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There is an ongoing oil sumping issue with some Harley-Davidson motorcycles equipped with the 2017-2019 Milwaukee-Eight motor and you should definitely be aware of so you know if your bike is affected.
Oil sumping or wet sumping is a condition where oil, instead of returning to the oil tank, builds up in the crankcase and cam gearcase, causing excessive friction and power loss. Sumping is when the suction side of the oil pump does not remove enough oil from the crankcase. When the flywheels rotate in the oil they turn it into an aerated state. Thus, oil gets trapped in the crankcase and does not return to pump. The Milwaukee-Eight oil sumping issue is because the stock oil pump may be inadequate.
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If you ride short distances, you'll likely never experience the sumping issue. After a shorter ride, the bike will build up oil in the crankcase and then you'll shut the bike down. On the next startup and idle, the crankcase will empty and you'll never become aware of the issue.
The Milwaukee-Eight oil sumping issue happens over time, so if you ride harder on those twisties or ride long distances at higher speeds on the highways, the issue is more likely to reveal itself. It's during these times the oil can build up in the crankcase.
The Milwaukee-Eight oiling system requires a fine balancing act to maintain the correct amount of oil pressure, oil volume and scavenging to eliminate wet-sumping while maintaining quiet operation and optimized power production without generating excessive heat.
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Oil sumping will result in excessive friction and power loss to your Harley M8 engine.
Excess crankcase oil is whipped into a froth of air and oil by the flywheel. This condition is called oil aeration. Aerated oil makes scavenging much more difficult and can hinder the return of oil from the rocker box area. The combination of these conditions often results in oil being forced out the head breathers, air cleaner contamination, oil leaks, loss of oil supply, lifter clatter, premature component wear, and potential engine failure.
You may get excessive oil blowback from the crank breathers inside your air intake. You may see excessive oil splattered along the right side of your bike while riding hard or long distances. Your air filter may become saturated with engine oil.
You may feel your bike has slightly less powerful as it would on a normal hot day. But eventually, the oil in the crankcase builds to the point that the crank is sloshing through the oil as it gets deeper in the crankcase. Eventually, the crankcase fills leaving massive rotational resistance. Efforts to accelerate are met with no response. The engine simply can’t rapidly change rotational speed because of the resistance.
Engine failure comes from there being so much oil build up in the crankcase, that the pan is starved leaving no oil to be pumped to the top end. The engine also overheats just from all the resistance of too much oil in the crankcase. The engine begins to overheat and components such as bearings, lifters, and worse, begin to fail.
The rider will never see an oil light which is quite disturbing and a significant design flaw.
Installing a new 2020 Harley oil pump is the only fix, which now comes stock on those 2020 and newer Harley models with the Milwaukee-Eight motor. Clearly Harley is aware of the oil sumping issue, which is why they re-designed the oil pump for the 2020 models and factory install it.
The dealerships will not say much about oil sumping in general and will just recommend you upgrade to the new 2020 oil pump for “better oil control and better oiling performance.” At your expense of course.
By installing the new 2020 Harley oil pump you'll avoid the Milwaukee-Eight oil sumping issue altogether.
Harley OEM oil pump kits:
- Oil cooled M8-HD Part# 62400238
- Twin-Cooled HD Part# 62400247
Note: There are some aftermarket companies also making a replacement oil pump that provide even better oil performance.
**If you appreciate all the free content we put out to help the biker community, please consider purchasing an aftermarket oil pump through our affiliates. No additional cost to you, but if you click through and make a purchase we do get a small commission. It definitely helps!!
Get an aftermarket oil pump:
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Oil pump changes:
The big changes to this new 2020 oil pump are in the scavenger gears. The original/faulty oil pump had a 10 tooth scavenger gear and the new oil pump comes with an 8 tooth scavenger gear, which will scavenge more oil out the M8. The new oil pump body was made to size for the smaller scavenger gear set.
The older faulty oil pump was designed to scavenge 60% from the cam cover area and 40% from the crankcase. The new 2020 oil pump is a 50/50 split when scavenging oil.
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Bud Bowman says
Harley needs to step up and take care of this issue at no cost to the customers that bought these bikes!!!!!!!!!!!!!!!
