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What's up everybody, it's Technicians Tuesday, and this week we are going to be
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comparing the differences between a Mercury's two-stroke oil system and a Yamaha's two-stroke
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oil system. These two systems have a lot of similarities, but also have a lot of differences
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The biggest of these differences is that the Mercury system operates by using crankcase
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pressure to pressurize the oil tank in order to feed the oil from the reservoir tank in the
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boat to the main oil tank on the engine. Whereas Yamaha uses an electric pump in the reserve oil tank to pump the oil up to the engine
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Now both of these systems consist of having an oil pump that is located on the engine that
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distributes oil to the different sections of the engine. Some go to the reeds and sometimes it sends the oil straight to the cylinders
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On other models the oil is mixed in before the carburetors and then also fuel injection models
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will send the oil to the VST. The difference between these two pumps is that Mercury's pump is electronically controlled
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where the Yamaha pump is mechanically controlled by this lever here. If this lever fails though, the oil pump automatically goes to wide-open throttle and will over-oil the engine
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You might say it's like a fail-safe feature. Now the way we can check whether these systems are operating is pretty simple
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For the Yamaha system, there's a little toggle switch located on the engine either right next to the oil tank or on the back of the engine here on the computer
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We can pull off the oil hose here from the tank and then with the key in the oil
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position, just hold the switch up and wait until the oil comes flowing out of the hose
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For the mercury system we have to have the engine on and running in order to check it but it just as simple Because it is a pressure driven system we can just unscrew the cap on the main oil tank and watch the oil level rise
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Then quickly tighten the cap back down before oil flows out and all over the place
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Both of these oiling systems are effective and have worked great for the entirety of the two-stroke generation age
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There are a couple of cons to each one of these systems though. For the mercury system, it is a little more basic and simple
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more basic and simple than the Yamaha system because it has less operating components to make
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it run properly. We have a hose that comes off of the side of the engine here that is our
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pressure hose. It then connects with the fill hose that has a blue line on it, indicating that it is the
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oil fill hose. On the tank there are two places for the hoses. The lower fitting that is off to the side is the
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pressurizing portion. Then the one in the middle goes down to the bottom of the tank where
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there is a pickup tube with a screen on it. The pressure forces the oil through this back up to the
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engine's main oil tank. There are O-rings on all of the caps to this tank, and if there is an
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air leak at any of these points, the system stops operating properly. So if the oil cap doesn't get
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tightened all the way down when the oil is filled, the system can lose pressure and thus stop pumping
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the oil to the main tank, which is where we have the next most common failure or con to this system
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The sensor inside of the oil tank has a float that sits around the sensor. Inside of that
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float is a magnet and as the float goes up and down the magnet moves along the sensor and lets the engine know if it has a full oil tank or not The problem that is most commonly seen is that either the sensor or the float and magnet fails and the entire oil tank has to be replaced if it is not the sensor that fails
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which in most cases it isn't the sensor that stops working, it's the float in the magnet
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Now for the Yamaha system it works great, it just has more components that factor in to
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to make it work. We have a sensor inside of the reserve oil tank that sits inside of the boat
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This sensor lets the computer know the level of the tank. Then we have an oil filter that is in line here on the bottom of the tank, as well as the
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oil pump that sits inside of the back of the tank here
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There is then a harness that runs from this plug that operates the pump and the float sensor
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all the way up to the engine, where it hooks into the engine harness and then goes through
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the engine harness to plug into the computer, as well as the sensor that goes inside of
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the main oil tank that is on the engine. That connects to the computer through the engine harness as well
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To simply break down the way this works, the float sensor here inside of the main oil tank
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has three settings to it. There's the top, middle, and bottom sections to the sensor
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The top portion basically turns the pump off, the middle section basically turns the pump on
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the bottom section turns on the audible alarm, throws the code on the gauge, puts the engine
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in fail-safe mode, and then turns the pump on as well. So as the float goes down, when it hits
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the middle, it will tell the pump in the reserve tank to turn on. If everything is working properly
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the tank will fill up and move the float back to the top which turns the pump back off If the sensor fails or the pump stops working or the filter is clogged and oil is not filling the main oil tank
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the float will go down to the bottom of the sensor, which tells the computer the engine is running
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out of oil. This will turn on the audible alarm and put the engine in fail-safe mode or an RPM
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reduction to 2,000 RPMs. So the con to this system is really that there are about five major
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things that fail and have to be troubleshooted when they do. There are both sensors from
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each oil tank, the harness that connects them, the oil filter on the reserve tank, and the
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oil pump on the back of the tank. It is not uncommon for any of these to fail, so it does
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take a little more time to troubleshoot this system. All in all, both of these systems have been
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in play for decades and are both extremely efficient and practical when it comes to making
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sure the engine has oil, and that in the case of an oil failure, the
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The operator is advised and the engine is protected from blowing up from running without oil
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We want to thank you for watching. Hopefully this has been an insightful video and if you learned something new today
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give the video a like and subscribe to the channel so you don't miss out on any of our technicians Tuesday videos
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Let us know about what you have experienced with your two-stroke oil system in the comments section below
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And then don't forget to check us out on our website at born-againboating.com
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You can also check out some of our other videos where we have a growing library of resources for all kinds of boat and outboard repair content
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Enjoy your Tuesday night and we look forward to seeing you next week
