Over the years I have seen engine designs come and go, and even some marine engine companies go out of business. So to prevent themselves from becoming obsolete, Mercury is always pushing the envelope to stay on top of the marine engine industry. Today I would like to give you my reviews on some of their newer motors.
The Mercury 150 EFI Fourstroke:
The goal of this engine was to make a simple, light, and reliable fourstroke motor. In the few years that it has been out, it has proven to be just that. Take the cowel off the motor and you will not see miles of wires going to and fro. The engine is set up for easy maintenance, so the oil and fuel filter are easy to access and the chart showing your maintenance intervals is easily visible on the side of the motor. The oil drain has a nipple for you to hook a hose to so when you open it, oil does not spill all over the place as it has done on past models and on the competitor’s engines.
To make this a reliable motor that will last, Mercury designed a big bore, short stroke 3 liter, 4 cylinder engine. Each piston is 4 inches in diameter, yet the stroke (back and forth movement or up and down movement in other motors) is only 3.62 inches. This gives the motor excellent torque as well. There is also only one cam shaft on this motor, this minimizes the moving parts and also cuts down on weight. There is one slight drawback however, at lower RPMs she has a shake, on some boats you will notice it more than others. At about 900 RPMs the balance shaft in the internal part of the motor has enough inertia to smooth out the vibrations. From what I have seen only a few people even notice this issue. On some of the past models there were some issues with the fuel system modules, the new “FSM” on this engine has been completely overhauled and perfected. I have not seen one issue with the FSM on the 150. Overall this motor is one of the best I have seen made, and it will be around for awhile. In fact they have had such success, Mercury has modeled the 75-90 and 115 HP fourstrokes off this engine.
The Mercury Verado 350-400 HP:
I have not seen one of these monsters yet, but I am looking forward to that day. So now boats that only have room for twin engines have an option to give them more horsepower. These engines are compatible with the Mercury Joystick Control system as well. I’ll go into detail about that system another day, but I can tell you this… there is no better set up on a boat with twin engines than the Mercury Joystick Control.
Since I brought up the Verado horsepower kings, I will take a moment to address a question that I often get asked by customers who want to increase their engine performance. The plain and simple answer to that question is you cannot. If you want more HP, buy a bigger engine. Here is why, and I will put it as simply as I can. A Mercury, and even MerCruiser engine, runs on what is called a Speed/Air density theory. This means at certain RPM the engine knows how much air is going through it and the ECM will adjust the fuel flow or pulse width of the fuel injector to keep the fuel to air ratio at about 15 parts air to one part fuel. If you bore the cylinders out, put an oversized cam in, and port and polish the head, you will have a lot more air in the intake than the ECU will know is there. This will cause you to run lean, have poor performance, and within hours, destroy the engine. Now if you are one of my fellow techs reading this and it is the first time you have heard this, it is very important to know if an engine is running poorly. You will need to check your barometric pressure reading. This tells the ECU how much oxygen is in the air which the computer also uses to keep the optimum air to fuel ratio. So here on the east coast I see the barometric pressure around 28.5-29.5 Hg or 14.1-14.5 PSI most of the times but if the sensor is wrong and it reads, say, 25.2 Hg, the ECU will think there is less oxygen in the air and will lessen the fuel pulse width at the injector causing poor performance, yet it will not show a code that the sensor is bad. The ECU just thinks it’s at a higher altitude. I have seen this frustrate good technicians who did not pay attention to the instructor when he was talking about this. I have seen it on three different engines, and all those engines had been to two or three different shops before they came to me, and it really is an easy fix. So if you are a fellow tech reading this, look it up and study it (there are questions on both the certified and master certified technician tests on this as well).
“The Little Guys” Mercury 2.5-3.5 HP motors:
These are good little motors, basic and simple, yet I see some people get frustrated with them. They are pull start, so some customers with less strength may have difficulty starting them. There is only one cylinder, so they will not be as smooth as their larger counterparts that have 2 cylinders. For the person who only uses it one to two times a year, they need to drain the fuel out of the carburetor (This goes for any engine that sits a lot). Fuel stabilizer will help, but only for about 3-4 months, if your motor sits 10-11 months out of the year, drain the gas from the carb or disconnect the fuel line and run it out of fuel. I also see people trying to push too much weight with these motors. If you have two people weighing 220+ on a 12 foot john boat, you will need a bigger motor. I have heard a complaint that they are louder than the 8-9.9HP Mercury outboards, and they are a little louder, but with that small of a motor if they took the same precautions to make them quiet like they do the 8-9.9 you would end up with a .5 HP motor. The 2.5-3.5 are good on the back of a canoe or kayak or even a lighter person in 10-12 foot john boat, anything else and you would want to look at a bigger motor. Also bring a small gas can with you, at wide open throttle you will only last about 35-45 minutes before you run out of gas with the little on-board fuel tank mounted to that motor that holds less than a half-gallon of fuel. I know this may sound a little negative, but what I am trying to do is prevent issues before they arise. They are a great engine when used and maintained properly. Easy to carry if you are on a river and need to go ashore to get past a section of rapids, or to hang on a shelf to store so they are out of the way, but they have their limits.
The MerCruiser 4.5L 250HP Sterndrive/Inboard motor:
This motor has been designed and manufactured by Mercury/MerCruiser, unlike the 4.3L which was a GM engine block. In the past the air intake would be facing the drivers and passengers, this would allow them to hear the air being sucked into the engine. On the 4.5L the air intake is facing the aft end of the boat making it a quieter ride. One of the things Mercury is trying to do is take the proven working parts from the outboards they have produced and use it as a universal part. This will help keep the cost down. You will see the water separating fuel filter is the same as the one used with the Verados. The FSM, exhaust valves, fuel injectors, and ignition coils are the same ones used on the 150 outboard mentioned previously. Ignition coils being used has eliminated the distributor cap, rotor, and spark plug wires that were used on previous engines. This motor will use a Catalyst to help keep the emissions down as well as have the capability to be used with the MerCruiser Axius system (similar to the joystick control system on outboards). For more info on motors and maintenance check out my other blogs on New Gas Tanks Old Engines, Ethanol Fuels Dos and Donts and Boat Motor Maintenance. To learn more about Mercury Motors and the many options available check out their website and give them a like on Facebook.
Master MerCruiser Technician
Master Mercury Outboard Technician