Hello,

This weekend I plan on changing the coolant and flushing the system out on my 87 190E 2.6 (M103). I have obtained MB degreaser and MB citric acid powder as per the plethora of posts on another list. The degreaser dilution is very clear from both the posts and the bottle itself -- 50g/L, or 450g for a 9L cooling system like mine. The recommendations for the citric acid dilution vary wildly however. There are, naturally, no instructions on the 500g bottle. Here are the 3 different amounts I have found:

Quoted from the Mercedes Microfiche, Engines 615, 616, 617.91 Mechanical III (not my engine, but how different could citric acid dilution be between engines...):

"Fill the cooling system with a 10% (100g / liter) solution of citric acid and water."

That works out to nearly 2 500g bottles of citric acid for my 9L system.

From a post on another list:

"The part # is 000 989 10 25 - that's enough to do one cooling system any size..."

About half the concentration of the previous post.

From a mechanic at Fletcher Jones MB in Newport Beach:

"Use about 3 tablespoons per gallon."

Huh?! There's probably more acid in straight tap water than that! I think he might have been mis-informed, so I am ruling that out for now (unless someone can verify that he was indeed correct).

So... Does anyone know how much should be used? I would greatly appreciate any input. Thanks!

John

At our dealer we use just 1 on a normal every 2 year flush. But if there was a running hot or scale problem we would use 2-3 depending on cooling system capacity. Of course mix in a gallon container with hot water, & then pour into engine.

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V

Drain the entire system. Flush it with water first, so you see a clear return. Dilute the citric acid powder in about 4.5 liters of water. Dump it in, top it up and run it up. Follow directions after that. This whole citric acid thing has taken on a life of it's own. No one seems to report a dramatic improvement after this flush is done, so it's a crap shoot. If you use the whole 500g bottle in 9 liters you get a 5% solution. 5%, 10%, whatever. No one can really come up with a number that will effectively cut through scale, etc. Personally, I don't think citric acid is useful for this application at all. If your radiator is to the point that you think it's that clogged up, then give it to a radiator shop and let the pro's do it right. If they mess it up, then you can always come back at them. Anyway, try it, you've got nothing to lose but time and $$$. You might clear some of the crud out of the block, but a good detergent or degreaser will probably give you the same result. Changing the coolant and monitoring the health of the cooling system is probably just as effective as flushing with a weak acid solution. Just my $0.02

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Jeff Lawrence
1987 300e
1989 300e
1987 BMW 325

[This message has been edited by jeffsr (edited 06-30-2000).]

Reading all of the above, I can't help but wonder if it wouldn't be easier to get a gallon or two of vinegar from a restaurant ($2.50/gal), and use it for an acid flush
After all, I believe acid is pretty much acid,- the strenght is what's important. This makes me start to suspect that MB uses a powder because its 'safer' than H2SO4 if you spilled it on your hand or other extremity. (ouch! )