I recently posted about a '90 150 merc oil pump problem that I wanted to convert to pre-mix. I found the problem to be the pump sensor, which is good, but along with that, I found the motor oil tank to be extremely diluted with gas. Seemed like about a 50/50 mixture. Further, I found a lower concentration of gas in the external oil tank. I removed all the oil/gas, cleaned both tanks, and partially refilled both with fresh oil. While test running the engine, I removed the hoses from the external tank, and pressed the 'air' port open. I found a small amount of gas exiting the air port along with the air. Does anyone think this is normal?<br /><br />Anyway, that seems to answer where the gas was coming from, although I don't know why the concentration of gas would be higher in the motor tank. I would have thought them to be the same, unless the previous owner added a lot of oil to the external tank, which is probably the answer to that mystery.<br /><br />FWIW, I originally suspected the 2 PSI checkvalve, but as a test, I applied a vacuum (using a miti-vac) to the oil pump side of the 2 psi check valve, and was able to draw some gas up the oil line about 1 ", under 25 inHg vacuum. I then tried to pressurize the 2 psi checkvalve by blowing on the oil line, and the pressure I needed to blow to flow the gas back into the valve seemed about right.<br /><br />TIA for any advice.,<br />Blueeyes.
