[Freemorfeem]

I'm grateful to have a place where I can ask this question. Thanks!

I have read every post I can find related to this and still want to post this.

Twice my 335 has overheated (yellow to red thermo icon immediately) twice in the last month.

Both times it was coolant spewing out from the expansion tank cap. The first time, I was ready to inspect all things related to coolant issues, but the cap was actually about 10mm backed from being fully tightened! So I refilled the coolant (1/4 gal), did the bleed, and moved on.

Second time I lost 3/4 gal. I saw coolant leaking from underneath the expansion tank. I figured it was cracked. I removed it and learned about the hole in the filler neck which clearly redirects spilling over coolant downward. My tank appears very solid, no issues. Refilled and bled the system again. Ran it for 5min, topped it off.

Seems simple: it's the cap, right?

I'm not sure, and here's why.

* I've had a feeling of "less power" recently. Was wondering if I had misfires or a boost leak recently. (no limp mode, just a little less beastly pulls).

* This wasn't too smart, but just before overheating, I had no warnings, but my boost was gone. So I went to a side street and did about 3 hard pulls to test and feel it out. Now I know I probably ran the engine hard as the coolant was leaking, thinking it was a boost leak. So, there was a clear huge loss of power with this coolant loss process, but also in the last few weeks I've noticed inconsistent power up/down... related or separate?

* My oil level has dropped to needing "+1 Quart" in the last month. (where is it going? out of the head gasket?)

* Note: I have no codes popping up. No gray smoke. I didn't see oil in the coolant when I pumped it out of the expansion tank before removing it.

My assessment is that I need a $15 cap or maybe my head gasket is going? Or...? Open to ideas. I'm going now to plug in my ODBII reader to see if there's something there that the DME didn't put on my display in the car, and I'm going to check visibly the head gasket (if I even can, never tried that one).

And if I need a cap, do you have any recommendations? My expansion tank looks really new, but the car has 125K. I just got it from a dealer 8 weeks ago and don't know if it's new or not. It does have German writing on it so maybe it's BMW OEM? Should I only get the BMW OEM cap then? There are three types of caps on FCP Euro.

Thanks a lot!

[bluewater328]

You’re not crazy. It happens. It even happened on my replacement cap a few weeks ago.

I swear the new generation caps (with the yellow arrow) are not as good as the last gen/originals. Replaced it, no more leaks or paranoia. Oh, and to get you through the last part, yes, there is a gap between the cap and the reservoir - you just never noticed it before.

So replace that cap (luckily I got lifetime warranty with FCP) and move on with your life.

I’m sure you’ll be like me and clean the whole area up and check it daily for the next week along with looking for pics of other peoples’ reservoirs with gaps below the cap (they exist)…and you’ll be fine.

[jacbo]

From the above sounds like new cap would be best thing to do. cheap and easy to fix.

have you checked your oil cap for milky residue? that's a tell tale sign of coolant mixing with oil due to failed gasket. but from what you describe i highly doubt your head gasket is at fault here

[Freemorfeem]

Ok, so I ordered two new caps! Got both the Genuine BMW and Rein. The current one looks like the cheapest one by FEBI.

And no, I don't see any mixing of coolant or oil anywhere. None of the head gasket symptoms are showing.

"Move on with your life" hahahah... well, overheating twice caused my Valve Cover Gasket to leak, hahaha. I had already ordered Plugs and Coils as I was feeling some loss of power. So I added a VCG to my Caps order. It'll be a HUGE job for a noob like me, but I'm going for it.

Also, side note... my Blower Motor is loud when I turn on the heater. Never noticed before because I bought this in the summer in TX this year. But in the bleeding via the water pump process I hear it. There is a recall for the wiring on the blower motor and I'm scheduled to go in for it next week.

I would not think that the blower motor could also cause overheating, but BMW says it can. below is a copy-paste from the BMW recall sheet (I can't find anything online about this connection between heater motor and overheating).

BMW sheet:
(the copy paste gives a bunch of squares, so I'll attach a pic)

[ryan stewart]

If they haven't shipped already you might want to consider just ordering the whole new bottle assembly as well.

I replaced my cap due to the plastic on the pressure valve failing and a couple of months later my bottle developed a leak at the back of the seam. It would fill and be fine but the moment the system got up to temp it couldn't maintain pressure because it was all blowing out of the back of the bottle.

The plastics just arent durable being heat cycled like that anymore.

[Freemorfeem]

Originally Posted by ryan stewart

If they haven't shipped already you might want to consider just ordering the whole new bottle assembly as well.

I replaced my cap due to the plastic on the pressure valve failing and a couple of months later my bottle developed a leak at the back of the seam. It would fill and be fine but the moment the system got up to temp it couldn't maintain pressure because it was all blowing out of the back of the bottle.

The plastics just arent durable being heat cycled like that anymore.

I agree with the advice, but I didn't order the expansion tank, too. The previous owner had replaced all vacuum lines, and coolant / radiator hoses. So much under my hood is new and clean and supple. I think the cap is newer, too. Just a piece of crap. When I removed the expansion tank it looked and felt really solid. Plastic still shines, not faded or brittle, etc.

Now that assessment and decision might come back to bit me, hahahah!