The listing says 420 hours on a 2017 F150, the seller says "mostly cruising", and the gauge agrees with the number. That's the whole story most buyers get. The ECU has a more detailed one, because on Yamaha four-strokes it splits the running time into seven engine speed bands, and that split shows what the engine actually did with those hours.
The seven bands
The ECU sorts time into these ranges:
- below 1000 rpm
- 1000 to 2000, 2000 to 3000, 3000 to 4000
- 4000 to 5000 and 5000 to 6000
- 6000 to 7000
Idle and no-wake speed land in the first band. Trolling sits in the first or second, depending on the boat. Normal cruise on most hulls falls between 3000 and 5000. The top two bands are where the engine was run hard. You need the M-JET DIAGNOSTIC dongle and app or a shop scan to see this, since the gauge only shows a single total.
Patterns and what they usually mean
Most of the time below 2000
Common on boats used for trolling, on pontoons, on charter boats that spend hours at slow speed, and on boats that idled at the dock a lot. It isn't automatically bad. But low-speed running for long stretches doesn't get the engine fully warm under load, and that's worth noting in an engine that also shows overcooling entries or a history of short trips.
Heavy time in the 3000 to 5000 bands
That's a cruising engine. If "mostly cruising" is what the seller said, this is where you'd expect to find it.
A big share in 5000 to 6000 and above
Run hard. Not a deal breaker on its own, plenty of engines live there on tournament bass boats. It does mean you look harder at compression, the lower unit and the prop, and you ask what it was used for.
Noticeable time in 6000 to 7000
On many engines that's at or past the top of the rated range. It can mean a prop that was too light at some point, a lot of time with the engine trimmed way out, or a boat that spent time with a bad hookup or ventilation. Ask about prop changes.
Where the bands don't tell the truth
The bands say nothing about load. 4500 rpm on a light skiff is a different life from 4500 rpm on a heavy cabin boat. They also don't show whether the hours came in one season or ten. Nor do they show maintenance. A low-hour engine with no impeller change in six years can be in worse shape than a high-hour engine that saw a shop every spring.
A quick pre-purchase routine
- Ask the seller before plugging in. Most say yes. The dongle goes on the diagnostic connector, the app runs on your phone, no laptop needed.
- Read the hours by band and screenshot them.
- Read the fault memory before anything gets cleared. A freshly empty memory on a boat that "never had a problem" deserves a question.
- Compare ECU hours with the gauge. A big gap has a reason, and the seller should know it.
- On a twin rig, compare both engines. Bands that differ a lot between two engines on the same transom need an explanation.
If you look at several boats in a season, a license that covers more than one engine makes sense. There are options for 1, 3, 5 or unlimited engines. More on the method on the page on engine hours by rpm, and the used Yamaha outboard inspection guide lists the rest of what to check before money changes hands. The hours are one piece. Compression, the gearcase oil and the condition of the bracket matter just as much.
