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Discussion Starter #1
Does any body know if the rear differential (for 4WD) is really needed very time you have an engine oil change?
I sent my MDX last weekend to the dealer for the first oil change (@4200 miles) and they suggested changing the rear differential oil. I didn't have them change it because the cost was $87.99 +tax.
I checked in the manual and it mentions that the engine oil and rear differential oil needs to be changed every 7500 miles.
First of all, does the oil need to be changed or just check its level?
 

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Actually, the owner's manual says to replace the Diff Fluid at the 7,500 mile point. The next replacement under normal conditions is at the 30,000 miles point and then every 30,000 miles there after. The severe schedule simply changes the 30,000s to 15,000.

I seem to remember reading somewhere that Acura considered it very important to go to the 7,500 mile point before changing the fluid for proper break-in...I can't remember where though...

It sounds to me like the service department is trying to pad their bottom line. Be careful with dealer recommendations. If the manual doesn't require it, and the dealer claims its required, tell them that because it differs from what the manufacturer requires, it should probably be done under warranty (i.e. for free).

For what it's worth, I am speaking from a lesson hard learned. I ended up winning in the end, the manufacturer MADE the dealer refund my money, but the process was long and somewhat painful.

JMHO
 

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Discussion Starter #3
Thanks jnbsdad,
I kinda knew that they were trying to "sell" a service which is not needed specially when they said, every time you change the oil.
Then the Acura will be the most expensive car to maintain and keep. Imagine, a $100 oil change every 3750 miles.
I also agree with the importance of changing the fluids after the break in period. I think they initially use certain types of metal conditioners that needs to be in these mechanical systems, i.e. Engine, transmission, differential or even radiators.
 

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What fluid are you guys talking? VTM or Rear Diff?
 

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Discussion Starter #5
I think the VTM is the rear differential. Lets say that VTM-4 is the electronic system that controls the torque transmitted to the 4 wheel drive.
Usually, front wheel drive has a differentail that is lubricated using the same fluid as the transmission (I am not sure though). Vehicles with rear wheel drive has a differential that require checking the fluid level every 15000 or so, but in the case of VTM-4, it may need more attention.
 

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The VTM-4 is the type of rear differential used in the MDX. The terms for the mDX are therefore interchangeable.

There is a TSB for the MDX that emphasizes the initial interval for the rear diff (VTM) must be 7500 miles. http://www.hondacuraworld.com/bulletins/MDX/SB00-035.pdf They use a special fluid and you'll get proper break-in. I'm not surprised a dealership is going AGAINST a factory recommendation- despite Acura's assurance that "ask your dealer- they are factory trained and know what is best for your new vehicle" (right)

I've done three changes, and eack time the fluid I drained out was perfect. Still, follow the factory schedule, and don't buy the dealers' garbage.

Use ONLY VTM4 fluid. this is the only stuff you should put in the Honda Variable Torque Management Rear differential... ($19 a gallon)

On another front, watch the dealer on the transmission service. 30k (severe) or 45k (normal service)- heard of one guy that had a dealer suggest it every 15k...

Ard
 

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Discussion Starter #7
Ard,
Just being curious. How did you drain and fill this VTM-4 fluid? Is it like a bolt that you remove to drain the fluid then another one for filling?
 

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Easier than the engine oil...

Yep. Two bolts- actually you take a 3/8" socket drive extension and insert that directly into the bolt head (has a square hole)

The fill is super easy: use a $4 hand pump from the auto parts store, and just pump into the fill until it runs out. Remove the nozzle, When it stops, the level is *just* at the edge of the hole. Replace the bolt and tighten.

Most differentials are 'on all the time', that is they are simply changing the drive shaft rotation to 2 90 degree outputs. A simple gear mechanism. Perhaps with a viscous coupling for Limited slip.

The VTM4 is active, and is controlled by electromagnetic clutches, and gets a lot of on-off-on-off. This is why the fluid is critical, and the change intervals are frequent. My RWD Q45 has a service to check the rear diff at 90k. Prior to that, you only look inside if you see a leak. For conventional diffs, I'd recommend Synthetic and change it at 60k.

Ard
 

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Ard,

Are there any differential bolt washers (similar to oil drain plug washer) that should be replaced when changing VTM fluid, or is it a matter of properly tightening the bolts to prevent leaking?
 

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Both

:)

That is, new washers AND properly tightening...

The part numbers for the two washers are (94109-20000 and 90471-PX4-000). If I recall, one is 18 and the other is 20mm. (Some dealers are only selling the first number for both locations...I don't know why.)

35 ft-lbs for each

Ard
 

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ardvarkus said:
The VTM-4 is the type of rear differential used in the MDX. The terms for the mDX are therefore interchangeable.

There is a TSB for the MDX that emphasizes the initial interval for the rear diff (VTM) must be 7500 miles. http://www.hondacuraworld.com/bulletins/MDX/SB00-035.pdf They use a special fluid and you'll get proper break-in. I'm not surprised a dealership is going AGAINST a factory recommendation- despite Acura's assurance that "ask your dealer- they are factory trained and know what is best for your new vehicle" (right)

I've done three changes, and eack time the fluid I drained out was perfect. Still, follow the factory schedule, and don't buy the dealers' garbage.

Use ONLY VTM4 fluid. this is the only stuff you should put in the Honda Variable Torque Management Rear differential... ($19 a gallon)

On another front, watch the dealer on the transmission service. 30k (severe) or 45k (normal service)- heard of one guy that had a dealer suggest it every 15k...

