I'm going to change my plug wires and O2 sensor soon to improve my mileage, but lately I get about 260-265 miles a tank from usually stop and go driving. Before I added STP complete fuel system cleaner I got about 225 miles a tank. I just added my second bottle (4,000 miles after the 1st) at the same time I changed my oil BUT I just ran out of gas at 230 miles! What the F*** is up with that? Anyway, does anyone know how much colder weather affects mileage, if at all? It started to snow here in CNY already and it'* been in the 30s and 40s. Also, because it'* less than 60 this time of year, I think my shop put in 5W-30 oil instead of 10W-30 couple weeks ago. Would this have any effect on mileage? My tires are at the right psi and I'm not racing my engine so I don't know why I ran out so soon. I usually keep it above 1/2 tank but I wanted to see how much this fuel system cleaner would help me out. Any help is appreciated. Thanks.

You have to be running gas out on the ground to get 12 mile to the gallon in a 3800. I'd check for fuel leaks. I get between 20-24 miles to the gallon in town and 28 to 32 on the road. If I have to fill up before 350 miles I get concerned. I've gotten 500 miles when traveling. Definately have a problem some where.

I also don't trust additives. I run premium 92-93 octane as it has more cleaners and I feel my engine runs more efficently. Many others dissagree with this view but it has always worked for me. I'd still look for a leak some where.

I was just talking to a friend of mine who has a GNX and he was wondering if you have a lock cap on your car. Someone might be stealing your gas. He gets 20-25 mpg and he only has two speeds, Go and Stop.

I check under my car all the time but there is never any leaking under the car. Maybe it leaks when I drive but i have no clue how I'd find out myself if it doesn't leak when it'* parked. I have the fuel door lock option already, and I actually got a lock cap a couple months ago (ex-girlfriend problem) for added security. My friend has a 94 WITH 40,000 MORE MILES ThAN ME and gets 350 miles to the tank! I'm going to change my O2 sensor, wires, plugs (again) and hopefully I'll find out if there'* a problem. Anyone have any more suggestions? Any help'* appreciated, thanks for those who replied already.

I run with 89 gas right now with my 94, does anyone suggest anything else?

89 should be fine. You have a 94, and if I'm not mistaken, you have 2 pre-heated O2 sensors. They should run about $60 apiece.

I beg to differ will. I have a 94 and I only have ONE o2 sensor!! Well, just had to say that. buh bye

Ok, maybe it was 95 that started with 2.......

That'* good news, anyway. 50% discount!

I live near Utica NY, so I understand the weather thing....
I'm also having mileage dilemmas on my 2000 SE. On my last tank, in a highway/city driving mix I ended up with 17MPG. Now, I hit the damn thing pretty hard, but I think I should be getting AT least 22-25.