Should I be using high mileage oil?

I have long wondered about what actually is correct on this question. The members of Bob Is the Oil Guy, who generally know their stuff, say that conditioners don't swell seals, they condition them, making them more flexible, which means switching won't be an issue, and you may even continue to see some lingering positive effects after you switch back to ordinary oil. Second, I've used HM oil, I've used synblends, I've used regular conventional, I've used full synthetic, switching between all of them, and it doesn't change a thing. One thing they say is that the more of a mixture of oils you have, the worse that can be, so you're more likely to burn oil on the first change after a switch, but after that it should be fine. All anecdotal, but in my experience, it doesn't really matter. Use what you like, and switch when you like.

 

It is only a bad idea if the engine didn't NEED it because of oil consumption.

How much oil was it using before you switched ?
How much is it using after ??

With that many miles, it is probably best to stick with it.

 

At 253k miles I wouldn’t bother with synthetic oil it probably eats lot of oil just use 40 weight oil.
That will help with the oil loss.

 

Call me a purist, but I use Toyota brand 5W-30 in my Prius. (Also Toyota brand 0W-20 in my Avalon). I've been told that Toyota oil has more detergents in it, and oddly it seems that more detergents might help keep oil control rings cleaned out, a problem common in modern day Toyota engines.

From what I understand, high mileage oil is supposed to have more zinc dialkyldithiophosphates (ZDDP), but there's also a cap of how much it can have if the oil is rated API SN. Which is why high mileage oil is, or at least used to be (I haven't checked recently) rated as SL oil and not SN oil. Any oil thicker than 10W-30 can also have more ZDDP, so any 40 weight oil may have more ZDDP even if it's rated as SN oil.

Higher amounts of ZDDP in engine oil is usually welcomed in the antique and performance engine crowd. The stuff helps keep metal from galling, which can be critical for old fashoned tappets for an example. But it is also linked to catalyitc converter failure. In other words, running any SL oil or 40 weight oil may kill your catalyitc converter quicker and at the same time doesn't really help prevent any galling with modern day style tappets.

For me, it's much cheaper to just replace the seals and gaskets than it is the catalytic converter. Even if oil burning is a problem, a new set of piston rings, valve guides and PCV valve (it's likely only one of those, not all) it's still cheaper to replace those than to try to fix them with a high ZDDP oil and end up having to change the cat.

 

Been running a high performance oil in my Prius for about 8 years has a big zddp package in it. Engine runs perfect. No problem with cats. Just very high quality synthetic oil.
In fact all my cars run it no cat issues. That's a really old wives tale btw.

And the "old fashioned tappets" you describe that's what the G2 motor uses. It has solid lifters. Why do you think it sounds like that?

Here's pictures of my engine at 150,000 miles.

 

Good to hear you've had good success with that oil. And thanks for the pics.

However, I'm still not convinced that ZDDP doesn't poison catalyitic converters over time. Something causes these to eventually stop working. Until there's a ZDDP/catalytic converter Mythbusters that can prove exactly what causes a catalytic converter to go out I'll play it on the safe side.

Of course another part of the equation is how much oil you are burning. If someone has an oil that has half the ZDDP but burns 10 times as much, he's still running 5 times the amount of the stuff through his cat. It seems to me that there is a correlation between burning oil and burning oil and dying cats. The +200,000 Prius I got has both an oil burning problem and a failing cat. Coincidence?

And yes, I already knew the G2 uses solid lifters. But no, I don't consider them the same as "old fashioned tappets". Just because they are solid doesn't mean they have the wear problems old engines had. The tollerances are much much higher in a modern engine, the materials much stronger and the momentum in the linkage (or lack there of) is much smaller. An old fashioned engine with the tappet, pushrod, rocker arm assembly, and a spring strong enough to overcome the forces of inertia to push that all back and not cause valve float would have close to the equivalent force as that of a 747 ballanced upon a postage stamp as the cam lobe tries to push all that against the forces of momentum at top speed. I'm sure a G2 also experiences a lot of force at the cam lobe as well, but with 21st century materials and machining, not early to mid 20th century.

But at any rate, do we really need more ZDDP? Are lots of G2 owners really having cam lobe failures all the time because they run SN oil? A quick search for "Prius cam lobe failure" didn't get me very many results. None actually.

 

Don't confuse him with facts.
His mind is already made up.

Obviously he knows a lot more than the engineers at the oil companies and car makers who write the specs.
And the EPA engineers who set the limit on zinc.

 

Maybe @edthefox5 has made up his mind. But @Banksy is asking what oil to use.

Simply put: a 2008 Prius is supposed to use 0W-20, 5W-20 or 5W-30 that's "Certified for gasoline engines" with the starburst symbol and says "API SERVICE SN."

Anything else, use at your own risk. High mileage oil may work just fine. It may even help the engine in some areas. But it also may do worse.

Me personally I tend to use whatever the manufacturer recommends. If there is an obvious problem, liked clogged oil control rings, then I'm willing to try something else. But I see no point in fixing what isn't broken. But that's just my opinion

Since I have an oil burning problem and believe it's due to clogged rings my plan is to just use Toyota engine oil for now, but do frequent oil changes, like every 3,000 miles. I may use an oil flush too for each oil change. If that doesn't work I may just pull the pistons and clean out the rings and put them back in if everything else looks ok.

 

Oh christ Sam Spade logged in I'm out.

 

BUT.....it certainly won't hurt anything.
It is made by the same people who make the oil for the brand new shiny engines, which is the situation that the owners manual recommendation addresses.

So, to repeat: One should NOT change oil just because the vehicle has a lot of miles on it.
The "high mileage" oil is designed to minimize excessive oil usage.
IF.....you do not HAVE excessive oil usage, then you should not consider using it.

 

nice, did you open up the cover to replace the gasket?

 

Yes when I changed the plugs I have a little borescope so looked in the wells before pulling the plugs and one
Well had about a 1/2 inch of oil in it.
Very very common to get a leak there with 4 bangers. So yes new gasket time.

 

Yes I run 40 weight

Circulates fine high quality oil.

 

Mobil 1 0W-40 works fine and is recommended in other non CAFE standard countries

 

Technically, yes.

The thicker the oil is the less efficient it is to pump; causing a slight hit in fuel economy.

Which is why more and more engines are being desiged to run thinner and thinner oils in order to meet higher fuel economy standards, including Prii engines.

Personally I don't see any need to run thick oil through an engine, as I think it's more of a bandaid to the problems it "solves".

 

I think higher mileage oil isnt necessary bad or good. One brand of HM oil can have less of the "magic" additives than other brand's non HM oils.
Oils are very complicated science and it depends on too many factors.
When gen 2 engine metallurgy was done it was 20 or more years ago. Ever since then oil became with lower zink and calcium etc but have more moly or just higher base stocks. So running SM oil or High mileage oil isnt bad on it's own. Also gen 2 engines have way less rubber seals to leak from (if its a concern) than lets say dodge charger or audi a6 engines

 

From what I understand the EPA had it planned out that all 2005 and newer vehicles would be built to run on lower zinc oils. If you have a 2005 or newer vehicle they don't want you to use SL or older oils. I think it's safe to say the Gen 2 Prius was built to use SN oil.

High mileage SL oil made sense for a while after 2005 since most of the high mileage vehicles were built long before that year and therefore not built to run on lower amounts of ZDDP and such.

But now we have lots of 2005 and newer vehicles that are high mileage but the EPA really doesn't want people to be putting SL oil or any oil with lots of ZDDP in them.