Greetings:

I am a long time Volvo 740 several 500,000 plus original on my first 740 wagon, and all other 740's avg 300,000 plus/850 (nice car) owner, and now I have a 89 240dl sedan. I have been using various synthetics over the years, however delo 15w-40 has been used in conjuction to synthetics particularly during the hot humid summer months (99% hwy driving). I have been using Valvoline's max-life too. Would my engine fair better with the Chevron delo 15w-40 or the Valvoline 10w-30 max-life, again most all of my driving consist of 99% hwy averaging 120 plus miles daily. I know these engines are very loose in terms of clearance etc, but would my gas usage be less if I just stuck to max-life 10w-30 or would the 15w-40 do better. My gas usage is moderate. The engine has only 163,000 plus original miles. What say you? Thanks in advance!