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Does Oil Have A Shelf Life?

By Larry Roll April 5, 2008



I'm curious as to whether or not unused motor oil (dino or synthetic) has shelf life issues? I have over a pint of unused Mobil 1 synthetic oil, 5W30, which is basically just a collection of unused remnants from quart bottles and 5-quart jugs used over the last few years. I've used maybe 20 or 30 ml. of it to lubricate my bicycle chain and other things around the house, but for the most part, there it sits. I keep forgetting to bring it with me whenever I change the oil on my Corolla, as I did just this morning. How long can I keep it and still use it in my car? I guess it's over 3 years old.

Another thing: My lawn mower uses almost that exact amount of oil, but specifies 30W, not multi-viscosity 5W30.

Can I use it? As it happens, the mower is overdue for an oil change.

Actually, someone did determine that there was a shelf life to motor oils. Not that they will eventually go bad, more in there additive packages will eventually settle out of suspension.

I think is was about 3-5 years for both conventional and synthetic. I've got some squirreled away that is a lot older - I wouldn't have any problems using it, as long as I shook it up well before using.

As for multi-viscosity motor oils in a lawnmower - it is OK to use if the straight weight oil cannot be obtained. I've also done that occasionally to my old lawnmower - still runs strong after almost 20 years.

its ok to use multi in your lawnmower. the reason its not suggested is because most mowers use splash oiling. well tecumsehs have a little oil pump that runs off the cam and pumps oil upto the top main bearing and to the top cam bearing as well. briggs use only splash oiling as best i remember. 10w-30, 20w-30, 5w-30, as long as its something 30 you're alright. mowers arent super sensitive to oil viscosity changes.

its ok to use multi in your lawnmower. the reason its not suggested is because most mowers use splash oiling. well tecumsehs have a little oil pump that runs off the cam and pumps oil upto the top main bearing and to the top cam bearing as well. briggs use only splash oiling as best i remember. 10w-30, 20w-30, 5w-30, as long as its something 30 you're alright. mowers arent super sensitive to oil viscosity changes.

My mower is a Sears Craftsman with a 4.5 hp Briggs & Stratton engine. I kind of suspected that it wouldn't be particularly sensitive to viscosity, as long as the max was 30W. I assume that once it's warmed up, the oil will be at 30W and should perform more or less normally. Maybe the lower viscosity when cold might permit it to be more completely lubed while it is coming up to maximum operating temperature.

I will do as another reply suggested and make sure the oil is well mixed, though I will do this by carefully rolling and inverting the bottle rather than shaking it, as to avoid filling it with air bubbles, even though they may not do any harm. I guess the oil gets splashed around pretty well in the engine anyway.

Now the remaining question is this -- does going from a dino oil to a full synthetic mean I can extend my oil change interval? It is nominally 25 hours, but due to the small size of my yard, I doubt I run that engine for even half that time each mowing season. I wonder if there's any way to put a Hobbs meter on an engine that size? Without any sort of a DC circuit, I don't know how you'd do it, even if it were economically feasible. I've seen professional riding-type mowers that had them, but they had a DC circuit for the ignition, electric start, and lighting, so they could wire it to the hot side of the ignition switch. I guess I'll just do as usual, and keep changing the oil each mowing season. I'll most likely make the change next weekend, if it ever stops raining...otherwise, I'll have to mow the whole lawn with my Poulan Pro string trimmer! I've already done that to fairly large, fast growing sections this weekend.

you can get an hour meter on ebay for cheap, it runs off a little watch battery and has a lead wrapped around the spark plug to know when the engine is running. they also usually have a tach function too, not that you care that your mower is humming along at 3500 rpm :laugh:

iirc they cost $30-$40 depending on brand and the seller. just get the cheapest one.

as for oil, its not the oil that wears out, its that it gets filled with crap since theres no filter. just use a decent conventional oil and you'll be fine, theres no easy way to add a filter to a push mower, its pretty involved and complicated and prone to problems....no easy way to drive a pump.

if you want a little more bang for your mower, do the usual maintenece like changing the air filter, plug, and cleaning the carb. then get a head gasket, pull the head, and shave it down some. bumping the CR a little can really get you through that thick grass. i had a 5hp tecumseh that would chew through wet grass a foot deep...because it was making about 7-8hp default_smile i actually had to dremel some valve reliefs into the head! also helped that i raised the engine speed about 1000 rpm. it wasnt very friendly on gas, but boy did it ever mulch! the grass came out in powdered form

Bikeman982

Motor oil will last for a long time.

You can tell if it is bad if you notice it has layers. Mix it up good and it would probably be fine to use.

Lawnmowers can use the multiweights.

You can use oil thats 5yrs old just fine. Just shake it up first incase the additives are at the bottom. I remember seeing a thread about this very topic on the bitog forum yesterday.

OK, already changed the oil in the mower using the "old" Mobil 1. The mower seems to like it just fine. I also pulled the spark plug, it looked fine so I just put it back in. Bought a new blade today at Sears, will change it out and then have the old one sharpened and balanced at my leisure. I know a guy who does that for $5.00 a blade. But a new blade is only around $13.00 so I may not bother. I could just sharpen it with a file if I could figure out a way to balance it. Does anyone know how they balance mower blades, anyway? How much out of balance can they be and not damage the engine? I did, in fact, hand-sharpen my blade, and there is a slight vibration when the machine is running, but doesn't seem any worse than usual. I did a cheap and dirty balance on it just balancing it on a screwdriver shaft, blade seemed to tend to remain level, with no noticeable "heavy" side. Comments, please.

i balance mine on a narrow nail hammered into the side of the work bench. a drop of oil on it and give it a spin. if each time i spin it it tends to stay one side down, thats the heavy side. take a little more off and rebalance. you'll be amazed how much better your lawn looks with a really sharp blade making a perfect clean cut.

and yes, bad vibes can mess your crank bearings over time.

Bad thing about sharp blades is they damage easy with sticks ect. If you have a clean yard it wouldnt be an issue. If you have a local lawn shop the blade prices could be better thans sears as has been the case for me.

Bikeman982

I always walk my yards before I mow them.

I pick up any sticks or items that the blade might hit.

So far, I have not sharpened my blade, but I think it is about due.

OK, already changed the oil in the mower using the "old" Mobil 1. The mower seems to like it just fine. I also pulled the spark plug, it looked fine so I just put it back in. Bought a new blade today at Sears, will change it out and then have the old one sharpened and balanced at my leisure. I know a guy who does that for $5.00 a blade. But a new blade is only around $13.00 so I may not bother. I could just sharpen it with a file if I could figure out a way to balance it. Does anyone know how they balance mower blades, anyway? How much out of balance can they be and not damage the engine? I did, in fact, hand-sharpen my blade, and there is a slight vibration when the machine is running, but doesn't seem any worse than usual. I did a cheap and dirty balance on it just balancing it on a screwdriver shaft, blade seemed to tend to remain level, with no noticeable "heavy" side. Comments, please.

Update: A friend of mine, who sometimes does lawn work for extra pocket money, sharpened and balanced my old blade. He had a neat little balancer which looked like a stepped cone, the blade just found the right flange that fit, and balanced on the cone which I'm assuming rests on some kind of pin or ball bearing mechanism. Neat -- I've never seen one before, but learned that they are quite ubiquitous. I'll pick one up next time I'm at the Home Despot.

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