Written by: Capt. John Banister, AMS®
What is a Marine Engine Survey?
A marine engine survey is an in depth mechanical inspection of the outboard engine on a boat or yacht. This is not an inspection that just any surveyor can perform. To conduct a proper mechanical survey on marine engines the surveyor needs to have professional marine engine technical training, factory specific engine training, hands on mechanical experience, (service, troubleshooting, and repair), and continuing education on the engines the surveyor is inspecting.
Without proper education, experience, and mechanical knowledge of the engines many things can be missed which can cause an owner or a prospective buyer of a vessel thousands of dollars in unseen damages, overdue maintenance or even the replacement of a faulty engine that appeared to run properly.
The Yamaha Versus The Mercury Outboard Engine Survey
For the sake of this article I am going to compare the Yamaha F300, 4.2 liter, V6 four stroke, 300 hoursepower outboard engine and the Mercury Verado 2.6 liter, in-line six cylinder, four stroke, 300 hoursepower engine. Both are common outboard engines that are in the market and are common to see on many recerational center console and walkaround vessels today.
The Yamaha F300 outboard engine can not be compared to the Mercury Verado 300 HP outboard engine. There are similarities but also many differerences. Because of the differerences the outboard engine survey must be geared differently.
The Yamaha F300 outboard engine is a naturally aspirated outboard engine, which means the air intake does not have forced air induction. A Mercury Verado 2.6 liter outboard engine is a supercharged engine. Air is forced into the air intake. The air is forced into the intake via double lobed mechanically spinning rotors driven by the crankshaft which increases air pressure up to two times higher than normal atmospheric air pressure. A supercharged Mercury Verado engine has components the Yamaha F300 outboard engines does not have. Some of these parts include an intake air filter, an EBC (electronic boost control) assembly, supercharger oil and water hoses, a supercharger boost charger temperature sensor, a supercharger pulley, and a supercharger vent hose. Supercharger failures or overheats will cause the Mercury Verado outboard engine to go into a “guardian” mode which will restrict RPM to idle only to protect the engine from catastrophic engine failure and is built into the programming on the engine’s PCM (propulsion control module).
The Yamaha F300 outboard engine is timed for ignition and valve overlap by a cam timing belt located on the top of the engine which is tightened by a hydraulic belt tensioner. The cam timing belt can clearly be seen on the top of the powerhead when the top cowling (outboard engine cover) is removed. The Mercury Verado outboard engine is timed by a timing chain located at the base of the powerhead and can not be seen when the top cowling is removed. The Yamaha F300 outboard engine cam timing belt must be changed when wear is seen or every 1,000 hours or five years. The Mercury Verado timing chain needs little to no service however there are sometimes rare cases of the timing chain jumping. Usually the signs of a jumped timing chain are MAP sensor faults that can not be corrected, incorrect ignition timing, and no air pressure drop from key on to the engine running. The timing chain should be visually inspected after leaks, sensors, and wiring have been checked. If the timing chain needs to be serviced, the powerhead needs to be removed and disassembled.
The Yamaha F300 outboard engine creates power by a powerhead mounted stator that is located just below the flywheel. The stator produces up to 70 amps of power through a rectifier / regulator with 55 amps of charging power. The Mercury Verado 300 HP outboard engine produces electrical power by a accessory belt driven alternator. The alternator is rated to produce up to 72 amps of power and will produce about 50 amps of charging power. In my experience as a marine mechanic, stators tend to last alot longer than alternators. The drawback to stators is when they do need to be changed, with parts and labor considered, the replacement can be two to three times the cost of replacing a bolt on alternator.
The Yamaha F300 outboard engine weighs 591 pounds. The Mercury Verado 2.6 liter outboard engine weighs 695 pounds (with a 30″ shaft length). The Yamaha F300 outboard engine requires 7.1 quarts of proper weight Yamalube 4-M FC-W engine oil or four stroke marine type engine oil (Yamaha recommends 20W-40 weight engine oil). The Mercury Verado 2.6 liter engine requires 7.4 quarts of Mercury brand, 25W-40 weight engine oil. There should never be any automotive type oil in the powerhead of either brand of outboard engine.
