The Ford Barn

petehoovie · 06-01-2026, 11:10 AM

When using E85 as a fuel instead of straight gasoline, the recommendation is to use one step higher grade viscosity engine oil than what you would otherwise use. For example, if you were planning to run 10w30 engine oil the suggestion would be to step up to 10w40. This compensates for the thinning effect of alcohol-based fuel because of the significantly greater amount of fuel required when running E85. Alcohol has been shown to act like a solvent with oil. This is why you would increase viscosity. This is especially true with carbureted E85 engines as they often run much richer air-fuel ratios. A great follow-up suggestion would be to test your used oil to ensure it is not compromised with excess fuel or alcohol in the oil. Several companies offer this service including Amsoil, Blackstone, and SpeeDiagnostix.

https://www.hemmings.com/stories/tec...9b1bcf9b99e50a

06-01-2026, 11:10 AM	#1
petehoovie Senior Member Join Date: May 2015 Posts: 11,643	Tech 101: Oil Viscosity Versus E85 > From Hemmings When using E85 as a fuel instead of straight gasoline, the recommendation is to use one step higher grade viscosity engine oil than what you would otherwise use. For example, if you were planning to run 10w30 engine oil the suggestion would be to step up to 10w40. This compensates for the thinning effect of alcohol-based fuel because of the significantly greater amount of fuel required when running E85. Alcohol has been shown to act like a solvent with oil. This is why you would increase viscosity. This is especially true with carbureted E85 engines as they often run much richer air-fuel ratios. A great follow-up suggestion would be to test your used oil to ensure it is not compromised with excess fuel or alcohol in the oil. Several companies offer this service including Amsoil, Blackstone, and SpeeDiagnostix. https://www.hemmings.com/stories/tec...9b1bcf9b99e50a __________________