How old is too old for motor oil put in a lawnmower?

Posted by l008com@reddit | askcarguys | View on Reddit | 33 comments

This is kind of a nutty question.

My grandmother died a year ago, and we're cleaning out her shed. My mother has been asking me to change the oil in my mom's snowblower and lawnmower and winterize/start up the machines.

So we're at my grandmothers and theres a bunch of unopened mobil1 10W-40 in there. A little thick for a lawnmower or snowblower, but should be fine. Theres are not high precision machines. The oil is old but probably not THAT old. It still looks like a normal plastic quarter container, its not like it's in a can or anything.

I texted my uncle and was like, those blue quarts of oil in nanas shed, how old do you think they actually are? He thinks they are probably from before my grandfather died. He died in 1991. This oil might be 35+ years old!

Thing is, it looked totally normal. I put it in both machines. I guess if the lawnmower shits the bed this year, I'll have to remember to change the oil in the snowblower again before Winter.

What do you think, is there a way I can determine the age of this stuff? Will it keep its basic lubrication properties well enough for a lawnmower even though its so old? I would never expect it to be so old if not for the fact that it's 10W-40. Whens the last time a car took that? I'm thinking my grandfather's old 1984 crown vic. Upon further reflection, I may have put this stuff in my go kart I used to keep over her house a little over 20 years ago. I haven't gotten rid of the containers yet, I'm going to have to take a closer look before I do, see if theres any identifying info on them.

I also tried doing a bunch of google image searches to see if I could find something that looked like a match, that might have a date on it. But no luck.

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tony22233@reddit

1972?

No_Educator_6376@reddit

The oil was a million years old before it was put in the bottle

random8765309@reddit

At 35 years the oil should not be used in an car or large engine. The additive will have degraded or settled out. That generally occurs over a period of 5-10 years. So 35 years is well past that.

If it not perfectly sealed, moisture from the air will degrade the oil in about a year. It will turn it slightly acidic.

However, since you are talking about a lawn mower, I wouldn't worry about it.

ContributionEasy6513@reddit

I wouldn't hesitate to use it given it still had a lid on it and was yellowish.

The oil systems on a lawn mower is done by 'splash lubrication', no fancy pumps. The main thing is you have something in it.

mobil1 10W-40

You are spoiling it, Most specify a monograde SAE40 of the lowest standard.

jondes99@reddit

The petroleum base is at least 10 million years old, I doubt another 35 years hurt anything. Use it!

nixiebunny@reddit

The additives aren’t that old, and this is synthetic oil. Mobil should know the shelf life of their oils.

Where do you think synthetic comes from?

The composition is different from the millions-of-years-old stuff. This shelf life question is best answered by a chemist familiar with the composition of motor oil.

Specifically a Tribologist. The additives will degrade, or settle over a period of 3-10 years. 35 year old oil is clearly a no-go for a car. For an old lawn mower, I wouldn't worry as much.

No_Durian_3444@reddit

Closed oil does not expire. I mean, it came from the dinosaurs or whatever after all.

Advanced-Elk-7581@reddit

It doesn't go bad on the shelf. Use it in your car.

The oil itself doesn't go bad, but the additive will degrade. Oil will pull in water from the air, which will break down the additive and turn the oil slightly acidic. For a lawn mower, I wouldn't worry about it. But I would never put that oil in my car.

ThirdSunRising@reddit

Well, in a car that’s old enough to run 1990s spec oil

edwbuck@reddit

It's all dependent on how well it is sealed, and if the environment has a high amount of humidity.

Water is the main killer of usable oil. If it's opened, damaged by water, or damaged by humidity (takes longer) then it's a matter of "how much damage before the oil permits the engine to get damaged."

AC-burg@reddit

This is the way and will die on this hill unless my car does and someone can factually link it to new old stock oil being used.

finnbee2@reddit

It should be fine in the lawnmower. If the snowblower is stored in an unheated building and the temperature is 20 below 0F there's probably better choices.

mckenzie_keith@reddit

I actually wouldn't use it. Also, if you do use old oil, shake it up first.

dunncrew@reddit

You old oil will ruin a lawnmower ?

