Topping Off Oil IMPROVED my Mileage!

This time of year, changes in mpg are usually temperature relate. Warmer temps mean better mpg, higher tire pressures, less dense air (every little bit counts!).

Except for extremes, oil level has little, if nothing, to do with mpg.

 

I think higher temps affect mpg in a couple of ways. First, if the car was dumb, warmer weather will improve mpg directly, faster warm up, less friction, and so on. Then secondly: the car is monitoring ambient temperature, and very likely modifies it's behaviours accordingly. If ambient temp is up enough, it might cross the threshold to an easier warm up program.

One trick I use, with partially warmed engine: when coming to a red light, turn the cabin ventilation temperature down, or (if needed) just shut the vent system off. It'll often cause the engine to shut down. The car sees when you're requesting cabin heat, will keep the engine running.

Vent mode can have a similar effect: on Auto the car will run the fan slower, and have a greater propensity to shut down the engine, when partially warmed. OTOH, if you've got mode set to heat/defog, it'll bump the fan speed up a notch, and more likely keep engine running.

 

I have always had good luck after adding oil, the cars like it

 

Thirdly: reduced cabin heat means reduced fuel needed to keep the engine warmed to operating temperature.

Fourthly: tire pressure increases a bit, slightly reducing rolling resistance and increasing MPG.

Increase in ambient temperature inherently forces an increase in pressure. Though small, it is real.

 

I've seen a minor improvement in mpg in my Gen III just about every time I top up. My mpg hovers around 46-49 mpg most of the time, almost all highway speeds. I wait until the dipstick is down about a third, then I measure my oil use on a gauge I made myself (6 oz. resolution) and calculate my oil burn. I usually top up with Toyota 0W20 but I have been adding some Valvoline Synthetic Blend High Mileage 5W20 from time to time. I used the same brand 5W30 in my 2008 Gen II which reduced oil burn over time. Anyway, on my next commute I almost always see the mpg upon completion of the trip around 51-52 mpg. I don't have a theory about this yet, maybe it's like Bisco says. The cars just like it.

 

Need to see how it calculates out at the end of the tank. But I'm sure the warmer temps was your difference. For me it's about longer highway trips with decent temps.

Posted via the PriusChat mobile app.

 

I have noticed a definite reduction when the oil gets 1/4 inch below the add mark.it's probably causing more friction. When you have a car that uses oil it's better not to let it get to the add mark and top it off more often. It seems the only thing that destroys the ICE is lack of oil. Oil burns up faster when it is at the bottom of the stick and it is easier to get into a dangerous level very quick.

 

If the friction in your engine has increased to the point where it is noticeable in your MPG numbers, I would think you are doing some serious damage to your engine. It should never come to that. If someone notices their MPG is higher after adding oil, they've waited too long to add it.

 

My gen2 has about 213k miles now. I purchased it with about 200k miles. Since purchasing, I have changed the oil change interval to 3500 miles approximately. Initially, I was using 10W30 Shell Rotella oil with Toyota oil filters (now I use Shell Rotella 40W with Toyota oil filters). I installed an oil catch can at about 205k. Oil catch can helps to catch spoils from the PCV valve such as water condensate, oil mist and unburnt fuel. In the past, I filled the crankcase with 3.9 quarts of oil at oil change. The result was that enormous amounts of spoils were captured in the catch can until the dipstick's oil level was half-way between the full and add dots on the dipstick.

As a result, I now only add 3.5 quarts of oil at each oil change which puts the oil level almost exactly between the half-way between the full and add dots on the dipstick (thereby reducing spoils captured in the oil catch can). Additionally, oil consumption has been reduced as long as I only add 3.5 quarts at oil change (meaning 1/2 quart needs to be consumed before arriving at the add oil dot). Currently, I consume a 1/2 quart of oil over about 2500 miles (about half as much oil consumption as when first purchased). Further, I get better gas mileage when the oil level is between half-way to the full dot and below on the dipstick. My theory is that all 1.5l Toyota motors have windage issues which reduce HP and decrease gas mileage when crankcase oil is ABOVE half-way between the full and add dots on the dipstick (and the more miles your Gen2 more likely results in blowby propelling oil mist generated by windage into the PCV system).

 

I had to Google "Windage", and I'm not sure I understand the concept completely as it relates to the PCV, but at least you have a possible explanation for what you have observed. Perhaps I do not need to be quite so particular about keeping the oil at the full line on our Gen 2, especially since I monitor the oil level very closely anyway (when I'm around). I do want to make sure it is at the full line when I'm leaving town for a few weeks and my wife is going to be driving the car. She does not monitor the oil level so closely.

 

Link1 (to Wikipedia article on windage): Windage - Wikipedia

Brief excerpt from Link1: Automobiles. In automotive parlance, windage refers to parasitic drag on the crankshaft due to sump oil splashing on the crank train during rough driving, and/or dissipating energy in turbulence from the crank train moving the crankcase gas and oil mist at high RPM. Windage may also inhibit the migration of oil into the sump and back to the oil pump, creating lubrication problems. Some manufacturers and aftermarket vendors have developed special scrapers to remove excess oil from the counterweights and windage screens to create a barrier between the crankshaft and oil sump.[6][7]

Link2 (to Amazon for windage tray): https://www. amazon. com/ s?k=toyota+windage+tray&i=automotive&ref=nb_sb_noss
Please note, the above windage tray appears to be for a high performance Toyota four cylinder motor (IOW, not for the Prius 1.5l). However, the fact windage trays exist for Toyota means that there are issues with Toyotas and windage.

Link3 (to Priuschat posting where 1/2 quart overfill threw codes and shut down motor): Oil overfill caused complete shutdown | PriusChat

IMHO, having a car that shuts down with a 1/2 quart overfill would make me very wary of overfills. Additionally, my personal experience with other cars is that overfills often cause seals to fail (IOW expensive and time consuming).

Link4 (to YT simulation of windage): https:// youtu.be/ twWBdqXkGdU

Video is a bit of an over simplification but gets the message across (namely, crankshaft counterweights hitting crankcase oil create oil mist and hp loss).