1999 Corolla Code P0171.

Some have slowed their oil consumption by going the other way - running a thinner motor oil viscosity. The idea behind that is if the oil control holes are not completely clogged, the thinner oil will be able to flow by and effectively wiped from the cylinder walls.

Some have had really good luck running diesel engine oil - like Delvac or Rotella. Those have a very stout additive package, that is tailored to help with metal on metal contact. The only drawback I see with those oils is their higher levels of phosphorus, which will shorten your catalytic converter lifespan. Usually a non-issue, but since you are consuming oil - you risk poisoning the converter much faster than normal.

Since yours sounds like the catastrophic amount of oil guzzling - if you are set on replacing it soon, just top off the cheapest oil you can find. At this rate, additives may not help you much - time to save as much cash as possible.

Assuming that you've already tried piston soaking and similar methods to try and crack those deposits out of the oil return holes.

Depends on your pain threshold. The 8th gen Corolla is a pretty reliable machine, aside from the EVAP issues that some have and the excessive oil consumption in others. Some have opted to fix the oil consumption by rebuilding the engine - running anywhere from $300-$400 for a re-ring, to as much as $3000 for a new or reman engine swap + warranty.

Could always get luck with a different used car - all depends on what you looking at and what is available in your area. My person record has been pretty decent so far - but I've tried to stick with ones that tend to be less trouble prone to start.

If you want to start with a Toyota - an option is to trade it into a 9th gen Corolla - as pretty much any tools, knowledge, even some parts you picked up on the 8th gen can be directly put onto the 9th gen.

Yup, chain tensioner leak - I don't I've yet seen anyone make it past 100K miles without changing that o-ring / tensioner.

Power steering hose DIY - I think I saw one one TN, possible there is one on here. Never changed one on the Corolla, so I can't really help out.

Plugs aren't too bad. The pic definitely shows oil consumption issue, but not really bad, yet. Plug is still able to self-clean, so that is a plus. Color on ground strap looks good as well - right in the middle where it should be.

Wow Dom, that's incredible amount of life from the o-ring on the tensioner. I'm betting that you removing it in checking valve clearances actually extended its life. When I replaced mine, it wasn't touched in almost 130K miles, the o-ring was visibly distorted when I removed it.

Bad-Dude - be careful when playing around with oil viscosity. Depends heavily on how the oil is being consumed. Thicker oil might slow down the oil consumption, as it naturally resists being burned off, but it has a side effect of clogging those oil drain holes even faster. Quite a few owners on other forums have resorted to running thicker oil to help slow consumption, only to have it suddenly start guzzling oil.

Another option is to try running a thinner oil and break up those deposits around the oil drain holes. Of course, this assumes that the holes are not completely clogged with deposits and that the cylinders are not too scuffed up. Some have gotten really good results with piston soaks to help break up those deposits - some having to run MMO or Kroil to help break those deposits up.

Same with oil additives - anything that is to added to the crankcase is hit or miss. Some have had luck with Lucas and MMO. Some swear by Auto-Rx, to which I actually had to tried out and see for myself ($26/bottle) - results were disappointing, found that it did squat. Engine deposits are too variable in composition - there are some that Auto-Rx will readily dissolve and some that it cannot. It will also swell up certain seals, depending on their composition - which is not unheard of for any solvent, but something to watch for in certain cases. Seems to work best if it stays in constant contact with the surface to be cleaned, but in an engine - much of the lubrication is splashed on components, which doesn't give this solvent much seat time to work.

Something like MMO (~$3-$4 a bottle) IMO, works as well if not better. I'd even use a flush over Auto-Rx - sure it would be very aggressive, but I'd also understand it better.

Italian Tune-up - make sure the car is fully up to temperature and run the nuts off it on the highway. Lots of WOT (wide open throttle applications) can also couple it with some engine braking (ie, put car in 2nd gear, run it up to redline, let off the gas and let it coast down, repeat).

The basic premise is to put the engine under load, preferably under WOT conditions. Really helps blow off any deposits in the engine, running it under heavy engine braking can also help loosen some deposits around the rings.

I agree with dom, for high mileage oils - pretty hard to beat Valvoline Maxlife High Mileage and Castrol GTX High Mileage. They run sales on them from time to time - good idea to stock up when they do.

There are a lot of good articles on TN on piston soaking. For some owners, it completely reversed oil consumption - others it slowed it down considerably. For the unlucky ones that didn't seem to get it to work, nothing short of a engine rebuild will fix oil consumption. Might be worth a shot to do some piston soaking - if are lucky you have a chance to slow this down long enough to get you to a new car.

As for oil consumption starting with the switch to Mobil 1 HM synthetic - probably just coincidence. Lots of the owners reported that their cars were running perfectly, no to little oil consumption - then almost in an instant they found themselves 2 quarts down on oil.