Which of the above would be better in the long run?

Note: 3000 mi syn oil changes are not an option, unless you can find it for me as inexpensively as regular oil.

I change my oil myself so labor costs are not a factor.

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86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project

http://juliepalooza.8m.com/sl/mercedes.htm

i would do the synthetic at 5 or 6k.

unless i had a car that was using some oil.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I'd rather have my engine running on fresh mineral engine oil than on dirty synthetic oil.
I've used mineral oil in my Benz since I bought it (1991), changed oil at 5K and the car still purrs like a kitten at 400K+

It doesn't matter.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Jackd, I noticed you were in Canada...do you mean 5K kilometers or miles?

5,000 km

On one hand I agree with all above comments. On the other hand there are a couple other factors to consider I think. First, I believe the main advantage of synthetic oil is not in extending change intervals but in gaining the technical advantages it provides, specifically in the areas of resistance to thermal breakdown at high temp, and superior flowability at low temps. Tom W makes a good point about not using synthetic if the car uses oil but he doesn't say why. One reason is that synthetic resists oxidizing so much that it will not burn completely. So it goes through the engine unburned and will clog up your O2 sensor. I discovered this in my Toyota the hard way. What drove this home was when I spilled some oil on my gravel driveway. I got my propane torch to burn it off. At first it burned a bit, but there was a portion of it left behind that would not burn no matter how long I left the flame on it.

And there are other issues I learned about when I did a used oil analysis at Blackstone Labs. That is interesting to do at least once if you are interested in such things which it seems you are. So in conclusion, I would (and do) feel much better having high quality oil for 6K or even 10K miles, over lower quality oil for even 3K miles.

Now let us never speak of oil again...

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I do it twice a year which for me ends up being 8000 miles with Mobil 1.

My Taurus I had since new using this proceedure ran 230,000 miles engine still running like the day I bought it. It burt oil when I got it new and burt just as much when I traded it in.

My F150, 160,000 miles never burnt a drop of oil in its life. Because I use it less some changes I perform at about 4000 miles some times I only change it once a year.

My 1988 560SL, treated for the past 32,000 miles with Mobil 1 at twice a year 8000 miles per change. Current milage 133,000 no oil burn 15.073 sec in the 1/4 mile.

John Roncallo

Sure.
There is a Santa Klaus and an Easterbunny as well !

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2007 C 230 Sport.

Yes, Santa is running dino oil and the bunny is running Delvac (I think), but he changes it pretty often, and he ALWAYS uses a fleece filter. Rabbit fleece I think.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra