[IndyJC]

So today was the 3rd time in twice as many months since I've had my F10 that I've gotten a low coolant warning and re-filled the reservoir with about a quart of coolant. I brought it to a certified BMW mechanic after the 2nd refill, they put it in the air looked everywhere and couldn't find a leak. It doesn't drop anything on the ground while it's parked, no blue/black smoke in the exhaust pipe, no coolant under floorboards or signs /leaks in engine bay, oil looks fine. I drive the crap out of the car (sport mode almost exclusively) so I was attributing to just driving hot, but after this 3rd refill I thought I'd check here. Any ideas?

[cdmulders]

My F10 started needing a top-up every 2-3 months. I didn't think this was normal. It turned out it was the thermostat housing that had developed a small leak. It was replaced, and all is good ever since, with coolant needing a top-up once a year at most. This happened over two years ago and my F10 was around 8 years old at the time.

[IndyJC]

Originally Posted by cdmulders

My F10 started needing a top-up every 2-3 months. I didn't think this was normal. It turned out it was the thermostat housing that had developed a small leak. It was replaced, and all is good ever since, with coolant needing a top-up once a year at most. This happened over two years ago and my F10 was around 8 years old at the time.

Thanks I'll have them check it out again, take a close look at thermostat housing.

[n3985]

Could also be micro cracks in the coolant reservoir, doesn't leak until it is hot/under pressure.

[Johnkwick]

Also take a look at the hose that goes into the auxiliary radiator (if installed). You can either look from wheel well (wheel well cover have to be removed), or peek from the top of the right side of bonnet hook

Mine is also leaking slowly, I spent days searching for small leak and found it in relatively well enclosed place. Funny thing is the leak was imminent when the coolant system is cooled down from the normal operating temp (around 100-110C) and have less pressure within

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[StradaRedlands]

Mine is doing this as well, but has a new pump/'stat. I think maaaaybe it's the reservoir cover as there is dried residue there, but not enough IMO to need a full liter top off.

[StradaRedlands]

Mine leaks when hot... confirmed it this morning. Just had Tstat done in October, thinking maybe something wasn't tightened up all the way, or the shop buggered up a fitting and now it's failing. Or something unrelated and just coincidental. Good times.

[psam535]

My 2014 535i developed a pin-size radiator leak after 140k miles and needed to be topped off weekly. My mechanic recommended replacing the associated coolant hoses, the thermostat, an oil pressure switch that apparently has a tendency to fail, the reservoir/cap, the drive belt, pulley, and tensioner “while he’s in there” given the age/mileage and because some of those parts apparently leaked or showed excessive wear. All of those items were original (except for the thermostat which had been replaced about three years ago with the water pump). Of course replacing all these items added considerable cost but I plan to keep the car a few more years as it’s in beautiful shape. I agreed to do it. Runs great. No more leaks.

Was it reasonable to replace all these items, or “overkill”?

[StradaRedlands]

Originally Posted by psam535

Was it reasonable to replace all these items, or “overkill”?

If you're going to be keeping the car for a few more years, then definitely a good call. Hoses and misc are each individually inexpensive, but add up. Best to get them done at the same time so you're not stranded by a $30 part.

[e4603]

psam535 - I would say at 140k miles, those parts are overdue for replacement.