I did a MGF manual gearbox fluid change recently. The car is 28 years old and I didn’t have exact history on whether this had been changed previously. So a bit of preemptive maintenance. The service schedule says to change this every 96,000 miles or 160,000 km. I’m thinking more often might be a good thing.
As with many things MGF I consulted trusted sources to learn about the process and what fluid/oil to use. One of these trusted sources is Dieter’s mgfcar.de website and specifically the gearbox refill page. This gave me the primary thing I wanted which was some pictures of the drain and fill points as well as practical guidance on the process. Additionally, being in the USA what would be the best option to use as replacement gearbox oil/fluid. For that I consulted with Mark Jones the NAMGBR Post-Abingdon registrar.
Gearbox Fluid/Oil Choice #
Skipping straight to the answer, if in the USA/Canada getting some genuine Honda Manual Transmission Fluid (MTF) is suggested as the best choice. The current part number is 08798-9031 which seems to replace 08798-9016. This is what Mark recommended and whilst on a UK visit he consulted with Dr. Ian Pogson. If you are not familiar, Dr Pogson worked for MG for many years during the MGF era, MGRV8 and also the resurrection of the MG TF. So, an extremely knowledgeable source.
It is slightly odd that the bottles of Honda MTF do not list any specifications.
Using the general specifications I found online the gearbox oil should be API specification GL4. There are also different “GL” specifications for gear oil from API which are shown on this Castrol website.
I also established the oil weight 75W80. On this basis I had obtained some Red Line 75W80 (50204). Fortunately I checked with Mark before using it. He had tried it and had problems with the gearbox within a very short period of time. So, based on his experience, don’t use this Red Line product. It may fit the requirements, but hands on experience says it is a problem.
The MGF workshop manual lists some specific versions of gearbox oil. All essentially MTF 94 from Texaco, Unipart or Caltex. Dieter’s website on gearbox refill page has some other brands/options to choose from. If you are located in Europe or the UK you will have a much easier time of getting the correct oil. It is widely available from various MG suppliers.
Quantity – How Much To Get #
Basically you want 3 quarts or approximately 3 litres. The refill quantity is noted as 2.2 litres or 2.4 litres for a dry gearbox. Having done it, trying to get by with 2 quarts won’t work. Just buy 3 bottles.
Draining The Gearbox #
Never drain something until you check that you can open the fill plug!
There is a good overview of the process in the workshop manual. I also looked at Dieter’s site, because he had photos of what to look for. It is quite a simple process with a fill plug and a drain plug.
When looking at the front of the car, from the rear, these plugs are on he left of center. Unless you have a pit or a lift, you will probably want to raise the car to gain access. This won’t matter for the draining process. I did lower the car, to flat, to complete the drain process.
The fill plug has a standard hex head and needs a 17mm socket or spanner (wrench). As mentioned in the beginning you want to check you can undo this before starting the draining process. As for the drain plug this is an indented, square plug that needs a 3/8ths bit. You can probably use a 3/8ths ratchet or, as I did, I used a 1/2 inch to 3/8ths adapter. This fit snugly and did not risk rounding out the indent.
Carefully remove the drain plug and have your oil pan ready because it does come out very fast at full flow! Once this is full drained you can move onto the refill process of your MGF manual gearbox fluid change.
Filling The Gearbox #
To get this right, the car needs to be flat, on a a flat surface. How you accomplish this will depend on where you are performing the work. It goes without saying, but I’m saying it, insert and tighten the drain plug first!
If you don’t have a fluid pump of some description, you will need some plastic tubing. This will need to fit into the fill hole and be long enough to reach the engine access area in the boot. Alternatively a long funnel with a smaller amount of tubing could work. Fortunately, I happen to have a pump. Much to my delight it fitted the bottles of Honda Genuine MTF. After adding an extension tube to the bottom of the pump, I could add about 800 ml of fluid before I started to pump air.
I had the car raised a little to provide access. There is a slight slope to my garage floor, which this somewhat offsets. My approach was to fill the gearbox fully and then let gravity handle the level afterwards.
After pumping in about 2.6 litres of fluid, I started to get the trickle of MTF from the fill hole. This was a relief. I only had the 3 bottles of fluid and was getting nervous I hadn’t remembered the capacities right.
With the gearbox full, I did multiple processes of lowering the car and removing the fill plug. On each occasion some fluid came out of the gearbox as we got closer each time to the correct level. Once you are familiar with the fill plug location you can reach in with your left hand to loosen/remove it without the car being raised. This would naturally be much easier with a lift or a pit to do this job.
Eventually you should get the right level of fluid as the workshop manual notes. Basically the fluid should be at the bottom edge of the fill hole. Then your MGF manual gearbox fluid change will be complete. Just make sure you don’t forget to put the fill hole plug back in place and torque to 35 Nm.
Other Materials #
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