Other than the cost of synthetic oil are there any other disadvantages?

I would say only that if your engine is heavily sludged the synthetic would do some cleaning, which is a good thing, but not if it causes blobs of sludge to clog an oil passage. Oh and it may clean off a false seal of sludge from a seal and make a leak, but then a good oil with seal conditioners (like Maxlife) should restore some of the original pliability of the seal and the leak stop, provided the seal was not physically damaged. For most engines these things should not be an issue and you should have no worrys.

Don't forget seal compatability as well. Some synthetics may cause seal shrinkage or swelling so be sure to check what you're using first. Although it's not so much of an issue with modern sythetics it's still something to be mindful about.

Not by my knowledge. Even costs aren't disadvantage. Going longer with oil changes costs will turn into (economic) investment.

Stories about seals are forgotten with newer synthetic oils. In some cases it can improve sealability (as it posted MC).

quote:

Originally posted by AFS:
Other than the cost of synthetic oil are there any other disadvantages?

One of note is that you might pick 5 quarts up and use it when there were 5 quarts of another brand left on the shelf that would possibly give superior performance at equal or less money .

The choice there is in having an idea how they are made and the type engine you have along with the service it see's .

Some range from excellent to good bang for the buck , some are just so so IMO .

quote:

Originally posted by Motorbike:
[QUOTE]One of note is that you might pick 5 quarts up and use it when there were 5 quarts of another brand left on the shelf that would possibly give superior performance at equal or less money.

I just read a post on another site by someone in the oil industry that said Mobil Clean 5000 oil is all Group III base oil. Now you can get Clean 5000 for $2 a quart. If true that it is Group III, that is a great deal considering that most Group III "synthetic" oils run around $4 or more a quart.

With Mobil Clean 7500 I understand you get a blend of Group III and PAO--astounding for around $2.50 a quart!

Every year a new bargain is formulated . To me , the 7500 is bargain of 2005 . I personally would not use a lesser oil at that price and would choose it over two mail order synthetics out there . The Citgo High Mileage oil was 2004's deal of the year . Crazy good add pack there with good base oils .

Just think of the potential to run to 5k easy without the residual being dead enough to harm the next new oil installed .

I'm not much for brewing as you know other than using that groovy Valvoline additive which I and others have proved works well but for a summertime spike , that Maxima I just posted seems like it would work well with the 5000 or 7500 Mobil oil

quote:

Originally posted by AFS:
Other than the cost of synthetic oil are there any other disadvantages?

Synthetics are not compatible w/ Mazda's rotary engine.