I think old oil will not meet its specifications.

ResponsibleBank1387@reddit

Oil is millions of years old. Sealed unopened so there is no extra moisture in it. Use it.

New-Patient-101@reddit

10w-40…..are you sure it was gas oil and not diesel? Diesel oil has a higher zinc content and might cause issues later with the cats, o2 sensors.

Glum-Welder1704@reddit

There should be a service API marking on the bottle. With a bit of research, you could tell approximately how old the oil is, and it will give you a clear idea of its usefulness. That said, I wouldn't put it in any car I care about. Modern synthetic oils are far better for that.

pinellaspete@reddit

Wasn't Mobil 1 always a synthetic oil? I think it first started selling in the 1970s as the first full synthetic oil.

OK, that would be better than non synthetic. The API service grade would probably still be better now. Like OP, I would use the old stuff in a lawnmower, but not in a car.

Does it look fresh? It should be fresh.

My brother stopped by the other day in his 1974 Malibu, and proceeded to pour a can of Valvoline 30 oil into the 350. He used a push-on spout. The can was so old it didn’t have a UPC code (1976). The engine was fine - er, it was drinking a quart every hundred miles at that point, so it didn’t matter.

2WheelTinker-@reddit

Just to baseline, you acknowledged it is the incorrect viscosity for your equipment but are worried about the age of the oil.

Which do you think is worse? 😉

Additives break down with time. You are knowingly using “expired” motor oil that may or may not cause damage in the short term. Likely not.

There is a full breakdown(no pun intended) on this subject available.

https://youtu.be/E1T4XFPgBeo?si=02mweKCbhRHueKRK

Additives break down over time when used. Not when stored. Engine heat and friction cause breakdown.

jules083@reddit

As for viscosity those little motors are splash lubricated and likely don't care. I've ran every from 5w30 to 15w40 in push mowers and log splitters and none of them seemed to mind the difference.

Usually I just dump in whatever happens to be on the shelf at the time. A lot of my junk has oddball capacities so there's always a few partial bottle of oil sitting on the shelf that I need to use up in something.

congteddymix@reddit

If it was a newer vehicle(like anything built in the last 30 years) I probably wouldn’t have used it but since we are talking yard equipment it’s possible these things are older then you think. Either way like you stated it’s a lawn mower and snow blower and a lot of those until recently were ass backwards enough to still want you to use straight weight oil(typically SAE 30). Long story short I probably would have did what you did since these are really simple engines and pretty much stay at one speed.

Also if you really want to know the age then look at the bottle for the API RATING, then google cross reference and it will probably tell you the time period it’s roughly from.

Sufficient_Fan3660@reddit

70 year old motor oil test - https://www.youtube.com/watch?v=-zHlxeu_yuM&list=PLjT3B9r2z3fXlvbP3tb9e056Q8O5krrCW&index=16

SpaceCat72@reddit

Maybe pour one whole bottle into a glass container. Look for discoloration or sediment/settling of recipe/additives. Look for dates on the containers. I'd think it would be ok for those small engines. Are they splash Oilers or pressurized? With or without filters? Under normal use, oil is changed every season.

NectarineNo4312@reddit

I found some old oil that was my father in law’s. A pain to get rid of, so I just used it to top off an old car engine. It’s all good.👍

Steve1101@reddit

Funny you mention this. I have 2 cases of unopened 10w40 sunoco brand motor oil that I found in the attic of my garage. It's so old that the plastic on one of the bottles cracked and leaked out and left a huge stain on the ceiling (which is why I ended up going into the attic to investigate). Anyways, I ended up using it for my lawnmower and snowblower and they're fine. As long as the bottle was sealed and there's no moisture in them I wouldn't hesitate to use it in any small engine. Now, modern oils are vastly superior, and I wouldn't use that stuff in any car I own but for a simple lawn mower or snowblower I think you'll be fine.