It would change the oil AT LEAST once a year, regardless of miles. I change my wife's oil (in the truck, smart azzes ) every 6 months, as she puts very few miles on it, and she mostly drives it three blocks to work every day and I doubt it gets barely warm. I take it out every now & then & get up to operating temp. And I do use Syn. Usually Valvoline.

 

Typically, I don't drive the truck on short drives. Usually if I drive it, I try to do at least 15-20 miles of driving at highway speeds. It may sit for 3 or 4 weeks at a time though.

 

Then I'd do once a year....

 

With the extra cost of synthetic, I'll probably just stick with dino unless I start driving the truck more. I've owned it for about 6 years and have put about 40,000 miles on it. I'm the second owner and the truck has had a pretty easy life with me other than towing a 5'er occasionally. The original owner owned it for 22 months and put 97K on it and then I bought it used when he traded it for an '03.

 

Don't say that too quick there!LOL! My wife, who gives me a dirty look when I hit the pedal hard on her X, comes home and tells me stories about smoking some dodge from the light. Then I take our 4 year old daughter to the store, at stop light she says "you need to beat that car daddy". All I can say is our X has made a speed demon out of my wife. She comes home and says she can't imagine driving anything else.

 

Well... the Ex is bone BONE stock, and the truck has a little something in the PCM (still unidentified as to exactly what it is), so my truck has better "go get 'em" than the Ex does. That being said, my wife actually has taken rather well to the truck and I know for sure she won't be quite as satisfied with teh Ex, but I'm not going to do any more tahn put my little PCM "upper" into hers... I'LL be the one getting the DP, TW, or PHP addon.

 

I'm running dino Delo (which I have, on-and-off, for the last 45 years), and my OCI is currently at 18,000 miles. This is based on the viscosity index dropping just into the range for 30-weight at that point.

During those miles, I add about five quarts of oil. Some is lost due to burning, but most is due to three bypass filters getting changed and needing refilling. That has the added benefit of allowing my additives package to not deplete beyond limits.

I'm not sure I save any money by running my oil out that far, because I spend it in lab reports and additional oil. However, I'm FAR ahead, knowledge-wise, of those that just routinely change it at a significantly-lower mileage interval, relying on "trust" alone.

Pop

 

THREE? When did you go the three units, Marv? I thought you only had a double bypass arrangement... ???

 

Wow!! That's some seriously A-R oil changing!! I like it.

 

I wasn't very clear about this.

I only have a single bypass filter system. In the course of 18000 miles, that single filter gets changed every 5000 miles. So that's actually four filters in 18K. At zero miles, at 5K, 10K, and 15K. The last filter only works for 3000 miles, then everything's new again.

I've done it the other way around, too, samples every 5000, and filters every 6000. That's less filters, and more samples. Filters are cheaper, so....

I don't think I've compromised my information much in doing so.

Pop

 

OK... I'm with you now Marv. Thanks for clearing that up. My next question was going to be along the lines of "Where in the world did you mount so many filters?"

I think you probably explained it quite well the first time, but I was probably too hasty in not thinking though what you said carefully enough before asking my question. I guess if I had thought about what you said more carefully, I would have probaly concluded what you just explained.

 

For my C7 the "normal" oil consumption is specified in terms of the fuel consumed not the miles driven. For example at 60 MPH while towing I average about 8 MPG which means my GPH=(MPH)/(MPG)=(60)/(8)=7.5 gal/hr and I change oil every 6,000 miles which is every 750 gal of fuel and that's almost twice as often as CAT recommends!

Considering that my C7 crankcase holds 28 qts I'm still changing 14 qts every 3,000 miles about like I did with my F350! With my F350 I was never down more than a qt at the 3K change interval and with my C7 I'm adding up to 2 qts before changing at 6K!

For my F350 I consumed 5.5 gal/hr while towing my smaller 5er at 60 MPH and that works out to about 275 gal of fuel per 1 qt of oil and for my C7 it's 750 gal of fuel per 2 qts of oil which is 375 gal of fuel per 1 qt of oil.

Since 750 gal of fuel costs about $1,700 and I can get 7 gal of oil and an oil filter for about $55 which is about 3% of the fuel cost I figure changing the oil and filter every 750 gal of fuel adds an extra 3% to my operating costs and I think that's a sound strategy for maintaining my C7 in top condition!

Some day I'll do a comprehensive post on the differences between my 7.2L C7 and my old 7.3L PSD but for this comparison lets assume that oil consumption is primarily caused by oil going past the rings and valve guides. Considering that my C7 has 18 valve guides versus only 16 valve guides for a 7.3L PSD the C7 might consume a tad more oil through its valve guides.

Comparing the total "swept surface area" where the rings contact the cylinder walls is a more difficult calculation which involves the Bore and Stroke of each engine. In general the total RCA=Ring Contact Area in^2 with the cylinder walls is given by RCA={(Pi)(Bore)(Stroke)(Nc)} in^2 where Nc=Number of Cylinders.

My C7 has a Bore=4.33", a Stroke=5.0", and Nc=6 and this gives RCA={(Pi)(Bore)(Stroke)(Nc)}={(3.142)(4.33)(5.0)(6 )}=408.15 in^2. A 7.3L PSD has a Bore=4.11", a Stroke=4.18", and Nc=8 and this gives RCA={(Pi)(Bore)(Stroke)(Nc)}={(3.142)(4.11)(4.18)( 8)}=431.83 in^2. So the 7.3L PSD has {(431.83 )/(408.15)}=1.058 or a 5.8% larger RCA and that predicts a 5.8% higher oil consumption!

Well I'm sure there's many other factors that determine oil consumption and I'd like to hear some opinions as to what they are?

 

Three things I'd add would be operating temp, sticking rings (as a factor of poor maintenance), engine programming, and air intake system. The reason I say engine programming and air intake is that some combinations of tuning combined with the AIS intake will cause the restriction indicator to trip. Although a temporary condition for too much restriction, I would argue if you are always tripping the indicator, you are applying excess vaccum to the crankcase ventilator. The 'doghouse' oil vent on the valve cover didn't appear to have a check valve so the vapors are under higher vacuum increasing consumption when the filter is dirty or restricted. An engine running too cold will use a lot of oil as well, however we are talking really cold, not just a couple degrees...

As for the oil addition, I just added a quart after 3,000 miles.