Burning a lot of oil. Need tips to reduce!

Whether or not you can do it yourself depends on what the cause of the problem is. If I take into account the fact that you say you can't find any oil leaks and that the oil is being burned off, the most likely problem is that you have broken piston rings and/or ringlands. This will allow oil to seep into the combustion chamber from the crank case. It will then be burned along with the air/fuel mixture.

If that's the case, it would require the engine being taken out and stripped to get at the pistons. It's not something you'd want to do yourself if you can help it.

Something you can do yourself to verify whether or not oil is being burned off is to inspect the condition of the catalytic converter. Though being a 13 year old car, the catalytic converter would be pretty black and sooty even in a car that does not burn oil.

All of first cheked its compression reading. If its abnormal . Get engine overhauled.

This is kind of a long shot, but I have seen it (on old Chevy 6's), and it's a lot easier than a ring job.

There are drains in the heads, to allow oil to return to the base. These drains can plug with sludge. This can 'flood' the top of the head, leading to leakage through the not-so-great valve cover gasket or down the not-so-tight-anymore valve seals.

To check, just remove the valve cover and assess. If there's a lot of sludge, you could try scooping it out.

This sounds like your head gasket might be blown. The amount of oil being consumed is remarkably high. There are far older cars that consume less, so I doubt it's the piston rings, unless there has been some trauma to damage them.

It seems like the oil is being burned, since you aren't finding any, but check your exhaust. The amount of oil being burned might cause a bluish tinge to your exhaust. It would also cause a distinctive oily smell (think weed whacker exhaust). Both would indicate the oil is being burned off in the engine.

Also check your coolant though, since it's possible for oil to enter the coolant system if seals (such as a head gasket) are broken. This would likely go two ways. I doubt this is likely, since eventually the coolant system would flood with oil if this were the case. Either way, if you see oil in your coolant, there's likely a problem with the internal seals, and could be a sign of a larger problem.

Nobody has mentioned advice specific to this car. Certain Toyotas manufactured in the early 2000s had a problem with piston rings, which caused excessive oil consumption. Chances are your problem is the same. So, the engine probably needs to be taken apart to remedy this issue. Whether it makes sense for such an old car is a good question. For such an old car, there is little chance of getting it paid by the warranty. I would just continue pouring oil to the engine while at the same time making a decision which car to purchase next. Newer Toyotas do not have this oil burning issue, so I wouldn't use this as a reason to choose another brand of car.

I inherited my Dads 2002 highlander with 3.0 v6, It was using about a litre of oil every 500k, the odometer had 260000k on it, after a bit of research someone mentioned the use of Seafoam oil additive. I thought what can it hurt?? I added the recommended amount to the oil and continued driving it adding oil as needed. Well the consumption decreased so I then changed the oil to a 15w40. I have since clocked over 6000k, 3500k of that towing a small holiday trailer to the west coast through the mountains and back. I check the dipstick today... down maybe 1/2 a litre. I believe the issue was gummed up piston rings and the Seafoam additive managed to loosen them up. So to sum up, $12 can of the additive fixed this car.