NC1 2.0 Sport Universal 75W90 or Syntrax universal plus 75w90

Technical Area Routine Servicing
2

Hi

Basically which oil for the rear diff, bought the Universal 75W90 semi synthetic, but noticed on MXparts website they sell Mobil 1 fully synthetic.

 

We sell Castrol at work so not sure which to go for now, the Universal Plus is fully the Universal is Semi.

3

There is no issue with the diff oil brands or synthetic vs no synthetic oil.

If you look at used oil analysis of diff oil, the main two issues are the diff oil being worn out by the surface pressure on the hypoid gear even with the EP additive and the high wear metals after even 30,000 miles.

Much higher wear metal rates compared to a gearbox.

There are no trends showing up of any real improvement in diff oil condition by using synthetic oils for cars on normal duties. Unless someone else can provide evidence to prove there is based on quantitative data.

I would change diff oil every 30,000 miles to get the wear metals flushed out or even earlier for the first change.

I repeat, I can find no data to spend extra money if there is an extra cost to purchase a synthetic diff oil, just get it changed on a regular basis.

In saying that most local garages will not change a cars diff oil at a service to keep costs down and many diffs outlast the bodywork of the car.

4

did mine a couple of months ago , heres what i used ,

 

 

 

changed gear box oil today @ 48370miles 

( GL4 )

 

 

while under there i did the diff oil  (GL5 ) as well , i had the oil in my garage from the last mk3

 

5

Thanks

 

Once again over thinking things by reading forums too much

6

I’ve always used this in my Mk1/Mk2/Mk3 diffs.  https://www.opieoils.co.uk/p-744-castrol-universal-75w-90-semi-synthetic-car-gearbox-oil.aspx

 

As long as it’s 75w 90 it’s a API GL4/GL5 oil your good to go.

7

Personally I would use a GL-5 EP oil in the diff with LS designation for the limited slip clutch pack. A general purpose GL-4/GL-5  gearbox oil may not have the additives to cope with the kind of load transfer on the diff.

8

I have just changed the gearbox and diff oils on both our MK1 and Eunos.

The important thing is to change the oil. I cannot stress that enough having inspected the magnetic drain plugs and seeing the metallic particles in suspension.

I went with the recommended castrol GL-4 for gearbox and GL-5 for diff(MK1 - MK2.5) - it seems similar advice for the MK3.

For me it was an experience worth sharing, so hoping to post a thread about these oil changes when it is proven we did right after a few more weeks and some miles.           

9

Exactly what have Mazda got wrong when they do not recommend a diff oil with limited slip additives when

  1. The early cars had the limited skip gubbins in a sealed container that did not allow the limited slip components of the diff contact with the oil. What help do the LS additives give here.

  2. The later cars with the Torsen diffs have no requirement for LS additives as they quieten clutch type limited slip diffs which the Torsen units do not have clutches.

  3. The additives used in the clutch type diff oils increase the oxidation levels of the diff oil which does not help unless you need them to quieten down the clutches. Therefore, shorter time between diff oil changes.

  4. The TAN ( total acid number ) of the diff oil increases against standard diff oil, again shortening the life of the diff oil.

 

10

I defer to your greater knowledge Eddie.