[5against8]

Having an issue and wanted to see if anyone has experienced it..* ('12 35i with 77k miles)

I was driving to work about 2 weeks ago and had the engine temp light come on (yellow not red) after about 30 minutes of driving. I also had little to no throttle response so I pulled over, restarted the car, at which point everything went back to normal. I initially suspected the water pump was going out but I haven't seen the oil temp go over 250F since this happened (I drove roughly 700 miles with no issues).

Today, a similar thing happened, except I noticed the throttle/shifting Issues before the temp light (again yellow) came on. I looked at the oil temp this time and the engine didn't appear to be overheating (roughly 230F). I realized that both days this happened it was raining (can't be
coincidence right?) Also it sounds like the radiator fan is coming on when this happens.

Any ideas on this, or has anyone experienced something similar? No other check engine lights or anything else out of the ordinary (haven't checked for codes yet). I do have a JB stage 1 installed, which I'm going to remove later today to rule out any issues. And.. of course my warranty ran out at 75k!

[MichiganMike]

I second your suspicion of a water pump problem. After 77K miles, a coolant pump problem is not uncommon.

The oil temperature generally will not rise as quickly as the coolant temperature. If the water pump is working intermittently or inefficiently, the oil temperature gauge may not rise much but the temperature in the turbo might rise quickly without sufficient coolant heat transfer.

It is possible your car is sometimes shifting into a limp home mode when sensors detect an engine temperature or coolant problem. There is too little data in my opinion to see the rain as more than a coincidence.

[5against8]

Originally Posted by MichiganMike

I second your suspicion of a water pump problem. After 77K miles, a coolant pump problem is not uncommon.

The oil temperature generally will not rise as quickly as the coolant temperature. If the water pump is working intermittently or inefficiently, the oil temperature gauge may not rise much but the temperature in the turbo might rise quickly without sufficient coolant heat transfer.

It is possible your car is sometimes shifting into a limp home mode when sensors detect an engine temperature or coolant problem. There is too little data in my opinion to see the rain as more than a coincidence.

I can clarify a bit on the weather. It hasn't rained here at all since the first incident, and I have driven about 700 miles since then (had several warm days where I was running at 240-250F for extended periods of time).

[momoboy]

I agree it's the water pump. It starts out as intermittent. That's what mine did. If yours is original at 77K you are on borrowed time. I'm not sure how the rain is playing into it but you will get to the point that restarting won't fix it and you will be stuck.

[Pinewood]

It appears this water pump (high failure rate) affects the petrol versions only as we have the diesel versions in the UK and no such issues.

[MichiganMike]

The following is from Turner Motorsport's web page:
"The N54/N55 water pump is electrically driven and varies output based on instructions from the engine computer. Under the best circumstances the pump drives only as much coolant as needed and will shut down or activate as load and performance demands change (combustion chamber temperatures are dynamically changed based on economy, normal, and performance demands). The pump can also run when the car is off to reduce heat soak in the engine and turbo(s). The water pump is now a factor in how much power and fuel economy your car is producing, making it all the more critical to replace during normal maintenance. If a fault or excessive temperature is reached, the dash cluster will display a yellow or red water temp icon depending on the severity of the condition. The car's electronics will begin shutting down various systems in the car to divert more resources to the cooling system. This can include reducing power output and activating 'limp mode'. "

Another thread on water pump failures in BMW's states:
"You can have a low oil temp and have a high water temperature. Since we do not have a water temp gauge BMW gave us these warning(idiot) lights."
http://www.1addicts.com/forums/showthread.php?t=755188

From the symptoms you noted, it seems likely that the water pump is in the early stages of failing and is not responding consistently to commands to increase coolant flow. You might take preventative action and replace the pump now or wait to see if it gets worse with an increased risk of being stranded somewhere or more serious damage should the pump fail completely.

[5against8]

Thanks for your feedback. It definitely was the water pump and/or thermostat. Don't know how the wet conditions were playing in but lots of rain here since the new one went in and no issues.