Onan oil consumption- what is 'normal'?

[Greentored 3,201]

Now that I've put the 520H through its paces after restoration, I notice this thing likes its oil. Im putting 4-5 hours on it per weekend and will use maybe 8 ounces in that time. Engine has 1300 hours, has a fresh valve job/decarbon, cylinders still had hone marks, ring gaps looked acceptable when rocking the piston to one side to view, guides perfect, new seals, zero mess coming out of the breather. Valvoline VR1 racing 10w30, remote mounted filter, plan to go to 20/50 once the weather warms up. She gives a little puff when I crack the throttle but thats it.

I know these opposed flattys tend to use oil and I really dont mind, but dang, this seems like a lot.  How much are you all going through, and does the old 'you gotta use straight 30' really weigh in here?

[JoeM 7,621]

for what is worth, I had a 520 with 1400 hrs on it and it used about the same amount. used 5-40 synthetic. My buddy ended with the machine, it runs great but the oil consumption is still about the same. He has a 520 with 700 or so hours and it hardly uses any oil. Straight oil probably wont help much. might just use a little less when the engine is cold. 

[cschannuth 3,795]

I had one that I bought new in 1997. I used the tractor to mow grass for 20 years and it didn’t use much if any oil. The one I have now with my front end loader on it I bought from Duke, Horse Fixer. I haven’t put very many hours on it but it doesn’t use enough to tell, if any with that limited use. 

[lynnmor 6,765]

I have four 20HP Onans, one bought new and all have over 1000 hours.  They all use a bit of oil, maybe half what you quoted, using 30W.  When new, that engine used a bit more for 100 hours.  All give a puff of smoke on a cold start and all have had the intake seals replaced in the past three years. 

[tom2p 2,393]

wow - 8 ounces oil per 4-5 hours is a lot - but then again has 1400 total hours ...

 

my guess - many Onan twins (especially 520H / P220) are put to rest due to valve seat / related issues before the 1400 hour mark ... so many do not get to this point 

 

I have similar 416H / P216 with around 1000 hours ... noticed it began to use tad more oil past few  years - but it still uses relatively low amount of oil ... maybe an ounce or two every 15 hours or so ?

 

This 416H is a 1994 I believe ; I've owned it for around 20 years ... synthetic oil basically entire life (Mobil 1 5w30) - original owner and then me 

 

Edited March 26, 2020 by tom2p

[tom2p 2,393]

do you run at full throttle a lot ?

 

i know many prefer to run at full throttle - but I almost never run at full throttle 

 

 

[Greentored 3,201]

9 minutes ago, tom2p said:

do you run at full throttle a lot ?

 

i know many prefer to run at full throttle - but I almost never run at full throttle 

 

 

Yep, guys say to wind em up, but this seems to have a 'happy place' around 2000-2500. I ran it up to 3200-3300 with the plow attached and pin it occasionally when just 'horsing' around. Heck, most of the recent hours were dragging brush, pulling a wagon and disc'ing at around 2 grand.

On a side note, this is part of the reason I am doing the HC gear swap- so I can maintain a decent ground speed but keep the RPMs down. She sure has more than enough grunt, I dont think the loss in torque to the wheels is gonna bother it much lol.

[cleat 4,948]

I almost never run full throttle either, maybe 3000 RPM using the 520HC.

 

I cut grass all last summer including running the bagger in the fall to pick up leaves.

 

I mow around 2 acres and used the 48" deck last summer.

 

I think once I had to add a tiny bit as it moved off the full mark.

 

I run 30W oil. Hours unknown as hour meter did not work when I got it but I would think it had a lot.

 

[Ed Kennell 35,738]

My '89 520H has 1600 hours  and uses no oil.    I run it where it sounds the best....3K.  

[JoeM 7,621]

I not sure, but have been told to run these small air cooled engines at 3K and up. There is a theory that the cooling fan is deigned to be most efficient and move the best amount of air at those RPMS. Less hot spots I suppose. ???

Those motors are probably good for upward of 5K....3k would be 2/3 RPM of max?

Maybe we can hear from a motor expert.

