Toyota oil burn theory

Let's face it. Toyotas are great vehicles, but you often hear of how older models become terrible oil burners. Here's what I've at least heard. (Disclaimer. I know nothing, but sure can google stuff.)

The problem

Let's first talk about the problem. Although there are many ways in which an engine can start to burn oil, most Toyota engines burn oil because of clogged oil control rings. The oil control rings are a mesh of sorts that are supposed to soak up oil as the pistons move down the cylinder (intake and combustion strokes). And as the piston moves up (compression and exhaust strokes) they are supposed to let some oil back onto the cylinder walls. That way the pistons and compression rings always have a thin film of oil to ride on. However the oil control rings will always pick up more oil than they need. For this reason there exist holes and sometimes grooves, called "oil relief holes (or grooves)" that do just that. They relieve the oil control rings of the extra oil and allow it to pass back down into the crank case below the pistons.

But what happens is that over time the oil control rings and oil relief holes (and/or grooves) can get clogged up, not allowing excess oil to flow back down into the crank case. And since it can't go anywhere else, the excess oil now passes up past the compression rings into the combustion chamber where it, well, combusts and hence the Toyota engine is now burning oil.

Of course the severity can differ from case to case. Some engines aren't clogged enough to make much of a difference at low RPM's when oil has more time to seep into the restricted holes, but can become real oil burners at high RPM's when the speed at which the oil needs to flow back is to much for the partially clogged holes. And other engines become completely clogged which causes them to burn oil constantly.

The cause
But what causes the oil control rings and relief holes (and/or grooves) to clog up like that in the first place? Well it seems to be a combination of 4 things, which if you can fix one of them might prevent the whole problem in the first place.

1. Small oil relief holes. Many Toyota engines are designed to use low viscosity oils which would tend to flow back quickly into the engine. Because of this Toyota is careful in not making the oil relief holes (and grooves) too big since that could let too much oil to flow back necessitating a thicker oil to keep the oil control rings properly soaked. But during cold starts, or for those using a thicker oil, the oil doesn't flow back through those small holes enough to wash out the sludge. And as a result, sludge will tend to build up.
2. Infrequent oil changes. As oil wears out it loses its detergent properties that help wash out the sludge and it also ends up containing more contaminates. All this, plus frequent cold starts, cause the oil to leave deposits in places where it doesn't flow much, like in the oil control rings and oil relief holes. Now a lot of people will point out that the owner's manual says that they can go for a whole year or 10,000 miles before changing their oil. What they don't understand is that applies only to people who long haul their vehicle for hundreds of miles a day cruising on the highway, since most of the miles with those kinds of driving conditions are with the engine fully warmed up and the oil flowing properly, washing out sludge as it does so. The year long oil change does not apply to the rest of us that use our cars to go to and from work, school, the store and other places where every dozen miles or so we're shutting the engine off, letting it cool back down to ambient temperature, and then cold starting it all over again.
3. Wrong oil. As mentioned before, messing with the oil thickness can cause it to not flow properly through the oil control rings and oil relief holes and/or grooves. But there's also the possibility of it not containing the right additives. When there's not enough of the right detergents and other additives the oil may not be able to wash away sludge from the oil control rings properly. Now, many people will swear by this oil or that oil as being the best, but the best oil is the oil recommended by Toyota. When asked about the type of oil to use, Toyota's response is,
   Of course the response was in relation to cars that use 0W-20, but the same principle applies to other vehicles that use other grades of oil. The best oil is Toyota oil since it has a specific additive package for Toyota engines. The next runner up for many engines is ILSAC certified oil. Other certifications are also helpful depending on your region. For an example, API oil certified as SN is another example. Now yes, a lot of people will say that using thicker oils, high mileage oils, diesel oils, high zinc oils and the like can help reduce certain engine problems once they start. But just keep in mind that using these oils is a stop gap measure to help extend the time before needing an engine overhaul and they should be considered a last resort only when there is an actual problem.
4. Low tension compression rings. Another part of the problem is the use of low tension compression rings. Toyota is also known for their efficient engines, and part of this efficiency is due to low tension compression rings. The less pressure that pushes the compression rings against the cylinder walls the less friction there is and hence the more efficient the engine is. But low tension rings also don't have as much force to help keep excess oil from passing them. This is also another part of the problem as to why the oil will tend to force its way past the compression rings instead of forcing itself in through the oil control rings and relief holes (and/or grooves).

