I have a very nice fiberglass cap for my 88 that I haven't used in many many years and I'm tempted to have it painted and re install it. Would adding a cap decrease my already poor fuel economy? I was going to take it to the dump and pitch it but I saw a nice older truck like mine with a similar cap and it looked good with a roof rack and all on it!

 

I believe mythbusters did a test on this, and it doesn't subract any fuel mileage. I think the amount it adds is negligable, but I have one installed on my dodge to keep the parts in the back dry.

 

i don't know about yours, but my cap weighs a ton. i noticed right away when i took it off that i had better acceleration and slightly better fuel economy, not necessarily because of wind/drag/whatever. I don't think it really makes that big of a difference in economy, not like 20mpg - 10mpg or anything, so i'd say if you like the look maybe it's worth a couple extra bucks at the pump.

 

Well HP and Torque are not an issue with my diesel