Hello All,

I have two 1996 Volvo 850 GLT Wagons: one has 420,000 miles and the other 350,00 miles. The one with 420,000 miles I purchased new, the other with 50,000 miles. I have consistently used conventional 10W-30 oil over the years. For reasons I can't understand, at this point in time is is cheaper to purchase a case of synthetic 5W-30 oil from Costco by 5 gallon containers than by the case of conventional oil. A concern that arises in my mind is: will the sudden switch to full synthetic risk blowing out the seals/gaskets on my two 850s and then I will be plagued with oil leaks?

I have in the past use synthetic oil in these cars for full oil changes, but only because conventional oil was not on hand or available in the moment without incident. Then I went back to conventional oil because it was cheaper. I change the oil and oil filer (Mann) every 5,000 miles.

I would welcome any advice or comments with regard to my concern. Thanks to all who reply.

Hugh