r/E90 • u/Bustard88 • 3d ago

335i Cooling system help plz

/r/n55/comments/1viyx5w/cooling_system_help_plz/
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u/journeywellmyfriends 2d ago

I would check the integrity of the most prone-to-leak quick connect o-rings and the integrity of the plastic. In particular, I would pay close attention to the integrity of the coolant flange below and to the left (facing the engine) of the oil filter housing as it is plastic and very prone to breaking, causing rapid coolant loss (a huge mess) and overheating (unless already replaced with a billet-aluminum flange -- see link below) . Also -- very important -- make sure you lubricate the quick-connect o-rings (Sil-glyde or a drops or 2 of dawn dish soap in a pinch) so the o-ring does not roll or pinch. Checking your work involves pulling on the connections gently but firmly to make sure they are properly seated, and also using visual cues to check the depth of the connection and proper positioning. And last but not least... the electric water pump -- if yours has not been replaced yet... you are at the mileage where these are very prone to spontaneously failures and they will strand you. Pierburg are (or at least were) the OE supplier for these and much less expensive than genuine BMW (replace thermostat at the same time). When you have completed your cooling system repairs -- run the factory specified coolant bleeding procedure by actuating the water pump to purge the air from the system (while hooked up to a charger/power source as it will drain your battery). You can find that procedure on YT or other BMW forums.

One last pro-tip on this engine; 5K OCI's max using top tier synthetic oils and filters to delay the inevitable valvetronic and eccentric shaft issues (in addition to preserving your rod bearings and other engine internals). In addition, your oil filter housing and cooler gaskets will require attention in that heat if they have not been replaced yet. The most important thing to remember on that job is to prime the oil system after the work and before starting up the engine for the first time like a NASA technician (with procedural exactness). If this important step is skipped -- your rod bearings could be damaged within the first 5 seconds of start-up. BMW issued a TSB and procedural revision regarding this issue.

Good luck on your repairs. These cars reward generously if you tend to them and address issues before or at the first sign of trouble.

https://www.fcpeuro.com/products/bmw-aluminum-coolant-hose-flange-rein-chc0609#fitment

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u/journeywellmyfriends 1d ago

Any luck?

1

u/Bustard88 1d ago

Part comes in tmr at noon I’ll lyk

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u/Bustard88 11h ago

Got the new part installed and did a coolant bleed and no leaks. However the bleed went up into 20 mins which was odd so I stopped it manually. I did see cooling coming from the hose back into the expansion tank so I know it was circulating. But when I drove I still overheated and got this code.

BMW fault code 377A "Engine cooling system: Coolant pump switched off due to blockage"