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Comment by jmrm | Hacker News Reader

I'm not a mechanic, but they can see the brand and model on the part and call the manufacture or just google it. If it's the same as the car's brand, or if they don't give any information, you can check forums to get that information, otherwise sometimes they can find this information in their AutoData service.

Checking that state of the fluid isn't difficult, as is bright red when it's new, and turns more and more brown when it's used, and it's mostly used normally between 50k and 100l AFAIK.

Buying the required fluid, and filter if needed, is as easy as looking it in the internet or going your local AutoZone, O'Reillys, AAP, or whatever you have near btw

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I'm not a mechanic, either. Googling is easy, and also is often imprecise.

That's why I was wondering how to contact GM about the 4L30E that they built and sold to BMW, as was suggested.

> Checking that state of the fluid isn't difficult, as is bright red when it's new, and turns more and more brown when it's used, and it's mostly used normally between 50k and 100l AFAIK.

Yeah, but getting to the fluid to see it is hard. They stopped putting in dipsticks, so hopefully there's a check plug somewhere you can get to.

Is the check plug really even necessary for a trans fluid swap a lot of the time?

I just drain mines and refill to specified amount, I've never once cared for a check plug and just change it every ~50k miles on most of my cars, regardless of color. It's usually not an expensive fluid.

With neither a dip stick nor a check plug, how does one know how that the transmission contains the "specified amount"?

I mean: Automotive fluids tend to shrink over time, for a wide variety of reasons. (And sometimes, they get bigger, which is usually even worse.)

How do you know that it has the correct level?

On most cars you simply fill till it starts leaking out of the fill hole - like changing oil, it normally doesn't require a precision fill, just close enough.

1. The drain hole is below the fill hole - open drain hole and empty using good old fashioned gravity.

2. Close drain hole.

3. Open fill hole.

4. Fill till it starts leaking out the fill hole.

5. Close the fill hole.

Not especially complex most of the time! Transmission fluid does not really shrink much over time, its a sealed system and it doesn't burn off the way engine oil can. Just doing it at regular intervals like 50k miles is absolutely fine on a lot of cars. If you really do care about hitting some specific quantity of fluid - you know exactly how much you are pouring into the fill hole, you can even measure exactly what came out the drain hole, but this probably is not remotely necessary.

Fascinating.

On the E36, which has no prescribed transmission service interval or dip stick, there are two transmission sumps -- and only one of them has a drain plug. Replacing the fluid means pulling one sump off completely...and pre-filling it prior to reinstallation.

On the Honda, which has a regular interval for transmission fluids and a dip stick, the fill plug is on top of the transmission. It would be a bad thing to fill it to that level. (I just refill using the dip stick tube.)

Also, I'd like to add that I am envious of the fact that you have never experienced a leak in any automatic transmission.

Some fluids are proprietary, like Nissan’s earlier CVT oil which probably costs more than printer ink. Using some near-beer brand often resulted transmission failure.

If its much more than 100 bucks, I'd be pretty surprised, honestly. A quick google shows most Nissan CVT fluids (even the OEM "unicorn tears") at ~80 dollars for the usual 5 quarts etc. Virtually all the "proprietary" fluids are just rebranded mainstream brands (castrol/Valvoline etc etc), most car OEMs are not in the business of manufacturing their raw fluids themselves.

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