I zero decked a 98 318 magnum and used .039 head gaskets and got an solid 2 mpg improvement around 75mph. It helped a tad at low speed but the biggest gains were high speeds. I re-used the rings and bearings, cam... every thing the same before and after. Both had no fan. I added 20 inch wheels and tires that were about 10% taller then the 16s I had on before and got another 1 MPG at 75mph. I sold the truck to my dad who drives super slow to save gas and he said he had to speed up to get good mpg from it. At 60 mph on the highway he said it don't do any better than 80mph.