I have noticed that the coolant level in the radiator of my 280E (W123) always drops an inch or so below the inverted 'T' guide, no matter how often I top it up.

Once it's dropped down a little, it stays there. And there's no leak, I've checked thoroughly.

The only thing I can think of is that it might be something to do with the radiator cap, which is marked '90', although there is an original M-B sticker on the fan shroud that says a 100 cap must be used.

I'm thinking the previous owner may have substituted a 100 cap for a 90 to prevent overheating, although this has never happened to me. Could this be the cause of the drop?

Any thoughts, gentlemen?

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Chris Hunter

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1977 W123 280E auto
Cayenne Pepper orange
289,000km
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Coolant pressure is forcing EXCESS coolant from the system. It's going out the overflow hose whenever the engine is hot enough to push cap open. The latest cap for W123 is 120 & that is equal to 17psi.

The higher the number on the cap and THE MORE PROTECTION you will have. When the coolant system pressurizes, the coolant that is under pressure is less likely to boil.

Use the 120 cap. (1.2bar)

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Benzmac:
Donnie Drummonds
300E
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM
OWNER OF MB AUTOWERKS .COM

Thanks for the advice. I've just been down to my local dealer and bought a 120 cap. They looked at the 90 cap and proclaimed it non-original.

Now I just have to hope that the hoses on my car hold out at 1.2 bar, as opposed to 0.9!

Incidentally, I had the cylinder head gasket replaced on the car recently, and when the mechanic filled up the cooling system, he only put a little bit of anti-freeze in ... the reason being, "it is better to let the new gasket seal before full-strength anti-freeze is added." Mmmm. I'm not sure about that one, I might drain half the coolant and replace it with Mobil One anti-freeze.

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Chris Hunter

1977 W123 280E auto
Cayenne Pepper orange
289,000km and goin' strong ... touch Zebrano.

I have this problem in my 1989 300se, which cap should I be using?

Thanks very much guys!!!



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Oliver Plante
1989 300SE 134k
1993 500SE 98K

Chris,

I would recommend that you flush the coolant system as best you can, followed by a fill of 50% antifreeze.

I think the technicians reluctance to put in antifreeze must be based on some old wives tale.

Good luck,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

Most all cars after 1988 should be using a 140 cap (1.4=21psi). The newest cars use a screw on cap that can vary pressure up to 2bar.

I think most dealers only stock the 140, but I used the 120 on my 91-300E and 95-S320.

jack