Once a year or just before placing into storage you should be changing your gearbox oil, a slightly messy but quite cheap and relatively easy job that will add years to the life of your gearbox. If you have internal corrosion or damage to the gears because you haven’t changed the oil frequently enough, you could be faced with a huge bill.
How often do you need to do it:-
100hrs or 1 year (unless owners manual says different)
Before you start you need to know
What oil are you going to use – Most recommend SAE-80W90 Check your owners manual
How much oil do you need – Not much, most use less than 0.2 Lt
You will need
A container for the used oil
A method of getting the oil in (Some oil comes in a squeeze tube)
An impact screwdriver – about £8.50 on ebay
A decent sized hammer to use with the impact driver
A filling tool about £13 on ebay which pretty much fits all gearboxes
This is a tube of oil which means you don’t need the filling tool above but it works out more expensive to use the tube for oil if you are going to change more than once or twice
We always use Rockoil MP Gear oil for our gearboxes, it’s British, cost effective and has never let us down. This oil meets API GL-5 & SAE 80W90
Draining the gearbox
With the outboard upright , use the impact driver to loosen the drain screws by selecting the largest size bit which will fit your screw slots, slightly rotate the grip in the direction you want it to turn (Anti-clockwise) and giving the exposed metal at the end of the grip a sharp tap with a large hammer. If they don’t budge, take you engine to a repair shop.
Make sure you have a clean drain pan under the outboard, first remove the top screw and then the bottom screw, the oil will flow out the bottom hole.
Inspecting the oil
When you are changing your gearbox oil, you’re not just replacing it, you also want to see the condition of the drained oil. Take a look at the oil which has drained out, you are looking for
- Water drops
If water drops come out take the engine to a repair center
- Emulsification which would show that water is in the gearbox this will appear as the oil looking “Milky”
If there is only a little emulsification then it may be best to flush the gearbox through with some gear oil before the final fill, just add about half the recommended quantity, refit the screws but don’t bother to tighten them right up, raise and lower the engine on the stand a few times to “slosh” the oil around, return the engine to the vertical position and drain out the oil you have used to flush it.
If the gear oil was very milky and the oil changed within the last year, you probably have water entering the gearbox and will need to either carry out a pressure test and repair or take the gearbox to a repair center. See the example below “Gearbox has milky oil”
- Signs of debris
Shine a torch on the oil and see very small flecks it’s no cause for alarm but anything bigger than small flecks you need to take the engine to a repair center.
If one of the screws is magnetic, this should be fitted in the lower position as this is made to collect any metal debris generated by the gears.
Filling the gearbox
Make sure you have the 2 drain plug screws with sealing washers fitted close to hand, make sure the Engine is vertical. Refill the gearbox using the squeezy tube or your gear lube pump.
The easiest way to use the gear oil pump is to screw on a common end fitting from a silicone tube as below which gives a push in tapered fitting that can be used again and again
Fill up through the lower hole until oil just begins to seep out of the upper screw hole, when oil appears in the upper hole fit the screw into the upper hole, withdraw the filler from the lower hole and fit the lower screw then tighten them both using a large flat bladed screwdriver, there is no need to go too crazy, the actual torque figure will be in you owners manual.
Changing the gearbox oil at the correct frequency is slightly messy but a really important job.
Gearbox has milky oil
As an example, look at the oil which is coming out this gearbox, you can clearly see the milky oil so it required further investigation
A pressure test was carried out and the gearbox was leaking from the input seal