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Cooling System Flush

Now something a little different from my usual Model Railroading posts:

I had a pinhole leak develop in my car’s radiator. Now, the original radiator lasted from when the car was built in late 1999 to mid 2005, and this replacement radiator lasted from mid 2005 to mid 2012, so the aftermarket radiator was better than the Mopar radiator, but nothing lasts forever. Unfortunately, while I was arranging for the replacement radiator, I had to add a lot of water to the system, diluting my coolant, and causing rust.

With an aluminum engine block, aluminum heads, and aluminum radiator, there isn’t much of a source of Iron or Steel to rust. I know the Bosch water pump I changed last spring had a cast iron impeller rather than the usual plastic one. Swirling around in the coolant, now highly diluted and lacking any corrosion protection, I figure that’s what’s caused the fine layer of rust everywhere.

No problem, I thought. I’ll just do a coolant flush and get rid of the rust.

Well, the devil is in the details. Nutritionists advise us to read the label and look at the ingredients. As a mechanic, I advise the same, but in this case, since the labels don’t have the ingredients, we have to obtain the Material Safety Data Sheet (MSDS) to see what we’re buying. I didn’t, and went ahead and bought some radiator flush “over the counter” from some reputable sources. I was shocked when each, in turn, didn’t work as planned, and after I looked at the MSDS, I learned why.

First up was Prestone ® Super Flush, purchased at the local Walmart. In fact, it was the only cooling system flush Walmart sold, but for less than $5, what did I have to lose?  The instructions say to use this product for 10 minutes after getting the cooling system up to normal operating temperature. I did, and when all was said and done, I still had a nice fine layer of rust in my hoses, in  the inlet into the water pump, and in my pressurized coolant tank. When I looked at the MSDS, I found that it contains Sodium Citrate (5-15%) and water. Sodium Citrate is a sodium salt of citric acid. While citric acid is one of those chemicals people have recommended to clean cooling systems (including Mercedes Benz), Sodium Citrate is not Citric Acid. It’s like comparing table salt (sodium chloride, or NaCl) to Muriatic Acid (Hydrochloric Acid, or HCl). Sodium Citrate is a food additive and alkalyzing agent. It will neutralize acids but won’t do anything for oil, gunk or scale, and as I found, won’t remove much of the rust, either. So  the best this will do is to neutralize residual acids left in the coolant that remains behind (in the heater core and nooks and crannies of the block) after draining spent coolant. None of these additives clean or descale the cooling system. There’s nothing to break down, disolve, or suspend any of the rust, minerals (scale), or oils (i.e. “sludge”) that might be in the cooling system.

Next up, I went to a local auto parts store, and bought the only product they carried, Peak Performance Super Cleaner and Flush. This product is to be put in the cooling system and left there for 3-6 hours of operation. In other words, you can leave it in there a couple of days.  This also didn’t do anything. Looking at the MSDS of it, I now understand why. It contains:

  • Water 63 – 64%
  • Ethylene Glycol 34 – 36%
  • Diethylene Glycol 0 – 2%
  • Denatonium Benzoate 30-50 ppm

Water just makes you feel good for buying a 12oz. bottle instead of a 6 oz bottle. Ethylene Glycol you might recognize as the active ingredient in anti-freeze. Diethylene Glycol is “present as an inadvertent byproduct of ethylene glycol production.” (Wikipedia) Denatonium Benzoate is a chemical used to bitter the Ethylete Glycol so it doesn’t taste sweet. It’s also used to denature alcohol. This is even worse than the Prestone product. All it is is a very dilute antifreeze. Probably just enough to lubricate the water pump for the 3-6 hours you’re going to leave this in your engine. The only cleaning this product does is to your wallet.

After doing some digging, it looks like Permatex Heavy Duty Aluminum Radiator Flush is a serious flushing agent. The ingredients are:

  • Citric Acid 10-30% – an effective remover of rust and corrosion and scale – see above recommendation, including by M-B.
  • TetraSodium EDTA 5-15% – Chelating agent – dissolves scale and holds it in solution.
  • N-METHYL-2-PYRROLIDONE <5% – Solvent/degreaser, often used as a paint remover, it’s especially effective at dissolving polymers/gums/gunk.
  • 2-Butoxyethanol <5% – A solvent/degreaser – will remove grease & oil
  • POTASSIUM HYDROXIDE <5% – Raises pH and also dissolves oxides
  • Dodecylbenzenesulfonic acid <5% – A surfactant (wetting agent) – a primary ingredient in detergents

Nobody around here carried it. I had to order it through Midway Auto Supply via Amazon. Glad I did. This is the only product that worked.

