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Thread: Transmission Oil

  1. #1
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    Transmission Oil

    Need Advice. My VX is ready for transmission fluid change. Last time was a flush 18,000 miles ago at the Isuzu dealer. (VX has 55k on it now) It currently has Dexron III in it. I would like to replace it with the closest thing I can to the original Dexron III but as you know, Dex III is no longer made. All I can find is the Dex/Merc multi-vehicle oil. Some have reported slipping when using Dexron VI so I am hesitant to try that. Need advice as to what mineral oil is working well out there. (I’m not ready to switch to synthetic). Can you guys tell me if you are having luck with a specific formulation by a specific manufacturer? Any advice is really appreciated.

  2. #2
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    I used o’riely’s house brand multi-grade for dextron III & IV. Seems to work fine.
    --------
    VX Status: Running Great! Build is coming along nicely...

  3. #3
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    Generally for ALL vehicles, whatever the OEM specified transmission fluid is...when supplanted by a newer version of said oil...the newer oil will have to be backward compatible with all older vehicles using this type of oil.

    https://en.wikipedia.org/wiki/DEXRON

    In any event, I've been using Valvoline full-synthetic for many, many years on various vehicles...and have zero complaints. Now bear in mind that I'm religious about changing it every 15,000 miles.

    https://www.valvoline.com/our-produc.../dexron-vi-atf

    I do not have experience with "AFT Maxlife" and can't speak to the pros/cons of it vs what I use. Always full-synthetic, never blends. Same reason I use Rotella-T6 for the engine oil.

    Your VX has very low mileage, so there's virtually zero reason to stick to conventional oils. NO conventional oil will ever outperform a quality synthetic oil. There's a lot of science behind that, which includes homogenity, sheer-resistance and a load of other technical things that are the cure for insomnia. I have no slippage with mine, btw, and I'm about to tick the 100k mark in the next several months. In fact, the only problem I think I have with my trans is the"GM standard roar" from the rear differential. Probably has to do with mileage wear/tear more than anything. But the trans itself shifts great and doesn't slip.
    Last edited by ipd : 04/17/2018 at 09:04 AM

  4. #4
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    Quote Originally Posted by ipd View Post
    Generally for ALL vehicles, whatever the OEM specified transmission fluid is...when supplanted by a newer version of said oil...the newer oil will have to be backward compatible with all older vehicles using this type of oil.

    https://en.wikipedia.org/wiki/DEXRON

    In any event, I've been using Valvoline full-synthetic for many, many years on various vehicles...and have zero complaints. Now bear in mind that I'm religious about changing it every 15,000 miles.

    https://www.valvoline.com/our-produc.../dexron-vi-atf

    I do not have experience with "AFT Maxlife" and can't speak to the pros/cons of it vs what I use. Always full-synthetic, never blends. Same reason I use Rotella-T6 for the engine oil.

    Your VX has very low mileage, so there's virtually zero reason to stick to conventional oils. NO conventional oil will ever outperform a quality synthetic oil. There's a lot of science behind that, which includes homogenity, sheer-resistance and a load of other technical things that are the cure for insomnia. I have no slippage with mine, btw, and I'm about to tick the 100k mark in the next several months. In fact, the only problem I think I have with my trans is the"GM standard roar" from the rear differential. Probably has to do with mileage wear/tear more than anything. But the trans itself shifts great and doesn't slip.
    Thanks for responding to my post. Do you do a flush? I'm thinking a flush would be OK since mine was flushed 18,000 miles ago.
    Do you also do a filter change every 15,000 miles?

  5. #5
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    Just the fluid every 15k. Probably could use a filter change though. I'd like to install a secondary filter, but I haven't gotten around to it yet. The advantage is that it's far easier to change--especially at every flush interval--and keeps the particulate trapping to a maximum.

    Always a 100% flush. Never the old-school "pan-drop" change.

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    Malibu_Robert (04/17/2018)

  7. #6
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    I want to do the same thing then. I'll put mine on a 15K schedule. Does your mechanic have a scan tool to read the transmission fluid temperature? I'm not sure if my mechanic has a Tech II compatible tool. That is one thing I am really frustrated with. I want to be able to pull the TFT data from the OBDII port. I haven't found anyone on the forums who have successfully done so. Everyone is just guessing at it. Some people estimate with their hand, others shoot IR thermometers at the pan. Problem is, the temperature of the pan could be very different from the fluid inside. I want to be able to check mine the correct way.

  8. #7
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    I have been using Aamsoil synthetic in my VX since 66K.
    No changes or flush since then. Now I'm at 185K.
    In otherwords do as little as possible.
    You can check out your current fluid by opening the upper drain oil a crack and dripping some fluid out.
    If it stains your fingers or smells burned, change it, if not, leave it alone. That's my two cents. Our transmission is identical to the Post Office LLV and they live up to their name.....Long Life Vehicle.

  9. #8
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    Smell/color is a poor method to check for contaminates, imho. If you want to be VERY precise, you can sent it off for analysis (like people do with engine oil). Aamsoil is quite good, no doubt--even with expense aside. But there's a lot more at play also. Are those highway miles or city miles? Are you a leadfoot, or do you baby-foot accelerate? Changing fluid doesn't inherently harm an engine or a transmission. The only times that has ever happened is when the engine/transmission was previously badly neglected, and the new fluid knocked particulates loose that caused damage. You can get by with the claimed 10,000+ oil changes that some oils claim too...but that doesn't mean it's a good idea. It has a lot to do with the blend of the oil, how quickly cleaning agents are consumed, etc. And a transmission filter is one of those "rarely changed" parts of a vehicle that can be quite full of particulates--even to the point where it starts requiring more frequent fluid flushes.

