The Yamaha OX66 has one of the most loyal followings of any outboard motor ever made. Decades after production ended, these motors are still running charter boats in the Gulf, fishing vessels in the Caribbean, and offshore center consoles up and down the Florida coast. When properly maintained, an OX66 is essentially bulletproof — and on the used market right now, they represent some of the best value available in high-horsepower outboards.
But not all OX66s are created equal. Year, configuration, and maintenance history matter enormously. This guide covers everything you need to know to find a good one and avoid an expensive mistake.
What is the OX66?
The OX66 designation refers to Yamaha's 66-degree V6 two-stroke engine paired with their proprietary electronic fuel injection system. Before the OX66, Yamaha's high-horsepower motors used carburetors — the EFI system was a major leap forward in fuel delivery precision, idle quality, and cold-start performance.
Yamaha produced the OX66 from 1996 through approximately 2005, in horsepower ratings of 200, 225, and 250hp. The 250hp version — the most common and most sought-after — is what most buyers are looking for when they search for an OX66.
Model year breakdown — what changed and when
1996–1999 (early OX66): The first generation EFI system. These motors are fully proven but older, and VST (Vapor Separator Tank) components on early examples are more likely to need attention. Look carefully at fuel system condition on anything from this era. That said, a well-maintained early OX66 is still a strong motor.
2000–2002 (mid-generation): Yamaha refined the EFI system and addressed several first-generation issues. These are often considered the sweet spot for OX66 buyers — the technology is mature, parts are plentiful, and these motors are young enough to have reasonable remaining service life without being so old that everything needs attention.
2003–2005 (late OX66): The final production years. Best parts availability, most current calibration maps, and some incremental refinements. If you're not on a tight budget, a clean late-production OX66 is the lowest-risk buy in this family.
Model codes — what the letters mean
OX66 model designations look like LX250TXRB or SX250TLRB. Here's how to decode them:
- First letters (LX, SX, etc.): Indicate the series and sales region
- 250: Horsepower
- T: Electric start with power trim and tilt
- L or X: Shaft length — L = 20" (long shaft), X = 25" (extra-long shaft)
- R: Remote control (as opposed to tiller)
- B: Model year suffix (changes each year)
Always confirm the shaft length — 20" vs. 25" — before purchasing. Measure your transom height first. Most offshore center consoles and larger hulls take a 25" shaft. Getting this wrong is an expensive mistake.
What to inspect — the OX66 checklist
Compression
Target 110–135 PSI across all six cylinders with no more than 15 PSI variance between the highest and lowest reading. Consistency matters more than absolute numbers — a motor reading 120, 122, 119, 121, 118, 120 is in excellent shape. One reading 135, 137, 134, 136, 135, 95 has a problem on cylinder six regardless of how good the others look.
Any cylinder reading below 100 PSI on a warm engine is cause for serious concern. Don't buy it without a full powerhead inspection.
The VST (Vapor Separator Tank) — the most common OX66 issue
The VST is the heart of the OX66's EFI system. It's a sealed tank that separates fuel vapor from liquid fuel and maintains the constant fuel pressure the injectors require. The VST contains a diaphragm and internal components that deteriorate over time, especially in motors that sat unused for extended periods.
Symptoms of a failing VST: rough idle, stumbling or surging at low throttle, hard starting when warm, or the motor cutting out and restarting. A VST rebuild or replacement runs $150–400 in parts depending on what's needed.
Ask the seller when the VST was last serviced. On any OX66 over 10 years old that hasn't had VST work done, budget for it.
Fuel injectors
The OX66 uses six low-pressure fuel injectors. They're durable but can clog or degrade after years of service, especially if the motor sat with old fuel in the system. Signs of injector issues include rough running at specific RPM ranges, uneven power delivery, or black smoke under load.
Injector cleaning is a routine service item and relatively inexpensive. Full replacement injectors are available and not prohibitively costly. This is not a reason to walk away — but it's worth asking about.
Oil injection system
The OX66 uses an oil injection system that automatically meters two-stroke oil into the fuel. Check the oil reservoir for cracks or leaks, inspect the oil lines from the reservoir to the motor, and verify the low-oil warning light works (it should illuminate briefly when you key the motor on, just like a car's oil light).
A motor that ran with a failed oil injection system and no manual oil mixing can have serious internal damage. If you can't verify the oil system works, walk away or have the motor inspected by a Yamaha-experienced mechanic before buying.
Gear case oil
Drain and inspect it. Amber or light brown = good. Milky or cream-colored = water intrusion from a failed seal. Metallic particles in the oil = gear or bearing wear inside the lower unit. Any of the last two are serious findings that should significantly affect your offer or your decision to buy.
Water pump and impeller
A failed impeller on a high-horsepower motor causes overheating within minutes. Ask when it was last replaced — every 3 years or 300 hours is the standard recommendation. If the seller doesn't know, budget $80–150 in parts for a new impeller kit.
Saltwater vs. freshwater history
This matters more on an OX66 than almost any other factor. A freshwater motor from a Georgia bass lake with 600 hours will typically be in far better structural condition than a saltwater motor with 300 hours that was flushed inconsistently. Look at corrosion levels on the powerhead, mid-section, and lower unit — they tell the story clearly.
Saltwater use isn't disqualifying, but it does mean closer inspection of anodes (they should be partially consumed but not gone), painted surfaces for bubbling, and any aluminum components for pitting.
Test run — non-negotiable
Never buy an OX66 without seeing it run. Cold start, idle, through the full RPM range. The motor should start within a few seconds of cranking, idle smoothly after a brief warm-up, and accelerate cleanly to full throttle without surging, misfiring, or hesitation. Watch the tell-tale for steady, strong water flow throughout.
What to pay
As of 2024–2025, OX66 250hp motors in good running condition with documented compression typically sell in these ranges:
- 1996–1999, higher hours (500+), freshwater: $2,200–$3,200
- 2000–2002, moderate hours (300–500), good condition: $3,000–$4,200
- 2003–2005, lower hours (<300), clean condition: $3,800–$5,500
Saltwater motors typically sell $300–700 below these ranges. Motors without compression test data or with unknown service history should be priced lower still — you're taking on risk that should be reflected in the price.
Walk away from any OX66 250 priced under $1,800 unless you're buying it for parts. At that price something is seriously wrong.
Why the OX66 is still a great buy today
The OX66 is the last of a generation of motors built before manufacturers started engineering for planned obsolescence. Parts are widely available, the technology is fully understood, and experienced mechanics are everywhere — including throughout the Caribbean, where these motors have been running hard for decades.
A well-maintained OX66 in good condition bought at the right price will give you years of reliable service and will be easy to maintain and resell. That combination — proven reliability, wide parts availability, strong performance, and reasonable used prices — is why these motors remain so popular long after production ended.
OX66s in our inventory
We frequently have OX66 motors in stock — compression tested per cylinder, documented, and ready to ship. Every motor we sell comes with a written inspection report. Browse our current inventory, or message us on WhatsApp with exactly what you're looking for and we'll reach out when the right motor comes in.