Low gas mileage after long overdue synthetic oil change

Including Hyundai, Audi, BMW, Mistubishi or any other car.
benhorton2
Posts: 3
Joined: Tue Jul 09, 2013 3:24 am

Low gas mileage after long overdue synthetic oil change

Unread post by benhorton2 » Fri Aug 02, 2013 7:11 am

I recently had my friend's 2003 Volkswagen Jetta wagon into the shop, which had gone 26,000 miles since the last oil change, the current mileage was 98000. They recommended the full synthetic oil and filter change for high mileage vehicles. Now she tells me her gas mileage has dropped significantly, a 100 mile drive cost her 25 in gas. I have read that synthetic oil works great if the car is properly maintained, but that the additives in the synthetic oil can break down deposits plugging worn seals. The car had been burning oil slightly before this oil change. The shop also used 5W-30 instead of the recommended 5W-40, but i don't think that would cause such a significant drop in gas mileage, although the thinner oil would seem to have more potential to leak. I figure the oil filter may also be getting clogged due to the broken down sludge build up. Would poor mileage be a symptom of either of these? Or is it possible that the engine needs to adjust to the new oil? Should it be driven, and will a switch back to conventional oil help, and if there is a like are there any additives i could use to safely help a leak? And if something is wrong, can I make the shop at least give me a new oil change or pay for the repair, as they were informed how long it had been since the last service, and they recommended this oil.

User avatar
carriedi
Posts: 2573
Joined: Wed Apr 10, 2013 12:42 pm

Re: Low gas mileage after long overdue synthetic oil change

Unread post by carriedi » Fri Aug 02, 2013 10:45 am

Unless you keep records of gas mileage all the time it's difficult to measure an anomaly. switching to synthetic oil shouldn't make a drastic change in mileage. 5w30 will get better mileage than 5w40 but maybe not enough to actually measure with normal driving. If gas is $3.85/gal. $25 would be 6.49 gallons. 100 miles / 6.5gal would be 15.4 miles per gallon. (don't know what gas goes for in your area) what is your friends normal mileage?

26K between oil changes is extreme to me. Was that 26K on regular oil or synthetic? Extremely long times (or mileage) between oil changes will cause severe sludge build up inside the motor. Regular motor oil gets dirty because of combustion gasses and debris goes by the rings and is captured in the oil. The oil filter filters the debris so it won't get into the bearing area and wear them out, (as much) Synthetic oil doesn't mix with the combustion gasses as much as petroleum oil does. That's why it looks cleaner after a longer time. It shouldn't make a big difference in mileage or oil leakage or usage.

I would tell your friend to keep track of the mileage for a couple of tanks and see what the gas mileage actually averages. then go from that.

Here's what not enough oil changes can do:
http://www.youtube.com/watch?v=cCHf7oSGdes
Browse "SIMILAR TOPICS" At The Bottom Of This Page.

  • Similar Topics
    Replies
    Views
    Last post