Quote: . I drive hard and fast, do exact refills and keep very accurate records.

How do you do an "exact refill"?

What do you use to "keep very accurate records" ?

Y'all may find this a bit quirky but it is how I do things and the engineering approach comes out!

All of us that fuel with diesel know how diesel foams while filling. As soon as foam builds up in the hose, the filler will click off. I could not put in more than 30-40 gallons before the filling operation would slow and after repeated click offs, could get another 10-15 gallons in the tank before I had liquid fuel (not foam) up to the neck of the filler. Foaming will vary a lot depending on fuel and temperature of the fuel!

I changed the location of fuel filler pipe at the tank. It was located at the back of the tank about half way up with a LONG hose. Would take 20-30 minutes to completely fill the tank. I shortened and moved the filler hose to the top of the tank.

Fuel filler location change

After the change I could fill with only about 5 click offs before I had standing fuel at the filler neck. Now this is where I get NERDY! I always level the coach before filling, I always fill to where there is liquid fuel standing at the top of the filler neck. If I can not level the coach or for some reason I can not see the fuel in the neck, I do NOT calculate mileage from that fill, only at the next fill adding the previous miles and gallons where the fueling operation was incomplete. A note is made if the fueling operation was incomplete.

I have a Excel spread sheet log that I use for ALL Barth issues. Fuel, oil changes, tire changes, brake changes, any upgrades or changes made, logged with date and mileage. This log is in my laptop, tablet and phone, all sync'd together.

I am glad I am not the only one with issues topping off. The good news, the Monarch has a filler on both sides, convenient but you get different results depending on which side is used. Foaming, burping back is common and there may easily be 10-15 gallons between sides. Need to check those filler hoses.

I need to keep a running log for average mpg, good idea.

Yes I am guilty of this type of data logging but... I remember a friend long ago commenting about his dad and his dad's friend comparing their trips to CA. and there was no mention of sights and experiences, it was all gas mileage and fuel prices. The other extreme.