How to prevent rusty bolts on the engine belly pan cover for $11 (or less)

**This is assuming your under tray uses the 3 older type clips (loose nut) up front and 4 newer types clips (integrated nut) in the rear. If your car already has all newer types clips, youd only need the nylon bolt and washer. This is more applicable for us northerners who have to endure salt.

I would have preferred using a strong plastic U clip or speed nut and reused the existing bolts. Metal bolts can be driven with a power tool without worrying about damage or rounding the bolt head or thread and can force its way in and out of a plastic nut. However, I cant find any suitable plastic nut so I resorted to going the other way . Not the most ideal but concept remains, nylon will not rust with metal!

Heres a pic comparing the different makeup. Left two is what it was, 2nd from right is what it is, and far right is what I would have wanted but cant find a suitable plastic clip. The plastic fastener in the pics are for fender liners and can also be found at Lowes/HD but the bend is not wide enough to fit over the panels thickness. Though about heating a piece of metal to widen it but think this may lessen the structural integrality of the clip and cause it to break at the bending point.



U nuts were from Lowes but nylon bolt and washer were from Home Depot b/c one or the other was either out of stock or didnt have the right size. Note these are all US standard sizes, NOT metric b/c Lowes/HD does not carry metric nylon bolts, nor doe they have the U nuts in metic. I choose to use shorter bolts but that is up to you. You can find metric nylon bolts (I believe are M6x1.0 ~20mm) online but in large quantifies and cost more than what I needed in smaller quantity, BUT can be had in black. If you can find 7 metric nylon bolts locally, you can reuse the 4 rear most clips as they have the integrated new nut feature and youd have to buy 3 more metric U nuts online or through the dealer for the front.


Metal U nut - $0.92/ea x 7 = 6.44
Nylon hex bolt $0.71/2 x 4 = 2.84 -bolt head fits 11mm drive socket!
OPTIONAL nylon washers $0.62/3 x3 = 2.84 -sucks that they come in packs of 3 b/c you need 7. You dont need washers to save a few bucks but I recommend it.






The finish product.







Its been 200 miles and holding strong. Didnt have time to cutout an opening for the oil filter but made my marking to do so next time. Also thinking of making a trap door access but not sure if it is worth the cost/effort (can't find plastic hinge for cheap).


Update:2k miles and holding perfectly strong.

This is an excellent idea! Living in Minnesota for the last 14 years, I have gone through numerous cars with undercarriage bolts converting to rust balls. It seems like the mod was done over 2 years ago. How are they holding?

I'm curious how they hold up in frigid temps. I used to just dip my bolts threads into engine oil before reinstalling at each oil change. This worked well for me.

Sold that car in Dec '12 with 50K. All bolts were tight but one did fall out. IF you were to try do this, I would suggest longer bolts. Ones I used were a bit short but not sure if that was the reason why one came loose/out. Ideally plastic faster with metal bolt would be better.

Nice ideal on dipping in oil. Does it build sludge?

No, no sludge. By the time 5k miles went by they appear dry at the next service. I did wipe off excess oil though.