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Transmission Question

I checked the transmission fluid in my car because the it seemed to be slipping. After checking, it registered as extremely low. I added 3/4 of a quart of fluid, whch seemed to bring it to the regular level. However, during my drive the next day, I noticed my tachometer was showing over 30,000 rpms at 40 mph. Any thoughts on what the problem could be?

“Any thoughts on what the problem could be?”

Yes!
Apparently, somebody slipped a turbine engine under the hood when you weren’t looking!
;-))

Seriously, however, I am pretty sure that you meant to say 3,000 RPMs, as your engine is most likely red-lined at about 6,000-6,500 RPMs. And even with a small engine, 3,000 RPMs at 40 mph is a strong indication of a badly-slipping transmission.

We don’t know the model year or the odometer mileage of your Hyundai, so we don’t know whether the powertrain warranty is still in effect. For your sake, I hope the powertrain warranty is in effect, because I suspect that the transmission is in need of being rebuilt.

If the warranty has run its course, I suggest that you take the car to an independent transmission shop in your area for diagnosis. Do NOT go to AAMCO, Lee Myles, Cottman, Mr. Transmission, or any other chain transmission shop unless you want to be told that you need a trans rebuild–even if a simpler repair is all that is necessary. Those chain shops are notorious for bad diagnoses, overcharging, and bad workmanship.

And, for future reference, transmission fluid should be changed every 3 years or 30k miles (whichever comes first), even if the mfr’s maintenance schedule does not specify this service. This is the maintenance plan that I have always followed, and in 47 years of driving, I have never had a transmission failure.

By contrast, we get posts in this forum on an ongoing basis from people who have never serviced their transmission, and who wound up with a problem like yours any time after ~90k miles. By 120k miles, trans failure is pretty much of a sure thing for those who don’t service it as I do.

Let us know what the trans shop has to say about your car.
Good luck!

& make sure you are checking the xmission fluid as specified by the manufacturer. Read how to do it in your owner’s manual. Or phone the dealership and ask them. Every car has a different procedure. On many you have to check the level only when the engine coolant is at normal operating temperature, and then you park the car, run the shifter through every gear selection in a specified order, hold each one for a specified number of seconds, then put it back into Park, and then you check the fluid level while the engine is running.

If you don’t follow the spec’d procedure, you can easily end up with too much fluid in the xmission pan, which can cause it to shift poorly or even damage an auto- transmission, just as much as too little fluid.

Also before thinking it is slipping, make sure it has shifted up to your higher gears. 3,000 isn’t bad for 2nd fear.

@ellyellis
Yea it might be a bad sensor dropping the trans into limp mode, good catch. A 60$ sensor MIGHT fix this particularly if this just happened all the sudden.