Your 2006 Corvette manual says to use Mobil 1 Synthetic oil and change it on the interval that the computer tells you. Does this really protect your engine well? Should you leave the used oil in your engine over the winter and risk internal corrosion? I received the questions in the email below from a subscriber and wanted to share my response. If you have any additional feedback that you think will help your fellow Corvette owners please provide your comments at the bottom. Here is the email with my reply following it:
Hi Jessie,
1) I would like to know that when you change your oil and it has just 1000 miles on it. Is it ok to keep the same oil over a winter or for up to a year? Or should you change it because it sat over time and moisture got in there?
2) I have a 2006 Corvette which has a computer that tells you the life percentage left on your oil based on revolutions. Currently, I am at 52% left and have gone about 5000 miles. If I go by the computer I could be waiting until about 10K. I belong to a Corvette Forum and have read many opinions on this subject. An engineer claimed he researched it and 7500 miles is when he changes it. It requires Mobil One Synthetic. Most people change at 5000 miles with the obsessive doing it at 3000 which we know is dumb. What is your opinion?
3) What is your opinion on Antifreeze? My Corvette manual tells me every five years. I only have 28K on the car and my rule of thumb is every 36K. Would you wait or change it based on years?
I really enjoyed reading your facts about motor oil. Keep up the good work.
Bob
Hi Bob,
Question #1 depends on the quality of the oil of course but for PAO based full synthetic oils like Mobil 1 or AMSOIL 1,000 miles is hardly scratching the surface of what they are capable of as long as the 1,000 miles of driving typically involved the engine running for at least 20-30 minutes.
I say that because it is important to get your oil hot enough long enough to boil out the moisture and condensates that come from short trips like to the corner store and back. If the 1,000 miles consists of 500 trips to the corner store then you need to change the oil because of the damage caused by fuel dilution, acids, and condensates coming from the combustion process. I’m guessing your recent 1000 miles isn’t just frequent short trips.
At 1000 miles of use your oil should have retained most of the TBN rating to help prevent corrosion in your engine in the off season. Once you shut your engine off there is no more air circulating through it. That means there is only a fixed amount of moisture and acid left over from the last run. As long as your oil is relatively fresh (like only 1000 miles) it will have plenty of additives left to protect it from the small amount of contamination left over.
Question #2 Are you going to drive more than 1,000 miles a season? Regardless of the oil life computer you will have to change oil and filter by the 1 year mark per GM. Oil analysis is really the definitive way to determine when the oil needs to be changed and it can be performed for about $20. The problem with the oil computer is an indirect method of suggesting an oil change as it does not actually sample or test the oil but instead makes some simplifying assumptions and correlates those to how the car is driven. It doesn’t know if you are driving on a dirt road which greatly increases the dust intake, filter, and oil contamination. The direct method is to perform a chemical analysis on the oil itself to verify how much of the additives have been used, how much wear metal is present, and how much suspended particulate is present.
I know Mobil has an oil rated for 15,000 miles and AMSOIL has oil rated out to 35,000 miles or 1 year. To me changing Mobil 1 Synthetic at 7500 miles in a 2006 corvette engine for normal city driving still has a comfortable margin of safety. Oil filter quality is very important here too so I am assuming you are using a very high quality oil filter.
Question #3 As far as coolant wearing out vs oil wearing out there is a fundamental difference on the timing vs use issue. See, oil is exposed to the combustion in the engine and is exposed to all the contaminants introduced into the engine from the air intake system and fuel supply system. The additives in oil are provided to help the oil survive this tortuous environment. The more you run the engine the more you “use up” the life of the protective oil additives.
Coolant on the other hand is essentially circulating in a closed system. It is exposed to air in the expansion tank but it doesn’t interact with any fuel or nasty combustion gases. Coolant does have additives to prevent corrosion in your cooling system so the quality of the coolant has serious implications. Coolant doesn’t wear out as dramatically as oil based on engine operating time therefore following the recommended change interval based on the calendar is important. I would say to go ahead and change it at the 5 year mark if you don’t reach your rule of thumb of 36k first.
Thank you for the questions and the feedback.
Jesse
I came across this good post in a forum about this same topic… check it out at http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1735142
If you would like to see the comparison data and test data proving which oil is best for your Corvette you can get the best motor oil report at the home page (or click the link).
