My car has 25k miles when purchased and previous owner said he never changed the diff fluid. First thing I did was diff fluid changed, the fluid still looked really clean. After putting only about 1000 miles, I decided to change the fluid again since I was bored and had a bottle of amsoil laying around that I didn't know. This time the fluid came out really dirty, like a grayish color. There were no particles in the fluid and the drain bolt only had a little tiny bit of gunk, close to nothing.

How can the fluid come out looking clean after 25k miles but is extremely dirty after only 1000 miles with the new fluid? I used Mobil1 75w-90 the first time. Is this something I should worry about?? There are no whines yet. Any suggestions or input would be appreciated. Thanks

 

Grey indicates a serious problem. Are you sure that bottle laying around was not contaminated? Was it a sealed container?

 

Send it in for analysis.

 

yea, grey usually means a ton of metal in the fluid...not good

 

The new fluid cleaned out some sludge that was adhered to the case of the diff. I had a similar experience when I bought my S2000, the old fluid came out clean, then my first Amsoil fill came out dirty on a short run, and then my second fill came out clean. I'd question the fact that the previous owner even did a fluid change.

Doing a short run like that was a good idea as it does help to flush out any gunk that may be present in the diff. The cleaning additives of the new fluid go to work pretty quickly, and group 4 synthetic fluids like Mobil1 and Amsoil are powerful cleaners. I would expect your next run to come out cleaner, but there may still be some cleaning going on depending on how bad the first fluid was, and there could still be some remnants of break-in wear material in there.

 

he already said the owner never changed the fluid

 

Damn I don't remember at all. I assume it should be sealed but don't remember. Should I change the fluid again 1000 miles later?

 

My bet is the cleaning action of amsoil

 

I used Mobil1 the first changed.

 

A high amount of grey material is likely from break-in since it wasn't changed until you opened it up, no amount of external contamination is going to create a noticeable change in the used fluid. I would do another short run if it was my car, it is cheap maintenance even if you are wasting good fluid. Maybe consider a 3000 mile interval and then go back to the Honda recommended interval.