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Yesterday, I received a "Check Coolant Level" notification on my 2024 AMG S63. Looked under the hood, the radiator cap is not in the front as with many cars, but I suspect (need a confirmation) it is the unidentified unmarked cap on the right (side of engine facing the car), back from the oil fill cap. I also wanted to check the overflow canister in the front right, but it does not have a fill line. The manual offers zero help on any of this, at least the one they gave me. Any confirmations from anyone would be appreciated.
The unmarked cap on the right side, near the oil fill, is the coolant expansion tank cap. That's where you check and fill. The plastic canister in the front is the overflow reservoir; you don't fill it directly. Only add coolant to the expansion tank when the engine is cold. Use only Mercedes-approved coolant.
The unmarked cap on the right side, near the oil fill, is the coolant expansion tank cap. That's where you check and fill. The plastic canister in the front is the overflow reservoir; you don't fill it directly. Only add coolant to the expansion tank when the engine is cold. Use only Mercedes-approved coolant.
Thanks for the reply. To confirm, don't use the expansion tank to fill (No. 2)
Fill at the cap labeled (No.1)
Are you sure #1 is not the coolant for the turbos? #2, I don’t think is the coolant expansion tank; I could be wrong as I drive a mere S580 Executive Line. Wouldn’t the coolant expansion tank be on the left side-in this photo as opposed to where you have #2 marked?
Are you sure #1 is not the coolant for the turbos? #2, I don’t think is the coolant expansion tank; I could be wrong as I drive a mere S580 Executive Line. Wouldn’t the coolant expansion tank be on the left side-in this photo, as opposed to where you have #2 marked?
Good question. I'm not sure. Of course, there is nothing in the manual. There is another fill tank on the left side #3. Then again, not sure where the windshield washer tank is.
Good question. I'm not sure. Of course, there is nothing in the manual. There is another fill tank on the left side #3. Then again, not sure where the windshield washer tank is.
the windshield washer cap is blue and I can see it in the upper right corner at the edge of the hood. By the way, your manual will tell you a lot more than what you’re getting here in terms of smart remarks (seen below)etc.
When I had my 2018 E63, I would periodically need to stop by my local Mercedes dealership to get the coolant topped off. They had a bottle handy at the drive through because this was such a common issue for that model. I would think/hope Mercedes would fix this issue with newer models, but maybe not. If your local dealer isn't too far from you, you might pop by to see if they can top it off for you while you wait.
Any coolant loss is a problem.
It is NOT evaporation.
It is a closed system, except for an overpressure valve, which should almost never happen either under normal circumstances.
Coolant loss always “boils down” to 2 issues.
A leak.
A gasket.
Oil in coolant or vice versa is a gasket, which technically is also a leak.
Almost anything else is a leak.
When I had my 2018 E63, I would periodically need to stop by my local Mercedes dealership to get the coolant topped off. They had a bottle handy at the drive through because this was such a common issue for that model. I would think/hope Mercedes would fix this issue with newer models, but maybe not. If your local dealer isn't too far from you, you might pop by to see if they can top it off for you while you wait.
Was at our local Mercedes dealer for my PA inspection a couple of months ago. I commented to the service advisor that I’d gotten a couple of intermittent “Check Coolant Level” messages on my 2024 S63 ePerformance. They topped off my coolant and commented that the turbocharged cars seemed to use a bit of coolant. Don’t know if that’s true or not. I’m just passing it on.
Was at our local Mercedes dealer for my PA inspection a couple of months ago. I commented to the service advisor that I’d gotten a couple of intermittent “Check Coolant Level” messages on my 2024 S63 ePerformance. They topped off my coolant and commented that the turbocharged cars seemed to use a bit of coolant. Don’t know if that’s true or not. I’m just passing it on.
I think that is a BS,. especially the car is 2024 not 2014 or 2004 for that matter.
In my opinion, there was an issue with the EQS where a software failure caused the battery to consume coolant.
Since the S63E is also a plug-in hybrid (PHEV), I believe it may be experiencing a similar problem. I would strongly recommend bringing this to the dealer and requesting a proper fix.
I’ll smell coolant sometimes after I park in the garage. Haven’t had the check coolant warning yet, but something is causing me to smell it.
I have the same issue...had the system checked and it was tight. Tech thought is might be windshield washer fluid getting a little warm from the engine. Similar smell apparently.
So, took it into MB. The filler for engine coolant is No. 3. No. 2 is engine overflow, coolant tank, and No.1 is indeed for the battery. Didn't know they needed it. (Did not get into what coolant they use for that)
Indeed, they commented that these dual-turbo AMG S63s run hot and have been known to need coolant top-offs.
A turbo that uses coolant would kill every part of the system after it… so with these cars using coolant, are you also seeing deposits of said coolant after the turbo? What side is it leaking on and is this coding your valves and pistons in coolant or is it coating your O2 sensors and cat in coolant. Coolant needs an exit, an exit can be found under prolonged vacuum. If the system is using coolant, it needs to be fixed imo. If mine used coolant (diff design though just as hot)I might even opt to email Mercedes corporate and ask them if these cars use coolant. They make sure to point out oil use in the manual.
edited to fix all the ai autocorrect spelling and word issues. Thankfully in before the site won't let me fix it to all make sense and not waste your time.
Last edited by Baltistyle; Sep 29, 2025 at 08:48 PM.
A turbo that uses coolant would kill every part of the system after it… so with these cars using coolant, are you also seeing deposits of said coolant after the turbo? What side is it leaking on and is this coding your valves and pistons in coolant or is it coding your O2 sensors and cat in coolant. Coolant needs an exit, an exit can be found under prolonged vacuum. If the system is using coolant, it needs to be fixed imo. If mine used coolant (diff design though just as hot)I might even opt to email Mercedes corporate and ask them if these cars use coolant. They make sure it’s to point out oil use in the manual.
I haven't noticed this on my 580 yet, but my 560 would blow through the cap to the reservoir, you could see the dried coolant. I replaced the cap a couple of times and it always started doing it again.
I haven't noticed this on my 580 yet, but my 560 would blow through the cap to the reservoir, you could see the dried coolant. I replaced the cap a couple of times and it always started doing it again.
I haven't noticed this on my 580 yet, but my 560 would blow through the cap to the reservoir, you could see the dried coolant. I replaced the cap a couple of times and it always started doing it again.
This is also the only place Ive ever had it my vehicle as well, and the same after a new reservoir. New cap works as you said. I bought a pack of two last time and expect them to last pretty well since the first cap had a life of over ten years. Never had to top up as it was/is just a few drops a year and I could never determine what might make it happen. Maybe it's "getting on it" before the thermostat opens naturally but these stats are supposed to open anytime under full throttle. Never have had a drop from the turbo coolant cap though.
Not sure if you saw the Legit Street Cars episode where Alex had a radiator leak at the cap and discovered someone had mixed the caps for the intercooler and radiator. This was on the terminator mustang. The intercooler cap is a lower psi in that case. I wonder if our caps have different psi ratings or if a slightly higher rated cap (a few psi higher) could help for the expansion tank. I know I dont buy stuff like that from the dealer so the aftermarket may not be perfect or better or worse.
Last edited by Baltistyle; Sep 29, 2025 at 08:56 PM.
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