Possible Vapor lock?

Bill Hertzel wrote:

There is no need to insulate the fuel line on the engine itself.
Any Vapors in the fuel lines will form in the suction area before the Fuel pumps.
Most likely just after the Coarse Fuel Filter.
The pumps may become starved for liquid fuel on the input side, but the high pressure on the output side will condense the vapors back to liquid.

The Bulk Fuel Distribution Terminals had to purge their winter fuel stock by May first.
The Retail Gas stations had until June 1st to switch over.
If any of the fuel in the tanks was purchased more than 4 weeks ago, some of it might still be low vapor pressure winter fuel.

If the liquid fuel is at 90°F ...
100LL has a service ceiling of 22,000ft.
Summer E10 has a service ceiling of 14,000 ft.
Winter Blend has a service ceiling of 5,000 ft.

At 70°F, the Winter Blend will be good to 14,000ft.

There is an assumption in the auto world that you are not going to find temps above 90°F in January in Colorado.

Fly the pattern down to minimum fuel and then top it off with a fresh fill.
Or ... drain the tanks and put the fuel in your car.

Bill, that RVP document you posted is outstanding! Very helpful and informative!

It's based on the temperature of the fuel, which is not something typically measured on GA airplanes. Let's say it's an 85F degree day, but the plane sits in the sun for several hours. Is the temperature of the fuel in an aluminum tank likely to exceed the outside air temperature?

Perhaps those using mogas should get in the habit of checking their fuel temperature, especially if the plane has been sitting in the sun.

(The one time I had vapor lock symptoms the plane had been sitting in the sun. I had a mixture of 100LL and mogas, but it was spring, so the mogas was likely winter blend. Definitely stay away from mogas in spring!)

Mike,

The fuel can get hotter than the ambient temp because it absorbs radiant heat was well as convective heat.  Aluminum is a very efficient conductor of heat so the fuel can warm quickly, especially in a wet wing aircraft with dark color paint.  As an example, the dashboard of a parked car can reach 160 deg F in one hour, while the air in that same car may only be 110 degrees. 

I've been wanting to get some real data on this so I recently installed a sensor to watch fuel temperature. In the attached photo, the plane is in the hanger during the morning hours and the fuel temperature has not yet reached the outside air temp. That would change quickly if I put the plane in direct sunlight.  I just installed this and have not had the plane out since, but once I play with it for a while I'll post some results. 

Jeff, any results yet from your fuel temperature observations? Also, would a 100 octane E10 type of fuel help alleviate some the vapor lock symptoms over say, a 91 octane E10 fuel. I'm unsure if there is any relationship between higher octane fuels (with ethanol) and RVP but thought I'd ask. Thanks.

Jeff Blakeslee wrote:

Mike,

The fuel can get hotter than the ambient temp because it absorbs radiant heat was well as convective heat.  Aluminum is a very efficient conductor of heat so the fuel can warm quickly, especially in a wet wing aircraft with dark color paint.  As an example, the dashboard of a parked car can reach 160 deg F in one hour, while the air in that same car may only be 110 degrees. 

I've been wanting to get some real data on this so I recently installed a sensor to watch fuel temperature. In the attached photo, the plane is in the hanger during the morning hours and the fuel temperature has not yet reached the outside air temp. That would change quickly if I put the plane in direct sunlight.  I just installed this and have not had the plane out since, but once I play with it for a while I'll post some results. 

I'm curious too how this fuel temp experiment went and what was learned.

Can you tell me what and how you made equipment to test RVP of fuel. I would like to have one at least for testing for a bit.
Thanks