Sacrificial Anode

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Product Specifications for the Rad Cap Anode


Installation Instructions for the Rad Cap Magnesium Sacrificial Anode







Congratulations, you have purchased the exciting new "Rad Cap" to stop Electrolytic Metal Erosion (EME) inside the cooling system and engine of your vehicle. This unique and patented new product has been several years in development and is the most effective and verifiable way to stop engine and cooling system damage from electrolytic activity. 


The "Rad Cap" uses the worlds latest technology in the cap sealing components. The "Rad Cap's" significant difference is in the "Anode" and spring mounting system attached to the bottom surface of the cap. Sacrificial anode technology will extend the life of all the aluminum components in your engine;  including heads, intake manifolds, water pumps, etc. Many users also report that the Rad Cap lowers the operating temperature of their engine under heavy loads.




1) To install your new "Rad Cap",  wait until the engine and cooling system are cold,  (after sitting all night without being started). Then without starting the engine, open the hood and carefully  remove the old radiator cap from the radiator. It should come off easily by applying pressure in a downward direction while turning the cap counter clockwise to the left.


2) Remove the "Rad Cap" from the plastic and cardboard packaging (if equipped) to verify that it looks just like your original. Make sure the release spring of both caps are the same, (expressed as 7 or 16 pounds for example).

You are now ready to install your new "Rad Cap"


3) The first step is to hold the "Anode" at the bottom of the spring mount in one hand, and gently pull the cap away from the anode in the opposite direction with the other. This extends the spring and "Anode" to their maximum length, making sure it will be submerged in the liquid of the cooling system.


4) If the radiator tank is not deep, and you can easily extend your finger into the liquid, you may not need to extend the anode's spring mount. Always extend the spring mount of the "Anode" enough to assure that it is completely immersed in the cooling system liquid of the tank.


5) Make sure the brightly colored plastic cover (if equipped) is all the way down over the "Anode", it will last longer while improving the effectiveness of the "Rad Cap".  Note: The "Anode" plastic cover (if equipped) has two round holes. The one closest to the spring mount is to indicate when it is time to change the "Rad Cap",  as it's useful life is about over.


6) The final step is to set the "Rad Cap" on the opening of the radiator and turn it clockwise (right) until it is in the fully seated in position (just like the original cap you removed earlier).


7) It would be best to check the "Rad Cap" every 30 days. It will show you just how much the "Rad Cap" is doing to protect your engine and entire cooling system. The worse it looks, the more it is protecting your valuable vehicle. If it is very dirty, GREAT! It is doing it's job.


1)  Not all Anode Caps are supplied with the yellow plastic cover. Various applications do not require this cover, however the sacrificial anode will work perfectly whether there is a plastic cover or not.

2) The Magnesium Sacrificial Anode MUST be submerged in the ionic liquid (anti freeze) to be effective. Extending the anode mounting spring to a maximum length is highly recommended. For additional protection in extreme cases, an additional anode can be placed in the engine or radiator to provide a secondary sacrificial anode.

3)  It does not matter if the anode touches any metal or plastic parts in the radiator or coolant reservoir. The anode does not work electrically, it works by chemistry.

4) The corrosion build up  that becomes visible on the anode is Magnesium Hydroxide . This is a normal decomposition of the anode is is an indicator of the sacrificial effectiveness of the  magnesium. Cleaning the build up is not required nor recommended, however the remaining un-corroded magnesium  will be slightly more effective when not shrouded by the corrosion build up.

5) The current trend in automotive cooling systems is to incorporate the use of a De-Gas Bottle (plastic reservoir) as a fill point and pressure control. Rad Cap Sacrificial Anodes are made for these applications as well, and work as long as the anode is submerged in the coolant.








Testing Specifications for Magnesium Sacrificial Anode Radiator Caps



Radiator caps with magnesium anodes were supplied by Rad Cap Products for testing. Two different testing methods were used to evaluate the magnesium anode. The two techniques were electrochemistry and immersion testing.




 Electrochemistry was performed on the magnesium anode supplied from Rad Cap Products. Two electrochemical techniques were used to evaluate the magnesium anode. The two techniques were galvanic corrosion and Ecorr vs Time. The test fluid used for electrochemistry test was proposed ASTM synthetic used coolant at 50% coolant at 180 F.

Galvanic corrosion was performed against the magnesium anode and the six metal specimens used for the ASTM D-1384. These six metal specimens are copper, solder, brass, steel, cast iron and cast aluminum. Six galvanic corrosions were performed and all six galvanic corrosions produced the same current of +20.8 uA.

The table below represents the data obtained from the Ecorr vs Time scans on the various metal specimens.



Specimen Potential in mV
Magnesium anode -1340 mV
Copper Coupon -310 mV
Solder Coupon -340 mV
Brass Coupon -120 mV
Cast Iron Coupon -440 mV
Steel Coupon -370 mV
Cast Aluminum Coupon    -470 mV




Immersion Testing

The other test method used to evaluate the magnesium anode was immersion testing. ASTM D-1384 Corrosion in Glassware was the method followed for immersion testing. The test fluid used for testing is the proposed ASTM synthetic used coolant. The testing was performed with the standard ASTM Test bundle and with the standard ASTM test bundle with the magnesium anode. The magnesium anode was placed at the front of the test bundle in front of the copper coupon separated by a brass spacer. The table below contains the weight losses for the coupons.







ASTM D 1384 Sample ASTM Used Coolant Specimen Corrosion Weight Loss (mg)
Specimen #1 #2 #3 Avg Max*
Copper 3 2 2 2 10
Solder 122H 111H 114H 116H 30
Brass 6 2 1 3 10
Steel 96H 184H 98H 126H 10
Cast Iron 772H 925H 762H 820H 10
Cast Aluminum 87H 105H 70H 87H 30
ASTM D 1384 Sample ASTM Used Coolant w/ Magnesium Anode Specimen Corrosion Weight Loss (mg)
Specimen #1 #2 #3 Avg Max*
Copper 1 0 1 1 10
Solder 0 1 0 0 30
Brass 0 0 0 0 10
Steel 11H 16H 1 9 10
Cast Iron 127H 123H 97H 116H 10
Cast Aluminum 7 7 8 7 30
Magnesium Anode -448 1734 70H 472 N/A




Note: * Maximum corrosion weight loss as specified in ASTM D 3306-94 specification for EG base engine coolants.

* Indicates Corrosion level at or above maximum corrosion rate specified in ASTM D 3306-94.




The set of coupons without the magnesium anode corroded much worse than the set of specimens with the magnesium anode. The magnesium anode does provide better protection to a cooling system with marginal coolant.



When Magnesium is immersed in warm water it begins to corrode (sacrificially) instead of the aluminum or other metals in the same solution. The Magnesium reacts with the water, (becoming a Magnesium cation) forming Magnesium Hydroxide and Hydrogen Gas as expressed in the following equation:

Mg (s) + 2H2O(g) -> Mg(OH)2(aq) + H2(g)

Important note: The above testing was performed in warm engine coolant, much like the conditions of your vehicle. It is a very very specific test designed to replicate real under hood conditions. Most of the other references to The Galvanic Series are measurements taken in seawater, since electrolysis and galvanic activity is a huge issue with ocean craft. While there is much saltwater galvanic test data that can be useful, the warm coolant testing above was done for the specific purpose of fighting automotive electrolysis. Specific, targeted testing pertaining to automotive aluminum failures. That's what we want, right?

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