Hours vs. Mileage OCI

[oiltard]

It seems that a lot of automotive manufacturers have abandoned the use of straight mileage as a determinant of oil life. Many (most?) newer cars come with oil life monitors that take other factors into account.

I have no way of running a complex algorithm to factor in engine tembperature or to count total engine revolutions, but what I can do is determine OCI based on total engine hours, like someone would for a piece of farm equipment.

I have an Ultragauge set up which counts this automatically, all I have to do is choose to display it. The way I figure it, the engine doesn't care if I'm cruising at 40 mph in 3rd or 55mph in 4th, but the odometer does.

So what would be the time equivalents of the old 3,000 miles OCI vs. a modern 7,500 or 10,000 OCI? What range is safe and reasonable to run an oil? And for someone who drives his car very mildly, is there a major flaw in the thought process that I might be overlooking?

 

[Artem]

Modern OLM systems take engine operating conditions into consideration when calculating oil life. Of course someone who drives gently, maximizing MPGs will get longer oil life vs someone who drives aggressively, idles a lot in traffic, in the exact same car.

Time that the oil was in use for also matters. Racking up 10k in 5 months vs taking a year of use to do the same.

 

[Burt]

Figure if you drive all highway miles, average 60 mph and change at 10,000 miles, that's 167 hours.

 

[tig1]

Since trying to keep track of time is not practicle(after all it's just a car)10K mile OCIs has worked well for me for decades.

 

[Corvette Owner]

You can't set up a OLM for a car engine using just engine hours. These are often used on Marine engines, but Marine engines are usually under significant load for most of their use, unlike car engines. I believe some farm tractors also use engine hours, but again they are usually under high load.

The car engine does care if it is doing city driving verses highway driving. In city driving, you have significant acceleration from lights (higher rpms per mile) and significant idle time (little load, but not good for engine). Using total rpms (with other factors) is the way to go.

If your car does not have an OLM, then using mileage and UOAs is the way to go. Car warranties are largely based on mileage oil changes. As long as your driving style doesn't dramatically change, this is the way to go. Companies have built up a large data base centered around mileage. Also, look at the factors in the Owner's Manual to determine if your driving is Severe or Normal, as they usually have different oil change intervals.

 

[oiltard]

Originally Posted By: tig1
Since trying to keep track of time is not practicle(after all it's just a car)10K mile OCIs has worked well for me for decades.


It's super simple with my Ultragauge. I just watch the little screen that shows how long the engine's been running since it was last re-set. And re-set it when I change the oil.

Auto manufacturers went to OLM's because simply using mileage is a very poor indicator of how much the oil's useful life has been diminished. Hours is poor also, but I think less poor, precisely because stop & go driving is worse on the car than cruising at 55.

If I cruise at 60 for an hour (to make the numbers simple) vs. sitting in stop and go traffic for an hour and only going 10 miles, the mileage formula treats the latter as being 1/6th as much a factor in oil life usage, whereas the time formula at least treats them equally.

A perfect world (or OLM) would probably count the latter situation as more severe and adjust the remaining oil life accordingly. My point is that I'd be better served using the very simple hours figure, which counts them equally than the very simple mileage figure, which treats the former as reducing the oil life to a 6x greater degree. The example of idling vs. highway miles would represent a more extreme disparity still.

167 hours = 10 k easy miles is a good starting point for the discussion. Anybody think 150 hours on my next OCI with quality synthetic in a car that's relatively easy on oil is safe, regardless of mileage? (time won't be a factor, I'll do that in
Thanks.

 

[Corvette Owner]

Originally Posted By: oiltard
Anybody think 150 hours on my next OCI with quality synthetic in a car that's relatively easy on oil is safe, regardless of mileage? (time won't be a factor, I'll do that in
Thanks.


My Corvette has both gas mileage and average speed memory readings which I reset every gas fillup. My average speed is usually about 33 mph (remember idling at 0 mph severely reduces average speed) . Using this would yield 4950 miles for your oil change, I think that is low for even severe service using synthetic oil ! But to answer your question, I think it is surely safe!

 

[volk06]

My f150 has a hour meter I reset each oci. Right now at 4400 miles I'm at 110 hours.

 

[DrDusty86]

For reference, my Escort has 6212 hours on it and average speed about 43mph. I change the oil at 5500-6,000 miles regardless of hours. Runs fine with zero consumption of RP.
Dusty

 

[oiltard]

Originally Posted By: Corvette Owner
Originally Posted By: oiltard
Anybody think 150 hours on my next OCI with quality synthetic in a car that's relatively easy on oil is safe, regardless of mileage? (time won't be a factor, I'll do that in
Thanks.


My Corvette has both gas mileage and average speed memory readings which I reset every gas fillup. My average speed is usually about 33 mph (remember idling at 0 mph severely reduces average speed) . Using this would yield 4950 miles for your oil change, I think that is low for even severe service using synthetic oil ! But to answer your question, I think it is surely safe!


Yeah, sounds like it may be a bit too safe and a waste of good oil. If 167 hours represents 0 idling, 0 acceleration and deceleration for 10 k miles (an impossibility), and your average of 33 mph is more normal (~300 hours for 10 k miles), I'm thinking 225 hours is a more conservative starting point. Next OCI will start there, I'll run some UOA's and see where I end up.

Thanks.

 

[zorobabel]

The best way would be to change oil at a certain number of gallons of gas used. This way you account for idling, cold starts, hard driving, freeway cruising... all factors basically, except time. I'm switching to this method.

