Lawnmower oci

[Lonnie]

I know that an accepted method to determine oci is hours used but that tells you little about the severity of service which might have an effect on the oil. So TeeDub has a formula for auto oci's based on gallons of gas consumed and I wonder if that would be a good method for the home lawn mower. Every time you fill up the 5-gallon gas can you change the oil. There are times when the grass is high and thick and I can use 2 or 3 times the amount of gas in the same time period, so a formula like this would work. The formula below is the general idea and would have to be modified but TeeDub applied a good idea to an actual formula.

TeeDub's formula

OCI(miles) = (C*)(aver.mpg)(sump-qts)(cubic inches/Hp**)

Where C* is an empirically derived constant, that depends on both the quality of the basestock and the robustness of the add pack.

** For turbo diesels, substitute ft-lbs of torque for Hp, as this is a better measure of turbodiesel output. If you were to use Hp, you'd over predict a reasonable drain interval.

As for the C* values, most of the work I've done has been with Amsoil, where I back fitted a series of oil analysis results and varied the C* until I was getting reasonable OCI's for engines of varying size and output. However as a first cut, I'd say a C* of 50 for a petroleum oil and a C* of 80 for an average quality, off the shelf synlube should be about right. The top tier, PAO/Ester synthetics (Amsoil, Mobil 1/EP,GC,Redline) are assigned a C* of 125. The Series 2000/3000 oils probably rate a C* of 150, i.e. they do last a bit longer than the regular Amsoil 5w30 or 10w30.

As a final note, the units in the above formula do not cancel to yield miles when you multiply them through. So just ignore that and use the numerical data and forget about the units. I know this bother some engineers , and I suppose you could assign some funky units to the C* value to get everything to come out right, but I haven't done that.

 

[Bill Kapaun]

Lawnmower engines are a different beast. Many crankcases are open to the atmosphere and can dirty the oil in a matter of minutes under severe dust conditions (done that). Dirty synthetic needs to be changed as soon as dirty dino! Same engine mowing thick, lush grass can go a lot more hours. You simply can't use a "one size fits all" formula.
Then there are the oil filter equipped engines to add to the mix.

 

[Lonnie]

I my case I'm just trying to figure out a simple indicator for when to change the oil so I don't forget. When I last changed the oil in my lawn mower is not something I remember well. So I'm thinking of just changing it when every I fill up my 5-gal gas can.

 

[flatlandtacoma]

I hope you aren't making this too complicated

If you have splash lubricated unfiltered Briggs the recommended OCI is 1 year max or 25 hours of use (severe service).

So if you use it nearly year round about an hour a week, change it every 6 months. July and January should be easy enough to remember.

The reason I don't think the formula would be very applicable to an unfiltered lawnmower is the oil won't be close to worn out at 25 hours. You are just changing the oil to get the dirt & junk out.

 

[Lonnie]

It's a Honda and I use for about 8 months of the year for 3-5 hours a week. In the other 4 months it's about 1-2 hours a week. I was just wondering about putting a certain amount of gas in the gas can and changing the oil when I fill it again.

 

[Jim 5]

Lonnie,

It sounds like you've adopted the "algorythm" used by BMW's Oil Life Monitor. Sounds like a decent way of roughly estimating the number of hours on a mower.

 

[Bill Kapaun]

Oil change every 5 gal. of gas MIGHT work out, depending on your conditions.
Examine the oil from time to time. Does it LOOK dirty? Rub some between your fingers- does it feel "gritty"? If it passes those tests, you are probably good to go.

 

[Lonnie]

I'm going to track the hours as best that I can and see what 5 gallons gives me. They work out a plan based just on gallons of gas used. I think the harder you work the mower the more gas you will use and this may work.

 

[Jim 5]

I agree, and that's the theory BMW uses for it OLM as well. The harder you drive the car, the more gas you use, and the less life is left in the oil.

It's crude, but if you work in a margin of safety, it's probably a really sound way of doing it. I think it's more scientific than just changing every X hours without regard to conditions or how hard the engine has worked.

 

[Steelhead]

don't forget cleaning and replacing the air filter or all those complicated math formulas and that Honda engine will go up in smoke.
gerchug, bang, boom, silence

 

[Lonnie]

I clean the washable part of the air filter every time I use the mower. I can't imagine letting it go.

When the mower is using two or three times the gas to do the same yard because the grass is thicker it might be useful to consider following the gas consumption as the indicator for changing oil. Maybe if a few of us try it we can come up with a lawnmower formula.

 

[Rlc2500HD]

Sounds like a good plan for the homeowner. Now if I was to use that in my business i would be changing oil every other day. A cheap hour meter cost roughly 10 bucks and on commercial mowers the oil is changed every 100 hours and filter every other just to give you an idea, at least that what I do to stay in warranty.

 

[Lonnie]

How many hours does it take a mower to burn a gallon of gas?

 

[Jim 5]

Quote:

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How many hours does it take a mower to burn a gallon of gas?

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I know you're trying to start with a rough baseline, but that's a tough one Lonnie. It's sort of like asking "How big is a house?"

My thought is that it would really depend on the mower (technolgy/displacement) itself, as well as how thick your grass is etc..

For example, my buddy just changed from a flat-head briggs to a OHV Kawasaki and noticed he got way more power, and the mower used significantly less gas. I think each owner would have to create their own baseline using their mower in their yard keeping track of hours per gallons. Once that was done, then you could convert the number of hours in your expected OCI back to the hours/gallon you you used. Then you could determine that you need to change your oil after around 5 gallons (or whatever suits you) to achieve an approximate 50 hours (or whatever suits you) OCI.