The solution

1. Change your oil often. If you don't have an oil burning problem yet, the best thing you can do is just change your oil often. Go by the most frequent oil change numbers in your manual. And always do what comes first. For an example if the manual says every 5,000 miles or 6 months, do what comes first. Don't wait all year just because you drive only 5,000 miles a year.
2. Use the right oil and oil filters. Don't cheap out. Don't go by what uncle Dwain thinks. Use only Toyota filters from the dealer or parts.toyota.com (watch out for counterfeit parts on eBay and Amazon) and use the oil recommended in the owner's manual and avoid any oil grade not on your oil cap and any of those "high mileage" or similar oils unless you already have a problem that needs to be bandaided for the present.

But what if you already have an oil burning problem. Well, doing what's said above may help. but may not fix the problem once it's there. Some have had a certain amount of success by taking the spark plugs out and squirting some sort of solvent down on top of the pistons. Of course there are a lot of risks in doing this such as hydro-locking your engine, damaging the cylinder walls or causing a fire.

Others have resorted to using a thicker oil or high detergent oil like a diesel oil. Again, this is to try to reduce the effects of a problem already there and isn't recommended to use as a preventative mesure.

But the best way, although the most expensive, is to have the oil control rings replaced, usually along with another set of pistons and compression rings, and then following through with frequent oil changes using the right oil and filters. Doing so also gives you (or the mechanic) the chance to see how the cylinder walls have held up under the condition of clogged oil control rings as well as a look at how rods and rod bearings are holding up.

I've also heard of people who drill out and enlarge the oil relief holes and grooves. Others put on higher tension compression rings. But these measures really aren't necessary, not to mention they can cause other unwanted side effects (like lower fuel mileage or needing a different oil viscosity than the rest of the engine.)

 

OIl type is for the most part a lot less important than oil change frequency IMO. And yes, I actually was referring to the starburst symbol when I mentioned the API-SN rating. But I'm not so sure the starburst symbol is internationally used since I do believe it's part of the American Petroleum Institute (API). This is why Toyota mentions the ILSAC rating, which is international. Still, it's better to have fresh oil of a slightly different grade or oil rating (sm or sl for an example) and change it regularly than to get something like Genuine Toyota Motor Oil at the recommended grade on the oil cap and wait a year or two between oil changes.

However one thing to keep in mind about those different grades Toyota will at times approve for use in their vehicles are a lot of times ambient temperature dependent. For an example, even in the USA many owner's manuals will usually mention somewhere the possibility of using a lower grade oil in colder climates.

As to the observation that most cars with 150,000 or more miles are oil burners, it's also true that most people nowadays do not change their oil regularly and many don't use the oil recommended by the manufacturer either.

 

I've seen that there have been similar recalls or TSBs for other Toyota cars. I'm not sure what the fix is. On one YouTube video it looks like the new pistons on a Camry had the oil relief grooves removed, which seems counterintuitive since less places for the oil to flow back should, in theory, make matters worse. But maybe it did have higher tension rings that made up for the difference.

I wish there were one of these for the Gen 2 Prius. I'm contemplating doing this to the 2006 Prius I picked up since it's an oil burner.

 

I had a 30-year-old car with over 400,000 miles on the engine that did not burn oil. It used only about half a quart every 5,000 miles at most. It was a 1985 VW Golf non-turbo diesel. The person I sold it to still has it and it still runs the same without any oil burning issues.