Oil weight

if your trips are mostly short IE: under 5 miles I'd recommend the 5-30 if you on the freeway for 20 miles to work I'd use it this summer and then the next time you buy more get the 5-30. You might want to monitor your mileage before you change it. If you get a drop then I'd just dump it and put in 5-30, but it's your call. Toyota recommends 5-30 as part of the emission cycle test.

 

I know from experience the heavier oil will reduce your Prius' mileage, no matter how you drive.

I run 5-30 up here in AK and have no issues. In fact, I switched to a 5-30 Mobil 1 synthetic at 5200 miles and my Prius hasn't used a drop! Still exactly on the full mark, and REALLY clean!

 

If it makes you feel any better, 5W-30 and 10W-30 have the same viscosity when warm. The first designation is for cold viscosity and the second for hot.

The old time oils only had one designation, like SAE 30. I agree with the guy at the parts store, in a warm climate the two oils aren't much different.

 

First of all, the Mobil 1 xW-30 oils are considered "thin" 30 weight oils. Most xW-30 oils will test at 11-13 cSt at 100 C. The Mobil 1 xW-30 oils will test in the 9.x cSt at 100 C.

Given your climate, there will be little to no difference in fuel economy. You might as well use up the 10W-30, then use 5W-30 Mobil 1 from that point on. Do *not* change it any sooner than 6 months or 5,000 miles! If you've read the used oil analysis I've posted, Mobil 1 has plenty of life left at that point.

On the flip side, a lighter oil will make a big difference in a cold climate. I'm still running a trial of Mobil 1 0W-20, and in a month or so will change it and do the used oil analysis. Comparing the 0W-20 to the dealer 5W-30 from last winter, my fuel economy is averaging around +5 MPG.

The average temps are -20 C and colder.

 

I wouldn't recommend anybody make drastic changes to the recommended viscosity unless they are at least willing to perform used oil analysis

 

That sounds reasonable, assuming you perform used oil analysis.

 

I have run Mobil 1 in Prius for as long as 13k miles, and the total base number was getting very low. It would be of interest to know of a suitable oil with better TBN, so as Jayman says, may we see a used oil analysis?

 

For oil analysis, you contact a lab such as

http://www.blackstone-labs.com/

They send you a small bottle. You sample warm engine oil and send it back. They send you the results with impurities found, viscosity, and total base number (if you pay extra for that). They tell you if the results indicate any problems with your engine. Blackstone for example charges $20, or $30 incl. TBN.

Synthetic oil is more resistant to thermal breakdown than conventional, so engines with it will not develop "varnish" deposits on the non-contact surfaces. It offers other advantages; some are certain and others somewhat controversial. They have been disussed at some length here in the past.

Any oil will accumulate impurities over time, its capacity (TBN) to neutralize combustion acids will get used up, and its viscosity may increase. At some point it will no longer adequately protect the engine.

Any oil that meets Toyota's specifications and changed (with filter) at their specified intervals, will probably never contribute to an engine problem. Some people (such as myself) prefer synthetic oil, and use oil analysis as a guide to appropriate extended oil change intervals.

 

What he said

 

I have heard that before too, but apparently Mobil reformulated their oil.

From their website for Mobil 1:
0W-30 oil is 10.3 cst at 100 C
5W-30 oil is 11.3 cSt at 100 C
10W-30 oil is 10.0 cSt at 100 C

(Note: Toyota recommends 5W-30 oil, although 10W-30 oil can be used if 5W-30 oil isn't available. I believe Honda says 10W-30 oil can only be used when the temperature will always be above 60 F.)

From their website for Mobil 1 Extended Performance;
5W-30 oil is 10.25 cSt at 100 C

 

The test range is almost a dead-heat as far as results go. The spec usually calls for a range of 9.3-12.5 cSt @ 100 C for xW-30 oils, with a high temp high shear spec of 2.9 cP @ 150 C.

In a modern motor with automated assembly and tight clearances, a lower viscosity oil will reduce friction and extend life. All those Ford's and Honda's out there running 5W-20 appear to prove that.

 

jayman,

Thank you for your continued analysis and observations. I will continue to monitor this thread for your 0W-20 oil analysis results you said would be available around the end of March from your Feb. 27th comment. You folks are providing a valuable service by sharing all this info to us newbies!!
Thanks again!

joe

 

I definitely agree that the automakers went with 5W-20 in an effort to reduce friction and therefore improve their average mpg that ever so slight bit.

But I am not sure that I would agree that it would extend the life of the engine. It would be my belief that under high heat the 5W-20 oil would therefore at least possibly be "too thin" and allow slightly greater wear. Otherwise why would Toyota call for 5W-30 if they could have done that little bit better with 5W-20?

 

Again, the field experience of Honda and Ford disproves that. When you compare a stable 0W-20 to an organic 5W-30 subject to shear, the mystery 5W-30 may be "thinner" at 150 C and high shear rate than Mobil 1 0W-20.

Usually, the minimum safe boundary viscosity at 150 C is around 2.5 cP, at a high shear rate of 10^6 shears/s. Mobil 1 0W-20 has tested at around 2.7-2.8 cP at 150 C. Mobil 1 0W-30 will usually test at around 2.9-3.3 cP at 150 C.

So the Mobil 1 0W-20 may be considered "borderline" at a very high operating temp under heavy use. As long as it's stable, does it matter? How about a cheap 5W-30 that under high shear tests at 2.0 cP?

The used oil analysis is a good indicator. Sometime towards the end of this month I should have enough miles for an oil change, and I'll send off a sample. I did an early sample at 4,000km and the wear metals were negligible.

Don't be surprised if Toyota starts calling for an xW-20 in their new cars/trucks. Ford not only made the change suddenly, they made it retroactive to older motors too. Mazda is part of Ford and they now require a 5W-20 in most of their motors.

Even DC now calls for 5W-20 in some of their new motors.

When you think about it, there is nothing different or unusual about motors comparing Honda to Toyota. The metals used are similar, including all aluminum blocks, and the clearances are similar.