[Riot18]

2 weeks ago the Engine Hot warning started popping up in the iDrive, there is a noticeable loss of power that comes with it and the fan is at full blast. I can't figure out what's causing it. I have no check engine light I also have no codes in the BimmerLink or MHD app. I tried bleeding the coolant system and the water pump turned on right away so I know it's working. What else could be causing the engine to overheat?

[Miska]

If you're sure you have the correct amount and type of coolant, and are 100% positive you followed the bleed procedure correctly, I would proceed to the next paragraph. If not, verify coolant and bleed procedure.

Is the electronic thermostat perhaps not opening? Maybe a weak water pump? There might be a code stored in the ECU if so... do you have a diagnostic tool to pull codes?
Have you ever mixed any stop leak in the cooling system?

Going past the electronic parts of the system, we could also consider that it could be burning coolant or mixing it with oil via a bad head gasket. But usually those are pretty obvious (white smoke from exhaust or milky looking oil), so we should probably focus on the rest of the cooling system first.

[Costello]

Looks like the water pump not working fine for me..

[CapNcrunchPoker]

Originally Posted by Riot18

2 weeks ago the Engine Hot warning started popping up in the iDrive, there is a noticeable loss of power that comes with it and the fan is at full blast. I can't figure out what's causing it. I have no check engine light I also have no codes in the BimmerLink or MHD app. I tried bleeding the coolant system and the water pump turned on right away so I know it's working. What else could be causing the engine to overheat?

I'd say there's a good chance that your water pump is failing intermittently. Especially on a 335, electric water pumps are known to fail a lot more often/ commonly than the non turbo versions N model engines. How many miles does your car have, and are you aware of any prior replacements to the water pump or thermostat? Is your car leaking at all anywhere you can see? Did it ever throw a yellow light or just red, or only yellow?

I had a very similar problem about a 2 weeks ago. I had the car on for about 10 minutes, parked to get gas, when I left the gas station I immediately got the red coolant signal and my car went into limp mode. Oil temp was @220. I parked the car and let it sit overnight, came back the next day checked the coolant level; it was perfect. I drove about 1k miles within the next week, having my car on for hours at a time at some points. The car never over heated, threw signals, did anything weird, check engine light, nothing.. UNTIL.. I was driving home from work one night a week later (4 mile drive) half way through the drive I'm smelling a slight burning smell coming from the AC. Boom, I get a yellow coolant signal, than immediately after a red one and I'm in limp mode again. This time when I popped the hood, there was a little bit of coolant that blew out of the seem of the expansion tank.

Water pumps are so notorious for intermittent failure on the E90 especially. Expansion tanks crack too and commonly need to be replaced. With 157k, an original thermostat, water pump, hoses, and expansion tank I'm just doing a complete overhaul. Ordered OE expansion tank, and Water pump kit (thermostat and coolant included), and all new hoses (Coolant Feed Pipe Hose, Coolant Hose, Expansion Tank Hose, Lower radiator hose, Upper radiator hose, and Coolant Hose O-Ring) the parts cost me $600 on FCP. The dealer charges over $700 just for a thermostat and water pump (not with install) so definitely good value there.

In my opinion, if you're going to get into doing this work you may as well just do it once the right way, and get it over with. BMW will charge a few hundred just to diagnose this issue and tel you want you probably already know and if they can't diagnose it the first thing they'll tell you is to replace the water pump. Don't waist your time and money just get it done. Get the parts on FCP and take it to an Indy you trust or have BMW install it for you just don't get the parts from them.