Slight diff whine

mcw739

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I recently fitted a 2nd hand diff, my own being rather clunky and the new one was nice and tight. I re-filled it with Millers 75W90 NT synthetic rather than a straight 90w. I'm getting a slight diff whine when warm around the 40-50mph mark and am wondering if I should have stuck with the heavier oil?
 

Mike_Hammond

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The later XKs use a 75w140 synthetic and the internals are just the same to be honest, unless it's electronic/LS then there isn't much in there to worry about other than big old bearings and gears. If it's whining then it's worn but unless it's major and there's no play/leaks on the shafts then it's not an immediate worry. A straight 90 will appear thicker at colder temps compared to the 75w90 which will be thinner when cold. But the viscosity should be exactly the same as the 90 at working temps. If you compared a hot 90 with cold 75 they would be a similar thickness for want of another term. The synth should also be more stable at higher temps. A 140 will maintain it's viscocity at much higher operating temps than a 90 too.

Obviously EP90 is cheap so you have nothing to lose but ultimately your diff will just need some proper TLC. If you still have the old one you could get it refurbed at a local transmission shop for relatively little I'm sure.
 
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