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MG MGB Technical - Choice of coolant

I have restored a MGB engine a few years ago. Cooling circuit is clean.

Intending to in stall an alluminum crossflow I wonder whether the standard choice is correct.

The normal alluminum thermotat housings always shows erosion/corrosion.

Has anyone investigated this subject

Frank
F Navest

Nobody given you an answer yet Frank? Oh alright, I will offer one. Use a coolant recommended for alloy engines and cylinderheads. The Triumph Stag had a bad reputation for corroded alloy heads, but it turns out many people were filling the coolant system with just plain water! Was not good for it. I cannot recall what is best but surely your radiator specialist must know? Mike.
J.M. Doust

Frank-
So, what types of antifreeze are available? Basically, there are four-

Traditional ethylene glycol antifreeze is toxic but highly effective antifreeze that contains silicates as an inhibitor to help prevent corrosion in an engine with mixed metals in its make-up. Be aware that there are also low or no-silicate ethylene glycol formulations (usually red) available which may not be suitable for all engines.

Propylene glycol antifreeze is another well-known and less toxic antifreeze formulation and usually contains silicates. Polypropylene glycol needs to be periodically changed or subjected to regular monitoring of freeze protection, pH, specific gravity, inhibitor level, color, and biological contamination, as once bacterial slime starts to grow within it, the corrosion rate increases. Another down side of this product is that if it is overheated, it will then turn very corrosive very quickly. Thus the need for troublesome regular monitoring of its pH level.

Both of the above products use inorganic additive technology (IAT) with iron and steel corrosion prevention provided by nitrites and aluminum protection by silicates, phosphates, and molybdates providing high lead solder protection, with borates helping to control acidity. All glycols produce acids in the presence of air (oxidants). These acids can reduce pH and cause corrosion. When the system pH drops below 7, rust will form on any ferrous metal, and nonferrous metals, such as aluminum, will also start to corrode.

Recently problems have been reported concerning the use of antifreeze mixtures using Organic Acid Technology (OAT) antifreeze. This was introduced in the mid-1990s and the products are biodegradable, recyclable and do not contain either silicates or phosphates and are designed to be longer lasting. Be warned that Organic Acid Technology antifreeze, when mixed with ethylene glycol, results in the formation of sludge. Some newer OAT products are said to be compatible with all OAT and glycol types and are green or yellow. Also, HOAT (Hybrid OAT), both are claimed to have a life of five years or 150,000km. However, these products do seem to cause problems in older engines; over and above the ability of it to find the smallest crevice and leak. OAT antifreezes have been accused of destroying seals and gaskets and causing a great deal of damage in older engines. For this reason, the manufacturers of OAT antifreeze products do not recommend their use in historic and classic vehicles.

The final category of antifreeze is HOAT. These products use Hybrid Organic Acid Technology in an ethylene glycol base with some silicates in the formulation alongside the organic corrosion inhibitors. The product is not recommended for use in historic vehicles.

So, what are we MGB owners to conclude?

• Only use IAT antifreeze in historic vehicles.
• Never mix different types of antifreeze without thoroughly flushing out the system.
• Always replace the coolant within the time scale specified by the antifreeze manufacturer as the corrosion inhibitors break down over time.

As a general rule of thumb, anti-freeze can remain in the cooling system for two years provided that the specific gravity of the coolant is checked periodically and fresh compatible antifreeze is added as necessary. After the second year the system should be drained and flushed by inserting a hose in the filling orifice and allowing water to flow through until clean. Refill with the appropriate antifreeze solution and add a quarter of a pint (0.15 liter) of anti-freeze to the expansion tank.

You will find that Ethylene Glycol based antifreeze is also less viscous at low operating temperatures than Propylene Glycol based antifreeze, the lower pump pressure thus reducing strain on the seals of the coolant pump.

Stephen Strange

The Prestone web site. http://prestone.com/products/antifreeze_coolant/product_list

Lists theirs as a balance that is compatible for both Aluminum and cast iron engines.
Bruce Cunha

Ah Stephen, I should have guessed your answer would be forth-coming. So informative too! Thanks, Mike
J.M. Doust

Hello Stephen,

Thank you for your elaborate write-up on the types of coolants available.

I get the feeling I will be best of with the ethylene glycol originally specified.

System is to be properly filled without any air pockets
with the correct mixture of water and coolant.

Frank



F Navest

This thread was discussed between 13/11/2011 and 15/11/2011

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