Hello All,

I bought a 2014 E63 S with 52k miles a little over a month ago. I noticed that the "low coolant" or "add coolant" light came on so I checked the coolant and it was significantly low. For about 4 or 5 days I would need to add coolant even after a short trip. My dad and I could not find any leaks, no steam, no smell, nothing. We also did an at-home combustion leak test and it came back good. No excessive white smoke out of the exhaust and also the oil is good as ever.

With all that information I took it into a shop the specializes in german automobiles I did not take it to Mercedes Benz right away because they are booked out 2-3 weeks. They did all the same checks and also did multiple pressure tests. They found out that one of the reservoir caps was not sealing properly so they replaced it. Well, the issue is still there so I took the car back (10/12/21) and they are currently (10/14/21) still looking at it. They have driven the car roughly 50 miles, 5-mile intervals, and pressurized the cooling system multiple times. Today (10/14/21) they mentioned that it held 20 psi all day, but they didn't have much time to look at it compared to the other days, yet it is still losing coolant.

Does anyone have any idea of what could be happening? With not a ton of driving, I have added about a gallon and a half of coolant. I used Peak 50/50 for European vehicles (states 2014 Mercedes and up). They are going to call some of their buddies at our local Mercedes Benz and see if they have any ideas, but if not then I will take it to Mercedes and have them check it out.

Please help. Much appreciated.

 

Folks have had issues with hairline cracks in the expansion tank. Some see the "crust" precipitating as an easy visual aid, others have put dye into the coolant and UV lighted it.

Not sure if 20psi is enough to force that crack open.

Hopefully not migrating into your oil.

Do a search, pretty common.

 

I appreciate your comment, but I can not tell if you fully read what I wrote or not. The oil is as good as ever, it would be a quick and easy tell if it was getting into the oil. Also apparently what is happening here is not too common as I have done tons of research as well as had it at a shop for a little while now and no one can figure anything out. I have an appointment at Mercedes Benz on Nov 2nd, so hopefully, they can figure it out. I just was not sure if anyone had any other odd coolant issues and any tips. I will say that using dye would be a great idea, I may try that as I am picking up the vehicle from the shop today.

 

I read quick and don't always get all the details. My bad if you already addressed, good luck!

 

Hello,

Did you ever get this fixed? I have the same issue. I replaced the expansion tank cap but still have the same issue.

Thank you
Steve

 

Mine was cracked reservoir and maybe lines I'd have to look it up. It freaked me out because it was the winter time and I decided to test out my AWD and snow tires "plowing" the deep snow in the driveway, pushing and packing it down. It was so deep the undertray was riding up on the snow. I couldn't leave the driveway because the plow blocked me in, so I left the car running while I cleared the end of the driveway. After I moved the car there was coolant on the white snow. If it wasn't white snow, and/or 15 minutes of idling there, I don't think it would ever have been enough to "find a leak" on a normal day looking under the car for leaks.

I hope it's as simple as that for you! The under tray catches a lot of stuff for some time before it spills into the real world. And driving might blow it all away, you may have to idle for a long time for it to start spilling over the tray. In my case I was jostling it around on snow making it "bounce" out. Do you have any virgin snow around to make it easier to see?!

 

perform a leak down test, local auto parts store may rent for free.

 

Have not found the exact cause, but the coolant is getting into the oil (no signs show head gasket so it could be a long list of things is what I was told). For my case the coolant was not leaking out onto the ground. I just bought a used engine (arriving 7/22/22) as we were unsure of how much internal damage had been done and would cost a lot to figure it out and fix it all. I was able to keep my “bad” engine so once they swap the engines they will take more of a look at it and who knows what that will reveal. I will update once they swap the engines and look into the bad one.

 

You bought an entire engine??? Well, that escalated really quickly. If you have to buy a new engine after finding a coolant leak, I don't think anyone wants to own a car like this.

 

You bought an entire engine??? Well, that escalated really quickly. If you have to buy a new engine after finding a coolant leak, I don't think anyone wants to own a car like this.