Mercury 2-Stroke Oil Change – 100-hour Service
Mercury 2-stroke oil change and inspection is the first step to 100-hour service. On a Mercury outboard with oil injection, start at the tank inside the boat. For premix models, this step will not necessarily apply. Using a flashlight, inspect the tank for any signs of contamination or water intrusion. Verify that hose clamps are tight, feed hoses are not cracked or checked, and that there is no water accumulation in the bottom corners of your tank. This oil is the lifeblood of your very expensive outboard, so inspect carefully.
Shop Recommended Products
Engine oil selection is critical to long life, so review the information in your owner’s manual to make certain you are using the 
correct products. Not all TCW3 oils are formulated the same, and different Mercury models do prefer specific oils. Mercury Marine offers a wide assortment of engine oil – both in blend and additives. If you are uncertain exactly which oil is best for your application, consult your owner’s manual.
If you do locate contamination in the oil tank, use a vacuum extractor to pull the remaining oil out of the tank for proper disposal. While good quality two-stroke oil is certainly expensive, running contaminated oil can lead to catastrophic failure. If you have never cleaned the bottom of your tank, prepare to be surprised by what you find.
Several laboratories provide performance testing of used oils, allowing you to learn more about the health of your engine. Blackstone Labs is one such provider, and they have a convenient mail-in kit that includes everything you need to submit an oil sample. They can also test gear oils, hydraulic fluids, and oils from your other vehicles or toys. Oil test results can tip you off to an accelerated wear condition inside of your engine long before any other symptoms show up. If you still want to know more about your engine, purchase an oil filter cutter and open the spent filter to look for evidence of contamination and metal dust or shavings.
Interested in the steps beyond Mercury 2-stroke oil change? Download the Full Maintenance Guide – How to Perform 100-Service on a Mercury 2-Stroke Outboard and then get your complete Mercury outboard maintenance kit today!
ahh 2 strokes don’t have a oil reservoir. whomever wrote this article is a idiot.
My 2 stroke has an oil reservoir. It mixes the gas and oil while the boat is running.
2-stroke outboards generally have an external oil tank with the oil and fuel mixture injected into the cylinder. The oil is consumed and the oil tank level must be maintained, replacing oil as it is used up.
I have 2-2 gallon reservoirs for the 2 stroke oil that gets automatically mixed with the fuel