After the dead Aux battery incident I thought I had solved my MPG loss from when the car was new. Turns out I had another issue. I have read all the stories about trans-axle oil and need for change so with 44k on the car I went ahead and changed the oil. After the oil change I went straight to shell and filled the car up and took a trip down the freeway. I drove 10 miles down then 10 miles back up after which I drove the side roads for about 15 miles. I had an MPG gain of exactly 7.7. I was unable to break 50mpg after the aux battery change and just assumed I would never see the 53mpg I was getting when the car was new. Well low and behold the car leaped above 50 from the start and hit 53 by the end. Boy I couldn't be happier. FYI The oil drained out a dark milky purple color. It looked horrible. It was way past the point of needing to be changed. I would say change it at 12k and then every 30k after that. I did not save any for analysis as it was bad and you could clearly see it. Any ideas why old oil causes such an MPG loss?
The old oil could have broken down and thickened up. Or, the crap circulating around may have caused slight increased drag/wear on bearings and the transfer chain With my FJ, I gained 2 mg just by changing all the gear oil (Front axle, rear axle, and transfer case) to Mobil Delvac Synthetic. I did this when my FJ only had 1,200 km on it
Driving to the gas station, filling up, resetting the MFD, and making a trip starting with a warm engine is good for a substantial (but artificial) bump in trip fuel economy every time. Changing the transaxle oil was a good move but that isn't why you saw an increase in mileage.
Used transaxle fluid usually will test at a lower viscosity compared to new, so I would not expect improved mpg from a fluid change. However its good to periodically drain the old oil to get the Si and Fe out of the system. I also observe ~30K mile change intervals. Let's see what happens to your mpg as you log more miles over the next few months.
Well after a few more short cold trips to the store, for an Xmas tree, to the drugstore and to get a movie I am still up over 6.5 mpg. Anyways cold or hot the car would not go over 50mpg as I STATED IN THE FIRST POST. ---->>>>The MPG is UP, WAY UP!<<---------
Well I suppose in any experiment with many data points there will always be some "outliers" that don't make sense and get ignored.
13% mileage increase from tranny oil change seems a little out of the realm of reality. If the oil in there was bad enough to cause that much friction, the tranny would be trash by now.
The NHW11 transaxle has about a 15% carry forward of the old oil from nooks and crannies that don't drain. No one has done a study of the NHW20 but I would be surprised if the carry forward wasn't in that range. You might want to treat the first change as a 'flush' and change again in 2-5,000 miles. Pity about not keeping a sample for analysis. The particulate load is what causes the oil to become 'dark' and these fine particles break the film layer. Changing the oil has removed most of these fine particles so the oil goes back to being a lubricant instead of a 'lapping' compound. Bob Wilson
Wow I guess I will have to spend an additional 50 bucks to drain again in one month. Thanks Is it normal for the oil to look so bad after 40k in an 08?
OK I see what I see. The MPG is UP. Anyone who has lost MPG and cant figure out why should change the ws atf oil. My oil looked like purple tar and needed changing a long time ago.
My first oil change at 53k, an NHW11, was pretty grim and smelled of paraffin. Until we tested a 325k mile sample, it had been the record. Overall, the trend has been worse for samples from dusty areas. Bob Wilson
The numbers only look bad because the MPG is so high to start with. The same % in MPG drop on a vehicle that gets 15mpg would barely be noticeable except to your wallet.
You may want to go on a more frequent oil change program ... say every 30k or 2-3 years. It is not that big of a deal and the potential mileage improvement ... well you've seen the evidence. If you have a gentle hill near the house so you can do a 'cold' roll down test, you might baseline the performance at freezing. Then every winter, repeat the test and when the roll-down test shows evidence of higher drag, change the oil. Just a thought. Bob Wilson
Well, probably the safest to use, as Toyota factory fills the car with it. Don't be surprised when you drain the fluid, that it is black Note: always open the fill plug first. If for any reason the fill plug is stuck, seized, or otherwise buggered up, you sure don't want to find out after all the fluid is drained Around 26 years ago, I learned that lesson the hard way
If you don't use Toyota fluid you risk damaging the insulation on the motor windings. Why take the chance with a multi-thousand dollar repair item.
