Mazda CX9 Rear Diff - Mobil 75W90

[an3_bolt]

Hello,

Mazda CX9 AWD, changed the rear differential oil at 100,000km (62,000 miles). The oil removed was looking good - nice honey colour. No junk on the magnetic drain plug.

Refilled using Mobil 1 75W90 LS. The manual specifies a GL5 80W90.

I have just dropped it 5000km later (3000 odd miles) as I am timing it up with a transfer case oil change. It is black! Smell is not bad (i.e. not burned), the MK 1 uncalibrated viscosity tester (eyeball!) looks about right. Heap of black goo on the magnetic plug - but no visible metal specks or shavings.

Can anyone think of any reason it would be black in such a short period of time (mostly 10-30km trips) and the reason for all the new found goo on the plug?

Does the Mobil 1 75W90 LS have a strong detergent pack? Maybe scrubbing out the previous 100,000km junk?

Is this something to be concerned with? I feel very concerned, but I do not have the in-depth knowledge of lubricants to justify any concerns.

Any recommendations for a possible course of action going forward?

Appreciate any thoughts on the matter.

Cheers

 

[stchman]

Mobil 1 LS probably cleaned out all the junk that the old gear oil didn't clean.

 

[SavagePatch]

I changed the differential fluid on our 08 CX-9 at roughly the same mileage for the first time a year ago with Royal Purple 75w90. My experience was the opposite of yours. The drained fluid was black and there was plenty of gunk on the magnet. I checked the fluid level last weekend when I changed the engine oil and the Royal Purple was still translucent and purple with little gunk on the magnet.

Good idea to service the transfer case too.

 

[gathermewool]

Your Mazda has an open diff and doesn't need the friction modifiers. why not just run a non-friction-modified lube?

I'll be going overkill in the Subie, swapping out the FF soon for Motul Gear 300. I don't plan to change it ever again after that.

 

[Bluestream]

Originally Posted By: gathermewool

I'll be going overkill in the Subie, swapping out the FF soon for Motul Gear 300. I don't plan to change it ever again after that.


How is that overkill? You are doing one fluid change then never again?

 

[gathermewool]

Originally Posted By: Bluestream
Originally Posted By: gathermewool

I'll be going overkill in the Subie, swapping out the FF soon for Motul Gear 300. I don't plan to change it ever again after that.


How is that overkill? You are doing one fluid change then never again?


Motul Gear 300 is overkill.

Because of this, I don't plan to change it again.

 

[Bluestream]

Originally Posted By: gathermewool


Motul Gear 300 is overkill.

Because of this, I don't plan to change it again.


Why is Motul 300 overkill? I dont get it?

 

[an3_bolt]

I hope Mobil 1 is not overkill!

 

[hpb]

In our now traded 2010 CX-9, I drained the rear diff at 40,000km and the oil was putrid. It really stunk! It was a funny grey colour too. I replaced it with the same Mobil as you used, but I never changed it again, so can't comment as to whether or not it turned black. I'd be thinking it's just cleaning some of the old gunk out.

As for the transfer case, good idea changing the oil, the TC is a known weak point in the CX-9. They're a pain to change, as there's no drain plug. I used to do mine with a cheapo version of a Mity Vac, with a long piece of clear hose to suck it out the filler. First time I changed the TC oil, again at 40,000km, it was like tar. I spent about half an hour making sure I'd got as much out as possible. At 50,000km, I changed it again, and while not as bad, it was still black and horrible! I have to admit, the thought of having to deal with a stuffed transfer case was part of the reason we didn't keep that car for longer.

 

[an3_bolt]

HPB - I am hearing you loud and clear.

Yes that transfer case is the whole reason I have stepped up the "look after it" campaign.

Transfer case went south at 100,000km. Fortunately did not strip out the transmission splines. Expensive fix at the Mazda service shop - so I imported my own new transfer case and had a guy put it in. Put 5000km on the new unit now and will change the transfer case oil in the next couple of days. I don't have a huge choice of oils here, but found some Redline 75W140 - so will give that a try in the transfer case.

Front wheel bearings done as well at 100,000km

Looked at transmission oil - supposed to be a don't touch. Not a chance - it was feral. Really bad. Drain and filled 3 times with the 3309, now looks OK. Runs fine.

Just did the serpentine belt at 110,000km (and changed tensioner and stretch belt as precaution). Serpentine was starting to show some cracks.

CX9 is now going towards 8 years and only 110,000km and had it since new - I am starting to think this thing is not going to last the distance even if I continue to treat it kindly with a kid glove and loving maintenance......I am losing confidence in this car rapidly. The more I dig, the more I find.

Might give the rear diff a couple of thousand on the Mobil 1 again, and take it from there. Could be the deciding factor to get a new car.....

 

[gathermewool]

Originally Posted By: Bluestream
Originally Posted By: gathermewool


Motul Gear 300 is overkill.

Because of this, I don't plan to change it again.


Why is Motul 300 overkill? I dont get it?


It's a very high quality oil, being used in an open diff-equipped CUV.

 

[zeng]

Originally Posted By: an3_bolt
Transfer case went south at 100,000km.
Front wheel bearings done as well at 100,000km
Looked at transmission oil - supposed to be a don't touch. Not a chance - it was feral. Really bad.
CX9 is now going towards 8 years and only 110,000km and had it since new - I am starting to think this thing is not going to last the distance even if I continue to treat it kindly with a kid glove and loving maintenance......I am losing confidence in this car rapidly. The more I dig, the more I find.
Might give the rear diff a couple of thousand on the Mobil 1 again, and take it from there. Could be the deciding factor to get a new car.....


