How do I winterise a Mercury two-stroke outboard?
I'm putting my boat's Mercury two-stroke outboard away until spring, and it will be stored outside where we get frost. What should I do about the petrol, cooling water and gearbox oil, and does it need fogging?
Answer
Winterise your Mercury two-stroke by treating the fuel, flushing and draining the cooling passages, protecting the engine internally and changing the gearcase oil. First establish whether it is carburetted, conventional EFI or OptiMax, as the fuel and fogging procedures differ.
Identify your Mercury model
Find the serial-number plate, normally on the transom bracket, and use it to identify the correct Mercury owner's manual. Horsepower and cowling graphics alone are unreliable guides, especially if parts have been replaced.
Carburetted two-strokes, conventional EFI models and OptiMax direct-injection engines need different storage treatments. Follow the storage procedure for your serial number, particularly the instructions for internal lubrication.
- Buy marine petrol stabiliser, the specified gear lubricant, new drain-plug seals and marine grease.
- Have Mercury or Quicksilver Storage Seal fogging oil ready if your manual specifies it.
- Check the two-stroke oil supply. Premix engines still need their normal specified petrol-to-oil ratio.
These two-strokes have no sump oil or oil filter to change, but the separate gearcase oil needs attention.
Treat fuel and flush
Add stabiliser to fresh petrol at the product's storage dose before the final run. It slows deterioration but cannot restore stale petrol or repair fuel that has separated after absorbing water.
Run the engine outdoors. Keep ignition sources away from petrol, and hands and clothing clear of the propeller.
- Supply cooling water using the arrangement specified for your engine: suitable flushing muffs, a sufficiently deep test tank or the approved flushing connection.
- Run at idle for the manual's specified flushing and fuel-treatment period so treated petrol reaches the engine.
- Check cooling-water flow. Stop immediately if the engine overheats or loses its water supply.
Some Mercury flushing connections are designed for use with the engine stopped. Connecting a hose does not necessarily make it safe to run. In a test tank, the water must cover the pump sufficiently, not just reach the intake grilles.
On carburetted models, drain the float bowls if the manual calls for it, catching the petrol safely. Do not routinely disconnect the fuel hose and run every Mercury dry. Multiple carburettors can empty unevenly, and injected engines have different requirements.
Protect internals and drain water
On many carburetted models, the storage procedure calls for fogging oil sprayed into the carburettor throats during the final idle, followed by cylinder protection through the spark-plug holes. Follow the manual's quantities and sequence. Too much oil can prevent the engine turning over.