hankn

mburnikas, correction, 8000 km over 14months, not 8km hankn

A full synthetic will last much longer it is a fact. I have gone almost 3X longer and could have gone longer based on oil tests (oil tested fine). The high levels of acid, tested as TAN levels will not be an issue. Your TBN will drop with rises in TAN (they are integral) and I would watch out for slugging long before acid becomes an issue. So your good factor called TBN is a buffer to fight acid. The TAN is the level of acid in the oil. So far in my almost 10 years of testing my oils, the TAN level is about #14 out of 20 things to look at when testing. Case-in-point, do not even worry about it. Also the oil full synthetic needs classifaction since some are really good and some are poor in level or TBN, ZDDP, Ca etc. Example, I have seen some full synthetic oils have TBN's of only 6 and some over 13. Again, price is related to higher levels. etc etc. Yes, there is a way to test for ph but again, if you have acid problems, you will have other issues as well. So spend the $20 and get the oil tested, not drain the complete system. PS. If you use a good synthetic oil (group 4 or 5) you can go much longer then 6 months. The problem with the full synthetics are most times they are a group 3 and they do not last long; but better then group 1 or 2 dino oils. ← thanks for your quick reply, mburnikas. Are u saying, under non-severe conditions, we can use "group 4-5 synthetic oil" for 18 months (3x longer- thats what u mean?) before changing the oil if the car is still under the KM specification ? Perhaps, if we dont do the testing as u suggested(due to inconvenience etc), we can safely change syn oil say about 10-14 months if the Km is below the Km specs, rather than the apparent wasteful 6 months. I personally have used top grade synthetic oil for 8km over 14months. The oil look normal/new for quite awhile until the last probably 2-3 months when it starts to turn abit black(about 20-30%). My car mechanic says the syn oil still looks good, such as waste to drain it, he says. After reading all these comments on this forum about changing oil in 6 months(!)/engine sludge, I decided to change it! But I sure would want to understand what its all about, especially wehn we pay premium for the qualities of top synethetic oil. I noticed that you dont address the Km done. You dont really care about that due to synthetic durability ? ( for average driving km distance) I presume Mobil 1 or Amsoil oil is grade4-5 type of oil. thanks again. hankn

From the many past comments on premium or regular fuel use, many said the difference has not been observed. Premium fuel has higher octane AND I assume in US, it also has cleaning agent in as well, eg in Shell Optimax, BP Snergy etc. It is possible for the following effect to take place ? If you have been using regular fuel regularly and you switch over to premium with cleaning agent, you may not notice the immediate difference after one or two tank filling as the carbon deposit has NOT been cleaned well yet. Perhaps if, you continue after a few tankful, the difference will be observed together from the benefit of higher octane power. (assuming the car is "tuned" to cater for higher octance level? - to take advantage of higher octane) Likewise, if you have been using premium regularly, perhaps the carbon deposit is minimal. If you siwtch over to regular, you may not notice the difference due to less carbon deposit interference. If you were to continue to use regular (without cleaning agent) or other fuel injector cleaner, perhaps the carbon will gradually begin to build up to interfere & reduce power etc. I have personnally observed premium gas (with cleaning agent) with octane 98 giving better performance/power boost than regular after switching to & using premium for awhile. But then it could be my imagination! Comments?

isn't there a way to check for oil acidity? In aquarium/tap water, cheap pH test kit is used easily to check for pH(acid/akaline) level. It seem such waste to drain "supposedly better, more durable" synthetic oil in 6 months with the low Km done/non-severe driving condition. Some one know?