I'm going to install an Autometer mechanical oil pressure
gauge in my truck. Can I use the supplied nylon tubing or
should I get the 4' steel braided hose for $40.00 extra. Anyone
ever have the nylon tubing fail in your truck and cause a mess or damage ?

 

You CAN use the nylon tubing, but it can (mine always has) dry out and get brittle and crack over time. I now use the copper line for my mech oil gage.

 

I've been using the nylon tubing for fuel pressure on my trucks for about ten years with no problem.
In fact my 1956 dump truck has had the same nylon tubing to the oil pressure gauge since I bought it used in 1964, not sure if it came with it when new or not.
I like pushing the small tubing though some 1/4" tubing to protect against kinks, cuts and abrasion. Makes it a heck of a lot easier to work with also.