TwinTurbo
…blowby is increased during idle…
Why?
MNH, you are not considering how taxis are driven. Lots of short trips. Lots of stop and go traffic. Lots of idling. Lead foot drivers. That is tougher on the engine than your typical driver. So I'd say that is equivalent to your 150K.
No it isn’t. Most engine wear occurs during cold engine startup…which taxis don’t do a lot. ANY person who drives in a city environment has short trips, lots of idling…Because they do have cold startups…they are much worse on engines.
“The point is you’re trying to make it sound like this great useful test”
The point is you’re trying to claim I said things I simply did not.
First you erroneously assume the CR test was based on one oil change.
I then simply provided some data showing the test was based on more than one oil change.
You then make the ridiculous interpretation that I said they drove one car 4 million miles when I stated clearly they used 75 vehicles.
Now you reveal your lack of understanding of tests and measurements.
A careful measurement of wear at 60K miles etc. is not a pass/fail test.
CR was looking for DIFFERENCES in wear caused by different oils.
If engine A shows more wear at 60K than engine B it’s reasonable to predict that engine A will reach its wear limits at a lower mileage than engine B; that mileage might be 150K or whatever.
[sigh]
Compression rings are designed to use the combustion forces to press the rings against the cylinder walls. They do not rely simply on their spring tension. Since combustion forces are far lower at idle, it makes sense that blowby would be higher. In addition, the temperatures the compression rings are exposed to at idle are lower, and while I’ve never seen any data to the effect, I could accept that the thermal expansion of the rings would be lower at idle, and the rings expand by closing up their gaps. In short, I agree with TT’s statement that blowby is higher at idle.
But I agree with TT that in modern engines it’s no longer a significant consideration. Engines are made far tighter than they used to be, and modern fuel metering is nowhere near as “dirty” as it used to be. Unburned excess fuel in idling carbureted engines washing the cylinder walls down used to be a consideration, but it no longer is.
First off this whole discussion is about 10k oil change interval. Then you interject this test which has NOTHING to do with 10k oil change intervals.
You then make the ridiculous interpretation that I said they drove one car 4 million miles when I stated clearly they used 75 vehicles.
I was just clarifying your statement. If it was so obvious then why didn’t you say 60k miles. Could it be because it doesn’t sound as impressive as 4 million.
Now you reveal your lack of understanding of tests and measurements. A careful measurement of wear at 60K miles etc. is not a pass/fail test.
Did you read their results…they couldn’t find any difference in oils…again…not relevant to the 10k oil change discussion. They then concluded that they didn’t need to run the tests any longer…which I find very disturbing. OH well…CR has testing at it again.
Which goes back to my point in my previous post, which everyone but @MikeInNH seems to have missed: cabs don’t have many cold starts, they run all the time. So in spite of idling and other things, the test was really easy on the oil, so all the oil looked great. If there had been something more like normal use, differences might have shown up.
@melott. You will find that, regardless of what the manufacturers says, taxi operation is not really that hard on oil, compared to frequent cold starts and short trips. Most cab operators go nearly twice the oil change interval and still easily get 300,000-400,000 miles out of an engine.
I once rode in a Cadillac limo with 650,000 mile son it and the original engine without any overhauls.
@Docnick guess what: that is what I was saying.