zeke37 24 #1 Posted July 16, 2021 Hello my 520H has developed a condition of fuel in oil. History is purchased last spring ran all summer changed oil fall, filled to capacity and checked on the stick. Over winter tried, but could not get it to start. Couple of days ago tried and it fired up and is running pretty good as I took it for a laps around the yard. Checked oil, was least a quart up, drained some and noticed it was thin and smells strong of fuel. New to these engines, any thoughts? Big Thanks, Tim Share this post Link to post Share on other sites
953 nut 55,316 #2 Posted July 16, 2021 Your fuel pump is a vacuum operated pump and when the diaphragm develops a leak the crank case vacuum will draw fuel into the crank case. I would suggest capping the vacuum line and get an electric low pressure fuel pump. 4 Share this post Link to post Share on other sites
Gregor 4,846 #3 Posted July 16, 2021 First thought. DON'T START IT AGAIN , until you change the oil, and fix the problem. 3 2 Share this post Link to post Share on other sites
Bill D 1,926 #4 Posted July 17, 2021 (edited) 2 hours ago, 953 nut said: Your fuel pump is a vacuum operated pump and when the diaphragm develops a leak the crank case vacuum will draw fuel into the crank case. I would suggest capping the vacuum line and get an electric low pressure fuel pump. I'll second this. Try Facet 40177 if you go with an electric pump. Edited July 17, 2021 by Bill D 1 1 Share this post Link to post Share on other sites
WheelhorseBob 1,549 #5 Posted July 17, 2021 Ok this may be obvious but both of my Onans look over filled if you pull the dip stick on a cold engine. Idk why but you have to pull it, wipe and reinsert to get the correct level. Not saying this is your issue. 2 1 Share this post Link to post Share on other sites
cschannuth 3,816 #6 Posted July 17, 2021 8 hours ago, WheelhorseBob said: Ok this may be obvious but both of my Onans look over filled if you pull the dip stick on a cold engine. Idk why but you have to pull it, wipe and reinsert to get the correct level. Not saying this is your issue. Mine too… 2 Share this post Link to post Share on other sites
Maxwell-8 4,277 #7 Posted July 17, 2021 9 hours ago, Bill D said: I'll second this. Try Facet 40177 if you go with an electric pump. Once did use an electrical fuel pump on a briggs, floods the carb like crazy. Share this post Link to post Share on other sites
Gregor 4,846 #8 Posted July 17, 2021 22 minutes ago, Maxwell-8 said: Once did use an electrical fuel pump on a briggs, floods the carb like crazy. I have the same problem with small block Kohlers. Doesn't flood it terribly, but seems to supply more fuel that it can handle. Maybe I need to adjust the float a little lower. Might help. No, these are not the cheap $20 pumps. 1 Share this post Link to post Share on other sites
zeke37 24 #9 Posted July 17, 2021 Excellent advice all!! I will remedy the issue and report back. Thanks Share this post Link to post Share on other sites
c-series don 8,723 #10 Posted July 17, 2021 10 hours ago, WheelhorseBob said: Ok this may be obvious but both of my Onans look over filled if you pull the dip stick on a cold engine. Idk why but you have to pull it, wipe and reinsert to get the correct level. Not saying this is your issue. Yes my 416 does the same thing even after its sat for a long time. Why is that? Share this post Link to post Share on other sites
Gregor 4,846 #11 Posted July 17, 2021 22 minutes ago, c-series don said: Yes my 416 does the same thing even after its sat for a long time. Why is that? Maybe it wicks up? Share this post Link to post Share on other sites
Handy Don 12,235 #12 Posted July 17, 2021 Replacing the diaphragm pulse pump is not hard or expensive. Many 520’s do just fine with “stock” components. Share this post Link to post Share on other sites
lynnmor 7,308 #13 Posted July 17, 2021 The dipstick tube on an Onan is large and the bottom end of it is immersed in the oil. As the engine cools, there is a partial vacuum and oil is draw up the tube. They all do that and a second dip is needed to get the correct oil level. 2 Share this post Link to post Share on other sites
oldlineman 1,481 #14 Posted July 17, 2021 great info., my 446 Ingersoll has always done that, 16 hp Onan, P 216 I believe. Bob Share this post Link to post Share on other sites
Lee1977 6,666 #15 Posted July 18, 2021 I have a 20 Onan and a 18 Briggs Vanguard that does the same thing pushes oil up the tube when parked. I think the crank case breather doesn't work well after it is shut down. Share this post Link to post Share on other sites
WheelHorse520H 708 #16 Posted July 27, 2021 On 7/16/2021 at 9:52 PM, WheelhorseBob said: Ok this may be obvious but both of my Onans look over filled if you pull the dip stick on a cold engine. Idk why but you have to pull it, wipe and reinsert to get the correct level. Not saying this is your issue. I believe you are supposed to check it twice with all engines, I always thought it was because the oil moves around but @lynnmor had a good point with it pushing up the tube. On 7/17/2021 at 11:39 AM, Handy Don said: Replacing the diaphragm pulse pump is not hard or expensive. Many 520’s do just fine with “stock” components. I have a stock pump on my 520 H and never had a problem except for when the gasket around the edge sealing the two halves goes. Share this post Link to post Share on other sites
jonw440 187 #17 Posted July 28, 2021 Just shut the fuel petcock off when your done. Simple Share this post Link to post Share on other sites
