I have the 67 up pretty high right now.  After I pulled the rear end and I got everything put away, I decided to power wash the driveway underneath the car (as I always do). When passing by the rear wheel wells, I pulled the wand up and began to blast the sides of the wheel arch frame. It looked like it had some thick undercoating on it, but in reality, it was just a thick layer of oily dirt combined with sand, you know the kind. It just sloughed off like, well, dirt. And not surprisingly, the frame was in really good shape under this mystery coating.

Question; Should I take my little cold water electric powerwasher, and go for it? Blast and flush the entire body (well most of it) underneath, no solvent, and rinse out the frame (it has a fair bit of of sand in it). Flush out  the braces. Then re-oil?

Or leave the protective oily dirt layer intact anywhere it's found?

I'm not worried about the massive mess as the driveway is being sealed soon. And the runoff will surely be ugly no doubt!

The car is in ridiculous shape underneath. You can wipe the floors down, and they truly look factory. Do I leave as is? Is there a risk to pushing water into the floor and brace seams?

It's something to be considered.

Cheers, Mark

Personaly I preasure wash the frame when on the hoist, I put the wand in all the frame holes and clean the inside of frame, then wash the outside. Try to get rid of anything that holds moisture. Not used to back east road grime, but from what I've seen from eastern cars out west do all you can!!! Could use a solvent spray gun and coat inside of frame rails, just a thought. I would just wash undercarriage as it is open and should breathe. I take it your not an enviromentalist ( neither am I ) soak in oil to preserve 

After you pressure wash spray every nut and bolt with fluid film or a similiar penetrating oil. Let the fluid film soak in then do the complete frame and undercarriage with rust check or krown. This product is available at Car Quest in spray bombs at $10.00 a large can. Lightly spray and let soak for a couple of hours and than repeat. The rust check appears to penetrate into the metal and the metal will look like new. Make sure the undercarriage is completly dry and air dry it with your compressor and a blow gun. 5 cans will be sufficient to do the complete undercarriage and it will drip for a couple of days. I have done about 5 vehicles in the past week that are daily drivers and the customers are very satisified with the result. The vehicles I have done are daily drivers that needed about 2 hours of banging with a hammer to knock of the surface rust scale, sand and dirt. I almost fill  a 5 gallon pail of dirt when the cleaning is complete.

Al

Thanks for the tips. I'm going to do it.

I'll put some grey matting down under the car to catch most of all the grease. I have access to an unlimited amount of the grey stuff like what you'd see under your car carpet. It comes about 3 feet wide. So I'll get about 3 strips about 20 feet long. I used it when I washed my engine bay, and it really worked well.

I have a gallon of pro oilspray and the gun to apply it. But I might just take it back in to a fellow I know who owns Anti Rust oil spray in Burlington. But I won't just soak everything like before. 

What kind of soap or solvent do you recommend I pre soak the underside in before the wash? Something bio degradable perhaps?

I've been using purple power degreasing in a one gallon containor. It is not anywhere near as good as a Korkay product I used in the early 70's but  I cannot find it anywhere. You can do the rust check yourself as I am really impressed with the way the spray cans work. You do not need a wandthe cans shoot at least 5 feet.

Al