The Yamaha F300 outboard engine has a rated wide open throttle (WOT) range of 5,000 – 6,000 RPM. The Mercury Verado 2.6 liter has a rated WOT range of 5,800 RPM – 6,400 RPM. The Yamaha F300 outboard engine should idle (after the warm up phase) between 650 – 750 RPM. The Mercury Verado 300 HP outboard engine will idle at 550 RPM.
Some basics of both engines: The Yamaha F300 outboard engine should have a fuel pressure of 37 – 43 psi at idle. The Mercury Verado 2.6 liter engine should have a fuel pressure of 48 psi at idle. Give or take three psi is acceptable. Oil pressure of a Yamaha F300 outboard engine should be at 50-51 psi at idle (after engine warm up). At 3,000 RPM the oil pressure should increase to 85 – 86 psi. The Mercury Verado 2.6 liter engine should have an oil pressure of 5 psi at idle and should increase up to 29 psi at 6,000 RPM. The Yamaha F300 outboard engine will burn approximately 25.6 gallons per hour at WOT. The Mercury Verado 2.6 liter 300 HP outboard engine will burn approximately 26.1 gallons per hour at WOT. Expect the acceleration to be about 20% faster in the supercharged Mercury Verado versus the Yamaha F300 outboard engine. Note: The fuel economy will vary depending on the size of the vessel, vessel weight, the number persons on board, sea conditions, and propellers installed on the lower units at the time of the engine survey. I tend to rely on the engine’s RPM range at WOT more than fuel burn and maximum speed because of these factors.
Compression testing of the cylinders should be done only after the engine is warmed up. In both engines allowable compression differences should be no more than 15% in each cylinder. Some engine service manuals recommend no more than 10% in compression difference. In the Yamaha F300 outboard engine, compression readings are typically between 170 psi – 210 psi. The service manual does not allow anything less than 101 psi. The Mercury Verado 2.6 liter 300 HP engine has allowable compression between 154 psi – 180 psi.
There are also many other differences in the Yamaha outboard engine survey versus the Mercury Verado outboard engine survey, such differences are sensor resistances, performance curves, temperature ranges of engine components, fuel sample testing, secondary voltages produced by the ignition coils, and oil analysis results (even in the oil analysis there are differences in metal and wear composition that are specific to each engine based on its use and storage). To list all of these items would turn this article into a book. Some of these known items that I look for I consider to be trade secrets that even the service manuals do not publish. I only keep that knowledge between myself and my customer as it separates the trained from the untrained engine surveyor.
The process of the outboard engine survey of both Yamaha and Mercury outboard engines is detailed and comprehensive. Typically if I am conducting the survey of the hull and outboard engines of a center console or walkaround vessel, the process can take most of the day (between six to eight hours). If the vessel is rigged with triple or quad engines, the process sometimes can take two days to complete. This is because I am not only looking for the current condition of the outboard engines, but also the “Gremlins” that may exist within the engine that would cost the new owner money and headaches in the near future.
