Which one is the coolant reservoir cap, and what is the other one????

[Manny G]

I cant find anything in any manual or website that says what the hell the cap circled in red in my picture is. It looks like a typical coolant cap, but the cap circled in blue is supposed to be the coolant cap.

So what is what?? I got low coolant messages and when I checked the blue cap, it is already just above maximum.

[M6-Coupe]

I'm not sure about the red one but for sure the coolant is the blue one.
Do you get the message constantly? Let her cool down and see if the message is disappeared. I got the same message one time while the level of coolant was fine. After cooling down, never got it again...

[Manny G]

Message is constant. I cant find info anywhere on what the hell the cap in the red circle is. I may or may not have added some coolant to it before I realize the blue cap was the coolant cap... LOL. The one in red looks exactly like every other BMW coolant cap I've ever worked with in the last 20 years.

[Manny G]

Just took it on a ~20mile ride up and down the highway, and the coolant temp error is gone. That other reservoir must have done the trick?

[M6-Coupe]

I don't think so. Must have been a glitch.... As I said I got the message one time ...

[Manny G]

Originally Posted by M6-Coupe

I don't think so. Must have been a glitch.... As I said I got the message one time ...

The glitch tuned on after a 'sprited' run yesterday, and lingered through the evening. Came on again this morning when my wife drove the car after it cooled down overnight, and even for me when i went to check it out after letting it sit for a few hours to cool. I added about just under a half a liter of bmw coolant to the red circled cap

[Bönz]

Originally Posted by Manny G

I cant find anything in any manual or website that says what the hell the cap circled in red in my picture is. It looks like a typical coolant cap, but the cap circled in blue is supposed to be the coolant cap.

So what is what?? I got low coolant messages and when I checked the blue cap, it is already just above maximum.

Engine cooling on the right (red circle), intercooler/DME cooling circuit on the left.

[Used2be]

Originally Posted by Bönz

Engine cooling on the right (red circle), intercooler/DME cooling circuit on the left.

I hadn't known there was a separate cooling circuit for the DME so I looked in the owner's manual to see if they specify that system. It certainly makes sense that there is one, but the engine cooling is definitely the blue circle, at least according to page 179 in the manual. I'd guess the DME cooling is handled by the cap in the red circle. At least it would take the same fluid (again, I guess) and isn't power steering or something else! Half a liter is a fair amount to add, have you noticed any fluid on the ground? Maybe a leak?

[Bönz]

See attached.

[Used2be]

Originally Posted by Bönz

See attached.

I don't know where your diagram was sourced, but turn to page 179 in the owner's manual that came with the car. It has the coolant level min/max indicator for the engine coolant in the left, blue circled reservoir.

[Bönz]

That would be page 195 of my owner's manual.

[E90Fleet]

Most of the new models now have 2 separate cooling systems.
Even 3 series will have this with the new facelift B48/B58 engines from July

[Used2be]

Originally Posted by Bönz

That would be page 195 of my owner's manual.

Sorry, I didn't think of the page changes that might happen over the different years. I have a 2013. I'd assume whoever labeled the diagram you posted just reversed the two labels and we can hope the red circle identifies the DME cooling system that you mentioned. Is there anything in your owner's manual that mentions the separate DME/intercooler cooling system? I haven't found anything in my 2013 manual.

[E90Fleet]

The Blue circled one with its little attached expansion tank (E in picture) is for the charge air coolers and DME cooling

[E90Fleet]

The red circled one ( 2 in picture) with a separately located expansion tank (1 in picture) is for engine and turbo cooling.

[Bönz]

Originally Posted by Used2be

Sorry, I didn't think of the page changes that might happen over the different years. I have a 2013. I'd assume whoever labeled the diagram you posted just reversed the two labels and we can hope the red circle identifies the DME cooling system that you mentioned. Is there anything in your owner's manual that mentions the separate DME/intercooler cooling system? I haven't found anything in my 2013 manual.

Your older manual simply isn't clear. Read it again. It doesn't say engine coolant. It just says "coolant". I'm right. You're wrong. E90Fleet posted pics from the engine technical manual that proves it. I have this too. Thanks E90, I just didn't feel like taking the time to do this.

[Ian335xd]

Originally Posted by Manny G

I cant find anything in any manual or website that says what the hell the cap circled in red in my picture is. It looks like a typical coolant cap, but the cap circled in blue is supposed to be the coolant cap.

So what is what?? I got low coolant messages and when I checked the blue cap, it is already just above maximum.

The engine coolant is on the left and the air charge coolant on the right.As you can see it has warning symbol on the cap on the left as this is engine coolant and gets very hot the other coolant runs relatively cool.

[Bönz]

Originally Posted by Ian335xd

The engine coolant is on the left and the air charge coolant on the right.As you can see it has warning symbol on the cap on the left as this is engine coolant and gets very hot the other coolant runs relatively cool.

Wrong again, but nice guess. You think both the owner's manual and tech manual are wrong? Here are pics from under my hood. BOTH have warning symbols. Clearly the one on the left is a low pressure reservoir cap (DME/intercoolers) while the one on the right is a high pressure engine coolant cap.

[E90Fleet]

Originally Posted by Ian335xd

The engine coolant is on the left and the air charge coolant on the right.As you can see it has warning symbol on the cap on the left as this is engine coolant and gets very hot the other coolant runs relatively cool.

Relatively cooler, but not cool. So they have to warn you it can burn


Charge air and DME cooler is on the left of the picture with the small coolant tank.

Engine and turbo coolant fill cap is on the right with hidden large expansion tank

[Used2be]

Originally Posted by Bönz

Your older manual simply isn't clear. Read it again. It doesn't say engine coolant. It just says "coolant". I'm right. You're wrong. E90Fleet posted pics from the engine technical manual that proves it. I have this too. Thanks E90, I just didn't feel like taking the time to do this.

From the diagrams that E90 posted I believe I am wrong. I don't understand why BMW uses the coolant section in the 2013 owner's manual to reference the DME cooling circuit though. If the warning light lit up on the dash to tell me the engine was over heating, I would do as the OP did and go straight to the reservoir that is pictured in the manual to check for fluid level. There is no mention of the other water cap to add water, and of course no way to visually determine its water level. The engine coolant cap in the 2013 model has no yellow warning label, just small black lettering molded into the cap cautioning not to open while hot. I'm glad this came up, now I know. Curious, does the later manual mention both locations for checking cooling water levels?

[E90Fleet]

2013 USA M5 manual

[E90Fleet]

Revised 2015 USA M5 Manual