In Montana, we have three grades of auto fuel: regular, midgrade, and premium. The first two may contain ethanol (I have never found any ethanol at my local Conoco station), but by law the premium fuel MAY NOT CONTAIN ethanol. This makes it easy to avoid ethanol.
I recently landed my Ercoupe in a hay field after an abrupt engine failure. Praise the Lord, I was totally uninjured and used no bad language, but my beautifully restored coupe suffered a collapsed nose gear due to a deep rut in the field near the end of the landing roll. It will be a while before she flies again. Need a rebuildable nose gear! No mechanical problems discovered. All fuel screens were perfectly clean. No water in fuel. Ambient temperature was 80 deg F and CAVU with low humidity. The O-200 engine was operating smoothly at 2400 RPM. Carb ice not suspected. The fuel mixture was about 80% mogas and 20% 100LL. Wing tanks nearly full; nose tank full. Official cause: "Undetermined." The NTSB rep and my mechanic are suggesting the problem was possibly "vapor lock." Both of these fellows "hate" mogas and think the mogas STC should not exist. I have read thoroughly and feel that EAA has done an excellent job testing mogas in the O-200. According to Continental, the O-200 was originally designed to run on fuel with a minimum of 73 octane and little or no lead. Question 1: Does Mogas have a higher vapor pressure than 100LL? Is it more prone to vapor lock than 100LL? Question 2: Has anyone ever installed a boost pump between the nose tank and the carburetor? Is there an STC? This pump would be similar to the electric fuel transfer pump used on some Ercoupe models with O-200. Many modern AC use an electric boost pump in addition to the engine-driven fuel pump. E.g., Piper Tomahawk, you flick it on during critucal phases of flight, such as take-off. Question 3: Does Marvel Mystery Oil help prevent vapor lock? What other ideas would help prevent vapor lock? BTW: I have flown this Ercoupe at -22 deg F ... the cabin heater would have been adequate if I didn't have to keep the windows cracked open to keep the wind screen from frosting up! Do you want to be warm or "see and avoid?" No vapor lock that day!! Also, I have flown it to 15,400' MSL on mogas. No vapor lock that day either. Sincerely, Mike Harrison Whitehall, MT (406) 560-5370 Verizon cell
