I have the 1998 LeSabre. Get ready replace upper intake manifold gaskets,and plenum maybe,and it's gasket. Old ones were plastic.new ones metal. It's not difficult do yourself if mechanically inclined and good torque wrench. Otherwise $1,200 job. Attempted mine, worked ok for 5 years, had cooling system flushed and it started leaking. My torque wrench not as good as a shops
The car is indeed speed for 10w30.use that in hot summers. Car book shoes covers cold temperatures and can be used save money and mileage.
Replace the dreaded plastic elbow left side just under ignition coil thingy. Mine broke soon as I bought it 2017. Had 94,000 miles now at 166,000. Best oil I found is Mobil extended performance..it advertises cleans sludge. That means attempts clean rings too and much better pour n flash point. Ran fram synthetic last year,engine loved it alot