Outboard Oil Ratios

Author: Stuart Buckingham   Date Posted:25 July 2017 

Blog Outboard oil ratiosAnyone who owns, or has owned, a two stroke outboard would have asked themselves the question; how much oil do I mix with my fuel? 100:1, 50:1 or 25:1? It is one of the most asked questions for those required to pre-mix their oil and fuel together. Below I have listed the oil ratios recommended by manufacturers and a few tips based on my experience.

100:1 - Mix 50ml of oil per 5ltrs of fuel. Recommended by Yamaha and Suzuki for most of their small two stroke engines up to about 30hp, this ratio requires the least amount of TCW3 two stroke oil. The result of using this ratio (less oil) is reduced spark plug fouling and less smoke. For older Suzuki outboards, pre-1997, I'd recommend running 50:1 as the information I've provided about is for current model two strokes.
Note: For commercial applications Suzuki recommends 50:1.

50:1 - Mix 100ml of oil per 5ltrs of fuel. Recommended by Mercury, Mariner, Tohatsu, Johnson and Evinrude this is my preferred ratio for all outboards including Yamaha and Suzuki. You can confidently use this ratio for any horse power and just about all year models. Whilst this ratio might see spark plugs fouling with extended use at lower RPM (such as trolling), in my opinion, it provides the best amount of lubrication for your outboard.

25:1 - Mix 200ml of oil per 5ltrs of fuel. This mixture is very rich and is usually recommended for running in brand new two stroke outboards and when running in rebuilt or reconditioned engines. If you have a rebuilt or reconditioned oil injected two stroke outboard (excluding Evinrude ETEC or Mercury Optimax) then you'll just need to add 50:1 to your fuel and let the oil injection system add the rest of the oil to make up the balance to get to 25:1. Most technicians will have their own opinion or view on how long you should run the 25:1 ratio for but, I always recommend between 8 and 10 hours. Unfortunately, you will foul plugs at this ratio and leave a very impressive smoke plume on engine start up but, outboards that have been rebuilt or reconditioned need this extra oil while the piston rings bed into the bores.

Oil ratios can be confusing and daunting. The last thing anyone wants to do is not use enough oil and damage their pride and joy. Hopefully, the above answers any questions you may have and gives you a better understanding of what ratio your outboard requires.

Shop for Penrite outboard oils & lubricants here. 


Comments (21)

Early 90s 25hp mercury

By: on 30 May 2024
I’ve got a 25hp mercury not sure of exact yr. And I’m trying to figure out what fuel ratio it needs to be ran with. Thanks

Outboard Spares Response
Hi, 50:1 is the most common fuel:oil ratio to be used with 2 stroke outboards. You will be fine with that ratio. Regards,

5hp mariner

By: on 18 February 2024
Is it easy to purchase & install a impeller?do I need a gasket set also ?

Outboard Spares Response
Hi there, Yes. Impellers are readily available for a Mariner 5Hp. There are a few different models so you will need your serial number to confirm the correct impeller. It is always a good idea to replace the gaskets as well however it may not be necessary if it comes apart ok and they don't break. Cheers

2012 suzuki 40hp 2 stroke

By: on 2 February 2024
What ratio should i run previous owner told me 30 to 1 but to me dosent sound rite

Outboard Spares Response
Hi there, Manufacture changed it to 100 to 1 which is fine if you intend to do lots of idling/trawling. However I would still run it at 50 to 1 to be able to run it at full speed and under load.

97 15hp yamaha 2 stroke

By: on 26 September 2023
What is the fuel/oil ratio on my outboard

Outboard Spares Response
Hi there, Yamaha recommend 100 : 1 however if you are going to run the motor under load and at speed more than idling and trolling I would suggest 50 : 1 to be safe. Cheers

1995 Johnson 150 HP

By: on 25 September 2023
Does it have automatic vro or do I mix oil ? Thanks in advance. Hope they are dependable engines. I don't know if 2 stroke or what. Rookie With Johnson.

Outboard Spares Response
They came out with VRO (Variable Ratio Oil) however over the years many of these engines got converted to premix due to fuel pump failure or owners peace of mind. You could first check by seeing if you have a remote oil bottle in the boat and if so see if it is connected. If all connected put some masking tape on the oil level and run 50:1 oil premix. Observe oil level after running a water test. If oil level drops then it is working. Motor will run smokey because it is getting double the oil from the premix. You can then continue to run the engine with unleaded fuel only and continue to add oil to your bottle. If there is no oil bottle and the oil line has been blanked off then it would be safe to say it has been converted to run premix. Happy & safe boating

Yamaha 100:1 30hp cv

By: on 16 September 2023
Can I run other good brands of oil in my 30hp cv 2 stroke 2 cylinder at 100:1 or is the 100:1 only for when you use yamalube? Thanks.

Outboard Spares Response
Hi there, It is recommended to run 50:1 with other oils. Cheers

Easiest way to convert oil to fuel ratio

By: on 1 July 2023
How about make this easy for an old man. How many ounces of 2 stroke oil do I need to add to 5 gallons of unleaded fuel to make my 2005 25 horse Johnson run like it should? I’ve read all the mil to li and itS just easier to ask. Thanks in advance!!

