The best I ever got with the three four cylinder Monteros I had was 17 MPG on the highway.

The best mileage I've gotten with my 88 Raider is 24.8. I use a homemade hydrogen cell that seems to help about 25% increase. The 24.8 mpg was achieved while doing 55mph. No I'm not trying to sell a hydrogen cell or anything like that. I built it after hearing a news report one evening. I actually built it to prove it wrong, but it ended up working. So I kept on using it. I use KOH as electrolite. There are a lot of people on HHO forums that will say it is dangerous, but then again so is battery acid and even gasoline. If treated with respect it is safe. My emissions on my raider dropped significantly when I used it while doing our gov. emissions test. I know there are people that will say it is a scam. I don't mind because I'm not trying to sell anything, the plans were downloaded FREE off the net. The cell is a dry version type which is much safer than the glass jar type. It cost me about $40 to build,and I will forward the plans free to anyone who wants them. My original mileage was about 19 mpg. I have been using it for about 9 months.