Anthony Moreno says
I agree. Noticed this weekend that mine is getting worse. The dealership in Temple Texas said they could install a sock, but it wouldn’t totally correct the issue. I hate to buy aftermarket parts for my bike but I guess I will have to and try and find a reliable Harley mechanic, since HD dealers are so expensive for parts and labor.
Temer J leary says
I got2020 heritage 500 miles pump failed new motor,
Harley just pi jed my neighbor s
21 street glide s failed oil pump
They latest of 6 oil pump revision did not fix boke
Now that’s funny. HD doesn’t recall anything. Would cost them money.
Ron Schaerer says
Best article on a sumping I’ve read so far. Thanks! Ron
Matt Couchman says
Thank you! Much appreciated.
Ride Safe & Ride Often!
~ Matt Couchman
Law Abiding Biker™ Team
Helping, connecting, entertaining, and inspiring as many bikers as we can worldwide!
maykol montilla says
hey Matt I love this article as I’m starting to deal with this problem now with my 2019 roadglide. my mechanic is 3 hours away and I wanted to know if I drain and fill the primary/transmission oil just for the ride would that be a safe route to go? also should I swap the motor oil aswell or does that not have anything to do with it?
Gary MacDonald says
2017 Ultra Limited 114 stage III upgrade when new. Considerable amount of oil in breather.
Dealership replaced oil pump under extended warranty.
Ryan Urlacher says
May have overfilled a bit. Oil blowback.
andrew cobarrubia says
Both my twin cam and my M8 107 have had blow by. I believe it is from riding hard. I am however, installing a new oil pump.
Louis Caporaso says
Excellent content as usual! Thanks for sharing this as I have just purchased a 2017 FLHTKSE CVO Limited with 5,400 miles on it. I’ll most definitely keep an eye on this now.
In the boating world, this is called cavitation. Air will get into the propeller path causing it to spin without grabbing water. RPMs will rise without the usual movement of the boat. Fix is to slide it into neutral, let the RPMs fall, then back into forward as the air bubbles clear. Same theory is going on in the crankcase with the oil and air cavitation. Perhaps more oil capacity would help solve.
Tom Gielow says
I’m late to your party, but this happened to me in November 2020. Unseasonable warm weather caused a ride to Sandusky for a lunch with the group. On the way home on the freeway, bike was running great. Started to lose power at 75-80 mph. I was leaving an impenetrable cloud of blue smoke. H-D fixed the problem for $3508! Jugs, pistons, oil pump, and a ton of misc. parts. Wish I’d heard this podcast when it was fresh.
Ryan Urlacher says
Alfonso Sanchez says
My stock bike over33k and never had a problem. Then I put a cam465, quiky push rods, plate and updated the OEM oil pump. Now I have sumping problems
Joseph P says
My 2020 heritage just died on me on the freeway with all of these simptoms, hot engine, low power (like runing on one cyl), exesive use of gas, i rode it like this for 30 miles since i had no option of stoping in the middle of nowhere and it finally stalled, waited 15 min and i was able to turn it back on. Took it to the dealer and found nothing. blamed it on my straight piped slipons. i put the original mufflers back on waiting for it to happen again.
could it be that the new pump allows for transfer after it cools off? maybe the engine shut down before it reached critical temps… i guess time will tell.
I have a 2019 fat bob, and this has just happened to me. Its amazing, just as he has described it, short rides, nothing happened, then long rides the problem shows up. Now the bike is leaking oil from the pipes.
I will be taking it to Harley, fingers crossed they fix it under warranty.
Has anyone talked to the techs at the service dept. and asked if they can vent the crankcase without voiding the warranty?
Bill Voorhees says
I have a 2021 heritage classic 107. Save symptoms, after a long ride at 75 – 80 mph, started using more gas and lacked power to accelerate. Who can I email at Harley-Davidson to get their response?
Does a Feuling vented dip stick installation help the issue and will it void my warranty? I would love a response from Harley.
My 2018 Ultra with 12K miles on it was not downshifting properly. I had the simple vent on the crankcase and the local dealership said it voided my warranty and wouldn’t touch it. I took it to another dealership and found a faulty bearing in the transmission and fixed it. Didn’t say anything about the vent.