[aelm7]

Recently I had a problem with coolant leaking on the passenger side of my car, had it checked out and turns out it was just a hose leaking. I got it changed but the mechanic was telling me my thermostat is broken, its stuck open apparently and wont close, so the engine doesnt cool properly. He was trying to convince me to get both the thermostat and water pump changed, but it seems only the thermostat is broken. anyone have this problem before?

Do i need to change both or just the thermostat?

[aelm7]

its a 2012 335i

[Efthreeoh]

If the thermostat is defective it will throw an emissions trouble code and illuminate the Service Engine Soon light. If you car does not have the SES light illuminated, then there are no emissions related issues with the engine.

What the mechanic is doing is making work for himself by telling you your car has a problem that is common for early model E90 cars. He is hoping you'll research the issue on the internet, find its a common problem, and have you convinced the work should get done.

I'd find a new mechanic.

My advice to you is research how to buy and use a BMW scan tool. The best ownership experience with these cars results from, at a minimum, scanning the car periodically for trouble codes so you can make informed decisions regarding repairs.

[nsjames]

Originally Posted by Efthreeoh

If the thermostat is defective it will throw an emissions trouble code and illuminate the Service Engine Soon light. If you car does not have the SES light illuminated, then there are no emissions related issues with the engine.

What the mechanic is doing is making work for himself by telling you your car has a problem that is common for early model E90 cars. He is hoping you'll research the issue on the internet, find its a common problem, and have you convinced the work should get done.

I'd find a new mechanic.

My advice to you is research how to buy and use a BMW scan tool. The best ownership experience with these cars results from, at a minimum, scanning the car periodically for trouble codes so you can make informed decisions regarding repairs.

this is excellent advice.

but yes, if one of them is failing and you're paying someone to do the work, they'll be right there and you should just replace both of them.
otherwise you will end up paying the labor to get there twice.

the question here seems to be if any part is actually failing.

[aelm7]

Originally Posted by Efthreeoh

If the thermostat is defective it will throw an emissions trouble code and illuminate the Service Engine Soon light. If you car does not have the SES light illuminated, then there are no emissions related issues with the engine.

What the mechanic is doing is making work for himself by telling you your car has a problem that is common for early model E90 cars. He is hoping you'll research the issue on the internet, find its a common problem, and have you convinced the work should get done.

I'd find a new mechanic.

My advice to you is research how to buy and use a BMW scan tool. The best ownership experience with these cars results from, at a minimum, scanning the car periodically for trouble codes so you can make informed decisions regarding repairs.

it hasnt shown the service engine light, but after parking my car in the garage after a drive, if youre standing next to the car you can feel some hot air, and even when the garage is closed it gets really hot, im not sure this is normal.

[kart23]

Heat from the engine after driving is completely normal, it gets hot and a failing thermostat isn't gonna change that.
The service engine light should have come on, but the way to diagnose thermostat problems is poor/no heat in the car with the heat turned all the way up, or the engine running below temp for a long period of time (significantly below 50% on the temp gauge.)

[whyzee125]

If the water pump isn't leaking, don't replace it. I know some people replace them preemptively because they fail so often but their failures are so random. I had one fail with less than a thousand miles on it and I've seen a few go over 200k. I'd leave it.

[opjose]

Having done one and then the other within a month, save yourself the cost and hassle, have him do both.

Normally when either one goes the other soon follows.

Btw: mine went at 38k miles.

Mechanic said he wished he had done both at the same time because it is the same amount of work for one or both and I would have avoided the extra labor.

[Vivek.]

How many miles, OP? I'm very wary of overheating and replaced my water pump and thermostat immediately when I got the car (@75k) since I had no record of it being done previously. Based on my research you're running on borrowed time with over 50k on a waterpump (N55 may be different, though, I'm N54)

I find some advice in this thread questionable because our electric water pumps tend to fail internally before they leak. I'd say better safe than sorry+stranded, replace both WP and T-Stat if they're over 50k/10years old --my 0.02

[Steve Sas]

Not sure about the N55 but the N54 water pump is a sealed units and should never leak.
What does happen is the permanent magnet rotor is encased in some sort of plastic and this seems to crack over time and peel off. Once this happens the plastic gets caught on the stator and requires increase torque during the starting cycle of the motor. I think (but could be wrong) the circuitry in the pump detects an issue and shuts off.

This is a manufacturing defect in the plastic used. Hopefully the new pumps use better plastics or even better none at all.