switching between synthetic and dino oil

Nope. But you could use it year round and go to the maximum oil change interval shown in the cars manual.

Different additive packages and base oil composition makes this hard on the seals in the engine. Manufacturers recommend sitcking with one or the other but not changing back and forth. Synthetic can be mixed with conventional though, and synthetic blends are available at reduced cost.

Approximately 11/8/03 19:14, F. Plant uttered for posterity:

No, not really. A synth blend may be a bit cheaper, particularly since you have the good sense to keep the change interval short, but even the most expensive synth is cheaper than an engine. You might want to consider just running synth all year around, as one of its other benefits is superior hot weather consistency and stability.

Approximately 11/9/03 05:30, Daniel M. Dreifus uttered for posterity:

Not that many engines have this type of problem, and for those that do, a shot of Marvel Mystery can usually solve it.

Making it more mysterious why swapping would hurt anything.... not that I disagree with sticking with synth or synth blend all year 'round.

That's not true. It doesn't make any difference at all.

Well duh, of course any particular oil maker is going to try to keep you from changing to another brand. Again, there is no truth to it.

That is true.

I combined two posts that both more or less said the same thing.

I design seals for a living. It does make a difference! It can make a huge difference depending on what you are putting in there and the material used in the seal. Different oils have different base stocks and additive packages. They can and do react differently with any given polymer. Select a good quality oil brand and weight that meets the specifications required by the vehicle manufacture and stick with it.

huge difference depending on

Different oils have different base

polymer. Select a good

vehicle manufacture and

I am curious, Morgan. Perhaps you could tell me something about your work. In my experience, which is more with the chemistry of the materials going past the seals than in the design of seals, most of our suppliers use a rather limited number of elastomers to make their seals. The type of elastomer is the most important factor in these seals, although the mechanical design can also enter into the equation.

Why would an elastomer that could be used successfully for dino oil, or successfully for 'synthetic', be more prone to fail if these two were alternated?

Straight PAOs used by Mobil and others used to cause leaks but esters and other additives cured that problem over a decade ago.

This can be true, but as was pointed out, this is mostly marketing and an attempt to retain customers.

But they are a rip-off. Often with only 10-15% PAO component ... and many are merely Group II and Group III blends. They are not worth $2.25 per quart when Group II+ Chevron and Pennzoil are avaialble for $1.00 - $1.50.

The "high mileage" oils have a 10-15% ester (Group V synthetic) component in the base oil and are a better value than the oils labeled as "synthetic blends." Pennzoil's is exceptionally good but it formulated on the thick side and not particularly useful for sub-zero temps.

I used to be against switching and "backyard blending" but I've seen people do it and then do a Used Oil Analysis (UOA) on the used "soup." The result showed very little wear.

Switching oils for the different seasons makes perfect sense.

--- Bror Jace

difference depending on

oils have different base

polymer. Select a good

vehicle manufacture and

This discussion kind of worries me as I have been using a blend of

80/20% regular/synthetic oil. What's the effect on the seal with the mix? What's the result of the "effect" on the seal? What are the symptoms? Will Marvel Mystery Oil cure the problem as the other mentioned?