As far as oil, I like full synthetic oil because of the heat dissipating properties. That and the idea those oils are always being improved with better additive packages. I think the conventional oil improvement days are long gone and the focus is in the synthetic market. JMHO

[bc.gold 3,399]

Simplicity 9020, 1975 with original CCK Onan two years half a liter of oil, this year she gets an oil change. I use engine oil derived from sweet crude.

 

Improper cross hatch will make it difficult for the rings to break in, most mechanics use Bon Ami added through the carburetor while the engine is running.

 

This tuber gives his opinion.

 

 

 

[tom2p 2,393]

9 hours ago, TractorJunkie said:

I not sure, but have been told to run these small air cooled engines at 3K and up. There is a theory that the cooling fan is deigned to be most efficient and move the best amount of air at those RPMS. Less hot spots I suppose. ???

Those motors are probably good for upward of 5K....3k would be 2/3 RPM of max?

Maybe we can hear from a motor expert.

As far as oil, I like full synthetic oil because of the heat dissipating properties. That and the idea those oils are always being improved with better additive packages. I think the conventional oil improvement days are long gone and the focus is in the synthetic market. JMHO

here is what we do know :

( generally speaking ; static variables )

 

increase in rpm = increased fuel consumption 

 

increase in rpm  = increased oil consumption 

 

increase in rpm = increased wear 

 

increase in rpm = increased combustion chamber temperature 

increase in rpm = increased fan speed / air flow 

 

after a certain point (rpm) - there is a chance the additional fan speed / air flow generated from increase in rpm will not offset the increase in combustion chamber temperature ... not to mention the other negative factors (listed above)

 

for example:  increase in rpm from 3000 rpm to 3600 rpm - does the increase in fan speed / air flow offset the increase in combustion chamber temperature etc ... my guess is probably not 

 

this does not account for running an engine at too low rpm where combustion / combustion chamber temperatures are not ideal and lead to carbon formation on internal surfaces (piston and head, etc) ... lubrication is not ideal .. (splash or pressurized) ..  

 

 

[tom2p 2,393]

9 hours ago, TractorJunkie said:

I not sure, but have been told to run these small air cooled engines at 3K and up. There is a theory that the cooling fan is deigned to be most efficient and move the best amount of air at those RPMS. Less hot spots I suppose. ???

Those motors are probably good for upward of 5K....3k would be 2/3 RPM of max?

Maybe we can hear from a motor expert.

As far as oil, I like full synthetic oil because of the heat dissipating properties. That and the idea those oils are always being improved with better additive packages. I think the conventional oil improvement days are long gone and the focus is in the synthetic market. JMHO

I don't believe the Onan twins in the Wheel Horse tractors are designed to run at 5000 rpm ... that seems a bit high - but that's just a guess 

 

 

btw - on this subject ...

 

had 100cc dirt bikes that revved to 12,000 rpm ...

 

my little Ninja 250 (EX250) street bike produces max horsepower at 12,500 rpm ... revs to a max 14,000 rpm ... 

 

 

Edited March 27, 2020 by tom2p

[bc.gold 3,399]

12 hours ago, TractorJunkie said:

I not sure, but have been told to run these small air cooled engines at 3K and up. There is a theory that the cooling fan is deigned to be most efficient and move the best amount of air at those RPMS. Less hot spots I suppose. ???

Those motors are probably good for upward of 5K....3k would be 2/3 RPM of max?

Maybe we can hear from a motor expert.

As far as oil, I like full synthetic oil because of the heat dissipating properties. That and the idea those oils are always being improved with better additive packages. I think the conventional oil improvement days are long gone and the focus is in the synthetic market. JMHO

 

Nope 3600 rpm connected properly to the governor, 1800 for gen sets.

 

Gen set uses 10 flyweights in the governor, to reach 3600 rpm as a general purpose engine  five have to be removed.

 

Run that engine at 5000 rpm you'll end up wearing pieces of an exploded flywheel.

Edited March 27, 2020 by bcgold

[JoeM 7,621]

10 minutes ago, bcgold said:

Run that engine at 5000 rpm

I am not saying to run it at 5k but I bet it could take it for a while. I suppose my thoughts are what is the concern of running at 3600? In reality, what are we saving? That seems like middle of the road for an opposing cylinder design. 

