Is the top mark really "too full" on the oil dipstick?

Nothing will swell the Teflon or Viton seals that most OEMs switched to like two decades ago. The superior material properties of these seal types is why they last so long. Therefore, switching "back" to regular oil will have no effect.

However, HEAVIER oil is typically sold to consumers as well as the high mileage part, so in that case, switching back to the OEM recommended weight of oil will cause consumption to return to the prior levels. Increasing oil weight (viscosity) has some serious potential long-terms side effects, but on the whole less damaging than running OUT of oil.

 

Looks like neither of those common issues is causing your concern. Was it ever overheated?

 

That statement seems contrary to the laws of physics.

Volumetric or Cubical Expansion Coefficients of Liquids

 

OK Mr. "not accurate".
How about you back up that claim with some actual facts ??
I have SEEN high mileage oil make a significant change in oil "usage" but can't really say how long that change lasted 'cause it wasn't my car.

I think you are blowing smoke.

 

I think I said that already.

 

You should know that cannot be done, because there are no peer-reviewed test, or "A-B-A" test that validates a SINGLE CLAIM made by these companies.

 

I think the point was that it's not going to make a visible difference. The volumetric rate of expansion for something like engine oil is WAY too small to see with an open container as large as an oil pan, even with huge temperature variations between two samples.

 

I know no such thing.
And suspect that you don't either because I doubt that you have spent the hundreds of hours of research time it would take to validate a claim like THAT either.
More smoke.

And for others following this part of the discussion................do a Google search for "high mileage oil" and decide for yourself. Consider that most of the matches of the first page or two are from oil companies, which might have some bias.

 

BINGO.
Or to put it another way, the expansion is so small that it won't be detectable on something as crude as a dipstick.
Expansion when hot is NOT the reason they recommend checking the oil level when hot.

 

Yeah I've never noticed appreciable difference in level, hot vs cold. Maybe it contracts slightly, but that balances out by more oil trickling back down? Who knows... Anyway and anyhow: level doesn't change.

 

It is recommended to check transmission fluid when it's hot not engine oil.

 

OK maybe with these cars.......but that is not universally true.

With some engines, it is important for the oil to be "flowing" right before the check.

 

For the record here, not trying to participate in, much less start a war. I have no agenda other than for casual users who rely on UBBs like PC for ACCURATE information about their vehicles to get it. I have no interest in anyone else's beliefs or not in marketing hype, it's a free country, spend your dollars on whatever makes you happy.

Toyota DOES instruct that the oil in the 1NZ be checked HOT. We all know what can happen if they are overfilled Since the transaxles on these cars do not even get to "normal" operating temps for a typical AT, the fluid volume is about 25% of that in a typical AT and there is no real leak path except for the axle seals, hot, warm, or cold seems mostly mute. They are also nearly impossible to check from under the hood, contrary to most vehicles on the road with dipsticks for the ATF level, although that too is changing

The volumetric change of neat "oil" is somewhere near 0.1% per 10*F, additives can play a huge role here.

 

With the 2G Prius, the difference between the two dipstick dimples represents 1.6 US quarts.

I hope you will endeavor to keep the oil level at the top dimple, and carry around a quart of oil and funnel with you since it is clear that the engine is rapidly consuming oil.

It is not easy to find the PCV valve which is hiding under the wiring harness running over the valve cover. It wouldn't hurt to replace the valve but that probably will not help the large oil consumption rate.

 

Trying to get back to the specifics of the OP.
Sounds to me like it was under filled at the dealership.

My opinion?
I've read lots of commentary that overfilling on a newer vehicle is actually potentially damaging. And yes, when most people, myself included have oil changes at a dealership, the problem isn't under filling it's most often the oil being over filled.

Again my personal opinion, but when I check my oil...Prius OR my vehicle today, I'm happy with any mark 3/4ths or BELOW the top fill mark.
If I'm showing less than 3/4ths or approaching the 1/2 way mark, while I don't panic or think any damage is done, I do add.

The battle I've had to fight with my Prius and now my Honda Fit, has been to have dealerships NOT overfill. I can say from experience most will overfill and then try to convince you THAT is not a problem. I actually think it would be refreshing to NOT have my oil overfilled. I would however expect that immediately after an oil change, that it is reading more than 1/2 filled.

On an older or higher mileage vehicle, just checking the oil level more frequently is wise. On a 2009 with 167K, I would at least check it every week.
And then I'd monitor the loss...and try to keep the level at the before mentioned marks.

 

Checking it 12 hours later is the correct true pan level of oil and the best way to get an exact base line on oil consumption. Every drop of oil that can drain back has.
An inch on the dipstick is about a quart and a half I THINK...I have never lost that much oil.

But a quart and a half is actually more than 40% of its total oil. Not good.

What that tells me is the car has seen a big oil loss somewhere in its life low enough the pump went dry and it logged a engine check light. That damages the oil control rings on the pistons and lets oil blow by.
But like Pat says keep throwing oil in it and listen for a bottom end rattle or knock.

 

At that rate on the dipstick your driving around with 30% oil loss. The top dimple is there for a reason. If the engine did not use splash lubrication I guess it wouldn't matter but it does and it does. It requires the oil to be at a specific level to get a specific splash amount.
Its a tiny little motor and requires every drop of oil it can get.

This is not rocket science.

 

What "Rate" are you talking about?
I'm saying keep it at the 3/4ths mark or higher but NOT above. I'm also saying monitor the oil level.

I do NOT feel it necessary to keep the oil exactly at the top mark. First of all? It's pretty difficult to do. Secondly, IMO there is a reason there is a low mark, and a high mark. I think you CAN be between those two marks and be perfectly fine.
If the engine required the oil to be perfectly at the filled level all the time? Why even have low dimple on the stick.

WIth any age, or mileage most peoples vehicles start burning or losing a certain amount of oil.
I feel if you keep your oil filled to the 3/4ths mark...or higher...you are fine.

In my (admittedly Honda Fit Owners manual) it says about checking the oil:

" ..check the oil level, it should be BETWEEN the upper and lower marks. Add Oil if Neccesary".

BETWEEN The upper and lower marks....

Yeah..it's not rocket science.

 

Hey,

If the difference between the two dots is 1.6 qts. and I measure my oil exactly in the middle between these dots (shortly after a drive), how much should I add to fill near the top dot?

(Prior to my last oil change, I think my Prius has been consuming a lot of oil.)

Thanks,
TTY04

 

A little less than 1.6/2 qts?