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  #1  
Old 05-05-2011, 02:34 AM
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Going to do the citric acid flush next week, quick question

Ok so I ordered 2.2 pounds of citric acid, I have 16 Oz of Shout, and I have some MB coolant.

Really all I need to know is how many Oz I need to pour into my cooling system before I run my car each time.

Currently I am going to drain the radiator, drain the block (does this plug have a washer that needs replacing?), refill with the shout mix (how much water?). Idle for 10 minutes, drain and flush until it is not soapy anymore.

Then I am going to mix 2.2 lbs of citric acid with warm water (how much warm water?) and pour it in the expansion tank? Should I fill the radiator with water too?

Then Im going to drive for 60 miles, drain the block and radiator, pull all of my hoses and flush with a garden hose. Fill with distilled water and drive and flush 3 times.

Then I will fill with a 50/50 coolant mix, burp the system by parking on a incline, opening the overflow cap and turning on the heat while idling for how long?

This all sound good? Really the only thing I am not clear on is how much water to put into the system, I dont want to put too little in...

Thanks!!


Last edited by frankengrant; 05-05-2011 at 02:55 AM.
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Old 05-05-2011, 03:19 AM
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Originally Posted by frankengrant View Post
Ok so I ordered 2.2 pounds of citric acid, I have 16 Oz of Shout, and I have some MB coolant.

Really all I need to know is how many Oz I need to pour into my cooling system before I run my car each time.

Currently I am going to drain the radiator, drain the block (does this plug have a washer that needs replacing?), refill with the shout mix (how much water?). Idle for 10 minutes, drain and flush until it is not soapy anymore.

Then I am going to mix 2.2 lbs of citric acid with warm water (how much warm water?) and pour it in the expansion tank? Should I fill the radiator with water too?

Then Im going to drive for 60 miles, drain the block and radiator, pull all of my hoses and flush with a garden hose. Fill with distilled water and drive and flush 3 times.

Then I will fill with a 50/50 coolant mix, burp the system by parking on a incline, opening the overflow cap and turning on the heat while idling for how long?

This all sound good? Really the only thing I am not clear on is how much water to put into the system, I dont want to put too little in...

Thanks!!
Just mix with warm water in a gallon bucket add to system and continue adding warm water until system is full.IMHO, I am not so sure I would drive 60 miles on a citric acid mix with an unknown system. I ran my car for 15 minutes max and then drained, rinsed etc. Better safe than sorry as many on this site have reported problems after aggressive treatment - both my diesels were treated this way with no problems, but again, I was being very conservative -too much too long can dissolve weak metals, careful -
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Old 05-05-2011, 09:56 AM
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please report back with your results.
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Old 05-05-2011, 11:10 AM
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where do you get citric acid?
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Old 05-05-2011, 11:20 AM
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Originally Posted by biopete View Post
where do you get citric acid?
OJ, not of the Simpson variety...

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Old 05-05-2011, 11:28 AM
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Perhaps you have a good reference which is why you've bought 6+ lbs of citric. But that sure seems like a LOT more than I'd want to put in.
How does 2.2 lbs become 6+ lbs?


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I could easily be wrong...
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Old 05-05-2011, 11:32 AM
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Originally Posted by frankengrant View Post
Really all I need to know is how many Oz I need to pour into my cooling system before I run my car each time.
That's not all you need to know. Flushing with citric acid is risky business. I would follow the FSM instructions to the letter. Even then, I would not expose my heater core to citric acid. Radiators are easy to replace; heater cores are not.
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Old 05-05-2011, 07:17 PM
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As tango mentioned, risky. What are you trying to solve? If it's a radiator problem, have the radiator ultrasonically cleaned and tested out of the car, if just basic gunk in the system try the detergent method.

Acid eats alkali metals as soon as it contacts them (aluminum et al), especially in the presence of less anodic metals (such as a massive amount of iron surface area). It doesn't wait 60 miles, not even 10-15 miinutes, it starts right away. If your heater core is marginal, it might not survive the treatment, or if it is still good, you're removing critical metal and shortening its life. If you don't need acid in the system then don't do it.

There is a lot that some mild detergent or even a good water flush can accomplish.
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Old 05-05-2011, 11:35 PM
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Citric Acid Source, Why, Amount, & Flushing

  • My average temps dropped by 5 degrees around town. Big difference was cooling capability on long hills. Probably 15 degree difference.
  • Why? Improves coolant contact with the water jacket surface.
  • You can buy Citric Acid at your local home brew supply store for about $3.00.
  • I went conservative as well and used 1/2 cup acid/gallon of warm water then topped off with water.
  • Ran it for about 5-7 minutes with the heater turned off then drained.
  • Let it completely cool (3 or so hrs), refilled with distilled h2O....repeated three times with the heater turned on.
  • Also drained via the block valve.
  • Also should remove the thermostat if you are going to do this because flaked material will probably get caught up in it. I forgot to remove mine (new) on the first drain. Pulled it out and sure enough some debris was lodged in it.
  • I've since added "WaterWetter" by Redline. Supposed to also increase cooling surface / coolant contact. Seems to help.
  • Currently running 2/3 distilled water & 1/3 MB Coolant.
I'm in Arizona this week and it is hovering around 100 F. A/C blasting on yesterday's drive up to Flagstaff (4,000' climb) at 70 - 75 mph and running between 80C (down hill) & 95C (long steep grades) water temps...

Beautiful. Wasn't that way prior to the flush!

P.S. Don't put cold water in your hot dry motor!!!
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Last edited by 86-300sdl; 05-05-2011 at 11:54 PM.
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  #10  
Old 05-06-2011, 12:55 PM
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Based on what I read here, and by doing a google search for other sources, when I was replacing the rad in my 1980 300td last summer I put my citric acid back on the shelf and just did flushes with mild detergent, then over and over with water, until things ran clear.