Typically, the following are some of the tests that are included in an outboard engine survey:
- Sea trial (running the engines at wide open throttle, backing the engines down, and hard over turns to inspect the steering assembly)
- Compression testing
- Borescope viewing of the cylinders and pistons
- Inductive testing of the ignition systems
- Infrared thermal imaging of the powerheads and lower units to ensure proper temperature anomalies throughout the engines while running
- Computerized marine engine diagnostics (includes dynamic testing, static testing, and component activation of the engine’s components)
- Inspection of the steering assembly
- Inspection of the engine’s electrical actuators or hydraulic systems
- Oil analysis to search for unusual wear metals and foreign substances in the engines
- Testing of the fuel to search for phase separation, excess water or Ethanol in the fuel
- Proper rectified and regulated voltage to insure the engines are charging the batteries when running
- An overall visual inspection of the engine to look for things such as galvanic corrosion, back probing, worn timing belts, proper belt tension, proper wiring connections, improper previous repairs, etc
If requested or recommended, I can conduct more advanced inspections and testing during the marine engine survey or analysis. I can also provide diagnosis or determine the mechanical failures. These advanced inspections and testing I can perform are the following:
- Digital data testing (on NEMA 2000 and CAN bus data systems)
- Stray current testing
- Battery load testing
- Vacuum testing
- Leak down testing
- Electrical parasitic draw
- Carbon monoxide testing
- Fuel analysis
- Coolant analysis
- Mechanical failure analysis
Digital Data Testing As Part of the Outboard Engine Survey
In more recent years digital data testing has become more important in outboard engine surveying and in proper diagnosis in outboard engine troubleshooting and repairs. Some outboard engines now have integrated digital guages that communicate with the throttle / shift steering command modules and the outboard engine’s computer. Yamaha refers to their system as “Helm Master” which is a digital electronic control (DEC) system that requires no mechanical cables. Their newer “Helm Master EX” is a fully electric steering system with no hydraulic steering components.
Mercury has their version of the same digital system known as Digital Throttle and Shift (DTS) which is a fully electronic throttle and shift control system that replaces their older mechanical steering system. Their steering rams in the in-line six cylinder Verado outboard engines are still hydraulic.
I have found in the service and maintenance side of my business, that sometimes the data in the digital gauges becomes corrupted or does not read correctly, and if so, can set the outboard engines in a “guardian” mode and in some cases will disable the electronic starting of the outboard engines.
Digital data (such as CAN bus and NEMA 2000 digital data) is a DC electric message based protocol system. It is like a digital morse code but the data transfers throughout the network in milliseconds. To fast for the data to be picked up by a multimeter. It can only be seen and monitored with a graphing meter or better yet, an oscilloscope. Outboard engines connected through these digital data systems communicate to digital gauges and navigation systems usually through a NMEA 2000 backbone connection. Outboard engine and command module computers that use CAN bus convert their data to the helm mounted gauges through a gateway that converts the CAN bus data into NEMA 2000 data.
How this system works is fairly simple. The system runs off a high / low voltage system (low is 1.5 – 2.5 volts and high is 2.5 – 3.5 volts). The two voltages on the high / low mirror each other to confirm accurate data to the ECU / PCM and also to the command modules and gauges on board. The resistance is 60 ohms in the NMEA 2000 backbone system. When a “T” connector, wire connection, terminator or gauge malfunctions, the data becomes corrupted and this clear high / low data can not communicate clearly. This is what causes digital gauges to not work properly, freeze, etc. Connecting the oscilloscope to the NMEA 2000 backbone allows you to see this data while you troubleshoot the system. Mirrored wavy lines is clean data. Lines that run into each other, in consistent high / low digital data and spikes in the data show that there is corrupted data. By isolating and disconnecting each “T” connector (if there are multiple backbones on board) one by one until the oscilloscope shows clean data is how you find the problem.
Somtimes the gauge itself can be the problem and there is no corruption in the data at all. One example I have run into is digital fuel level gauges. Calibration of the fuel levels in the digital gauge (that are inputted manually by the boat operator) will sometimes not read properly or not at all. So although the fuel sender is working, the gauge will not take the calibration or inputted data and the fuel in the gauge or digital data will read low or empty. This can cause the outboard engines to show false error codes on the gauge even though the gauge shows there is gasoline in the fuel tank. Using special software, I can connect into the NEMA 2000 backbone and confirm if the digital data system is actually reading the fuel or nothing at all. There will be no fault codes in the engine mounted ECU / PCM or in the command module under the helm. Somtimes this was the only way I could confirm the problem.
