get both done at the same time.
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