No Summer Blend Gas?

I'm sure you guys have seen in the news where Trump is not going to require a switch to summer blend to help with prices this year. I'm wondering if that's going to be the whole summer or if they're just pushing the date back. I run almost exclusively mogas in my RV12 and now have to consider if I want to do that this summer because of the risk of vapor lock. What are you other mogas users planning to do?

rdockery_3 said:

I'm sure you guys have seen in the news where Trump is not going to require a switch to summer blend to help with prices this year. I'm wondering if that's going to be the whole summer or if they're just pushing the date back. I run almost exclusively mogas in my RV12 and now have to consider if I want to do that this summer because of the risk of vapor lock. What are you other mogas users planning to do?

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I plan on continuing to use 91 octane premium and choosing routes along airports as the temperatures heat up.

My reading is this allows E15 year round. I use E0 Rec 90 zero ethanol. Typical of the news, it is not covering non ethanol and non E15 blending and vapor pressure.

Caveat emptor. Around Sun n Fun time there are always vapor lock stories from winter blend carried into warm spring.

If you run a pressurized fuel system like SDS or EFII, this matters exactly zero.

airguy said:

If you run a pressurized fuel system like SDS or EFII, this matters exactly zero.

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I think the ethanol limit for using the SDS system is 15%.

Reid Vapor Pressure is the culprit here, and all who run mogas will need to pay attention. While ethanol content plays a small role (in terms of allowance to exceed the non-ethanol Reid Vapor Pressure by an additional 1.0 psi), RVP is the primary concern. (RVP and temperature are related in that gasoline with a higher RVP will vaporize at a lower ambient temperature and/or lower altitude than gasoline with a lower RVP.)


For reference, 100LL vapor pressure is limited to 49kpa (7.1 psi) max per ASTM D910.

I had quite a scare during my Phase I testing with engine roughness due to fuel boiling in the carb on a warm day with winter-blend mogas. Please use caution.