Yesterday I changed the engine, gearbox and differential oils on my
new mx5, so I thought I'd write a quick post saying how I did it just in case
it's useful for another first timer. My car is a 51 reg mk2.5 1.8 s-vt, with 6 speed gearbox and limited slip differential.
The oils I went for were:
Engine: Valvoline Engine Oil (Durablend FE Semi-Synthetic 5W30 Engine
Oil (5 Litre))
Gearbox: Castrol
Driveline Syntrax Universal 1L x2 for the gearbox
Differential: Valvoline High Performance Gear Oil GL-5 80W90 1Ltr for
the differential
Got all the required crush washers (sump drain plug, gearbox drain and
fill plugs and diff drain and fill plugs) from the local Mazda garage. The
parts needed to be ordered in though so took a couple of days to arrive.
Started with the engine oil, took the car for a quick spin to get it
warm and drove the front end of the car up onto ramps so I could get underneath.
Put the oil drain can and tray underneath the engine and removed the drain
plug, making sure that the location of the drain can allowed for the arc the
oil will form when the plug first comes out. Left the oil draining and prepared
the new filter by putting a thin film of oil on the seal around the edge and on
the threads in the centre. Once the oil had pretty much drained, looked at
removing the oil filter and found the only way I could actually get my arm in
to remove it, would be to remove the strut brace (4x 13mm bolts). With the
strut brace removed, took the filter off (for me this was easy as it unscrewed
with only a little effort). I tried to unscrew it quickly as because it is
located horizontally, it starts to leak oil down the side of the engine, and
when it is fully unscrewed, turn it upright so as to restrict the amount of oil
spilled. Then I wiped around the hole, where the filter would seal and
carefully put the new filter on as to not get crap in it as it's quite tight to
manoeuvre the filter down. Tighten the filter by hand and then check that the
oil has stopped draining underneath. I had to lever the old washer off of the
drain plug, then cleaned up the surfaces on the drain plug and sump, replaced
the washer and torqued the bolt to 26lb/ft. Refilled with oil, putting in about
3 litres first, then checked the level whilst adding a little more each time.
Ran the engine for a minute or so to get the oil flowing through the new filter
and then rechecked the level and added a little more. Engine oil done. Just
needed to clean up the oil spill from the filter and check for any leaks.
EDIT: If you have a 6 speed gearbox, take a look at this link before proceeding: http://www.miata.net/garage/tsb/s05_112_02.html (thanks to Alan for the reminder about this.)
Then, on to the gearbox oil change. First, we jacked the car up
underneath the diff and put two axel stands under to make the car level. To
access the gearbox, I removed both the underside protection panels, the one
towards the rear of the car is held on by 4 23mm nuts and two 23mm bolts. These
were the hardest to remove as they are open to all the elements, but with some
SAS spray and a longish bar they came off ok. The panel further forward is held
on by 4 10mm bolts which came undone no problem. With these two panels off,
there were no problems with access to the gearbox. Cracked the fill plug off
first, and then the drain plug. Got the drain can in place and removed the fill
plug and then the drain plug. Surprisingly, the oil came out quicker than the
engine oil, and because of the wider flow, made a splash on the top of the
drain can. Left this draining whilst we went for lunch. After lunch, the flow
had stopped, so cleaned up the two plug holes and bolts and changed the washers
over to new ones. Put the drain plug back in and torqued up to 30 lb/ft. To get
the oil back in, we used a tube with a funnel on the end fed through the engine
bay and into the gearbox. The oil flowed incredibly slowly, so this method took
ages (I wasn’t timing, but it felt like it was at least half an hour), but it
did work. When the correct level had been reached, the oil overflowed from the
fill plug, then put back in the fill plug after cleaning the surfaces and
torqued up to 30 lb/ft. Gearbox oil done. Put the underside panels back on (the
larger panel has holes on one end, and forks on the other, so if you put the
bolts into the chassis first, then slide the panel in and put the bolts in the
other hand, this means you can easily do it yourself, this will also help
during disassembly).
To change the diff oil, we took the car down off of the axle stands and
ramps. My drive has a flat section, which leads into a sloped section, so I put
the back end of the car over the point where it changes, to give a little more
access, but the car could be jacked up to help. No panels to remove for access
here, so just cracked off the fill and drain plugs. This would have been easier
with bi hex sockets, as there was not much space to swing the bar, but it was
just about possible by using my shoulder to lift the body of the car whilst
lying on the floor. One of the plugs is 23mm and the other is 24mm. Again, got
the oil pan under the car and took out the drain plug, taking into account the
arc, and drained the oil out. Once the flow had stopped, cleaned up the contact
surfaces for the drain and fill plugs, changed over the washers and torqued the
drain up to 35 lb/ft. The oil bottle had a tube that you pull out, then put
into the hole and squeeze, which is excellent for getting half of it out, but
the idea only really works if you can get the bottle upside down, which you can’t.
So I filled the remainder using a 20ml syringe… This took a while, but again,
it worked. Once full, as with the gearbox, the oil overflowed the fill hole and
I put back in the fill plug and torqued to 35 lb/ft.
There may be steps here that I’ve missed, but this covers the most
important stuff. Hopefully useful to someone.