Honda's recommended service schedule for the differential fluid
is 15,000 miles for severe usage and 30,000 miles for normal usage. After this exercise, I would recommend that you change your diff fluid at about 7,500-12,500 miles depending on how you drive your car.
This is obviously at the rear of the car looking up at the differential. The
drain plug is on the bottom, while the fill hole is up higher. The drain plug
can be removed via a 23mm socket and socket wrench. The fill plug can be removed
via a 23mm closed box wrench. Torque settings are 33lb*ft for both when you
close everything up.
This thick, brown/black fluid drained out or should I say "glooped"
out of my car after only 12,500 miles! Being a heavy weight oil and ambient temperature being about 65F explains why the oil drained out in this slow fashion. You may want to try draining it when the differential fluid is slightly warm. In my case, I just let it drain out for a very long time. Honda recommends 15,000 miles for severe
usage while 30,000 miles for normal usage using their Honda MTF. Given my
experience after this, I will be replacing the fluid every 10,000 miles with a
better synthetic gear oil or every 7,500 miles with the Honda MTF.
The drain plug has a weak magnet embedded in it. This enables it to pick up some
sludge as shown. Try to clean the plug as much as possible to reveal the small
magnet. The magnet is not very strong, but I suppose it does it's job. One trick
I've learned is to find an old broken hard drive and to tear it apart. Inside,
you will find a very small, but very powerful magnet. Wrap this magnet in some
very thin fabric and simply attach it to the outside of the drain plug. It makes the magnetic plug more effective.
I used a simple hand pump to transfer the oil up into the fill hole.
Before the fluid change, my differential always had a 3-4 step jerkiness accelerating out of my street corner in the morning. This happened only in the cold mornings and on the first turn. After the fluid change, the differential felt slightly better with a 1-2 step softer jerkiness in the first turn in the morning. A side effect now is that there seems to be a louder whine coming from the differential. Post your comments about your experiences with other fluids below.
I threaded the tube through the top as shown to get a better angle into the fill
hole. The car should be level while filling so you can jack up your car onto 4
jack stands. A lazy man's method can be to jack up only the rear of the car and
then refill with 7/8 quart. You can see how much you are using by the clear line
in the bottle. Once done, simply lower the rear and then excess oil will spill
out. Be careful to catch this oil or else you'll have an unpleasant smell in your garage.
Redline Fluid Usage by Shawn Church
Given the apparent fragility of the S2000 rear differential, I decided to try a more aggressive approach to differential fluid. I turned to Redline's Shockproof line of fluids, which are designed to provide superior protection while maintaining or reducing friction levels in the differential.
I performed my first fluid change using Redline's Heavy Duty Shockproof fluid. Redline claims that the Heavy Duty formulation of this oil has the protective performance of a 75w250 oil, but the fluidity (read friction) of a more conventional 75w90. It also has special additives designed to handle shock loadings (such as a 7,000 rpm drop clutch launch?). The Heavy Duty is a thick red fluid, as opposed to the gray of the OEM fill. It is also very thick and required some hard work with the hand pump. Immediately after changing to the Heavy Duty (after about 10,000 miles on the stock fluid) I noticed several things. First, the LSD effect seemed more pronounced. Since gear type diffs are not supposed to need friction modifiers to perform effectively, I can only assume that the thicker nature of the fluid may have contributed to this (or the breakdown of the old stock fluid). I also noted that the differential was quieter and smoother. Finally, while no dyno testing was performed, no apparent loss of acceleration was detected.
After 6,500 miles with no ill effects on the Heavy Duty, I decided to try the Lightweight, which has the protection of 75w90 but with much lower friction properties (30w motor oil). The Lightweight is a bluish color and is noticeably thinner than the fresh Heavy Duty. After pumping in the Lightweight no noticeable difference was noticed in the performance or noise of the diff. However, after 6,500 miles, the differential is again making some noise when cold. This leads me to believe that the Lightweight, while suitable for short term use in racing applications, may not be appropriate for long interval use in a street/track car, particularly one that must go through many warm up/cool down cycles. Thus, it is my recommendation that if you want to use Shockproof gear oils from Redline, that you stick with the Heavy Duty for multipurpose uses. The Lightweight is acceptable, but may not provide sufficient protection over longer change intervals.