My car: 1999 Subaru Legacy (Outback wagon), 150,000 miles.
Climate: Austin Texas Baby
I had observed a drop in my gas mileage of 30%, down to about 15mpg for the last few tanks. I took the car in for a free ‘multipoint inspection’ at the dealer and was told it needs a few things: a bulb in my blinker, a brake flush, fuel system cleaning, and it has an oil leak at the separator plate (expensive to get to & repair). I replaced the bulb and I’m going to get the fuel system cleaning and brake flush, but I haven’t done those yet.
Instead of getting the expensive oil leak repair I decided to try Oil Stop Leak, a Blue Devil product recommended by my local AutoZone guys. Note that I have never seen any evidence of the oil leak (no drips, no smoke, never noticed the oil was low though I admit I don’t check it much), but I did see online that it’s a fairly common leak on this car because Subaru used to use a plastic part that eventually fails.
I put the stop leak product in and followed the directions (had to run the car continuously for a couple of hours), and now, on the very next tank of gas, I’m getting my normal mileage again.
Could the stop leak have impacted my gas mileage by that much?