I change my oil every 3K miles so oil breakdown is less of a factor. Frequent oil/filter changes in my opinion are very cheap engine insurance.
J

 

and...cheaper than synthetic, if you follow Toyotas required change interval, to keep warranty in force

IMHO

 

I've been corresponding with Woods Bros. Racing, an Amsoil synthetic oil distributor. (Search for Amsoil thread on this site for more info.) Here is a quote from an email by Travis Woods, in reply to my question about Amsoil's 0W-30 vs. any 0W20 oil:

"As for the 0W-20 and all other 20-weight oils, I personally feel that they are too light, especially in severe duty and hot climates. More and more new cars are coming with these lighter oils, and I am pretty sure the sole purpose is to increase gas mileage and/or comply with emissions regulations. The downfall to this is that the new engines will likely wear out significantly sooner due to bearing wear and cylinder wear. The automakers did the same thing several years back with manual transmissions when they switched them from using gear oil to automatic transmission fluid. The result was more bearing failures at lower mileage (90,000-140,000 miles)."

 

My understanding is that some of the newer engines have tighter tolerances that also make using the thinner oil a requirmenet so that it can get everywhere it needs to get. And while I respect their opinion, I know that there are plenty of these cars on the road going 100k + miles. I think for average driving 0W20 or 5W20 is not going to casue significant wear. The truth is that the initial start up is what casues the most wear and 0W20 gets the key components protected faster and better. With the frequent starts and stop of the ICE in the TCH I would want oil that gets moving everywhere as soon as possible. And wither way since it has been a long time since I kept any car anywhere near 100K for me the point is irrelevant. I would be fine with convential oil, but choose synthetic becasue especially on 4 cylinders I swear I feel a difference on inital cold performance.

 

The Prius and TCH ICE engine startup is a very gradual process compared to a "conventional" ICE start.
The MG1 turns the engine through several revolutions before an injector is even fired and then only 2 injectors and then 4.
With the amount of time the TCH's ICE is off, the wear and tear due to engine starts is more than offset by the ICE offtime.
J

 

True, but getting oil there faster and keeping a better lubricated surface is still better. I was sold on Synthetic with my ex-wife's 91 Celica, I have a steep driveway and on cold morning starts the engine was real rough climbing the hill, after synthetic you could feel how much smoother it was and seemed to strain less pulling up the extremely steep hill.

 

I got turned off to synthetics when the valve guides in my Tercel wore to a point it was burning a quart of Mobil 1 per thousand miles after only 40k miles on the car and I was changing the oil every 3k miles even with Mobil 1 at that time. Started with Mobil 1 on that car at 5k miles.
I am sure things have improved but no thanks. I'll stick with the manufacturers recommendations going forward.
J

 

I'm not sure that you can blame that on Synthetics, as long as you use the weight oil the mfg recommends.

 

There was something wrong with that car which had nothing to do with the type of oil you were using......

 

Actually I can blame it on the Synthetic. This was quite a few years ago and Mobil 1 deteriorated the valve guide seals which lead to the failure. With under 50k miles toyota wanted several thousand dollars to repair the engine.
I traded the car in on a Hyundai. An even bigger mistake than using Mobil 1.