Highway trip can change OCI?

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5,471
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Da Swamp
Hello, all, I'm just back from a trip to Knoxville, TN, and the Smokies. The big grey beast, the Buick, and I did about 1600 miles, a lot of highway (ca. 70 mph) and plenty of steady cruising at lower speeds, plus some good exercise for the car going up and down mountains in TN and hills in AL. The car performed like the thoroughbred it is. I had just changed the oil, to Castrol GTW 5W-30, and had 1000 miles on it before I left; now I have about 2600. The OLM dropped much more slowly, as I'd expect with lots of highway. Normally at 2600 miles I'd be 3 months into my OCI and be looking at 64% life left. However, it's now reporting 74%. Assuming I don't have any hurricane emergencies this summer, I'll probably be back on the usual 850 miles/month, and the oil life goes down by about 12.5% every month. Can I leave the oil in there until late September/early October, which I estimate will leave me at about 14% life left (a 6K OCI)? Or should I change it at 5K, around the end of August, which should have about 27% life left?
 
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15,056
Location
Canada
GTX is a good oil. It can do the OLM interval with ease. I did 8k, through a Canadian winter, mostly stop-and-go driving, with FS 5W-30, and the oil wasn't 'completely' shot (1.5 TBN).
 

Bill in Utah

Staff member
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12,849
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UT
 Originally Posted By: Rob_Roy
I would just follow the OLM and change the oil when directed.
 Originally Posted By: addyguy
GTX is a good oil. It can do the OLM interval with ease. I did 8k, through a Canadian winter, mostly stop-and-go driving, with FS 5W-30, and the oil wasn't 'completely' shot (1.5 TBN).
Agree with both of these guys! \:\! Follow the OLM and be happy!
 

Benzadmiral

Thread starter
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5,471
Location
Da Swamp
That sounds cool. Drew, since I find it hard to change the oil myself and just have my regular mechanic grab a sample for a UOA when he does a change. Otherwise I'd give it a try. If I ever have a garage, I'll get ramps, etc., and try one of the valve devices I've read about here, so I can not only change oil again, but take samples in between. So, late September (still viciously hot here) and ~6K miles it is!
 
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22,188
Location
Colorado Springs
My pops is taking a business trip next week in his Olds 88 (same engine, 3.8L). The Chevron Supreme 10w-30 has 3,500 miles on it now, half of which was all highway. By the time he gets back, it'll have 5,500 miles on it. That'll be the longest I've ever done an oil change interval!
 
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782
Location
Alberta
Here is a 8794 mile OCI on Castrol GTX 10W-30 … BITOG and the TBN was still 4.4, lot sof life left in the oil. After spending 3+ years on BITOG, I have to say that I think Castrol GTX 5W-30 and 10W-30 are the most impressive, or "robust" conventional oils I've seen. From the UOA's I've looked at, they run 5-6k miles easily. Castrol seems to blend the GTX with thicker base oils, leading to a more robust motor oil (but giving up some of the cold-cranking CCS, and cold-pumpability MRV numbers). So, Castrol GTX may be the best normal or hot weather conventional oil on the market, but not the best if you need to start in -20C or colder weather.
 
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15,056
Location
Canada
 Originally Posted By: Drivebelt
Here is a 8794 mile OCI on Castrol GTX 10W-30 … BITOG and the TBN was still 4.4, lot sof life left in the oil. After spending 3+ years on BITOG, I have to say that I think Castrol GTX 5W-30 and 10W-30 are the most impressive, or "robust" conventional oils I've seen. From the UOA's I've looked at, they run 5-6k miles easily. Castrol seems to blend the GTX with thicker base oils, leading to a more robust motor oil (but giving up some of the cold-cranking CCS, and cold-pumpability MRV numbers). So, Castrol GTX may be the best normal or hot weather conventional oil on the market, but not the best if you need to start in -20C or colder weather.
I couldn't have said this better myself. Agree 100%!
 
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712
Location
St. Louis, Missouri
I read at USoilCheck that you don't want your TBN to fall below 3 (as below 3 is very low). And, of course, you always like to see TBN higher than TAN, or engine wear accelerates at an abnormally high rate. Here's part of the quotation: Total Base Number (TBN) TBN is a property usually associated with engine oils. It is defined as the oils' ability to neutralize acid. The higher the TBN, the more acid it is able to neutralize. This quality is also referred to as alkaline reserve and is directly proportional to the amount of active detergent contained in the oil. New engine oils typically possess TBN's from 5.0 to 15.0, depending on manufacturer and intended service. As the oil is used, it becomes contaminated with acids and the TBN drops. Generally, TBN levels below 3.0 are considered too low and indicate that the oil should be changed. One cause of TBN depletion relates to the use of low quality, high Sulfur fuel. During the combustion process, this Sulfur turns to Sulfuric acid and in turn, accelerates TBN depletion. As discussed previously, overheating and over-extended drain intervals can cause oil oxidation. The products of oxidation are acidic and will cause the TBN to drop. Greatest benefit is derived from the TAN by comparing it to the TBN. TAN increases in service as TBN decreases. The point at which these two numbers meet has been indicated as the maximum useful oil change interval for that type of engine in that type of service. Studies have shown that when TAN exceeds TBN, engine wear accelerates at abnormally high rates.
 
Messages
712
Location
St. Louis, Missouri
 Originally Posted By: Drew99GT
I believe TBN is measured differently at various labs, so one labs TBN cutoff is different then anothers.
You must be right, because I read some comments written by a Blackstone tech on a customer's UOA sheet, and the Blackstone tech said a TBN below 1 is too low, whereas at USoilCheck, a TBN below 3.0 is considered too low. I wonder what accounts for the differences between labs when it comes to picking a number below which they consider TBN to be too low.
 
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