Citric Acid Cooling System Flush - PeachParts Mercedes-Benz Forum

N41EF · #1 09-17-2007, 11:05 PM

Ok, 2000 C230k, had green coolant and a leaking overflow bottle. Replaced bottle and new pressure cap, and coolant return hose that was leaking. Drained all coolant from radiator and flushed with prestone radiator super cleaner that I ran for a day of errands. Did three or four drain and fills to get the water somewhat clear, then bought the citric acid and ran that for a few hours. First drain was nasty. black and green with all kinds of sediment and crap. Been through 4 more drain and refils, and the water started to clear up, now is back to black and green nastyness. I drain the car everynight and refill with plain water, drive to work and back, then drain next night after it cools down.

1. How many drain and fills does it usually take to get back to clean water?

2. The citric acid flushed all kinds of stuff loose, anyone use it on their other cars? I'm thinking about getting another container to flush my land rover.

3. Does a M111 have a block drain? looked left side forward of the starter, found nothing. The right side is so covered up can't see anything there either.

I want to see clean water draining out before i fill with the DI water and mercedes coolant. The car does seem to run cooler, between 80 and 85 in traffic, of course the weather has cooled a bit too. Was running close to 100 in traffic with max AC on.

RKreutzer · #2 09-20-2007, 07:44 PM

Hi there,
I can't help with the engine drain plug but if you measure the volume you put in the system and compare it with overall coolant capacity from the Owners Manual, you can roughly estimate how many % you are replacing each time. I flushed my 420 a few years ago and it took about 9 flushes to have less than 1% of the original fluid left.
You should also have the heater on, I believe, to have the water circulate there.
I used hot water and did it over an evening back then.
Good luck

LUVMBDiesels · #3 09-20-2007, 07:56 PM

When I did the 300SD and the BMW, I removed the thermostat so that i could flush and drain without letting the car get too hot for me to work on . I also unplugged the mono valve so that it would circulate through the heater core.

I have done both the MB and the BMW and have great success with the flush.
One thing that I did was to leave the acid mixture in the car for a week of driving (about 400 miles) before starting the flush. If you cannot find the block drain, I would suggest getting one of those Prestone flush and fill caps and a new heater hose. I would cut the cap into the old hose while you are flushing and then replace it with the new hose when you are finished. It took me at least five flushes with me flushing at night and then driving the car during the day to get the water half way decent. I then did a marathon with the thermostat out flushing and filling until the water was clear. I would make sure that the water is clear and dos not feel 'slippery' as that is a sign of the acid still being there. I would not bother to fill with MB coolant until you are completely free of the old stuff.

This also makes the best time to change out your hoses and thermostat if you have never done this before.

I am planning on doing the truck this fall, but once it is all nice and clean I am going to hate filling it with "Death-Cool"

Good luck

N41EF · #4 09-21-2007, 11:29 PM

Well, finally got clear water out. I found the block drain on the engine, passenger's side back part of block, just forward of bellhousing, had a nipple on it to hook up a hose even. With the car cold, i hooked up a hose that would keep water from pouring in the O2 sensor, I cracked the drain open, until a trickle came out, and opened the radiator drain till a trickle came out, then started car and commenced filling the overflow bottle. I caught the radiator drain water, and checked it as it gradually cleared up, the water from the block drain got very, very hot, the radiator water got warm, I made sure the thermostat opend and ran the heater to flush it out too. It took about 14 gallons of water to get all off the black/green/crud out, then I turned car off, and ran about 5 more gallons through to let the car cool down. One the water from the block had cooled enough to touch I stopped filling and let all of the water drain out. I had the flush in the car for a day, and did four or five drain and fills but was still getting black crud out. Once cleaned out I filled with MB coolant and distilled water, and will do it again again in two years.

I plan to replace the intake gasket on my Land Rover this fall, and after seeing how much crap the citric acid flushed out AFTER I had used the prestone super cleaner I'll do an acid flush of it too. The citric acid isn't cheap, but why would you ever use anything else?

RKreutzer · #5 09-22-2007, 08:35 AM

Congratulations.
You can buy citric acid over the internet for a lot less than from MB. A quick google search brought up Brainerd Chemical, where it is 6.49 per pound or 23.75 for 8 pounds. I'm sure there are plenty of other sources.
Tap water will be fine too, MB is not calling for distilled water.
Hope your car runs cooler now.

TheEngineer · #6 09-22-2007, 10:10 AM

Litmus strips ! I have used Litmus paper strips for years to test the coolant. The blue paper strip turns pink in acid, the pink strip turns blue in basic. I want to see the pink strip turn a little blue.

Chad300tdt · #7 09-22-2007, 10:27 AM

I got 2.2 lbs. (which is needed for 1 flush) of citric acid from my local homebrew supply for about $6.

Kestas · #8 09-24-2007, 10:32 AM

[QUOTE=RKreutzer;1626209]... Tap water will be fine too, MB is not calling for distilled water...[QUOTE]
MB calls for demineralized water, which is not the same as tap water.

RKreutzer · #9 09-24-2007, 12:36 PM

I like your handle, Kestas...

Here is the quote from my owner's manual, page 104 Coolants:

"The engine coolant is a mixture of water and anticorrosion/antifreeze, which provides corrosion protection ..."

Further down:
"The water in the cooling system must meet minimum requirements, which are usually satisfied by normal drinking water. If you are not sure about the water quality, consult your authorized MB dealer."

There is also nothing on the antifreeze label that calls for special water.

Stoney · #10 09-26-2007, 11:15 PM

Unless my chemistry memory is bad, the major active ingredient in Prestone Super Flush (the 6 hour drive clean type) is Citric Acid/

Considering the local MB Dealer doesn't even STOCK the MB Citric Acid flush, I have been using the Prestone in double strength and have had very good results.

Ford 4.0 V6, MB 104, Volvo B230 were all descaled and flushed clean with the Prestone product (when used double strength) with no apparrent damage to the head or block.

CamelotShadow · #11 09-26-2007, 11:47 PM

Congrats on what seems like a cleaner radioator & water jackets.

I had a hot engine problem
I am not as handy
anyway my mechanic replaced the radiator
I suppose its best I didn't spend money haveing it flushed
may have been a waste
may have been ok

It seems even w a new radiator
a flush might be in order to clear water jackets

I have some scum on top od the coolant nowe after the radaitor change
anyway guess it just means I have good circulation now & its purging the system
I;d think a flush still could help my system

Anyway may all your efforts be fruitful!