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Old 03-18-2001, 10:02 AM
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Join Date: Apr 1999
Location: Apex, NC USA
Posts: 176
Read all the posts about the citric acid flush. One question though. How does one flush water through the cooling system to remove all the old coolant and susequently the citric acid solution?
1991 350 SDL
183,000 miles

1982 240D
130,000 miles
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Old 03-18-2001, 11:50 AM
Hazen's Avatar
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Join Date: Jan 2001
Location: Redmond, WA
Posts: 57
The process goes something like this:
First you drain the old fluid from the radiator and the block. Your manual will tell you exactly where the drains are.
BTW.This fluid is attractive to pets and children as it is sweet, but very toxic. It'll kill 'em if they get enough, so drain and dispose of at your local McParts store, or take it back to the dealer from whence you bought the new stuff and flushing agent.
Secondly you pre-mix the citrus flush in a gallon of water making sure it has completely dissolved. This procedure is also in the manual.
Thirdly, close the drains and open the bleeding screw/bolt. Fill the system through your reservoir a bit at a time. Start the engine, turn your heat on to max and let it come up to operating temp. Let the flush circulate through the system for 5-10 minutes after the temp gauge reads normal, ie, 80 -85 degrees Centigrade.
Fourthly, shut off engine and drain flush as in first step.
Fifthly, close radiator drain and fill through reservoir with clean water. Again start the engine and keeping the reservoir full with clean water let it circulate through the system until it is running clear from your block drain - maybe ten minutes.
Sixthly, drain radiator.
Seventhly, close block and radiator drains to proper torque, mix water (I use distilled) and anti-freeze-corrosive (I use MB's) and fill radiator through reservoir. When full start engine (Heat still at max) bleeding screw still open and keep adding mix at reservoir as the level goes down. Do this until mix begins to flow out of bleeding hole. Close bleeding screw at proper torque and let engine come up to temp. Keep an eye on reservoir level until it stabilizes at the Max line. Check for leaks and tighten leaking parts incrementally until leaking stops. If you have to exceed torque values to stop a leak, DON"T! Something else is wrong. Back out and re-torque. Breaking drains/radiators etc. can turn a simple inexpensive chore into a journey of the damned! For the next week keep an eye on the reservoir and keep adding fluid as your system burps itself.
Additional bits:
Since I do this for all our vehicles every two years, I also replace their thermostats and radiator/reservoir caps - preventative maint. and cheap. I use OE.
Where heater core lines are readily accessible I cut in a "T" from a Prestone flush kit to facilitate the flush. Follow the directions on the kit.
Some MB's have a seperate procedure for flushing heater core. Your manual will tell you.
Also a great time to replace hoses if they need it -dry brittle-soft spongy- bulged - the usual signs.
Really a messy plebian chore. On the other hand it uses up an afternoon and gets me out of doing stuff SWMBO wants me to do that are messier and more plebian!
Hazen Arnold
Happiness is a well stocked
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Old 03-18-2001, 03:38 PM
Wm. Lewallen
Posts: n/a
Hazen Arnold is right about the citric acid flush, but to really do the flush right you should first do a degreaser flush. Acid alone will not remove any oily deposits in the cooling system. The MB degreaser part no. is 001 986 21 71.
It cost about $11. You can also use TSP;available at hardware stores. Cheaper, and more readily available is just a plain non-foaming dish washing compound. It works just as good. As for the citric acid, you can get it at the super market. Look in the home canning section. Or get it from the MB dealer. Part no.000 989 10 25. Cost about $17.
The whole flushing procedure will take about an afternoon, but most of the time will be spent waiting for the chemicals to do their jobs.
Bill Lewallen Lexington,Ky. The Bluegrass State, where the grass is really green, and our coolant is Green.
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Old 03-18-2001, 04:13 PM
240Joe's Avatar
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Join Date: Nov 2000
Posts: 525
Just a thought. I think flushing your cooling system is a good idea to replace the old worn out coolant (it does wear out I'm told), but in my experience, flushing won't cure most overheating problems, and I don't seem to get much of any curd out of the system when I do it.

Over the years, I've had cars that would overheat and the causes were usually bad thermostats, or ignition timing too retarded (gas engines), and radiators that needed to be "rodded" out to remove the insulting layer of scale.

The cars that needed the radiators rodded did have their systems flushed out periodically, but still plugged up their radiators.

Maybe Bill has more insight into my observations.


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Old 03-18-2001, 05:06 PM
Wm. Lewallen
Posts: n/a
Joe, and others;
I guess the water here in Central Kentucky is fairly soft because I've never used distilled water in any radiators,and we have a still in the laboratory that makes three gals/hr.I do use the distilled water in our batteries.
Maybe the reason we don't have scale in our radiators, is the fact that we use the green coolant(Prestone). Shhh, don't let everyone know we are using the best and most popular brand of antifreeze.
Bill Lewallen Lexington,Ky. The Bluegrass State, where the grass is really green, and we use the Green coolant.
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