The stuff I read did not fill me with optimism for doing the acid flush on a car of that vintage.
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Old 05-06-2011, 04:26 PM
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Wow some really good posts here. Thanks a lot guys. I guess I am reading the wrong threads here because I took my plan directly from old posts :O

Thanks a lot! I will do a very mild citric acid flush, 1lb for 10 or so minutes.

So dont let anything into the heater core? Mild detergent? I assume it is very dirty in there, my heat did not work for years (I assume) until I recently replaced the monovalve.

Also how do you fill these cars radiators? Fill from top hose until you cant fill anymore? And then fill expansion tank to "fill line" (right over the sensor plug)?
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Old 05-06-2011, 04:53 PM
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I've had my '90 300D less then a year. The PO wasn't terrible but he wasn't very good when it came to caring for the car. So I'm going through and doing a thorough job.

I flushed my system about 2 weeks ago. I used distilled water for everything. Pure water is an amazing solvent.

First I drained what was in the system, then I filled it with tap water, ran the vehicle on the road for 10 minutes or so with the heater on high. Then I came home, emptied the system and filled with distilled water and a commercial citric product (I'm not saying is better then using the pure crystal as you are, I'm just saying what I did) and drove it for 15 minutes with theater on high as per the instructions on the bottle. Then I came home, flushed the system and filled it a second time with distilled water and one bottle of the commercial citric flush, drove for 15, etc.

I then filled the system with distilled water, drove for 15 minutes with the heater on, drained, refilled, drove and drained. The water coming out at this point should be very close to neutral, pH ~7. If in doubt see if you can find some litmus paper or better yet universal indicator paper. if you know a lab guy let him test your pH if concerned. But two good flushes with distilled water (powerful stuff) after driving will clean it up.

Then I drained again, partially filled with distilled water, added Purple Ice (similar to Wetter Water) and added enough quality anti-freeze (designed for aluminum systems) to obtain a 40% AF/Water ratio. I live in the SF Bay area so the 40% mixture is fine, maximum protection is around 60% but the system will run cooler at the lower concentrations of anti-freeze.

This is much more thorough then most will do and probably then is needed. I've got the tools, I usually know what I'm doing (yeah right) and I like having high confidence it's done right. I sold my last MB diesel at 400K (miles) and I'd like another 250K out of this one. There are a lot of experienced people on this board and many of their comments are valuable so I'm not claiming to have the best answer.

Last edited by sjh; 05-06-2011 at 07:01 PM.
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Old 05-06-2011, 05:57 PM
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Quote:
Originally Posted by sjh View Post
I've had my '90 300D less then a year. The PO wasn't terrible but he wasn't very good when it came to caring for the car. So I'm going through and doing a thorough job.

I flushed my system about 2 weeks ago. I used distilled water for everything. Pure water is an amazing solvent.

First I drained what was in the system, then I filled it with tap water, ran the vehicle on the road for 10 minutes or so with the heater on high. Then I came home, emptied the system and filled with distilled water and a commercial citric product (I'm not saying is better then using the pure crystal as you are, I'm just saying what I did) and drove it for 15 minutes with theater on high as per the instructions on the bottle. Then I came home, flushed the system and filled it a second time with distilled water and one bottle of the commercial citric flush, drove for 15, etc.

Then I drained again, partially filled with distilled water, added Purple Ice (similar to Wetter Water) and added enough quality anti-freeze (designed for aluminum systems) to obtain a 40% AF/Water ratio. I live in the SF Bay area so the 40% mixture is fine, maximum protection is around 60% but the system will run cooler at the lower concentrations of anti-freeze.

I'm sharing what I did. I had my reasons but there are a lot of experienced people on this board and many of their comments are valuable.
if this is the exact procedure you followed, you still have a lot of acid in your system.
I'd dump it ALL and flush several more times with tap water, then fill with distilled water, drive for 10 minutes, then dump THAT then fill with a good % mix of coolant,water wetter and distilled water.
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  #14  
Old 05-06-2011, 06:42 PM
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if this is the exact procedure you followed, you still have a lot of acid in your system.
I'd dump it ALL and flush several more times with tap water, then fill with distilled water, drive for 10 minutes, then dump THAT then fill with a good % mix of coolant,water wetter and distilled water.
Thank you John. I had meant to be helpful but I left out one VERY important step.

After the final citric flush I filled back up with distilled water, drove the car for 15 minutes with the heater on came back, flushed, refilled, drove for 15 minutes with heater on, came back emptied and then proceeded to fill with distilled water, Purple Ice and 40% anti-freeze.

After John's very necessary comment I went out to the car, took a 200 mL sample and tested with my pH meter (I own a business with lab facilities). The pH was 8.9. That is very slightly basic. NO acidic components of any consequence.

To give you a basis for comparison tap water here has a pH of 8.5 and the distilled water I have has a pH of 6.1. If any citric acid was present the pH would be in the 2 to 5 range.

John's comment above about flushing etc after the acid is essential. However, I prefer not re-introducing tap water if you have access to distilled it's a much better solvent, will dissolve more junk, then tap water.

Thanks for catching my screw-up. I'll go back and edit my original posting.

Last edited by sjh; 05-06-2011 at 07:14 PM.
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Old 05-06-2011, 08:47 PM
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I don't know if anybody else tried this, but I found it much easier to flush the block not by removing the plug (mine was frozen and would not come out) but instead disconnecting the heater core hose and butting up my watering hose to it, and just run water through it till it came out clear from thermostat hose. This way you don't have to go under your car

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