Dirty Differential?

[asiancivicmaniac]

Car is a 2006 Miata with 10x,xxx miles on it. Car was purchased used with 70k miles. Never had a rear wheel drive car before so I didn't even know what the differential was. So I dumped the fluid in the diff at 107k miles and it was dark and the magnet on the drain plug had a lot of fine metallic particles so I assume it was factory fill. I put SuperTech Synblend 75w-90 back in it and drove a few hundred miles and drained-and-filled again. The oil that came out was again dark and metallic particles were present on the plug. I just thought it might be from whatever old fluid that didn't drain out. Then I did drain and fill #3 after a few hundred more miles and it was still dark, which surprised me since the new gear oil is almost clear. Ultimately I will put Valvoline Synpower 75w-90 in it.

Is it possible for a differential to form sludge from running on the same fluid for too long? Or is it normal for the fluid to turn dark that quickly? Should I keep doing drain and fills until I notice the fluid coming out looks cleaner or should I just put the final fill in and not worry about it?

 

[BRZED]

I believe flushing twice with fresh gear oil should be sufficient. The third fill should be good to go. I've never seen sludge come out of a differential, but presuming severe neglect I guess it's possible. Gear oil is foul stuff to begin with, especially if it contains sulfur.

 

[nyumski]

it also happened to me when i bought new toyota innova, it was about 900 kilometers in odometer and feel something's wrong, apparently, there's something in magnet drain plug, there is somekind of metal particles on it, so i changed it with mobilube hd 80w90 until now and will be tried to change in next 15000 kilometers. and checked if either there is or not.

 

[barkingspider]

Drain and fill w your valvoline syn 75w90 and that will be the last time til the car stops working or u sell it.

 

[4wheeldog]

What usually shows up in diff fluid that has run a long time is oxidation, of the parts with iron in them. If the thing is not noisy, don't worry about color too much. And.....As long as the stuff on the magnet could be described as "Paste" rather than "Shavings", you really do not have a problem.

 

[440Magnum]

Originally Posted By: 4wheeldog
What usually shows up in diff fluid that has run a long time is oxidation, of the parts with iron in them. If the thing is not noisy, don't worry about color too much. And.....As long as the stuff on the magnet could be described as "Paste" rather than "Shavings", you really do not have a problem.


+1 on this.

When I bought the 99 Cherokee that my daughter drives, I dumped and filled both differentials and the transfer case. The front diff fluid was grey with very, very fine metallic particles, and I thought "oh great, I'll be changing this thing out soon. But I looked through the previous owner's records and he had a receipt from an oil change where they noted "front differential fluid was grey"... from 80,000 miles prior! So I did about 4 refills in a span of about 2 years, and sure enough it's stayed clean ever since. Never even hiccuped.

Differentials are TOUGH pieces of equipment, and also its hard to get a complete drain on most of them that don't have a dedicated drain plug (which yours may, I don't know). At any rate, don't read too much into the fluid color if the unit is quiet.

 

[4wheeldog]

Originally Posted By: 440Magnum
Originally Posted By: 4wheeldog
What usually shows up in diff fluid that has run a long time is oxidation, of the parts with iron in them. If the thing is not noisy, don't worry about color too much. And.....As long as the stuff on the magnet could be described as "Paste" rather than "Shavings", you really do not have a problem.


+1 on this.

When I bought the 99 Cherokee that my daughter drives, I dumped and filled both differentials and the transfer case. The front diff fluid was grey with very, very fine metallic particles, and I thought "oh great, I'll be changing this thing out soon. But I looked through the previous owner's records and he had a receipt from an oil change where they noted "front differential fluid was grey"... from 80,000 miles prior! So I did about 4 refills in a span of about 2 years, and sure enough it's stayed clean ever since. Never even hiccuped.

Differentials are TOUGH pieces of equipment, and also its hard to get a complete drain on most of them that don't have a dedicated drain plug (which yours may, I don't know). At any rate, don't read too much into the fluid color if the unit is quiet.


In my (Limited) experience, front diffs on 4X4 vehicles actually are more subject to oxidation than the rear, because the fronts don't get up to temperature as a regular thing. So....Whatever moisture there is gets used up attacking the iron parts. And....The EP additives seldom get hot enough to do their best work.

All that said, the front diff is subject to so much less actual run time/wear that you might break one, but it is unlikely you will wear one out.

 

[meep]

gen 2 miatas are my favorite. fantastic vehicle. Is it a 5 speed? the transmission drains from a bolt on the bottom and fills from a bolt (4-sided plug) halfway up the left side of the casing, towards the front. Swap that lube too. do your research on fluid type--- to make sure you don't risk any problems to the syncro's.

beware of the hydraulic clutch circuit. flush those fluids---- which can basically be done by opening the bleeder on the slave cylinder (looks like a brake fluid bleed valve) and just letting it drizzle out, while replacing the fluid in the reservoir. easier than brakes because it flows on its own w/o pumping. that fluid is probably original, and needs to go.

good luck and have fun!

Honda civic batteries can be shoehorned into the trunk at 1/3 the cost of the mazda part.

do /not/ swap the factory alloys for aftermarket--- the suspension is tuned to the weight of those wheels, and most aftermarket wheels can't be had at the same weight.

motors are very stout. it's the same cast iron block out of a ranger, highly under stressed in this car.

 

[SOHCman]

Also, if a diff is exposed to water, for instance a flood car, or water crossings, or boat launching, it will yield similar results. It's important to change the fluid any time its exposed to water obviously.

 

[gathermewool]

I notice the OP hasn't responded in this thread, but I'll post anyway.

Which rear differential does this have? If it's a clutch-type LSD, could the color be residual clutch fines being "washed" off the diff?

I experienced similar color in my STI with a Torsen (gear-type LSD) and, while I wasn't able to find an exact answer online, I recall reading something somewhere about how certain Torsens are known to discolor gear lube.

I'll second that one final gear lube change, with the lube of your choice, is all you'll need. So long as the diff isn't making noise I wouldn't worry, either.