    The most reliable method to read fluid temp is to have a gauge installed--permanently. If you are concerned with your transmission fluid temp (and keep in mind that there IS an optimum operating temperature and that a transmission can be operated below that under suboptimal conditions), consider adding a transmission cooler. Placement of said cooler will take some clever engineering, as the existing radiator cooling on these vehicles is already relatively poor; you don't want to obstruct airflow to the radiator at all. However, if you are using/making an aftermarket bumper, or not afraid to heavily modify the existing one, you can easily find placement options that will suffice.

    p.s.
    speaking of airflow, I've long desired a replacement hex-pattern grille that eliminates the "teeth" and has more peak CFM potential than the stock grille.

  10. #9
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    Just for the record, you have to know you really can't change your transmission fluid, you can only change about a third of it. The rest remains kept up in trays that cannot drain . Transmission service is an excersise in futility.

  11. #10
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    I disagree. If a transmission is build as how you describe, then it's even more imperative to flush it religiously--because only cycling fluid through can ever hope to hit 99%+ of all of the fluid. It's similar to how you normally never have to worry about the age of the gasoline in your tank, because you refill with new gas prior to draining it completely. Which means that the old gas blends with the new and you mitigate the risk of old gas gelling/congealing (which it tends to do within about 60 days if untreated). Flush, run it & cycle the fluid around, flush, repeat. By sticking to a shorter change interval (eg. 15,000 vs mfg recommended 30,000) you are likely to hit these so called "cannot drain" areas.

  12. #11
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    Talk to Jerry Lemond, leave the transmission alone unless the fluid is burned smelling.

  13. #12
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    I don't know who that is. And I'd like to hear some rational explanation. Because this sounds a lot like saying there's no need to change the oil or flush the radiator.

  14. #13
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    Jerry Lemond was a regional QC guy for Isuzu (IIRC). He has been very visible in Isuzu forums providing lots and lots and lots of advice -- based on his work as a factory "rep". That said, it's hard to tell if blacksambo's post was meant for the OP (meaning not yet time to flush unless "burnt") or if it's advice ... in general. If the later, I'd have to disagree with it DESPITE the appreciation I have for Jerry's knowledge/feedback. If he's replying to the OP, I'd agree with it. 18k doesn't WARRANT fluid change UNLESS you are just fastidious. Compared to engines, transmissions/axles don't have the fluid contamination of an engine. There is no carbon source -- like in the engine. Transmission/axle lubes do degrade over time but the first six months is the most....and no one swaps fluid THAT often. Over time (after that), fluid provides enough of a barrier to allow transmissions/axles to last their normal 200k and beyond. The question is whether you want to shoot for more? I didn't see it mentioned above, but HD service tends to decrease change intervals by about half. So...15k WOULD be advisable if you tow (for example).

    This isn't totally different than the issue of engine oil changes. Most oils/manuals say 5k (or more) between engine oil changes. Yet many do it every 3k. On the flip side, I've heard of tests where they never changed oil except to top if off as it was used. They "caught" the oil with a filter change at some long interval (30k?) just to make sure the filters never failed. From what I recall that kind of a test ended up with similar life -- compared to 3k champions of maintenance. You COULD question the issue of dirt/deposits in these 15k synthetics (as mentioned above). I (like them) tend to doubt an oil's ability to stand up to contamination over THAT many miles -- most because it LOOKS dirtier/different. Analysis would support that too. But, I'm not sure tests have ever showed how wear is accelerated using longlife lubes? Everything I've read points to following manuals and not necessarily getting worried about being "over-the-top" with maintenance. At some point, you'd be wasting money. Heck...there's even been studies showing the cumulative cost of oil changes (for fanatics) and how they could buy another engine (with the extra money) at the end of the engine's "projected life".

    Bottom line leads factory reps to recommend following manufacture's advice. Many of those reps have seen cars travel well beyond what they SHOULD have when neglected. As such, they aren't going to tell you "more is better" if it hasn't been proven.

    For the point of this thread, I would agree 18k isn't enough service to worry about a flush/change....unless it's been sitting for years.
    2001 Ebony VX and 1989 Custom 383 Corvette

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  16. #14
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    I'll buy that logic. ^ I know my VX is almost extinct breed. Should anything happen to the engine/transmission, I doubt the ability to find/procure replacements. If that means I baby mine a bit more because of the pucker factor...so be it.

    P.S.
    Our engines are already notorious for burning oil. While mine has never done that since I've owned it *knock on wood* I am not going to chance it. I'll keep mine studiously clean just in case.

  17. #15
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    The transmissions aren't really unique (that I know of)...as they were used in Troopers and Pilots....among others? The engine is more unique. I can't remember for sure, but the "stroked" 3.5L version of the standard 3.2 might have been an option in Troopers? If the block doesn't seize/grenade from lack of care, there's no reason it shouldn't be able to be rebuilt. To me, the unique parts are the body components. As long as people drive like idiots and crash cars, there WILL be parts.

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