Underseal ,Rust prevention. Is it worth it. ?

I would agree to this. My FJ had some corrosion under the bitumen.

I can't see any corrosion.

Roger

The Plug itself and on the edges of the hole.

So I did (and would) treat the Jimny underbody and all inside spaces with corrosion prevention. I used a fat (8kg) but there are various options.

The plug appears to be rubber, I still cant detect any corrosion and the only FJ I know of is made by Toyota!

Roger

In some European countries the Gen3 Jimny is known as the FJ, with the Gen4 being the GJ.

Sorry for my unclear writing or pictures. The rubber plug is what I exchanged the rusty metal caps with and a FJ is an Gen3.

The metal caps were rusty after 3 years and the location is above the fuel tank under the bituminous coating, so in a somewhat protected position.

And I thought that this was the original question - if there is corrosion under the bituminous coating.

What cannot be easily seen is that in the area of the body where the rusty metal cap contacted the body there was corrosion.

A lot has been learned by car manufacturers over the years concerning corrosion and how to defeat it but the basic fact is that car bodies and chassis are made of mild steel and that stuff rusts, corrodes and ultimately crumbles to dust. A major problem is where there is the chance of paintwork being damaged by a hard metal fitting that breaks through the paint and leaves raw steel open to the elements. This is where the problems start. The use of rubber grommets to fill the hole is ideal but I would add bitumastic or similar to complete the job.

Is this the only problem area and are the body to chassis mountings ok? They appear to be vulnerable to serious corrosion but only after about 10 years.

A point of interest is that Suzuki now offer a 12 year anti perforation warranty on the bodywork of Gen.4 Jimny's.

Roger

ps. I am disregarding any other materials used in body chassis construction. Suzuki use steel

In the early 1970's I worked in a research laboratory in Harrogate where one of our projects was developing corrosion resistant steel for the motor industry and the like. We developed a system called "chromising" which was principally a powder of ground chromium and traces of other base metals which was spread of the surface of sheet steel, aided by a chemical flux then run through a rolling mill and heated to bond it to the surface. The pilot plant at Eaglescliffe was a great success and the material could make a car exhaust last over 15 years easily. Body panels correctly protected where drilled would last forever. It never went into production, we believed, because of the massive vested interests in the replacement parts industry. Shame.

It was up Harlow Hill, Albright and Wilson, in front of the Tobacco Research buildings where we used to get free fags from the lab girls there !!