quote:
Originally posted by moribundman:
In a gas engine, will a diesel-rated oil lead to an increase or a decrease in cam lobe and valve lifter wear compared to a friction-modified synthetic that was desigend for gas engines? What about the reduced amount, or lack of, friction modifiers in diesel-rated oil?
Like Doug touched on, cam lobes in a diesel engine are placed under extreme pressures during operation, and having a lubricant that can protect properly is absolutely vital to long life and proper operation.
For instance, just the other day, I witnessed with my own two eyes a late model Volvo day cab with a ISM Cummins come in to the shop...upon teardown, the cams, for lack of a better word, were "flaking" apart..lobes were literally falling to pieces. Exact cause is unknown, but I can easily tell you the owner or maintenace dep. was not taking very good care of the lubrication needs of this engine...entire top end of engine was coated in a black varnish and coated with a high level of soot.
Older engines could get away with lower quality oils and less than ideal mainteance practices, but like I mentioned, modern engines exert such high pressures on cam lobes that a high quality oil with a great barrier/extreme pressure additive package is gonna be required.
With that said, I firmly believe, that based upon intended usage, an HDEO synthetic can protect cam lobes better than a PCEO synthetic oil.
I don't care much for friction-modified oils unless I'm trying to acheive maximum fuel efficiency levels, but I'd much rather have MAXIMUM WEAR PROTECTION than maximum fuel economy...but that's a whole other discussion.
Like I've said, HDEO's are meant to put up with exteme camshaft lobe pressures, and thus the additive package is designed to tackle this challenge, so I'd easily say that an HDEO will offer lower lobe wear levels, but because they aren't heavily GF-3 friction modified like modern passenger car oils of lighter viscosities, you'll be exchanging higher levels of protection for a small, and most likely unnoticable drop in fuel economy.
Sorry if I repeated myself too much...
BTW, I don't know if I can make this more clear:
Only reason for friction modifiers = fuel economy
That's the only reason (IMHO)...
[ February 21, 2004, 01:49 AM: Message edited by: Jelly ]