Update (7. July 2015): Permatex no longer carries this product. After doing some research, Motor Medic by Gunk C2124 Super Heavty Duty Radiator Flush – 22 oz. and Motor Medic by Gunk C2232 Super Heavy Duty Radiator Cleaner – 32 oz. are both the same product as the Permatex Heavy Duty  Aluminum Radiator Flush. The MSDS files show the same ingredients and they come in the same bottle, just have different labels.

I rinsed the system with distilled water, then did a fill with the recommended Zerex G-05 coolant. This is the same formulation as the Mopar 5 year/100,ooo mile Hybrid Organic Acid Technology (HOAT) coolant, and is also sold by Ford as their Premium Gold Engine Coolant. The Mopar coolant is about $5-$10 more expensive per gallon than the Zerex or Ford brands, and since I need more than one gallon to fill the system (mixing with distilled water), the savings is rather substantial.

Thanks for reading!


  1. Anne wrote:

    Thumb up!!!

    Tuesday, September 18, 2012 at 12:46 | Permalink
  2. Irwin wrote:

    I do not believe the MSDS for PEAK – it is exactly their antifreeze as you say.
    Tractorsupply lists different ingredients for PEAK Super Flush ––1022659

    Gluconic acid supposedly would remove calcium deposits if a decent concentration is provided.
    From other sites I was led to NAPA: their low priced MAC provided flushes are also loaded with cleaners as well as 30% citric acid.
    I saw the Permatex listed, likely have to order ahead

    Monday, October 29, 2012 at 21:06 | Permalink
  3. Arved wrote:

    I found this MSDS for MAC Radiator Flush: contains Gluconic Acid and Sodium Hydroxide. Doesn’t the Sodium Hydroxide neutralize the Gluconic Acid? That would leave you with a worthless salt.

    Tuesday, October 30, 2012 at 00:09 | Permalink
  4. Jim wrote:

    I am glad I found this site. I just started to google the active ingredients in coolant flush. Your site came up as one of the results. You saved me a ton of time researching each ingredient from the MSDS. Thank you for the Permatex product. I will be ordering some soon!


    Saturday, March 21, 2015 at 20:40 | Permalink
  5. Arved wrote:

    Glad I could help. I hope your flush goes well. Mine went very well. No more rust in my cooling system!

    Sunday, March 22, 2015 at 23:44 | Permalink
  6. anita wrote:

    Thanks, I m happy I found this site through google. Very much needed information

    Wednesday, May 27, 2015 at 05:55 | Permalink
  7. PETE wrote:

    Thanks for the information. I am about to flush a 1993 Ford (IH) 7.3 IDI diesel ( brass/copper radaitor and cast iron block/heads) with visible rust and scale in the radiator. It looks like that the Prestone Super Flush might the best bet unless I do a home brew flush with citric acid or oxalic acid following up with baking soda neutralization.

    Thursday, November 12, 2015 at 08:56 | Permalink
  8. Arved wrote:

    I’m glad I could help! Good luck with your flush. If you can check pH (such as with a pool test kit), that would make sure you have just enough baking soda to neutralize. You may also want to consider a little lye to neutralize, but if you’re going to use anything powdered, I’d dissolve it first so you don’t end up with powder abrading things or changing the pH of your coolant later on. Final flush with distilled/deionized water is also a good idea.

    Thursday, November 12, 2015 at 20:42 | Permalink
  9. SUBODH KUMAR wrote:

    An appreciable efforts had been done for learners.

    Thursday, December 3, 2015 at 02:02 | Permalink
  10. Hale Ramsey wrote:


    Thanks for your post on cooling system flush products. Prior to a career change, my family ran a radiator shop for 10 years and one of the things I learned is that there is a need for quality information about cooling systems and how to maintain and repair them. I am currently dealing with a system that has been “repaired” with some sort of “stop leak” goop that did little but gum up the entire system. Having been out of the business for some time, your post provided good information on products currently available and some guidance on which ones to avoid or pursue. Thanks for posting the MSDS information. It saved me a lot of time.

    Monday, December 12, 2016 at 17:26 | Permalink
  11. Arved wrote:

    Good luck with that gummed up cooling system!

    Happy New Year,
    – Arved

    Wednesday, January 4, 2017 at 14:36 | Permalink

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