[RavinW]

Hi guys, I'm new. I looked high and low for a resolution but none to be found to this day, so I thought I could get some help from this forum. I own a 2018 BMW M Sport which has a coolent leak with no trace. it was pressure tested couple of times but no leak to be found. I found just one post somewhere in Redit I think that said it could be the evaporator. any help on this would be much appreciated and thanks in advance

[MidtownMike]

You don't mention what model type or engine, but if a pressure test shows no leaks, then you should try replacing the cheapest part: the expansion tank cap (coolant filler cap). That is the only part that is not tested in a pressure test, and they are known to fail.

[eff32fl]

Originally Posted by MidtownMike

You don't mention what model type or engine, but if a pressure test shows no leaks, then you should try replacing the cheapest part: the expansion tank cap (coolant filler cap). That is the only part that is not tested in a pressure test, and they are known to fail.

Yes my coolant cap just had to be replaced (for the big expansion tank). Check for dry coolant around it. Dry coolant on the threads is another thing to check which will make it a lil difficult to remove. Just like $45 for a new one if that's the cause. For me at least, the plastic lip that holds on the o-ring deteriorated.

[MidtownMike]

Originally Posted by eff32fl

Yes my coolant cap just had to be replaced. Check for dry coolant around it. Dry coolant on the threads is another thing to check which will make it a lil difficult to remove. Just like $45 for a new one if that's the cause.

$45 even seems a bit on the steep side.
My BMW dealership charges € 21,50 ($23).

[eff32fl]

Originally Posted by MidtownMike

$45 even seems a bit on the steep side.
My BMW dealership charges € 21,50 ($23).

Yeah it was something like that don't recall the exact price. Just saying it's not like a $500 fix 😎

[RavinW]

Originally Posted by MidtownMike

You don't mention what model type or engine, but if a pressure test shows no leaks, then you should try replacing the cheapest part: the expansion tank cap (coolant filler cap). That is the only part that is not tested in a pressure test, and they are known to fail.

Sorry my bad, its a 318i M Sport F30 1.5l turbo

I replaced the cap and Tank, but still I have the problem, I need to fill 0.5 litres of Battery water every week

[eff32fl]

Actually I found my invoice it was $45 USD at my dealership. I got screwed I guess lol.

[eff32fl]

Originally Posted by RavinW

Sorry my bad, its a 318i M Sport F30 1.5l turbo

I replaced the cap and Tank, but still I have the problem, I need to fill 0.5 litres of Battery water every week

Interesting. I'm not sure what it could be if the pressure test passed and you replaced the coolant cap.

Maybe a more experienced user can chime in.

[TX552]

Put automotive dye in your coolant tank and use UV light to see where it ends up. Few bucks on Amazon. Take off the engine cover and as many plastic covers you can to find the leak.

[RavinW]

Thanks for all your valuable help guys, I will try the things you guys mentioned and post back on findings.

by the way can it be the evaporator ? is there a coolant line to it?