743 fuel leaking into oil

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New member
Mar 15, 2023
hey guys I have a 743 that I keep getting a ton of fuel in my oil. I bought the machine used from a friend and the Motor only has prob about 700 hours on after it was rebuilt. The oil level got so high the first time it started pouring out of the blow by tube. I instantly thought the worst. I checked the oil just and all I could smell was diesel fuel. Since I had a hydraulic leak on one of the steel lines behind the motor I decided I was going Park the machine pull the motor, replace the lines, and run a compression test while it was out. Checked compression and had 448,448,449,450. I noticed that the return line was pinched behind the fuel tank and figured ehh maybe was it. Changed all filters, fluids, glow plugs and put it all back together. Ran about a full tank through the machine and a halfway through my second one it happened again. So here I am! my thoughts are it could either be a stuck injector or the injection pump. Just wondering what else should I check or if im missing something. Anyway the fuel lift pump could leak? The thing is the machine runs great starts right up now loss of power. Any ideas ?


Well-known member
Mar 1, 2018
yes the mechanical fuel pump would be the first thing to check, some people take it out and machine a cover plate to go over the hole and use a electric pump. I suppose it could be the manual priming pump on the injector pump but ,that would not be where I would look first.


Jan 1, 2021
Same issue on Dad's Ford Diesel Tractor. Replaced the injector pump due to age and sitting. Within two years, was getting fuel in the oil. Replaced fuel pump on the injector pump three times with minimal change. Pulled injector pump and took it to a shop. Insides were completely rotted out. Shop said they could tell it sat more than was used. True, as it only used when I would come to the farm to bush hog the fields 3-4 times a year. Anyways, his advice... move fuel storage tanks inside out of the sun due to condensation; due to the amount of water (ethanol) being added to all fuels, run the tractor weekly for at least 30 minutes so it is not sitting in the pump eating away; use fuel additive or conditioner with every tank. I also started using a couple of ounces of two stroke oil for added lubricity to every other tank of fuel. Following this advice and replacement of the injector pump the problem was resolved. With a "freshly" rebuilt engine, I would look in that direction first.