Operation of the outboard motor Tohatsu The 18 horsepower capacity requires regular maintenance, and one of the most important steps here is replacing the transmission fluid in lower unit. It is the quality and quantity of the lubricant that determines the durability of gears and bearings, which experience tremendous loads while driving. Owners often wonder how many liters or milliliters of fluid are needed for a full replacement to avoid underwatering or overflow.
Late maintenance can lead to emulsifying lubricants, coffee slurry and, as a result, rapid wear and tear of expensive knots. The correct amount of oil in the Tohatsu 18 gearbox provides efficient cooling of rubbing parts and protection against corrosion, which is especially important when using the motor in salt water. In this article, we will discuss the exact specifications, necessary tools and step-by-step algorithm of actions.
For two-stroke models of the series M18B2 and four-stroke versions MFS18 The procedure may have its nuances, but the basic principle remains the same, and it's important to understand that using the wrong type of lubricant or breaking the refueling technology can cause the whole of the lower unit to fail. Let's take a closer look at all aspects of this process.
Technical specifications and required volume
Determining the exact amount of lubricant is the first step to successful maintenance. Tohatsu The 18 hp oil volume in the lower gearbox is standardized by the manufacturer, regardless of engine tactility, and according to official documentation, the lower unit crankcase must be filled strictly with the same oil volume. 320 milliliters transmission oil.
This volume is relevant for standard length of a lower unit (S, L, XL). If your motor has an elongated leg, the volume may vary slightly, but in 95% of cases the standard specification is used. Using a measuring glass or syringe larger than 500 ml will allow you to accurately measure the required amount of liquid.
⚠️ Warning: Never rely on the volume of the can you buy, as standard packaging is often 0.5 or 1 liter. Pouring "by eye" without level control through the control hole is not acceptable.
It is important to note that 320 ml It's a working volume that allows the gears to be completely submerged and oil fog to lubricate the upper bearings, and a lack of fluid will cause overheating, and excess can create excess pressure that will squeeze out the osteoils.
Buy oil with a margin: a standard liter jar will last for 3 full replacements, which is more economical than buying small tubes of 0.5 liters.
Choosing the Right Transmission Oil
The quality of the lubricant directly affects the life of the units. Tohatsu The main standard is the API classification GL-4 or GL-5, but the manufacturer often specifies specific viscosity requirements.
The best choice will be oil viscosity SAE 80W-90 or SAE 90These viscosity classes provide a stable oil film at high loads and temperatures. The use of wet clutch friction modifier automotive oils is not required here, because the gearbox does not have friction discs, but oxidation resistance is important.
- 🛢️ Tohatsu Genuine Gear Oil - original liquid, fully complying with the specifications of the manufacturer.
- ⚙️ Yamalube Gear Oil A high-quality analogue, often used by owners of equipment Yamaha and Tohatsu / Nissan.
- 🌊 Liqui Moly Marine Gear Oil German product with excellent anti-corrosion properties for salt water.
- 🔧 Motul Transgear Expert Synthetic oil, which provides stability of specifications over a wide range of temperatures.
When choosing oil, pay attention to the label "Marine" or "For outboard motors"; these formulations contain additive packages that prevent emulsification when water enters and protect non-ferrous metals (bronze gears) from corrosion.
Tools and training required
Before you start the procedure, you need to prepare the workspace and tools. The oil change in the Tohatsu 18 gearbox is a neat operation, but it doesn't require complex equipment. You need a flat horizontal surface to keep the motor strictly upright.
The key tool is a screwdriver or a special key for drain plug screws, and don't forget to use the waste liquid container, because it's strictly forbidden to drain into the ground.
☑️ Oil replacement tools
Pay special attention to the condition of the drain screws, they often have magnets that collect metal shavings, before installation, the magnets must be cleared of plaque, if the magnets are found to have brass dust (the color of the gears), this may indicate wear of a pair of gears, which requires diagnosis.
Step-by-step instructions for oil replacement
The replacement process starts with heating the engine if it's just running, or, conversely, with a complete cooling if you plan on a full diagnostic. The optimal replacement is with a warm but not hot engine when the oil is good. Put the engine upright, checking the position of the lower unit.
First, spin the bottom drain screw by substituting the container. Give the waste liquid a full drain. Then unscrew the top control screw. This will provide better fluid current and air access. Rinse the gearbox with a small amount of fresh oil if the old one has been heavily contaminated, although this is not always necessary for standard TO.
Then you fill it up. Put the nose of the syringe or supercharger in the bottom drain hole. Start slowly pumping the new oil. The key is that you pour the oil from the bottom up, pushing the air out through the top hole.
