1982 Mercury 115 Hp Outboard Specs

What You're Actually Dealing With

The 1982 Mercury 115 HP outboard isn't one single model in the way most people assume. Mercury shipped a handful of variations under that nameplate, and the specs shift depending on whether you're looking at the Big Farm series or a performance-oriented variant. This matters because someone will tell you the shaft length is 20 inches and then you mount it on a transom that needs 25 and you've got a $300 adapter plate situation on your hands. Displacement sits at 134 cubic inches, which works out to roughly 2.2 liters per cylinder in the V-8 configuration. Total displacement is 2177cc. Bore and stroke are 3.50 by 3.56 inches. Compression ratio varies by market and specific year revision, typically sitting somewhere between 8.0:1 and 8.5:1 for the Big Farm versions. The engine was carbureted—two Holley-type units feeding each bank—and that's one of the things that makes these survive. Mechanically simple in a way that a modern EFI system is not. Horsepower rated at 115 at 4500 RPM. Torque figures from Mercury around that era run closer to 125-130 lb-ft at roughly 3000-3500 RPM. Shaft length depends entirely on the model suffix. Long shaft is 20 inches. Extra long is 25 inches. Some regional variants had shorter shafts, but those are rare and usually marked differently on the transom plate. Weight is roughly 490 to 520 pounds dry, depending on whether you're counting the prop and any factory accessories bolted on at the mill.

Prop selection range typically runs 13 to 19 pitch aluminum props. Mercury recommended a 15 or 17 pitch for general duty on the Big Farm. If you're running a heavier boat or pushing against a current, you drop pitch. Lighter load, higher pitch. This isn't guidance, it's just what I've seen work across dozens of these engines over the years.

Where People Mess This Up

The transom mounting pattern on the '82 115 is not universal. Mercury used a specific bolt circle that's close to—but not identical with—Evinrude's pattern from the same era. I've seen people try to adapt an Evinlude mounting bracket onto a Mercury transom and end up with misaligned bolt holes and a prop that vibrates at 3000 RPM because the engine sits slightly off true. Measure twice. The manual calls for a 3/8-inch bolt pattern with specific spacing, and if you're fabricating an adaptor plate, use the actual engine, not a catalog drawing. Another thing nobody warns you about: the oil injection system on these. The 1982 Big Farm 115 used a mechanical oil pump fed by a separate tank. The pump is driven off the camshaft and the ratio is fixed. That means your mix ratio is determined by how far you open the throttle, not by a computer. At low RPM you're getting more oil per revolution than you think. I had a client who ran these engines on straight gas for "just a season" and ended up replacing three crankshaft bearings and a connecting rod because the lower unit wasn't the only thing that failed. The big end bearings on these don't last long without lubrication. Always use the correct oil tank and check the pump diaphragm before you assume the problem is fuel.

What the Specs Don't Tell You

The 115 from this era was designed as a work engine, not a speed demon. It makes power at a moderate RPM range and it's built with heavy internals to handle sustained load. That's why the weight is high. A 1982 Mercury 115 is noticeably heavier than a 2000s-era 115, and that weight is structural. The crankshaft is solid, the block is thick cast iron in places where a modern engine would use aluminum. This means it will run for 10,000 hours if you maintain it, but it also means lifting it by yourself is not happening. The cooling system is open-loop with a raw water impeller in the lower unit. Impeller replacement is straightforward but you have to remove the lower housing to get to it. I've seen people try to flush these through the water pump inlet without removing the impeller housing and end up with a cracked housing because they forced the flush adapter in wrong. Use the proper flush kit and don't exceed 30 PSI. The passages in the block are small enough that pressure can crack the casting if you push too hard. Ignition is a points-based system with a magnetic pickup trigger. The timing is adjustable but not infinitely variable. You set it with a timing light and a wrench, and once it's set, it holds. The capacitor is a common failure point—I've replaced maybe a dozen of these over the years and the capacitors always look fine until they don't. If your engine misfires at idle and the problem comes and goes with vibration, check the cap first. It's a cheap part and it's under the flywheel, which means you're removing the prop and possibly the flywheel cover to get to it.

The Honest Assessment

This engine is reliable but it's not efficient by modern standards. Fuel consumption at wide open throttle runs somewhere in the 12 to 15 gallons per hour range depending on boat weight and prop selection. At cruising RPM it drops to maybe 8 to 10 GPH. That's not terrible for a work engine of this era but it's nowhere near what a modern 4-stroke EFI does. If range and fuel cost matter to you, this is something to factor in. Parts availability is actually decent. Mercury still supports many of these through the aftermarket and a number of independent shops keep inventory. But OEM parts for the 1982 model year specifically can be harder to find than later Big Farm versions. If you're rebuilding, check whether your engine number falls into the earlier production run or the later one. The later runs have some updated gasket sets and revised carburetor jets that make maintenance easier. The 1982 Mercury 115 HP outboard is a solid, workmanlike engine if you need something that will run and run and run. It's not pretty, it's not efficient, and it will remind you every time you lift it that weight matters. But for a boat that needs a dependable powerplant and you're willing to maintain it properly, it still does the job.