Regular maintenance of the bottom of the outboard motor is critical to the durability of the entire power plant. Tohatsu 18 The importance of a timely transmission oil replacement is often underestimated, relying on the reliability of the Japanese assembly, but water, sand and an aggressive environment do their job, requiring the owner to pay attention to the condition. gearbox.
The process of replacing the fluid in the lower gear crankcase does not require complex equipment or specialized skills, but it must be performed strictly according to the regulations. Ignoring this step can lead to expensive repairs of gears and bearings, the cost of which is much higher than the cost of preventive maintenance. In this article, we will discuss in detail the process of oil replacement, the choice of materials and the typical errors that are allowed in the maintenance of 18 horsepower engines.
⚠️ Warning: Before starting any work, be sure to shut down the engine and let it cool completely. Working with a hot engine can lead to burns, and accidental start-up can lead to serious injuries.
Frequency of replacement and selection of transmission oil
Manufacturer Tohatsu For new engines, the first replacement must be made after running, which is usually 10 hours or one navigation season, then the procedure is repeated every 100 hours of operation or once a year, whichever comes first. If you use the boat in heavy conditions, such as in salt water or in frequent overloads, the interval should be reduced.
Choosing the right lubricant is the key to keeping the gears quiet and not corrosive inside the gearbox. Tohatsu 18 It is recommended to use special transmission oils for outboard motors, which have water-repellent properties, usually these are liquids of the viscosity class SAE 90 or SAE 140, which do not contain additives that cause corrosion of non-ferrous metals (preferably compliance with the specification API GL-4 or GL-5, but without aggressive sulfur compounds).
- 🛢️ The original Tohatsu Gear Oil is the best choice, guaranteeing compatibility with all seals.
- ⚙️ Synthetic analogues – provide better fluidity at low temperatures and stability at high loads.
- 🚫 Oils for cars – it is strongly recommended not to use car transmissions, as they can destroy the glands.
When buying oil, pay attention to color: gearbox liquid is often greenish or blue, making it easy to distinguish leakage from water or fuel.
It is important to understand that the volume of the crankcase of the 18 hp model is approximately 300-350 milliliters (the exact value is always indicated in the manual of a particular modification). Do not pour oil "on the eye", since overflow can lead to extrusion of the glands due to excessive pressure during heating, and the subdiluted one - to oil starvation of the upper bearings.
Tools and preparation for work required
To make a good replacement, you'll need the minimum set of tools that any experienced water-engineer has in the trunk, and the main tool will be a syringe for pumping oil, because you can't fill the gearbox from the bottom up by accident, because of the design of the case, and you'll need wrenches of the appropriate size to unscrew the plugs.
Prepare a waste liquid tank in advance to avoid polluting the environment. Transmission oil is an oil product and its discharge into water or onto the ground is strictly prohibited by environmental regulations. Also, have clean rags on hand to wipe plugs and threaded joints from dirt and sand.
☑️ Preparation for oil replacement
Special attention should be paid to the condition of the sealing washers on the drain plugs. Complete with a new engine or oil, often come copper or aluminum washers. These must be changed every time you perform maintenance, because a single use deforms the metal, and the tightness of the connection will be violated. If there are no original washers, you can make temporary soft metal, but it is better to purchase the original remix. Tohatsu Propeller Kit Or analog.
Step by step: draining old oil
The replacement process starts with the engine being upright. If the boat is standing on the trailer, make sure it's aligned so that the oil glass is fully and evenly distributed when filled. Find two lower unit stoppers: the bottom (drain) and the top (control/fill). Tohatsu 18 They are usually located on the front or side of the gearbox leg.
First, gently unscrew the top plug. This action is necessary to create a message to the atmosphere, otherwise the oil will flow out in jerks or not completely drain from the vacuum. Then insert the container and unscrew the bottom plug. Let the waste liquid drain completely; this process can take from 5 to 10 minutes.
What to do if the oil doesn't flow?
If the bottom cork is not unscrewed, the gearbox may no longer have oil or it may have become an emulsion. In rare cases, the hole may be filled with wear products or dirt.
Look carefully at the color of the draining liquid. Normal oil should be transparent, amber, greenish or blue (depending on the brand). If you see a milk emulsion, this indicates that water enters the gearbox, in which case simple oil change will not help, you need to diagnose the glands and possibly replace the cuff seals of the shaft.
⚠️ Warning: If metal shavings or large particles are visible in the leaked oil, this is a signal of serious wear of gears or bearings.