 

[yesthatsteve]

Originally Posted By: oiltard
Originally Posted By: Corvette Owner
Originally Posted By: oiltard
Anybody think 150 hours on my next OCI with quality synthetic in a car that's relatively easy on oil is safe, regardless of mileage? (time won't be a factor, I'll do that in
Thanks.


My Corvette has both gas mileage and average speed memory readings which I reset every gas fillup. My average speed is usually about 33 mph (remember idling at 0 mph severely reduces average speed) . Using this would yield 4950 miles for your oil change, I think that is low for even severe service using synthetic oil ! But to answer your question, I think it is surely safe!


Yeah, sounds like it may be a bit too safe and a waste of good oil. If 167 hours represents 0 idling, 0 acceleration and deceleration for 10 k miles (an impossibility), and your average of 33 mph is more normal (~300 hours for 10 k miles), I'm thinking 225 hours is a more conservative starting point. Next OCI will start there, I'll run some UOA's and see where I end up.

Thanks.


225 is probably a good starting point for a quality syn. 15,000 purely highway miles at an average speed of 60 is 250 hours, and pretty much any name-brand syn would do that and more in a well-maintained engine that's easy on oil.

I do about half of my miles on outer suburban roads with light traffic, speed limits between 45 and 60, and few traffic lights. The rest is pretty evenly split between interstate, regular suburban driving, and short trips, with about an hour of idling at the kids' schools each week.

My Ultragauge shows my average speed at 33.5 mph, about where I thought it would be. At 225 hours, that puts me about 7500 on an OCI, which is probably about right. Based on this discussion, I probably won't run a synthetic past 250 hrs/8500 miles in my application. I probably wouldn't take a dino past 180 hrs/6000 miles, either.

 

[vortex9]

Originally Posted By: zorobabel
The best way would be to change oil at a certain number of gallons of gas used. This way you account for idling, cold starts, hard driving, freeway cruising... all factors basically, except time. I'm switching to this method.



+1 (easy when you keep a log book)

 

[oiltard]

Originally Posted By: zorobabel
The best way would be to change oil at a certain number of gallons of gas used. This way you account for idling, cold starts, hard driving, freeway cruising... all factors basically, except time. I'm switching to this method.


Hey, I like it. Going to think this through and try to determine how best to memorialize gallons burnt. I know I could keep mileage and mpg in the Ultragauge and then do the math myself, but there may be an even easier way.

Thanks for the great idea!

 

[oiltard]

The more I think about gas usage as the best single factor "OLM" I can use to determine my own OCI's, the more I like it. And the better sense it makes.

If I drive my car like heck, take short trips, and sit in traffic in the winter, I get abour 30 mpg. So 200 gallons = 6,000 miles. That's severe use. And a good syn should be ok for that interval.

If I drive it all downhill and coast as much as I can on warm days, I can approach 45 mpg. That means 9,000 miles for the same 200 gallons.

These are both extreme examples for my car and I will always fall between the two over any length of time greater than a single tank of gas. But 6-9k depending on severity of service is perfect, and tracking a nice round number of 200 gallons should be easy enough.

Thanks again to all of you.

 

[kon75]

"For reference, my Escort has 6212 hours on it and average speed about 43mph. I change the oil at 5500-6,000 miles regardless of hours. Runs fine with zero consumption of RP.
Dusty"

Wow! How many miles did you rack up for that amount of hours driven? How and why did you keep track of all the hours and average speed?

 

[surfstar]

Ultragauge can keep a trip meter of gallons consumed also.

 

[oiltard]

Originally Posted By: surfstar
Ultragauge can keep a trip meter of gallons consumed also.


You are correct, sir! I realized this after my last post on this thread. Only up to about 18 gallons used since 2 oil changes ago (first one made it 200 miles before the dealership accidentally dumped it). I'll go to at least 156 (~150 on the bulk ?w20 that I have in there now), then start with 200 once I have my proper oil choice in there and start sampling and increasing from there.

 

[davison0976]

I am a numbers junkie and, among other things, I record engine time elapsed every time I fill up gas, after which I reset the on-board clock until the next fill up.

To me using engine hours for determining OCI makes most sense. At one point I figured if I spend 1.5min warming up the engine and then driving 15min to work on town roads with plenty of traffic lights that's different than cruising on a highway for 6hrs to visit my family. Different in terms the number of engine revolutions vs mileage covered.

In conjunction with UAO here are my latest findings

Vehicle: '13 Wrangler
OCI Engine Hrs: 198
OCI Miles: 5,815
OCI Time Period: 2/15/2014 to 8/30/2014
Motor Oil: Amsoil SS 5w/30
Oil TBN Left: 5.3

Based on the TBN I can safely run 300hrs on Amsoil SS, as oppose to 198hrs during this OCI.

Now, I had done a UOA with Amsoil XL oil, and my TBN with 201hrs OCI was 1.8, which is on the low side.

I am trying Pennzoil Platinum this OCI, and am planning to run it for 200hrs. Will see how it does. Research goes on!

 

[babbittd]

Originally Posted By: oiltard
If I cruise at 60 for an hour (to make the numbers simple) vs. sitting in stop and go traffic for an hour and only going 10 miles, the mileage formula treats the latter as being 1/6th as much a factor in oil life usage, whereas the time formula at least treats them equally.


Very interesting.

http://www.government-fleet.com/article/...ive-idling.aspx

According to research by Ford Motor Company, one hour of gasoline engine idle time equals 33 miles of driving.