General Car Conversation
Lexus Fanatic
Joined: Oct 2003
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From: Virginia/D.C. suburbs
CL Community Team
Joined: Feb 2007
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From: IL
....and plastic coolant reservoir caps, just like is the problem on his S560. I've never seen a metal reservoir cap that wasn't aftermarket. And even then, they'd still have to have a seal of some sort, which is presumably what failed.
At no time has Steve intimated that there is a problem with his radiator cap.
At no time has Steve intimated that there is a problem with his radiator cap.
Lexus Fanatic
Joined: Oct 2003
Posts: 94,602
Likes: 271
From: Virginia/D.C. suburbs
Of course not....not on newer vehicles. But they were standard on older vehicles...as were many metal parts that are now plastic. In fact, on the cars I grew up with and learned to drive on, there were very few if any plastic parts, period, except for distributor caps and maybe windshield-wash-bottles.
Thread Starter
Lexus Fanatic
Joined: May 2012
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From: Maryland
We’re talking about the reservoir cap, not the radiator cap. The MB reservoir cap is pressurized though, which other cars I have had it’s not…
Cant even see the radiator cap in this car it’s all under the plastic shrouding
Cant even see the radiator cap in this car it’s all under the plastic shrouding
CL Community Team
Joined: Feb 2007
Posts: 9,414
Likes: 632
From: IL
Of course not....not on newer vehicles. But they were standard on older vehicles...as were many metal parts that are now plastic. In fact, on the cars I grew up with and learned to drive on, there were very few if any plastic parts, period, except for distributor caps and maybe windshield-wash-bottles.
Pretty sure the whole thing, including the cap, is plastic.
Lexus Fanatic
Joined: Oct 2003
Posts: 94,602
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From: Virginia/D.C. suburbs
All the cars I remember from the 70s, including three we owned, had plastic coolant reservoirs with plastic caps. I don't have much experience with cars more than 50 years old, but for example, here's the coolant reservoir from a 1955 Buick Super:
Pretty sure the whole thing, including the cap, is plastic.
Pretty sure the whole thing, including the cap, is plastic.
Yes, that just repeats what I said earlier......that cars of that vintage had a few plastic parts, but very few.....mainly distributor caps, underhood fluid-reservoirs, and (sometimes) red taillight covers. In fact, the cars I learned to drive on (60s-vintage Plymouth Valiants) still had metal master-cylinder-reservoirs for the braking system.
Now, that's not to say that everything about plastic parts is bad....plastic doesn't rust or corrode like metal. But, in general, they lack the strength and heat-resistance that metal parts do...and they heave a tendency to crack and break.
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Lexus Champion
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From: FL
Plus, it's cheap to make plastic stuff aka just pennies per unit piece.
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From: Ohio
That is not a radiator or tank cap, that is a pressure bottle and that cap is the moderator for system pressure and vapors.
There is no rad cap on cars that use that style of coolant system at all, it is a non-overflow tank type setup and that cap is what functions similarly to a traditional overflow type system rad cap except that it is NOT intended to allow coolant to freely flow past it to a storage bottle when the system reaches operating PSI. It is also the emergency vent point if the coolant level reaches a very high state under heat or for other reasons, it is not supposed to allow/have a need to pass coolant. The reason I PMed Steve is to further explain the system and to tell him what to check since there may be an actual issue with the cap being the first victim.
There is no rad cap on cars that use that style of coolant system at all, it is a non-overflow tank type setup and that cap is what functions similarly to a traditional overflow type system rad cap except that it is NOT intended to allow coolant to freely flow past it to a storage bottle when the system reaches operating PSI. It is also the emergency vent point if the coolant level reaches a very high state under heat or for other reasons, it is not supposed to allow/have a need to pass coolant. The reason I PMed Steve is to further explain the system and to tell him what to check since there may be an actual issue with the cap being the first victim.
Lexus Fanatic
Joined: Oct 2003
Posts: 94,602
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From: Virginia/D.C. suburbs
Excessive pressure in the cooling system is usually caused by overheating. Is the temperature gauge (or warning light) normal? The S-class has a good-sized engine and power, which can produce a lot of heat even without a turbo.
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Lexus Fanatic
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From: Maryland
The cap should be designed to withstand the heat the engine makes under normal conditions.
I did have this thought, remember how I added those covers that mysteriously Mercedes stopped putting on the car in 2019? I wonder if maybe this is why they removed the covers? This reservoir is underneath one of those covers
How mine came from the factory:
We assume that this was a cost savings measure, but maybe it wasn't...
Lexus Fanatic
Joined: Oct 2003
Posts: 94,602
Likes: 271
From: Virginia/D.C. suburbs
The cap should be designed to withstand the heat the engine makes under normal conditions.
I did have this thought, remember how I added those covers that mysteriously Mercedes stopped putting on the car in 2019? I wonder if maybe this is why they removed the covers? This reservoir is underneath one of those covers
However, I can't state with credibility that the cover you stuck on directly caused the cap-problem...I'm not enough of an engineer to do so.