Sequence of action:1. Untwisted bottom screw -> Pour the oil.
2. Unscrew the top screw -> Blow/Wash.
3. insert the nose of the syringe into the bottom hole.
4. Pump until oil appears in the top hole.
5. Twirl the top screw without removing the syringe.
6. Add a little more and quickly twist the bottom screw.
When the oil starts to flow out of the top control hole, it's a signal that the gearbox is full. Without removing the supercharger, quickly twist the top screw to fix the level. Then, while continuing to hold the pressure in the syringe (so that the oil doesn't go back), quickly remove the spout and twist the bottom screw.
⚠️ Warning: Always use new sealing washers under the screws. Reusing old aluminum or copper washers often leads to leaks after a few hours of operation.
What to do if the oil is over the edge?
If the top screw continues to leak out when you twist, you may have a traffic jam or a broken screw geometry, and try to sway the lower unit lightly or tap it with a rubber boulder to get the air bubbles out.
Diagnosis of the state of the reducer by oil
Fluid can tell you more about the health of your motor than external inspection. The color and consistency of the oil are important diagnostic signs. Normal oil is a clear oil of amber or light brown color without foreign inclusions.
If you find that the oil has acquired a milky, coffee or emulsion hue, it indicates that water has entered the gearbox, water could penetrate through worn-out paddle shaft coils or through loosely twisted screws, and running a motor with water in the gearbox will corrosion the bearings and gears in a matter of hours.
| State of the oil | Colour | Probable cause | Action |
|---|---|---|---|
| Norma. | Transparent, amber | Staffing | Planned replacement |
| Emulsion. | Muddy, coffee, white. | Water intrusion | Replacement of osteologic fluids, defects |
| Metal shavings | Silver gloss on the magnet | Natural wear and tear | Washing, oil change |
| Brass dust | Golden raid. | Wearing gears | Urgent diagnostics of the reducer |
The presence of large metal shavings on screw magnets also requires attention. Small silver is acceptable, but large fragments indicate the destruction of bearings or gear teeth, in which case simple oil change will not help - you will need to open and repair the lower unit.
Regular visual inspection of the oil allows you to identify problems with the tightness of the osteoils at an early stage, before expensive repair of gears.
Replacement intervals and seasonal storage
Maintenance regulations Tohatsu It requires that the gearbox oil be changed after the first 10 hours of running (for new engines) and then every 100 hours or once a season. If the motor is operated in intensive mode or in an aggressive environment (sand, silt, salt water), it is better to reduce the interval to 50 hours of motoring.
When putting the boat for winter storage, changing the oil in the Tohatsu 18 gearbox is a mandatory procedure. You can not leave old oil for the winter, since the moisture contained in it (even in microscopic amounts) can cause corrosion of the inner surfaces during downtime.
Pouring fresh oil before winter creates a protective film and displaces moist air from the crankcase, which ensures that in the spring, when you first start, all the knots are reliably lubricated, and remember to also lubricate the splints of the paddle shaft with a special consistency lubricant every time you change the oil in the gearbox.
- 📅 First replacement: After 10 hours of work (break-in).
- 🔄 Routine replacement: Every 100 hours or 1 time per year.
- ❄️ Conservation: It is needed before winter storage.
- 🌊 Extreme: After each exit into very dirty water or when hit by an obstacle.
Keeping these intervals will extend your engine life for years, and remember that the cost of a liter of oil is not comparable to the cost of repairing or buying a new lower unit.
Can I mix different oils from different manufacturers?
Technically, GL-4 and GL-5 oils are compatible, but chemical additive packages may differ from brand to brand. Avoid mixing. If you add, try to use the same brand as before, or completely flush the gearbox.
Frequently Asked Questions (FAQ)
Can you use regular 10W-40 engine oil in a Tohatsu gearbox?
It is not recommended to use motor oil. Transmission oils have a different structure of additives designed for high pressures in gears (EP additives).
What to do if more than 320 ml leaks during drainage?
If much more leaks (e.g., 400-500 ml), this may indicate that the gearbox has previously been filled with excess oil or water has been leaked into the crankcase, and if less leaks, it means that the level was below normal, which is dangerous for bearings. In any case, pour the control hole before the jet appears.
How often should the sleeves be changed on the sleeves?
The sealing washers are disposable elements. They need to be changed. every time The aluminum they're made of is deformed when they're tightened and loses its sealing properties when they're reused.
Why is the oil in the gearbox blackened?
Light darkening of the oil during operation is normal, it is saturated with wear and oxidized, but if the oil has become black and thick, like oil, it may indicate overheating of the gearbox or a long interval of replacement. The presence of metallic luster in the black oil is a bad sign.