This photo of the oxidized thermostat housing on the intake manifold reveals just how damaging this electrolysis process can be on aluminum intake manifolds. This can occur with aluminum cylinder heads as well.
A Question Of A Corrosive Nature
Michael Breeding, via Car Craft e-mail: I'm working on a '60 Corvette doing semirestoration work for a friend of mine. I'm looking for a square-bore aluminum intake for a small-block Chevy that has an oil-fill tube hole in front. The existing Torker manifold has deteriorated around the thermostat hole. It showed up bad after bead-blasting and now it leaks. The only repair I can think of is to use a little JB Weld on the area. I've included a photo of the problem area.
Jeff Smith: This is a common problem with all engines. The corrosion is created by electrolysis, which is basically a chemical decomposition process. Let's get to the fix first, then we can talk about why this occurs and how to prevent it from destroying your choice aluminum intake manifold and heads.
No-Rosion contains an additive that not only extends the life of antifreeze but also greatly reduces the risk of corrosion of soft metals, like aluminum, due to electrolysis.
The quickest, least expensive fix is as you suggested, Michael. JB Weld is a two-part epoxy that can also be machined. The biggest hassle would be finding a shop that can cut a new shelf for the thermostat. Another, more permanent fix that is also more expensive is to have a competent welder repair the corroded area and then have a machine shop weld both a new shelf for the thermostat and the thermostat housing. It might also be possible to have the manifold repaired by a metal-spray process. This would be especially helpful for rare, OE manifolds where replacement manifolds in OE condition are impossibly expensive.
The cause of all this corrosion is also worth looking into as well as preventive measures you can take. Electrolysis is what causes much of the problem. This occurs in an area of the cooling system where you have two dissimilar metals (such as aluminum and steel from the thermostat) in close proximity submerged in an acid solution. This is also the formula for a lead/acid storage battery. If you remember something called the periodic chart of metals from chemistry class (OK, we didn't either, but trust us on this), as a grossly oversimplified explanation, the chart lists these metals from top to bottom based on how easily they corrode. Aluminum is right up there at the top with magnesium. These metals easily give up free electrons when subjected to the electrolysis process that occurs in a cooling system, especially in the area around the thermostat.
'Cc Quickies
"R" Is for Rare
This is a one-of-107 '93 Cobra R Mustangs. It represents the first Mustang built by Ford's Special Vehicle Team (SVT). Note the 17-inch, black-painted wheels with bright, pony center caps. The cars lacked A/C, stereos, power locks, and power windows.
One way to fight this electrolysis process is to minimize the acid level in the cooling system. You can do this by not using antifreeze (which is acid-based), but that does not work well in winter conditions. Or, you can drain and flush the antifreeze every one to two years. Or, you can use a product that we've used for several years called No-Rosion from Applied Chemical Specialties, which is a pint bottle of chemicals intended to minimize the corrosive effects of electrolysis with an additive called molybdate. Using this additive can extend the drain intervals up to five years and also minimize corrosion in the cooling system for those who prefer to use straight water.
Another tip is to use distilled (NOT de-ionized) water when flushing the cooling system. Distilling water eliminates most of the solids from the water, which minimizes deposits that can form in the cooling system. It's also a good idea to add an overflow tank to your system that will collect any purged coolant from the radiator. Then, when the engine cools, the coolant is drawn back into the radiator, maximizing its efficiency. This also reduces the need to periodically open the radiator cap. Every time the cap is removed, additional air is introduced into the cooling system, adding oxygen that will enhance the corrosion process. This is one big reason why most new cars are equipped with overflow systems.