I do not get readings with new a Racor 500 2-micron filter element AND a full fuel tank. I DO get a vacuum of a couple of inches when drawing fuel from nearly empty tanks through a clean RACOR 500 2-micron filter on the stbd side (port engine has a Racor 900). I get vacuum rise on all three of my filters (two 500s and the one 900) Racors as soon as the 2-micron filters start to clog, and the vacuum, once it starts to rise, typically takes a couple of long cruising days or more to rise to 5 inches Hg. My engines will run with 10 inches vacuum, but I usually change the filter element at 5. Thus, as far as I can see, I am getting exactly what I want out of my auges - a warning that it is getting to be time to change the filter elements. In 28 days of running on my Tennessee River 2344-mile run last Fall, I changed the Racor 500 2-micron filter (stbd engine) twice and the Racor 900 2-micron (port engine) not at all, based on vacuum gauge readings. The four (2 per main engine) on-engine, spin-on Racors with clear bowls and water alarms are 10-micron and were not changed. If an engine should ever die, and I see no vacuum, then I know I likely have an air ingestion problem (or VERY unlikely, a spin on filter clog), and it is time to energize the electric fuel pump to keep the engine running and the air out - I have been to this place. So, that's another good reason to have the gauges - troubleshooting. FYI, the generator Racor 500 2-micron filter was changed before the trip and ran for over a hundred hours without showing vacuum rise. I have a set of fuel line vacuum gauges mounted in the engine room in the outlet hoses from each Racor, AND I have another set of remote gauges measuring vacuum in the same piece of hose mounted up in the main cabin where I can monitor them from the lower helm. There used to be Fram canister filters mounted between the two sets of gauge tap points, but I removed these rusty, clumsy things as superfluous - the gauges stayed. So now there are redundant gauges measuring the same piece of fuel hose. The engine room gauges are just over the Racors, about 6-8 inches from the tops of the tanks. The remote gauges up in the main cabin are maybe a foot above the tops of the tanks. I notice no real difference in their readings. This works extremely well for me and has given me increased confidence in the boat and one less thing to worry about on long runs. Anybody who ever had unexpected engine hunting or just plain old engine shutdown underway might be justified in having a nagging lack of confidence in his boat. I did for several years until I got the fuel cleaned up (I changed filters at 200-hour intervals before the remote vacuum gauges were installed), the air ingestion problems cleared up, and the vacuum gauges installed where I could see them underway. No problems in about five to seven years now. Rich Gano CALYPSO (GB-42-295) Southport, FL