Engineering error or wrong material?
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Junior Member
Joined: Aug 2007
Posts: 21
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From: West Seattle, WA
'69 280SL, '95 E320 Wagon, '86 Toyota SR5 Truck, '69 Honda Trail 90,
Engineering error or wrong material?
On this '95 E320 wagon I found the coolant recovery tank cracked and leaking. Unlike other cars, this tank is under radiator pressure and exposed to hot coolant. It is made from Polyethylene and cracks under pressure with age. On other cars the coolant recovery tank is not under pressure: The pressure cap is on the radiator, the tank only catches expanding coolant. On my W113 the tank is also under pressure, but it is made from brass. Are there other Mercedes models that have a metal tank I could fit? Can the plastic tank be repaired? Anyone else having the same problem? Any good ideas?
Last edited by TheEngineer; Sep 6, 2007 at 10:32 PM.
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From: San Diego Californ-i-a
89 300TE, and 68 280sel
I just replaced mine about a month ago, they are innexpensive and quite easy to do. They are using the same materials today, so I am guessing that the problems just come with age.
If you are looking for a local supplier of parts at great prices try www.mercedessource.com I used to work there and they have some of the best prices I can find anywhere.
If you are looking for a local supplier of parts at great prices try www.mercedessource.com I used to work there and they have some of the best prices I can find anywhere.
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Joined: Mar 2007
Posts: 203
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From: California,Washington,St.Croix
Very Slow Mercedes
Engineering error???? this is a 12 year old tank exposed to 300 Degree heat for the last 12 years,,,you should call Mercedes Benz and thank the engineers for making such a good piece of plastic...You have a nice selection of cars but up until the W124 they are rudementary,the perfection on the
w124 will never be allowed again in our lifetime...Even the almightly AMG cars of today do not have the build quality of the W124..
w124 will never be allowed again in our lifetime...Even the almightly AMG cars of today do not have the build quality of the W124..
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Joined: May 2003
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From: Motor City
95 E320 Cabriolet, 108K
To add -- many manufacturers, including the American ones, are increasingly switching to pressurized plastic overflow tanks. Get used to it. Brass is incredibly expensive nowadays.
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Junior Member
Joined: Aug 2007
Posts: 21
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From: West Seattle, WA
'69 280SL, '95 E320 Wagon, '86 Toyota SR5 Truck, '69 Honda Trail 90,
Engineering error???? this is a 12 year old tank exposed to 300 Degree heat for the last 12 years,,,you should call Mercedes Benz and thank the engineers for making such a good piece of plastic...You have a nice selection of cars but up until the W124 they are rudementary,the perfection on the W124 will never be allowed again in our lifetime...Even the almightly AMG cars of today do not have the build quality of the W124..
From an engineering perspective however: Polyethylene is a very good material for many applications. A pressurized tank containing hot coolant is not one of them. Proof of this observation is the failure of this part. As I pointed out in my earlier post, When the tank is not pressurized and merely an overflow tank and doesn't get very hot, then Polyethylene is a very good choice. Mercedes, of course, knew this. On my '69 280 SL the pressurized tank is metal. But plastic is much cheaper and lasts as long as the first owner statistically keeps the car. I can buy a new tank for $32. So what am I complaining about? I can also check the coolant level visually and because the tank gets dirty after so many years, it's easier to throw it away than to clean it. It's a design philosophy thing and you have correctly observed that the older cars have "built quality". The new designs are built to be cheap and to be replaced after use. When an engine goes bad, it is replaced by a new engine rather than rebuilt. Easy, and no liability by the rebuilder. Same thing for other components. Systems become modular. If the clock fails, you must replace the entire instrument panel. Cars have become an appliance like a microwave or a lightbulb. You may have noticed that some people cherish old cars/motorcyles and spend a lot of money on restauration, far more that it would cost them to buy a new model. And many people admire these old classics. It has been said that men are primarily motivated by ego and I admit that it deeply satisfying to fix something that was claimed "unrepairable"
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From: Bellevue, NE
1995 E320 SE, 162,000 Miles (Sold) 2007 CLK350 Cabriolet 2014 ML550
I, too, am an engineer of sorts. For what it's worth, these tanks have a very low rate of failure. The pressure is only about 1 bar and polyethylene is actually pretty stable. IMO, MB made a good call with this tank. Now if they could make the AC evaporator last that long... 
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From: West Seattle, WA
'69 280SL, '95 E320 Wagon, '86 Toyota SR5 Truck, '69 Honda Trail 90,
Ok Guys - I give in! I see that at the mercedessource.com they list the tank for $32 and I just ordered one. Thank you myfirstbenz for pointing out that supplier! I was wrong to complain!
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From: REHOBOTH BEACH DE
88-300CE TWIN TURBO, 99-C43, 05-G55K, 71-280SL, 94-E320 CAB, 08 CLK63 BLACK SERIES
I, too, am an engineer of sorts. For what it's worth, these tanks have a very low rate of failure. The pressure is only about 1 bar and polyethylene is actually pretty stable. IMO, MB made a good call with this tank. Now if they could make the AC evaporator last that long...
Couldn't agree more....just about any new production vehicle uses a similar style, albeit with more modern compounds.
Would rather have a "plastic" product that is inert to the coolant, then worry about a "lifetime" metal container that secretly is contributing to rust in my cooling system !!!
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Joined: Jul 2007
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1994 E320 Dragon Wagon
Yeah, mine is the same spec thick plastic. They indeed are high-pressure. The neck is reinforced with metal around the cap seal also rated in lbs.
I'd just get a new plastic tank, mine is 12 years old and original. That's a pretty good life span.
There is a method to "weld" poly-plastics gooing the crack with a soldering iron. Great for no pressure applications not your Boiler Tank though.
I'd just get a new plastic tank, mine is 12 years old and original. That's a pretty good life span.
There is a method to "weld" poly-plastics gooing the crack with a soldering iron. Great for no pressure applications not your Boiler Tank though.
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Junior Member
Joined: Aug 2007
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From: West Seattle, WA
'69 280SL, '95 E320 Wagon, '86 Toyota SR5 Truck, '69 Honda Trail 90,
Yeah, I talked to my friendly, local plastic fabricator about welding: He said:
" Buy a new tank. The cracking indicates that it has become old & brittle. If we weld, it'll just crack somewhere else or where it has been welded".
" Buy a new tank. The cracking indicates that it has become old & brittle. If we weld, it'll just crack somewhere else or where it has been welded".