Qualifications of an Outboard Engine Surveyor
All surveyors are not created equal. Some engine surveyors have had extensive training as marine mechanics on outboard engines and are excellent in their trade as engine surveyors. Some have never stepped foot inside of a classroom to learn the engines they are paid to survey. To be honest I have seen non-certified, untrained surveyors conducting surveys on engines they are not qualified to handle let alone make any assessment of their true condition.
The best way to know that you are getting a legit and certified engine surveyor is to simply ask to see their credentials. I mean, to see their actual engine certifications and verify (if need be) their training with the engine’s manufacturer. As you have already read, the Yamaha outboard engine is not the same outboard engine as the Mercury Verado outboard engine. Although there are some similarities, they function and operate quite differently. It takes specific factory training and time turning wrenches on these engines to properly learn them and to give an accurate assesment of their true condition. A warmed over engine inspection with marine engine diagnostics looking for active fault codes and compression testing is not nearly enough. Not all existing problems with outboard engines will be listed in the active fault codes. Fuel system problems, valve leakage, excess carbon in the engines, and lack of maintenance are not sensor related and will not be in the diagnostics computer. There is other testing that needs to be done in a proper outboard engine survey. Missed items can cost you alot of money if simple things like improper maintenance, low vacuum pressure, and even an unusual sound is heard that only a factory trained engine technician can detect.
Sometimes seemingly obvious rough running outboard engines can have very simple, non-issue problems such as improper TPS (throttle position sensor) voltage, a loose ignition coil wire or a loose hose connected to the throttle body. A factory trained marine mechanic can easily detect these issues and correct them on the spot and move on with the outboard engine survey. An untrained engine surveyor will not recognize these minor issues and can give a false analysis of the outboard engine, in essence killing the pending deal.
Some other things to look out for when searching for a marine engine surveyor: A diesel engine mechanic is not a gasoline engine mechanic. These are two completely different worlds. Only hire an engine surveyor that has training and knowledge on the specific engine(s) you need surveyed. A sea trial is essential to the engine survey. No true assesment can be made until a full load had been put on the engines. Some hull surveyors purchase boot leg or after market engine diagnostics equipment and offer marine engine diagnostics as part of their service. If you go that route, understand they are not certified marine engine mechanics and they may miss obvious problems that are clearly in the data section of the engine diagnostics report. Sensor fault codes (active or inactive) is only a fraction of the data that needs to be obtained in a proper marine engine diagnostics test. Do not accept a marine engine survey report or engine diagnostics report that was conducted in the past on the same vessel. It will not reflect the current condition of the engines you need surveyed. Trust me, most times the cost of the engine survey more than pays for itself. If the seller or selling broker throws you road blocks about having the marine engine survey conducted, do not care more than they do. Chances are they know something you don’t about the vessel they are selling. South Florida is the Mecca of boats for sale. Move on. If you can, I recommend attending the engine survey. You will learn alot about the engines you are purchasing with your vessel and you will see first hand if there are any problems during the survey so nothing is lost in translation. Before hiring any surveyor, ask the seller or selling broker for all of the maintenance records of the outboard engines. Also research for any service bulletins on the engines you are purchasing. Be sure those services were performed by seeing the invoices or contacting the manufacturer with the engine’s serial numbers for confirmation. If the seller or selling broker can not produce these records or enough of them, assume these services may have been skipped and rely on your engine surveyor to give you recommendations. Communicate with your engine surveyor about anything you know about the engines from the seller and selling broker. You are a team. It is not a test. The information may be crucial to the findings from the engine survey and will help you make a better informed decision about your pending offer or whether to purchase the vessel or not.
I am currently certified on Yamaha, Mercury, and Honda outboard engines and MerCruiser inboard engines. I have specific factory and technical trade school training on Evinrude outboard engines, Suzuki outboard engines, and BRP, Yamaha, and Volvo gasoline inboard engines. I attend yearly annual training from factory training schools throughout the United States.
My combined training, education, and technical certifications can be found here.
I am always happy to serve as your hull and / or engine surveyor if I can. Feel free to contact me for more infomation based on your specific needs. For those in the market, happy hunting and fair winds.