Forum:
Hi All
'91 Fourtrak TDX 2.8
Have just read a recent post from 'Assasin' where he mentions Electrolitic corrosion.
I had problems removing the small screws holding the front sidelights,rusted solid and had to drill them out,retaped and replaced them with stainless steel allen headed set screws, I then replaced the mild steel screws holding the rear lights in place with stainless steel allen set screws,all coated with 'Copper coat' grease, thought that I had a fool proof method of ensuring that I could always remove the screws,with no problem with rusting . But have I just encouraged corrosion on these fasteners.
I have had this form of corrosion on my MK 1 landy ,mild steel fasteners on ally bodywork,a powdery deposit rotting the ally body work, the original fasteners were galvanised, not just plain mild steel.
Comments any one on this.
Edward (ews)
Stainless
Being of the age that i am, i remember the MG range of cars, these suffered terribly from corrosion of the inner and outer sills, then someone came up with a bright idea, fit stainless steel inner sills. Many owners were enthrauled with the idea of corrosion free inner sills; the answer to all their problems, so they thought, after about a year, or following a good British winter, along with copious quantities of salt, they experienced problems.
Inner sills were still intact, but they were falling off, literally, and the problem was the mild steel around the stainless sill was corroding badly, many blamed the welding, and others blamed many other things. Any disimilar metals in contact with each other, particularly stainless, brass, copper, and many of the aluminium alloys used on modern vehicles cause electrolytic reaction. Electrolytic reaction is where the less noble metal, or the metal more liable to corrode, corrodes far more quickly than the more noble metal, this situation is considerably worsened when we introduce electricity, or corrosive elements such as salt.
Manufacturers turned to isolating these metals from each other, this is why we have plastic fittings on car items such as lighting, and other components where differing metals are used, this prevents direct contact with disimilar metals.
Land Rover's with aluminium bodies suffer terribly with the problem of electrolytic reaction, this is why they tend to suffer from bodywork deteriorating, particularly around the rear bodywork.
Prevention is simple, ensure mild steel, and other metals are not in direct contact with each other, if you want to use stainless fixings, drill the bodywork and fit a plastic bung into the body, fit the stainless fixing through the plastic bung, this prevents direct contact between the metals.
Preventing corrosion
You could try using a sacrificial anode as used in marine applications. Basically a block of more reactive metal such as zinc is bolted to the chassis somewhere and the idea is that the electolytic reaction between the dissimilar metals causes the most reactive metal (in this case the block of zinc) to corrode instead of the fittings or the hull of the boat (or chassis / body of car). I have seen products of this sort advertised for cars in the past but have never tried them out. Just about every boat on the sea is protected in this way so it must work.
Might be worth googling to find out more.
Regards - Alastair.
Sacrificial Anode
Yes, you are correct boats use these devices, it is possible to use them on motor vehicles, but they do not work in the same manner as they do on boats. To work properly, they need submerging in water, and the reason you do not see them advertised for cars any more is their very limited effectiveness.
Motor vehicle manufacturers have chosen a different route, this is to design vehicles with no contact between disimilar metals, this is why most fittings are plastic, a natural insulator, and this is why they are screwed to vehicle bodies with steel screws, thus not having contact between disimilar metals.
Where disimilar metals need attaching together, the manufacturers insert plastic plugs into the body, the outer part of the hollow plastic sleeve contacts the body, while the stainless steel screw goes up the middle of the sleeve, giving a fastening which is not in contact with steel.
Good thought though.
Stainless steel fasteners
The original bolts on both my Sportraks were stainless but the captivated nuts are miled stell and they rust and cause the problem. You are lucky, my last bulb failure cost me a new lens as the only way to get the swine out was to break the lens and remove using a mole wrwnch.
I have found that Copper slip helps but dissappears quite quickly. I have had better success, not obviously 100% on my older car with PH grease. This is water proof white grease that if applied liberally remains intact. The alternative is to grind off the offending steel nut and then uses a smaller and longer stainless nut bolt and washer.
I find it odd when manyfacturers go to the trouble of using stainless bolts with mild steel nuts as once the corrosion is in the nut the lot ceases. It's like Diahatsu's use of steel self tapping bolts and those dreadfull spring clips that they secure those plastic wheel arch extensions on. These clips ruct immediately and intirn attack the metal of the wings. Of course this remains un seen beneath these plastic extensions untill the damage is severe enough to show above them.
Good Luck
OLDMINIMAN
M J Young