Eamo wrote: does it have to be bmw kev? what about waxoyl? thats what i used on mine

Eamo - I'm thinking about doing the underside of the E36, is it expensive, big job?

I'd recommend waxoil, this stuff is good but, can be messy  (wear gloves).

With the need to underseal the entire car (as winter was approaching), I done a total underseal (DIY) done in October 2006 using waxoil on my E36 Coupe..brake pipes, arches etc...takes around 3 hours to do with a bristle brush and a tin of waxoil.

(BTW: I done my rear arch inner lips in February 2006, so when I came to do the total underseal, I found these were still good so, no need to redo them)

I also found a couple of rust scabs in the inner wing panels and removed scabs with a wire brush then cleaned with water despersant fluid, allowed to dry and coated with POR15 waterproof paint (amazing paint). Once dry, another coat of POR15 was added and allowed to dry. I then coated these painted areas with waxoil also.

I've recently purchased some to do the chassis on a customers Morgan. It actually says that you can go straight over rust as it "cures" it. I can't imagine it would??

I have also been advised to mix it with some engine oil - almost 50/50 mix, especially when blasting the stuff inside chassis legs, etc. I can see some logic in that, as if you get a bubble or pocket of air which the wax oil has trapped, then you will have problems in that area in the future. The engine oil thins the wax oil and reduces the risk of creating pockets of trapped air.

HTH's