My old but reliable 2003 Ford Focus has just passed its MOT with no work needing doing, but the chap who did the MOT said the sub-frame is showing signs of corrosion. This is currently just cosmetic. The MOT report says:
Sub-frame corroded but not seriously weakened Front [5.3.3 (b)(i)]
Sub-frame corroded but not seriously weakened Rear [5.3.3 (b)(i)]
But the mechanic said that the corrosion is likely to become bad enough to fail within a year or two, and given the age of the car it would be beyond economic repair. The value of the car is probably only a few hundred pounds given its age and rather battered state.
Some decades ago when I was more of a car nut and drove a vintage MG I remember we used to regularly clean up the chassis with wire wool then coat it in waxoyl to inhibit corrosion. I'm wondering if this would be worth doing to extend the life of my Focus. But I'm not in a position to do this myself so I'd have to pay a mechanic to do it, and I guess that could easily come to more than the value of the car.
I realise it's impossible to make a definitive comment without seeing exactly where the sub-frame is corroded and how bad it is, but I would be interested to hear any opinions as to whether this is likely to prove worth while. I seem to recall that waxoyl doesn't last that long and I had to reapply it every year or so, but presumably you could just paint the sub-frame with Hammerite for a longer lasting fix.
I'll add an update to this in case it's useful for anyone else with the same problem.
I took the car to my friendly local mechanic (not the garage that did the MOT) and he said the corrosion was very slight and that the MOT garage had exaggerated a bit. He did a quick clean with a wire brush and sprayed on some waxoyl, and he said that's all that is needed for now. His advice was to keep an eye on it and if it's significantly worse at the next MOT, or the one after that, then it would be worth getting aggressive with some POR 15. Until then just carry on.