I am like ED. I think there is an RPM the the machine runs best. 

I do like to mow wide open. An she will get into the governor quite often. 

In my mind, keeping the oil clean, and the fins cleared out would be of much greater "life sustaining" value than lower rpm / lugging when using high loads.

Men a lot of good points.....good discussion. 

[bc.gold 3,399]

The Onan generator engine running at 1800 rpm asl use a different camshaft profile then the faster running engine. Of the 3 generator engines I dissembled all were like new inside.

 

The Onan engines designed as over square, piston is larger in diameter then the stroke is long. Over squares obtain horse power at higher rpms to a point before it falls off the scale.

 

Most motorcycle engines are over square, usually have very thin piston rings and a very small flywheel, needle bearing connecting rod with rollers or tappers on the mains and have very little horse power getting into motion. You have to really bring the RPMS up to get off the starting line.

 

A square engine is another engine design meant to operate in the higher rpm range.

 

Under square engines run at lower RPms and they're capable of developing a tremendous amount of torque at low RPms, these are the back bone of industrial engines found in forklifts, welders and tractors.

 

Edited March 27, 2020 by bcgold

[Greentored 3,201]

Love a discussion that gets technical, especially when it has pistons and/or gears!

As for the original issue, thoughts are shes just a little tired, maybe cylinders out of round. Certainly nothing Im going to chase and attempt to fix, at least not right at the start of the season. If I had known this ol girl was going to have this much grunt there would probably be an older model with a 10 or 12hp in the stable instead. Id sure miss that opposed flatty sound though, especially through the stack on her

[bc.gold 3,399]

A four stroke engine after firing, the power stoke has to not only supply power to the accessory being powered but also carry the rotating mass through three dead strokes, exhaust, intake and compression before the power stroke takes place again.

 

To minimize on fuel consumption most engine manufactures will use a flywheel weight with just enough mass, stored kinetic energy from the power stroke to carry the rotating mass through the exhaust, intake and compression strokes.

 

The Onan and Wisconsin engines are well known to be heavy on their use of fuel, both engines use a flywheel in excess weight, this excess mass has more kinetic energy stored than is needed to carry the engine through those dead stokes.

 

If you listen to the Onan when she gets into spot of heavy wet snow and she begins to struggle that oversized flywheel is doing some of the work while the governor opens the throttle to bring the engine back up to its specified rpm's.

 

Four cylinder engines with power stroke for the resting sisters, multiple cylinder engines above four cylinders will have a power stroke taking place before the last power stroke reaches bottom dead center. This is refereed to a power overlap.

 

Diesel engines higher compression using a fuel not as volatile, have much heavier flywheels.

 

The neatest engine I ever disassembled was a WWII nine cylinder radial, eight of the connecting rods connected to one called the master. The master being the only one connected to a crankshaft journal.

 

 

Edited March 27, 2020 by bcgold

[Macgyver 90]

The oil consumption you described is on the high side. First thing check the compression. I'll bet the rings are out of spec. As far as operating rpm on the Onan anything between 2000 and 3500 is fine because it has an oil pump to get oil to all the moving parts. The Kohler singles were splash lube so more rpm more lube.

As far as air cooling it does just fine and there is a way to improve that..

[Greentored 3,201]

On 3/31/2020 at 10:26 PM, Macgyver said:

The oil consumption you described is on the high side. First thing check the compression. I'll bet the rings are out of spec. As far as operating rpm on the Onan anything between 2000 and 3500 is fine because it has an oil pump to get oil to all the moving parts. The Kohler singles were splash lube so more rpm more lube.

As far as air cooling it does just fine and there is a way to improve that..

compression was 110/115# after a valve job, installing a new intake seat, and decarboning. To help with cooling, I cut the belt guard to aid the rear cylinder, installed a remote oil filter, and even fabbed and installed a cover for the filter 'hole', and punched two small holes in it for the oil lines. I also removed the tube that extends from the shroud to the air cleaner and blocked it off.

She purrs like a kitten and has more than enough grunt, so plans are to run it for the season and keep adding oil, then tear her down over the winter and ring it, or even find one of these super low hour Onan gensets for 150-200 bucks and swap em out