Sudden Drop in MPG and Oil Consumption - for 2 Days?!?!

So I have an interesting situation on my 2017 TRD PRO DC. Truck has 64K, and no recent changes.

Went out to a remote site, towing the SxS, all flat roads, used ECT and drove @65 MPH the whole way, truck ran fine and got about 17 MPG.

Upon leaving, I noticed the MPG suddenly dropped to 12.5 MPG. No changes in truck performance, and things seemed to be fine.

Reset all the Eco fuel consumption and trip records when I got home, and each drive during the next few days ended in the same poor gas mileage, and fuel gauge movement verified.

Seems to run fine, no codes or issues. Made appt with dealer for next week for 65K service, recall on light, and to check truck out.

On way home, got a “Oil level low - add or replace” warning on the dash display. WTF??!! Stopped at a nearby parts store, truck was indeed two quarts low. I did the last oil change 6500 miles ago, filled it correctly, no leaks, truck has never burned oil, (nor has any Toyota truck I’ve owned).

To make it even more mysterious, after I added the two quarts of oil, truck MPG improved to even better than normal.

Would it be possible for a really bad tank of gas make this happen? I typically use one reputable station, but I wonder if there was too much water or something bad with the gas. Reason is because I filled up at Costco prior to getting the warning about oil.

Any thoughts?? Never seen anything like this. Would like your thoughts or opinions before I drop it off at the dealer. I will be changing plugs, and going over the truck thoroughly this weekend.

Thanks!!!

 

See any smoke from the tail pipe?

 

No ideas. But Costco has good quality gas. Has a “Top Tier” rating.

 

I've gotten bad gas at Costco before. From their food court too. Not sure that's your problem though. Oil can only escape the engine so many ways and 2 quarts is a lot. Did you check your timing cover gasket, oil drain plug tight, oil filter canister tight? Are you sure you lost the 2 quarts all at once or over time?

 

PCV valve was stuck open. It would consume oil and get poor mileage. 2 Qts. Would seem like a lot of oil though.

 

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I fill up at Costco all the time and tow a SxS while getting if I'm lucky 12 MPG, so I say it's got more to do with being 2 qts. low on oil.

I'm more curious on how you got 17 MPG lol.

 

When you change your plugs, look at them close. Maybe compare them to the ones in the link below. Which also had an oil issue.

Best of luck to you.

https://www.tacomaworld.com/threads/big-2gr-fks-engine-problem.406251/

 

Agreed that the PCV Valve could be a culprit.

However, how did you determine your MPG? Lots of factors can influence the trip MPG. The only real way to test is doing the math at the pump.

 

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Any oil under the truck?

 

Watch your oil consumption/color, and track your mileage. I would look at it each 100 miles. You might check it in the AM and on the same, flat surface for consistency. I’d pull the plugs and check for oil burn. If they are all dark and oily/carbon coated, you could have a PVC issue or other intake based leak. If you have one or two dark plugs and the rest are tan/clean, you are more likely to have a valve seal or oil ring issue.
Of course, these are only diagnostic indicators which point you in a direction to do some more evaluation. Given the age of the engine, I would think it’s more likely a failed PVC, if you are not losing oil via a leak.
One other possibility is the oil loss is incidental and the mileage is related to some other engine management device. If you have a device starting to go bad, it won’t always throw a code. I have had the happen a number of times with other vehicles. Start by figuring out what happened with the oil. Was it burned, did it leak, or did you misread the level? A low oil condition will not cause a loss in mileage. Too much oil can cause a small loss and result in some being burned or burping out the dipstick tube. Too much oil can result in windage in the crank case which will rob a little power, but not like what you are describing.
Once you have drawn a conclusion on the oil issue you will know if it is related to the loss in mileage if it is being burned in enough quantity to discolor your plugs. If not, you likely have an engine management issue. Mechanical issues like I mentioned earlier, such as a valve seal or collapsed oil control ring are a tertiary consideration since they are less likely. Address the simple first. Don’t pull a head just to find out it’s a PCV.

 

You likely wouldn't, the catalytic converters run so hot any oil burned, the smoke wouldn't be noticed.

 

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