2004 Toyota Corolla LE Fuel Economy

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2004 Toyota Corolla LE Fuel Economy (3/25/08, updated 3/22/10)

The grey line represents actual fuel economy, in miles per gallon (mpg), for my 2004 Toyota Corolla LE. The darker line is a moving average spread across the last 5 readings. Mouse over for annotations, which are just to the right of when things happened. Up till 55,000 I could still hit 41+mpg on long trips but it decreased rapidly from there and I've been troubleshooting why. It isn't a normal thing like a bad oxy sensor, just the regular aging of an engine, but most people I've spoken with say that as the end of the line and I wanted to know if it could be helped. A few things have been found:

Techron: I often filled up with Texaco gas that had Techron in it, and when I moved I could no longer do that. I add a bit of the concentrate before every fill up now. That's what finally ended the downward spiral. Car companies use it when going to do the EPA measurements of fuel economy. 'Nough said.
AMS SSO Oil: The car's never had non-syn oil in it, but I wondered if some were better, etc. Since 100,000 miles or so it's been using AMSOil's SSO 0W-30 Full Syn oil on the extended change intervals they recommend. It's supposed to be one of the best, I'll let you all read why. Fuel Economy has been rising since I switched to it as well, but there is no way to tell what is due to Techron and it.
Engine Flush: I read the 1ZZFE engine has a reputation for getting stuck rings and an engine flush could fix that. I was burning oil before, and I didn't after. Still aren't either. I did this when I switched to AMS Oil.
Gaskets: Vacuum was getting weak so the intake manifold and throttle body gaskets were replaced. That bought me 2 PSI. I'm almost back to base line now (19psi vs. 21psi).
Wear: John at NEDyno thinks the bearings and crankshaft are worn and recommended Restore, which I'll try at the next oil change. It'd be great if this works. In the next car I'll probably use a pre-oiler like an Accusump to try to address this as early as possible.
Seasons: John also mentioned the fuel in winter gas (December to the end of March) is oxygenated with menthol to help with cold starts and can be less efficient as a result. There's definitely something to this:
Nokian Tires/Tyres: Low rolling resistance tires are standard on new cars and at some point we typically junk them for "better" tires with improved handling and the like, but lose the low rolling resistance. Nokian's cracked that problem and is using environmentally safe rubber too. I have the WRs (stop on a dime... in snow. I love 'em) and will get WRG2s soon to replace them. Lifetime was two years/80,000 miles.
Oil Testing: AMS sells testing kits from OAI. It's extremely useful to get an idea of if your oil needs to be replaced and what is happening inside your engine. Typically fleet managements use this so they can save money by doing oil changes when they are needed, rather than as often as the recs. I conducted a test after an oil change at 127,788 miles, sampling then as well as 2436, 4148, and 5733 miles later. The sample dates were 1/11/09, 2/14/09, 4/12/09, and 7/24/09 respectively. Here are the results in graphical form:

The blue bar is how the fresh oil looked so we're looking for deviations from that. For the most part the ppm changes weren't that interesting, even the Iron (Fe) which went from 2ppm to 23ppm. It isn't enough to really worry about. As Nitration and Oxidation increase Total Base Number (TBN) will decrease. When TBN hits one or two it's time to change the oil. I ran one test after 15,000 miles and TBN was 1.86, but Oxidation and Nitration were pretty high too. The second to last chart is viscosity which is a measure of resistance to flowing, not ability flow. Thus increasing viscosity as we see here means the oil is less able to lubricate things. It actually starts out a bit too low but recovered quickly and is in a good range for the whole test.

The only troubling reading here is the amount of soot increasing like it did, which indicates the fuel isn't burning as well as it could. The reading is still way under anything that would be considered abnormal, but it could be due to the weakened vacuum we addressed with the gaskets. I also know my engine isn't sucking in as much air as it used to when the throttle is wide open, which could also explain the soot. Hopefully I'll have more on this soon.

Why? Most of my childhood was spent in rural Maine, looking up to people like Senators Cohen, Mitchell, and Snowe. There's a park in the middle of the state called Baxter which was given with the express condition that it remain "Forever Wild". That sense of preservation seems to be in the core of everyone from the state. "Reduce, reuse, recycle" wasn't a tagphrase, it was a way of life. I'm trying to identify how we can keep our cars in better shape, longer, instead of buying new ones. It's that simple.