How you explained the bad conditions of transfer case and transmission of this CX9?

 

[an3_bolt]

Sorry - I do not fully understand your question. But I will try my best:

The transfer case on the CX9 is not a serviceable unit according to Mazda. Their solution to any issue or problem of the transfer case is to replace the unit. The transfer case does not even have a drain plug in it.

It is has become quite clear to me that not servicing the transfer case with new oil most probably resulted in its failure on my vehicle. When I opened up my failed unit it was clear that the oil had turned to goo and the unit basically then decided life was too hard and gave up. The same transfer case is in other cars, and there are other discussions regarding such as the Ford Edge with the same problems......and solutions. The obvious choice for me is to service it with fresh oil - suck it out and refill.

The transmission likewise is supposed to be a non-service unit. From the oil I observed in my transmission - it has polarised my thoughts on the matter to where I will service it regularly with fresh oil.

I do not have anywhere near the understanding of lubricants that many display on these forums. However - from what I have seen in my CX9 - even blind Freddy would question the concept of non-servicing. I know what I will be doing - not advising or telling anyone else what to do.

Please let me know if this does not provide an appropriate answer to your question.

Sorry about the thread drift - it all started with the rear diff and black oil!

 

[hpb]

Sorry mate, it was probably me who steered your thread off topic...but I'll keep going anyway!

No doubt your research online had similar results to mine, it seems the tiny amount of oil in the transfer case can easily overheat, and as a result it turns to goo. Had I kept the car, my plan was to keep changing it every 10,000km, and cross my fingers. I was using Nulon fully synthetic 75w140. Financial circumstances changed, and we were able to upgrade, while getting more for the Mazda than I expected - a rare win!

Since I've already derailed things, roughly what did the transfer case replacement set you back? I'd have been tempted to tap a drain hole in the new unit, just to make oil changes easier in the future.

Good luck with the mighty Mazda - they are a magnificent vehicle, we were very sad to let ours go, such a pity they have that [censored] Ford transfer case!

 

[an3_bolt]

The Mazda service centre wanted over $3000 - fitted.

Unfortunately for them, I had prepared in case of what I thought it was - prior research prevents getting ripped!

Bought mine from the US, airfreighted and delivered for under $700. Guy to install was about $400.

Bit of a price difference for a bit of mouse clicking! Same result - new transfer case and running.

It does drive nicely and we do use the 7 seats quite often. But I won't be going back for another one....just gotta keep this one running for a bit longer - unless there is a imminent reason for another course of action.

 

[hpb]

Gee that's not too bad, I'd budgeted a couple of grand if ours had died, and would've done exactly the same as you. I'm all for supporting local businesses, but not when a little net surfing can literally save thousands!

 

[zeng]

I mean mechanical parts from Japanese like Mazda are normally durable.

Just wonder ?

Agree with you to regularly service with oil replacements for components longevity, even though manufacturer says otherwise.

Edit:
an3_bolt & hpb, exactly what oil specs are in manual for tcase, transmission and differential ..... did you fully comply?

 

[an3_bolt]

The transfer case appears to be made by Ford......the engine is a 3.7L Duratec - Ford also. Wedged in sideways! There is other stuff that is not Mazda as well.

Transmission off the top of my head is Asian. No problems with its operation - However I do not agree with the "do not service" concept and resulting fluid condition. I was lucky when my transfer case died - it did not strip the splines on the transmission.

Anyway - digress - rear diff oil black after 5000km.

 

[zeng]

Originally Posted By: an3_bolt
The transfer case appears to be made by Ford......the engine is a 3.7L Duratec - Ford also. Wedged in sideways! There is other stuff that is not Mazda as well.



Ok, tcase is non-Mazda. Even then, Ford shouldn't be that bad in my opinion.



Originally Posted By: an3_bolt
Transmission off the top of my head is Asian. No problems with its operation - However I do not agree with the "do not service" concept and resulting fluid condition. I was lucky when my transfer case died - it did not strip the splines on the transmission.

Anyway - digress - rear diff oil black after 5000km.


Originally Posted By: an3_bolt
Mazda CX9 AWD, changed the rear differential oil at 100,000km (62,000 miles). The oil removed was looking good - nice honey colour. No junk on the magnetic drain plug.

Refilled using Mobil 1 75W90 LS. The manual specifies a GL5 80W90.

I have just dropped it 5000km later (3000 odd miles) as I am timing it up with a transfer case oil change. It is black! Smell is not bad (i.e. not burned), the MK 1 uncalibrated viscosity tester (eyeball!) looks about right. Heap of black goo on the magnetic plug - but no visible metal specks or shavings.




The honey color 100,000 km (orig oil?)was on top of situations ..and generates no sludge/oxidative byproducts for it to pick up, hence no blackish oxidative byproducts could possibly be left behind.

I don't see how M1 75W90 picks up some blackish stuff attributing to honey color oils???

I may be flamed for suggesting your M1 75W90 operates with much thinner EHL film thickness compared to spec'ed 80W90 , hence differential is spending more 'times' on boundary lubrication ...... and generates oxidative grayish/black colored products ?? ..... so consider this possibillity , OP.

 

[an3_bolt]

Thanks Zeng - appreciated