Washing and filling of the gearbox
After the old liquid is completely drained, it is recommended to carry out a preventive washing of the insides of the crankcase, which can be done using a small amount of fresh transmission oil or a special washing compound. Pour about 50-100 ml of liquid through the bottom hole, sway the engine and drain the wash. This will help remove the residue of the old lubricant and fine metal dust.
Now, the main step is filling, insert the nose of the syringe with new oil into the bottom drain hole, start slowly pumping the liquid. The key is that the oil should fill the gearbox from the bottom up, pushing air through the top hole, and as soon as the oil leaks out of the top hole, stop pumping.
| Parameter | Meaning / Description | Note |
|---|---|---|
| Volume of crankcase | ~320 ml | Depends on the specific modification of 18 hp. |
| Type of oil | SAE 90/GL-4 or GL-5 | Special for outboard motors |
| Replacement interval | 100 motor hours / 1 year | First replacement after running (10 m/h) |
| Moment of tightening of traffic jams | 15-20 Nm | Do not pull so as not to break the thread |
It's important to keep the air plugs out, so the injection rate should be moderate. If you pump too fast, the oil can just envelop the walls without filling the volume, which will lead to a false feeling of a full gearbox. Make sure the oil level is stable in the top hole before you extract the syringe.
Installation of traffic jams and leakproofness control
When the gearbox is full, you need to quickly and carefully install the top plug with the new sealing washer. In a sharp motion, remove the spout of the syringe from the bottom hole and immediately twist the bottom plug. The main task at this stage is to keep the oil from leaking out and not to start the air in. You need to act confidently and quickly.
Twirl the plugs at moderate force. The aluminum alloys that make up the gearbox body. Tohatsu 18Excessive force can cause the thread or the cork itself to deform, which in the future will cause difficulties in the next maintenance. Use a dynamometer key if possible, or rely on a sense of proportion.
The correct sequence of cork swirling is first the top, then the bottom, and this prevents oil from leaking out and vacuuming.
Once the plugs are installed, wipe the surface of the gearbox with rags, removing the oil residues. Start the engine and let it work at idle speeds for a few minutes. Visually inspect the area around the plugs for leaks. The absence of oil droplets confirms the work done and the tightness of the joints.
Diagnosis of malfunctions due to the state of oil
The leaked oil is a great diagnostic material for the health of your motor, and if the fluid is normal in color and smell, the gearbox is operating normally, but changes in the appearance of the lubricant can indicate hidden problems that require intervention.
The presence of silver metallic dust on the magnetic tip of the bottom plug is permissible in small quantities — this is the result of natural burning of the gears. But if the magnet is hanging large pieces of metal or shavings, it indicates the destruction of the bearings or teeth of the gears, in which case the defective and repair of the knot is necessary.
- 💧 Water in oil - indicates damage to the osteoil of the paddle shaft or sealing of the gear shift rod.
- 🌫️ Emulsion (mayonnaise) - the result of mixing oil and water, often occurs when a hot gearbox is sharply cooled (entering cold water).
- 🔥 Blackening of oil - indicates overheating of the node or critical wear of rubbing pairs.
If you find water in the gearbox, don't just change the oil. The water is heavier than oil and accumulates at the bottom of the ossuary. Even after replacing some of the water, it can stay inside, causing corrosion. It's recommended that you flush the knot several times with transmission oil, let the motor work on idles so that centrifugal force displaces the moisture, or contact a service to replace the os.
⚠️ Warning: Never use the motor with water trapped in the gearbox for a long time. Bearings and gears corrosion develops rapidly and can completely disable the unit in one season.
Frequently Asked Questions (FAQ)
Can I use motor oil instead of transmission oil?
Motor oils have a different additive package and viscosity, and they don't have the necessary anti-sharp properties for the gearbox hypoids, and they can cause accelerated wear of gears and damage the glands.
Why did the oil in the gearbox turn white (emulsion)?
White indicates water, most often the fault is worn-out oal of the paddle shaft, and water can penetrate through microcracks in the case or due to temperature changes under sharp cooling, require replacement of oals and washing of the knot.
How much oil does Tohatsu 18 need?
The exact volume depends on the year of release and modification, but on average it is about 300-350 ml. It is better to buy a liter canister, as part will go to wash or top over the season.
Do I need to wash the gearbox with gasoline or kerosene?
Use aggressive solvents to wash the gearbox is not worth it, as they can damage the internal seals and osteoils. For washing, it is better to use cheap transmission oil or a special washing liquid for gearboxes.
How often should I change the sleeves on the sleeves?
Sealing washers (copper or aluminum) are disposable elements and must be replaced with each oil change procedure to ensure tightness and prevent costly lubrication from leaking out.