XSeries-forum

Hi there,

I've just completed the front/rear differential fluid change and I was worried about under filling so I emptied, then pumped fluid in until it started to spill out of the fill hole and got the fill plug back in as quickly as possible.

Now, my dilemma is... should I have left the plug out until it stopped dripping? I was more concerned with under filling than over filling however i've read articles/threads online advocating both methods so any advice would be most welcomed.

Interestingly I removed the rear diff fill plug fully before undoing the drain plug and fluid flowed out... this suggested to me a flow out of the fill plug is correct, but I didn't do this with the front diff.


Would you remove the fill until it stops flowing then close it off, or leave it with the steady flow?

Thanks very much in advance.

If the cars level, fill until it runs out, if it's s trickle overfilled I'm sure you'll be fine.
The gearbox is a different story and requires a set procedure to drain and replenish to correct level.

The problem with overfilling is the volume removes the air gap for expansion of fluid as it heats under use, combined with removal of air gap for pressure increase due to splash fed bearings, overfilling tends to cause what looks like seal failure, though in reality it's simply too much fluid.

It will be fine. The fill plug is at a certain level to stop overfilling, i.e. Diffs, gearboxes etc.
All our equipment at work have a fill plug at a max level to prevent over filling leading to hydraulicing etc. It's Ni on impossible to overfill them, even slightly too much oil results in it pouring out a lot faster than you manage to fill it.

Thanks fella's.

Horizon... once again your wisdom has made me feel much more at ease. Although I count myself as a fairly intelligent individual the thought processes of the engineers that create the parts for the cars we take for granted every day absolutely blows my mind. The more I learn about cars, the more I want to learn.

Just popping back to say all is well with the diff fluid change, seems to be running perfectly with the new fluid for the last few days. (Castrol syntrax longlife 75w-90 used).