I am a fairly new member here but I know some stuff about rust. I dont drive my E38 yet
I took some precautions: here is what I did:
-took the car to my friends garage. Hoisted
-checked undercarriage thoroughly
-Sanded any surface rust i found (did not have any
-hosed undercarriage and dried with high pressure air.
-used rust resistant primer (canadian tire, spray bottles) and sprayed entire metal parts such as gas tank, diff, tranny etc.
-after primer dried, used flat black rust resistant paint (canadian tire spray bottles), make sure to create a thick layer.
-used engine enamel paint for the exhaust system since it gets hot.
-cleaned fenderwalls completely, sprayed gravel gaurd
-sand blasted calipers and primed and painted with caliper paint (please be reasonable while chosing color) I used black
-once the undercarriage is dried, sprayed rust check coat and protect generously.
-used motomaster bearing and balljoint grease on all ball joints ans suspension links.
-Steam cleaned engine and sprayed with wd40
-This makes the undercarriage look clean and neat as for the engine bay i dont like spraying oil in their...it looks dirty.
- It cost me about $100 dollars because i tend to be very generous on the sprays.
- If you do drive the best thin to do even after all the protection is to wash your car regularly especially in winter.
- no need to spend 15 bucks everytime. IT going to get dirty anyways. The idea is to remove salt from undercarriage. 2 or 3 bucks at the high pressure self car wash places are perfect. Your car will not be shiny clean but it will get rid of the salt. Make sure to spray the undercarriage thouroughly.
On older cars, a special mixture of asphalt and oil can be used...creates a thick layer. Done on my 4runner not the bimmer