Outboard Spares Response
Hi there, To run your 25Hp Johnson at 50:1 you will need (12.8 exact) say 13 ounces of oil for 5 gallons of unleaded. Cheers

1986 Mercury 45ELPTO, Serial 0A996425 - Oil Inj Sy

By: on 8 May 2023
Hi, I just purchased a 1986 Bass Tracker Tournament TX 17'er, everything is original right down to the tires. The oil injection system is shot and I haven't had much luck finding parts or a replacement for the 1986 Mercury 45HP 2cycle. So, I am thinking in order to utilize the engine, not sure it runs as yet, I will need to mix oil and gas in the 6 gallon outboard tank. I hate to assume, but would the recommendations above at 50:1 be okay? The owner had absolutely no documentation for ANYTHING. Any HELP! would be GREATLY appreciated. Thank you for your time and assistance, and any info you can offer. Dave

Outboard Spares Response
Hi there, I would stick with 50:1. That is what the manufactures recommend.

mercury blue band 50hp

By: on 17 April 2023
Hi what’s the best mix for a mercury blue band 50hp

Outboard Spares Response
Hi there, 50:1 using a tcw3 approved marine two stroke oil. Cheers

1984 yamaha 115

By: on 27 August 2022
I have a 84 115 and it has never been rebuilt and having trouble finding the best oil ratio. The motor looks really clean and shouldn’t have many hours but I’m not sure thanks!!

Outboard Spares Response
Hi, I'd be running the engine at 50:1. 100ML of TCW3 Outboard 2 stroke Oil to 5 Litres of unleaded petroleum.

Premix through an Automotive Carburetor??

By: on 11 August 2022
I have been searching all over the net and I cant find any info on this subject, I have a 2 Cycle 85 Horse Chrysler Force, estimated manufacturing date around 1985-1986, and I want to use it as a mountain runner Kart racer. So I want to change the Orientation of the Motor to a flat style Motor an I really want to use a downdraught Carburetor, but I cant find any large enough for the application, so my question is will an everyday Automotive Carburetor ,say like a Bendix Stromberg WWC 2bbl, work on a 2 cycle and flow 2cycle mix through the carburetor ok?

Outboard Spares Response
Hi there, I'm not sure on that one. That's not something I am familiar with. Good luck with that. Sorry I couldn't help you out

Fuel/oil mixer rate

By: on 17 July 2022
I have a 2006 mercury 9.9 4 stoke, so I mix the fuel and oil in the tank. If so what kind of oil. Thanks

Outboard Spares Response
HI, 4 strokes take straight unleaded fuel without any oil in the fuel. The outboard has it's own Oil Sump to hold 4 stroke Oil (not 2 stroke oil). Imagine your 4 stroke outboard as a car where you just use fresh unleaded fuel and once a year you complete an oil change. Cheers

What oil ratio to run in a 40hp Maxus 2 stroke…

By: on 18 June 2022
Just wondering if anyone knows what the recommended fuel/oil ratio is for a Maxus 40 horsepower 2 stroke outboard?

Outboard Spares Response
Not sure on Maxus Outboards but to be safe I'd mix at 50:1.

Best oil

By: on 14 June 2022
What is the best oil to mix with?

Outboard Spares Response
This is a question that will have divided opinions!! Ha! Use a good quality 2 stroke TCW3 oil that has a reduced smoke formula. The OEM, Yamalube, Quicksilver/Mercury, Evinrude Oils are all great from my experience. I also like the Australian Penrite Oil as a non-OEM brand.

150 2 stroke Yamaha

By: on 2 August 2021
The oil ratio on a new powerhead on a 150 Yamaha outboard

Outboard Spares Response
Hi, Brand new or reconditioned powerheads should run 25:1 for the first 4 to 6 hours. You could then run 50:1 after this. Regards

40 HP mariner yamaha 1979 model

By: on 29 January 2021
Hi guys please assist. I have these two motors however do not know the fuel mixture as some old small motors use to run a 100:1 ratios where as most are 50:1. How will I know. I also do know that fully synthetic has its own mixture like 75:1.

Outboard Spares Response
Hi, If I owned one of these engines I'd be running 50:1 with a decent TCW3 2 stroke engine oil designed for pre-mix. If you're doing a lot of idling and slow trolling you could reduce the ratio a bit if you found you are fouling plugs but honestly I think 50:1 should be fine. Cheers

2 stroke oil

By: on 1 August 2020
A Great Rule Of Thumb on 2 stroke oil small engines = less oil 100-1 / 50-1 Engines before 2000 and beyond large or small 50-1 new engines 25-1 / 20 to 40 liters

Oil suitability

By: on 12 March 2020
Are you able to use the same oil as for aircooled engines such as chainsaws etc

Outboard Spares Response
Hmmm. Good question. Outboard oils are designed for water-cooled engines. I would not suggest it. Cheers

John

By: on 10 August 2018
Thanksamundo for the post.Really thank you! Awesome.

2 Stroke oil

By: on 25 July 2017
Is the said ratios needed for large hp 2 strokes . Year 2000 forward . As Most are oil injected anyway . What's the reason for adding oil to the fuel mix if the motor is running fine . No rebuild ect . Dose it save oil being injected .

Outboard Spares Response
If your outboard is oil injected, and hasn't been rebuilt, then you won't need to add any oil to your fuel. But adding oil to your fuel will not change the amount injected by the engines oil injection system.

Ratio

By: on 25 July 2017
Simple divide 1000ml or 1 litre of petrol by ratio = the required amount of oil per litre of fuel i.e 1000 / 50:1 = 20ml of oil per litre of fuel Or I.e 1000 ml of petrol divide by 100:1 = 10mls of oil per litre

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