I blatantly ripped this from another forum. My thanks goes out to the original poster.. Here it is.
I recently had two very interesting discussions this week with Mazda Canada on the subject of synthetic oil.
The Customer Service Manager (at head office, not a dealership), and a representative at head office BOTH said: the use of synthetic oil on ANY Mazda vehicle will nullify the warranty.
I asked the Customer Service Manager at Mazda's Head Office if this policy only applied to the RX-8 (where synth is not recommended), and I was told twice, No - that the policy applies to ALL Mazda cars sold in Canada.
Mazda Canada apparently doesn't care if the synthetic oil is 5-20 and meets all API and ILSAC specs. It nullifies the warranty.
When I pointed out that there is absolutely NO documentation in our owners manuals banning synthetic, they replied that nevertheless THIS was the official policy of Mazda Canada for all vehicles.
The reason I called Mazda Canada in the first place, is that I wanted to know if it was permissible to use a synthetic 5-30, because as we know, there are very few synthetic 5-20's available. Just Amsoil, and now Pennzoil, and Castrol Syntec (very new). Most Mazda dealerships in Canada don't offer a synthetic 5-20 oil change, and instead were putting in synth 5-30's.
Head office for Mazda Canada says not only will Synthetic 5-30 nullify the warranty, but so will the synthetic 5-20!!
To me, it's outrageous. But that's what they said: twice and unequivocally.
The funny thing is that the DEALERS themselves (I polled 6 of them in the Toronto area) say a synthetic 5-20 is fine for the warranty, as long as it meets specs.
I think Mazda Canada had better clean up its act, and inform both its customer AND its dealers what its official policy is IN writing, or we're going to see some serious lawsuitsin future years, if engines start to fail.
ASIDE: I asked Mazda Canada why a synthetic 5-20 would nullify the warranty on an engine that calls for a 5-20, and I was told (again on two separate occasions) is that the problem with many synthetic oils is that they "do not burn", and that Mazda engines are not meant or designed to work with oils that have this property.