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Mike V.
Mike V., Subaru Technician
Category: Subaru
Satisfied Customers: 25013
Experience:  Certified Subaru Technician, factory trained by Subaru.
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Subaru forester: Have 1998 Subaru Forester which appears to

Customer Question

Have 1998 Subaru Forester which appears to drive sluggish ever since I have used synthetic oil. Is this a problem. I read that older cars need lead in oil whish synthetics don't have.
Submitted: 2 years ago.
Category: Subaru
Expert:  Mike V. replied 2 years ago.
Hi there,This really shouldn't be a factor to be honest. Older cars did need the lead in leaded gasoline, but the oil shouldn't really matter, the synthetic has good lubrication properties.Perhaps if you can describe what is happening I can point you to the problem.Is the check engine light on?
Customer: replied 2 years ago.
no. When I accelerate fro a stopped position the car hesitates the appears to buck slightly and I sense a gear shift and the car drive near normal
Expert:  Mike V. replied 2 years ago.
Ok, first, check and make sure the air filter box lid is on tight and there aren't any leaks. If they checked or changed the air filter the same day they changed the oil, this could be a factor. The car uses a mass air flow sensor that will read the amount of air coming into the system and if it's not sealed up tight it can throw off the fuel mixture and give you this hesitation.Second, I see this quite a bit with bad front O2 sensors. These rarely set a code, but if it's running out of range it will give you the hesitation on acceleration. Basically both of these, the O2 and the mass air flow play a huge part in the fuel mixture, both can be reading wrong and cause the issue without ever setting a code so the check engine light comes on.I believe one of these is the most likely culprit. I have switched over my own older vehicles to synthetic without any problems so I truly do not believe the oil itself is the factor.Please let me know if there is more I can do, also please rate my answer, I would surely appreciate it.Thanks so much!