drain intervals for synthetics

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Dec 11, 2002
I am looking to switch to a 10w30 synth in my 27K mile '96 Z/28. The oils I'm considering are Royal Purple, Mobil 1 and Redline. What would be a reasonable drain interval for these oils. The car is now serving as daily driver and will see 2000 miles a month (mostly freeway). I also planned on using Napa Gold filters (made by Wix).

Use oil analysis to tell instead of using a yardstick that works for the other guy. It takes the guesswork out of the equation. It will also save money in the long run.

If you do not race that car 10,000 to 12,000 miles confirmed with analysis will work with those oils. I like the R's better than the M unless you doctor it.
Take a look at the anlysis section of the website, and see the results others are getting with different oils before deciding. I agree with Terry you should perform analysis to be sure you are working within the limits of the oil on your specific vehicle. You should be safe with mostly highway miles to perform the first analysis at 5000 and then go from there. The tests are anywhere from $18-28 so for a little bit of money you gain confidence in your drain intervals.

There was a Mercedes that ran 0w40 Mobil 1 that put up some pretty good wear numbers after 13000 miles. You can these results in the anlysis section.
Thanks, I'll check that section. I will likely do analysis in the future, just looking for some safe numbers for now. From what I have read 6000 mile drains appear safe with most synths.
I have a friend whos '85 big block Suburban has over 300,000 mi mostly towing a dragster to and from races. He uses 10w-40 Redline and changes it once a year. Then his son puts his used 20,000 mi oil in his car and uses it somemore!

Originally posted by pedaltothemetal:
I have a friend whos '85 big block Suburban has over 300,000 mi mostly towing a dragster to and from races. He uses 10w-40 Redline and changes it once a year. Then his son puts his used 20,000 mi oil in his car and uses it somemore!

That last sentence seems a little scary to me.
6k drains are totally safe for 90% of the drivers out there when using synthetic. The only exceptions would be if you have a very worn out engine, or if you're running one of the Toyota sludge monsters (and even then 6k might be ok with the right synthetic).

But like others have said, oil analysis is the best way to figure it out for your particular situation. Otherwise you're just guessing. I prefer to know for sure that the interval I chose is not too soon. I don't want to be under my car more often than needed, as I get older I enjoy changing oil a lot less. I do enjoy taking oil samples and sending them to the lab though.

[ December 13, 2002, 06:47 AM: Message edited by: Patman ]
After living and breathing and doing and yes even standing up for extended oil change intervals, I really think one of the most critical things in an otherwise healthy car, is driving "style".

If you do a good flush, run your choice of synthetic (not sure why you excluded Amsoil) for a short "flush" period say 3K - 4K miles. Drain and change filters, refill - Then start the car, get on the highway. You could drive for 25K+ miles stoping only to eat, sleep and do potty..in other words of all the lousy oil ads - short trips are MURDERon oil.

I live in Lynden and am forced to occaisonally negotiate Seattle from time to time (what now - 3rd or 4th worst traffic??) - that crap and just driving 1 mile to work....well I wouldn't expect any oil to be happy 10K+....

That said your driving style, car, oil and then go say 5000 miles with those oils and see how they hold up in analysis if good push for 7.5K, etc....
Big Block,

All things being equal, there are a number factors that determine oil change intervals ...by order of priority I feel these are:

1) The severity of the driving conditions - far and away the biggest factor

2) The mechanical condition of the engine, including any engine mods

3) Specific fuel consumption - generally the more fuel you burn for a given # of miles, the more quickly you contaminate the oil

4) The size of the sump - a Nissan pickup has a 3.5 qt sump ...a V-6 Mercedes has a 8.0 qt sump. As a result, you can run drain intervals several times as long in the Mercedes w/ the same oil.

5) Fuel quality - particular as it relates to sulphur content and soot in diesel engine applications

Since every application is different, it is impossible to make blanket statements about drain intervals. For all I know, your engine could be way out of adjustment in which case the oil might degrade very rapidly. You need to take Terry's advice and test your oil several times at various change intervals to establish a conservative drain interval for your particular situation.

Thanks, some very good points here. Pablo, I have nothing against Amsoil, I would be open to trying both Amsoil and Schaeffer in the future based on the positive feedback from users. I chose RP, M1 and RL simply because they are what appear to be the best oils I can buy over the counter locally.
Scott, if you don't do this already, put a longer oil filter on your LT1 as well. Then when oil change time comes, put in exactly 5.5 quarts of oil. The higher amount will extend the oil's life versus running 5.0 quarts. I run 5.5 qts in my 95 Formula, with a K&N HP3002 filter. You could also run the AC Delco PF1218 or Mobil 1 M1-302. I'm not sure on the part numbers for some of the other good filters (such as Bosch premium, Supertech, STP, Amsoil SDF etc.) but these are also good choices.
Also consider Amsoil 0w-30. This has a very long drain interval and is there best stuff. All the oils above will do the job. Tooslick, I sent you a message.

[ December 14, 2002, 10:34 AM: Message edited by: buster ]
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