When it comes to the differences between 2 stroke and 4 stroke lawn mower engines, the use of oil is one of the most important. As most people know, a 2 stroke engine requires oil to be mixed in with the gas that it burns. On the other hand, 4 stroke engines have a separate reservoir that stores oil and circulates it through the engine. Using gas without any oil mixed into it in a 2 stroke mower will cause serious problems, and so would running a four-stroke engine without any oil in the crankcase. But how about using motor oil labeled as 2 stroke oil in a 4 stroke engine? Maybe you used to have a 2 stroke mower, and recently bought a 4 stroke mower, or maybe you just bought the wrong oil by accident. Whatever your case is, let’s take a look at this scenario.
Can You Use 2 Stroke Oil in a 4 Stroke Engine (The Short Answer)
Yes, you can put 2 stroke oil into the reservoir of a 4 stroke engine, but I wouldn’t do this regularly. Because they’re not designed for the higher temperatures that a 4 stroke engine reaches, 2 stroke oils won’t last as long or perform as well.
What Will Happen When Using 2 Stroke Oil in a 4 Stroke Mower Engine?
If you decide to use 2 stroke oil in a 4 stroke engine, there will be a few side effects. What I mean by this is that oil meant for 2 stroke engines will perform a little bit differently than the normal 4 stroke engine oil would.
Different Oil Thickness
Most four-stroke engine oils are multi-grade oils meaning that they are rated at both hot and cold temperatures. The reason that multi-grade oils can behave differently based on temperature is because of additives called detergents. Two-stroke oil, however, is never multi-grade. If you mix multi-grade oil with gasoline, it will break down. For this reason, 2 stroke engines don’t use multi-grade oil.
But, when it comes to putting single grade, 2 stroke oil into a four-stroke engine, you will just encounter a lower viscosity when hot. This means 2 stroke oil will be thinner after the engine is warmed up. This isn’t a huge deal but it can put extra stress on your mower, and that’s why you don’t really want to be using this oil in a 4 stroke engine regularly.
Hotter Engine
One way that 2 stroke oil will put a bit of extra stress on your lawn mower is by causing the running temperature of the engine to increase slightly. Since it will normally have a lower viscosity when hot, your engine parts will be moving a bit faster than usual.
Possible Oil Leaks
On older and worn 4 stroke engines, the use of 2 stroke oil could result in a bunch of oil droplets flying out with the exhaust fumes. This is also due to the single grade, thinner characteristic of 2 stroke oil. Since 2 stroke oil is meant to be burned off in the engine with the fuel, it doesn’t perform as well when recycled over and over again.
Equal Lubrication and Compression
Since two-stroke oil is meant to be burned off, it has very high lubricating properties. Because of this, your engine should actually be supplied with the same amount of lubrication, even if it runs a tiny bit more roughly. The same is true for engine compression. Using 2 stroke oil in your 4 stroke engine shouldn’t hurt the compression.
I Accidentally Put 2 Stroke Oil in My 4 Stroke Engine – What Do I Do?
If you’ve accidentally put 2 stroke oil in a 4 stroke engine, it usually isn’t a big deal. The only time you should be concerned is if you’ve added oil directly into a 4 stroke engine’s fuel tank. You should never mix 2 stroke oil in a 4 stroke engine’s fuel. This is also true for any other oil or adding fuel that has been premixed with oil already. If you get oil into the fuel of your 4 stroke engine, your safest bet is to drain the fuel and replace it with fresh gas.
If you put some 2 stroke oil into the oil reservoir of your 4 stroke engine, the engine and tool will probably be fine. As far as what you can do, there are two main things: run the oil until it’s time for an oil change, or empty the oil and put normal 4 stroke engine oil in.
Based on my research and personal experience, I would probably opt to just run the 2 stroke oil in my 4 stroke engine until it’s time for an oil change. For example, if it comes down to whether you’re better off running your 4 stroke engine with too little oil, or adding a bit of 2 stroke oil to the oil reservoir, you’re better off adding the 2 stroke oil every time.
However, if you live in a climate with very hot or cold temperatures, using multi-grade 4 stroke oil is the way to go. In this case, drain the engine oil and refill the reservoir with the correct amount of 4 stroke oil.
I accidentally put pre-mixed 2 stroke oil and petrol into my 4 stroke lawnmower that I kept for my chainsaw. It ran then cut out. Can I just drain it out without causing any damage?
Hi Douglas,
My take is that you won’t have to worry about any damage if you drain the oil and gas mix and replace it with fresh gas. But since you did run the engine with the 2 stroke mix, you will probably have some oil that has made its way to the tip of your spark plug.
No worries though, this will clean up easily. As far as the rest of the engine goes, the majority of the oil that was mixed in with the gas will burn off pretty quickly. It might be a good idea to add some fuel system cleaner to your next tank of gas if you have some. Oil could gum up the carburetor a little bit as well.
Good luck 🙂
Tom.
Nonsense. 50;1 gas/oil mix will absolutely NOT hurt a four-stroke engine.
Hi David,
I agree that using a mix such as a 50:1 mix isn’t going to hurt a four-stroke engine, but I would say it will cause some performance issues. Using oil in the fuel with an engine not designed to be lubricated through the combustion chamber isn’t a great idea, especially for those with limited mechanical skills.
Problems with vaporization and gasoline combustion can occur, leaving those with limited mechanical knowledge confused about why their lawn mower is running differently. I wouldn’t want to tell somebody that it’s ok when it’s technically not.
Thanks for your comment.
Cheers, Tom.
Hi. Can I use 4 stroke engine oil in a 2 stroke engine top up?
Hi Mario,
If it were for one-time use, then I would say that it would be ok, but it’s not something that you want to do on a regular basis. The two oils are specifically designed to carry out the same job but in two completely different ways. So, you won’t achieve optimal lubrication by using 4-stroke oil in a 2-stroke engine. Now, I have done this myself a couple of times in an emergency, but I haven’t experienced what it would be like to switch the oil type long term. So, I would say that if you want to get the most out of your engine and have it last as long as possible, then make sure you only use the right type of oil.
Thanks for the question.
Tom.