Changing transmission fluid for the first time on an old Prius?

Prius transmission isn’t traditional automatic transmission. In traditional automatic transmission there’s lots of hydraulics inside and if transmission fluid isn’t changed for long time dirt in old fluid can be only thing keeping the transmission working. Changing Prius transmission fluid shouldn’t cause any bad things to happen. Unless you screw up something while changing it.

But I don’t know what those lights mean. If transmission is already bad changing fluid won’t fix it…

 

Wherever you got that 23 point inspection, I would not return there. They seem to check items that need attention randomly. There is really no way to check the transaxle fluid level on the 2004. And your brakes should be checked again by a professional to make sure it's acceptable at 150k.

It should be fine to change the transaxle fluid now, make sure you use Toyota ws fluid and preferably have it changed at a place familiar with the prius

 

I strongly suspect your bad millage is down to the tyres fitted. Please let us know as much detail about the tyres you have, make, type name or number, size, and tyre pressures you are running at.
Changing the transmission oil will do no harm and in fact it will do good.

John (Britprius)

 

I must be superstitious, 'cause there's something compelling about "long time dirt in old fluid can be only thing keeping the transmission working". Just the thought that it's working fine, you change the fluid, and then something bad happens...

Still, I can't rationally see a reason to not change the fluid, it's long overdue.

 

It would be best if you can give more detail on the Cooper tyres, but I do not believe they are LRR "low rolling resistance tyres" and as such will affect negatively your mpg figures. Your psi figures do not make sense if you have not added air after coming down from altitude.
The difference between LRR tyres and ordinary tyres can mean the tyres more than pay for themselves in fuel saved over there life.

John (Britprius)

 

How are you calculating the mpg?

 

The outside temperature makes a big difference in the operating efficiency. Gasoline engines and batteries operate more efficiently at warmer temps. Operating the cabin heater also usually causes a noticeable drop in mpg. Trip duration and route are also large factors. Driving trips of under 15 minutes each way usually delivery significantly lower mpgs than longer trips. Some routes are also better suited for fuel economy than others, even in the round-trip. There are numerous factors to consider.

There was an account here on Priuschat (I wish I could find it again) of a maintenance shop manager who was performing Prius transaxle fluid changes on higher mileage cars, but was experiencing such a high transaxle failure rate after the fluid changes that he stopped performing the service. Possible theories include sediment or sludge loosened during the refill process. Changing Prius transaxle fluid is a polarizing issue. Most enthusiasts and forum participants are proponents of changing the fluid, but it isn't on the maintenance schedule and I bet that most Prius owners out there never have it changed. I'm at 45k miles, so I might change it sometime soon, but I'd be personally reluctant to change it at 152k.

Is the yellow mark on the brake portion for the fluid or the pads/shoes?

My favorite tire pressure is 44 psi in front and 42 psi in back. It seems to roll really nicely and deliver good mpg and handling while wearing the tires evenly. If I drop the pressure to 35 psi, it feels like I'm driving around on mattresses--I don't like it.

 

At high altitude there is less oxygen pulled into the engine this in turn means the car compensates for this and injects less fuel. Further the less dense the air the easier the car travels through it "less drag". These put together could explain why you got better fuel economy in WY.

John (Britprius)

 

If this is the method used, it won't be accurate. You would have to go with a running average with all your tanks and mpg combined. The gas tank has a bladder and it's very inconsistent in terms of amount of gas you can get in per tank

 

What is your AC usage compared to in WY? It can take a little while for the computer to fully adjust to the different elevation as well.

Like JC said, don't worry if this was your first tank in KS. I've had tanks that were unusually low followed by high or vice versa, but the average of the MFD mileages was about the same as combining the pump mileage.

 

IMO, it is a combination of things. The bladder is doing it's thing. You can't go by tank to tank. The tires are probably not LRR tires. The air pressure from the different elevations effects it. And many other things too come into play.

If it were my car, I would change the transmission fluid. Simply drain and refill with the Toyota WS. While you are it, clean the throttle body and the MAF sensor. Install a new air filter and fill it up with some good Tier 1 fuel. Then drive it normally and see if it does not improve.

If the tires are not LRR (low rolling resistance) there is little you can do anything about that at this time. My best suggestion would be to fill the tires to the maximum amount of air pressure that is marked on the side of the tires, and maintain two pounds more on the front tires than the rear. When you get the next set of tires, be certain to get LRR type tires. Do some research on your own and know what you are buying. A recommendation from a dealer is simply them selling you a set of tires that they want to move. That does not always mean those tires are the best tires for your money and or your vehicle. Saving a buck or two when fitting tires can actually cost you more in the long run if you don't go with a good LRR tire. Also, anytime new tires are installed, traditionally the MPG will be lower until those tires are broken in. It varies the amount of miles to break in a set, but usually the MPG will improve after 3 to 6 thousand miles.

Last but not least, if you are not using "Synthetic Oil" AND your car is NOT using or burning oil then change over to a good synthetic oil. Mobil 1 is what I recommend for the Gen II Prius. 5W-30 is what you need. Remember 3.9 quarts maximum with a filter change. Anything over that is over full. Check the dipstick level. If it is over the top dimple, you have too much oil in it. It is not a good idea to run excess oil in the Prius engine.

One other thing that might help you would be to change the inverter coolant and also make sure that the spark plugs were changed at 120K. Also make sure they are the correct Iridium plugs.

All of the things above will help to improve your gas mileage. If you want your car to last another 100,000 miles you will definitely need to maintain it very well. Don't be surprised if you have to work on the traction battery soon. Your pack is a minimum of nine years old, with over 150K on it. By all standards the pack is out of warranty. Some folks make it to 250 or 300 with no battery problems. Others don't. It would not surprise me to learn that your modules are getting weak at this time.

I wish you the best of luck Emily.

Ron (dorunron)

 

Count on the fuel pump, which is embedded into the bladder fuel tank expiring in the next 30k-50k plus miles.

Understand and plan to replace the whole assembly.

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Mike raised a very important point on the US models of the Prius. The fuel pump/filter is inside the tank which is a sealed unit. There is no access to the inner mechanism. It is rather expensive and somewhat labor intensive to change the tank. So do be aware of that.

I would not worry about any of these things. Just handle whatever needs to be handled as time passes by. If you keep her maintained properly, and repair things as they break the car should continue to operate normally. The main thing is whether the cost of repairs are justified as some repairs can get a little pricy. But are not all vehicles like this at some point in their life?

Best of luck to you,
Ron

 

Emily,
I have changed transmission fluid in my 05 after 150,000 miles. It didn't cause any problems whatsoever and it really needed it. I highly recommend you change your tranny fluid ASAP.

 

I changed my transmission fluid after 150,000 miles also, it was quite dark. No change in anything afterward. The previous owner went to the dealer for all maintenance, so I was surprised that it still looked like the original oil. I bought the car at 148,000, did the change around 158,000.

 

Yes, the tire pressure and rolling resistance are very important. 3-pound reduction in pressure will drop mileage considerably. But I have seen something else. That's too much of a drop. After getting my car back from Toyota, I was getting 36 mpg. I pulled the air cleaner out and thought I heard a slight pop. The filter was clean so I replaced. Then the mileage went to 46 mpg. I suspect the component located in that area. I think the mass air flow sensor is located right there, and I'm not sure if there's a throttle position sensor. This has happened 2 or 3 times with taking the car to the dealer. I have some suspicion that monkey business is going on. Who knows?