Buying used car: Change all fluids

Ask the Auto Doctor


I’m considering buying a 2008 Lincoln Navigator with 90,000 miles on it. I want to know how to service / recondition it to get the best service and life from this high-mileage vehicle. What is the protocol for fluid changes, oil types, oil, and / or gas additives?

— Sam


First, 90,000 miles is no longer considered high-mileage. Normal servicing I recommend includes brake and power steering fluid, antifreeze, transmission fluid, transfer case fluid, as well as front and rear differential fluids. You should also change the spark plugs and fuel filter (if external). Perform oil changes three times per year if the vehicle is running on conventional oil, twice per year if using synthetic. This is a big workhorse SUV that should bring you years of service. The one problem that will come up in time is the air suspension, if equipped. Swapping to a conventional system is a very good option, compared to paying to repair the air suspension.


I have a 2008 Saturn Vue with 53,000 miles with a new starter and new body control module. The key is getting stuck in the ignition and producing no power; I get the key out and shake the computer box lightly on top of the battery and the power comes on. Also, the turn blinkers, radio, and cruise control cut out. My local mechanic and General Motors garage couldn’t find anything wrong. What can I do to get this fixed?

— Virginia


We have heard about a lot of problems and some recalls with General Motors faulty ignition switches and key cylinders. The first step is to call a GM dealer with your VIN number and see if there are any open recalls on your Saturn Vue. If not, find a AAA-approved repair shop. A full check of all battery and chassis connections is also needed.


I read your recommendation to the owner of the Corvette with the 40-Series tires that are giving him a harsh ride, and that he should change them out from the run-flats over to all-season tires. I own a 1986 Corvette with all-season tires and a new 2019 Corvette with the run-flats. My 2019 ‘Vette with 32 psi on the run-flats rides smoother than does the 1986 ‘Vette with all-season and 32 psi. Why am I getting a smoother ride?



Older vehicles had suspension systems that were hard-riding, no matter what kind of tire or what kind of pressure was in them. The spring-arm design was all we had back in those days. Today’s suspension systems were not yet imagined back the 1980s. I own three Corvettes; the 1971 rides hard and handles poorly compared to the C6 models, including my ZR1. The non-run flat tires demonstrate a major ride difference.


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