Ard

Hmm, this TSB indicates 7,500 miles or 6 months, whichever comes first. So, if you only drive 6,000 miles a year (like my wife, really, work & back 4 miles, makes me take her everywhere else), you would need to change the VTM fluid at 3,000 miles. The fluid doesn not need to be there for a minimum amount of miles, only maximum. The TSB also states not minimum limits, only maximum limits, noted by the terms, "whichever comes first." There also is nothing to indicate any particular break-in element to the fluid, nothing to make us think that the original fluid installed in the VTM is anything different than the VTM fluid used by Acura dealers. I think there is a sense of black magic paranoia here. Relax guys!
 

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Bruce-


Where ya going with this?

Just because there is "nothing to indicate any particular break-in element to the fluid" are you claiming this to be proof there is, in fact, nothing special about the fluid?

(In fact Acura has indicated otherwise, but not in writing.)

Likewise, there MAY be competing issues with changing the fluid: Acura engineers may have wanted a 7500 mile interval on breakin, but also realized that fluid age was an issue, and therefore limited it to a 6 month limit. Again, being able to construct a scenario in which the 6 month limit occurs at 3000 miles does not mean it should be changed at 3000 miles, or even that it is equal to change it at 3000 versus 7500.

We really have no idea what is optimal, so I just follow the MANUFACTURERS recommendations (not the dealer).
 
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Ardvarkus

The manual also states 2-years or 30,000 mile intervals after the first 6-month or 7,500 mile change. Therefore you could be changing your VTM-4 at much lower mileage if you don't do 15,000 miles a year. Do you really think this is necessary? I changed my VTM-4 fluid at 5,600 miles (6-months) and at 2-years will likely have less than 20,000 miles or thereabout at 4-years 40,000 miles instead of 60,000 miles. Do you think it is really necessary to change the fluid on an age basis? If the fluid just sits there and doesn't get used as often does it deteriorate? I will follow the 2-year, 4-year schedule to keep up the warranty but I do wonder if this is really necessary. No one to my knowledge as ever discussed this aspect of the warranty which also includes oil changes. If anyone knows the answer to the time changes versus mileage changes please let me know

Thanks
 

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JR-

I really don't know the specific technical answer to that question.

Of course, we should all follow the maintenance schedule, just to protect the warranty.

Oil doesn't have a 'shelf life', so why would it need to be replaced if it sat in your crankcase for 6 months with zero miles versus in the box?!

I think the answer is elsewhere:

In some motor applications, they do not track mileage: my tractor, jet engines, trucks, etc all use hour meters that measure running time. Running time is THE measure for wear and oil performance. Look over at theCastrol/Valvoline/Mobil sites and many technical reports list hours not miles. In fact, 50 hours is a typical interval for industrial diesel oil change. Just so happens that 50 hours at 60 MPH is... 3000 miles.

But, if you only drive 8 miles a day to work, at 8 miles an hour, you will rack up 60 hours in three months- but only 480 miles.

Since the MDX (and any other passenger vehicle in the US) has no engine runtime meter, the time/distance metric is likely the best compromise.

It is also the reason the "severe Service schedule" includes short trips, idling, etc.

My 2 cents

Ard
 

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Ard, Excellent post, and I fully agree. Loose.
 
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Ardvarkus

As I said before I will keep to the 6-month schedule (about 4-5,000 miles) to fulfill my warranty requirements. In my case though the MDX is used solely for pleasure mostly going to and from Arlington, VA (about 210 miles roundtrip) to visit the grandkids at highway speeds (75mph) and other pleasure trips. Practically no stop and go driving at all so I don't really qualify for severe conditions. In my opinion changing the VTM-4 fluid every 15-20,000 miles is probably overkill but I will continue to do it until the warranty expires. After that I think I will go with the mileage (30,000 miles regardless of the time interval). 4-5,000 miles per oil change or six months I believe is a reasonable mileage and period of time so I will continue on that schedule after the warranty expires. Thank you for your explanation though, I wasn't aware of hours interval for other machines, and it makes a lot of sense.
 

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There can be good reasons for changing oil based on time vs. mileage. A vehicle with low mileage may sit idle most of the time with infrequent but relatively long trips. However, it might also be driven regularly for short distances (<10 miles). In that case the engine doesn't really heat up enough to evaporate the water that condenses in the crankcase. Emulsifying the water in the oil creates sludge, which is why frequent short trips is considered 'severe condistions'.

However, I don't think there is a similar condensation problem in the transmission or differential, so I suspect that experience their breakdown based primarily on mileage.

- Conrad
 

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NO-

I'm away from the service manual, but my recollection is that it is less than 50 ftlbs- (36?-sorry, don't recall)

Are you sure you've got the correct plug? Both use a 3/8" drive extension to fit right into the plug.

If it is indeed drastically overtightened, the dealer should fix it for free.

Ard
 

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There is a difference between the factor VTM-4 fluid and the fresh stuff. It looks like there is metallic dust in the VTM-4 fluid.

When we first emptied out the VTM-4 fluid, the mechanic and I thought that I had done something worse than poke a hole:
http://www.acuramdx.org/forums/showthread.php?s=&postid=175680#post175680

Put after further analysis, there's way too much of that dust in there to be from anything I did. I think it is in there for the break-in.
 

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