: Just bought a 99 Deville - question about the oil

09-14-12, 06:22 PM
I just picked up a 99 Deville with 55,000 miles. The car is super clean and looks to be in mint condition. I purchased it from an elderly couple who kept in very good condition and have all service records stashed in the glovebox. They told me they purchased the car used from a dealer about 5 years ago with 35,000 miles.

Since then, they have have been running synthetic oil in it. From what I understand, conventional oil is best for the Northstar.

Would it be best to switch back to a conventional oil, or should I stick with the synthetic oil? Everything looks nice underneath with no oil leaks currently.

09-14-12, 08:34 PM

Use whatever tickles your fancy. Either will serve you well. Just use 10W30, NOT 5W30.

And change the coolant every 2 years.

09-14-12, 10:18 PM
Thanks for the welcome. Just from what I've read here in the short time I joined, Northstars have a tendency to leak and is more prone to leak with synthetic. I was thinking about maybe just running conventional Castrol GTX 10W30.

Like I said, no leaks so far but if it could be avoided with conventional oil I'd be glad to switch.

09-15-12, 10:07 AM
First of all, it will leak no mater what oil you use (if it is going to), and secondly, if it's gonna leak, it would have done so by now. Use whatever oil you like best.

09-15-12, 11:08 AM
Run whatever brand or type of 10W-30 oil that floats your boat. The engine could care less. 7.5 quarts exactly, keep the level at the middle of the hashmark, no higher.

Apparently the previous owners ran "synthetic oil" for 20,000 or so miles - and you don't know what was run before that - so according to your hearsay, the engine should be happily leaking oil. Is it ? (My 2002 Northstar has run synthetic oil for over 60,000 miles, the outside of the engine is absolutely dry and it gets over 4,500 miles per quart.)

FWIW, You are in a Forum for car repair and maintenance advice: people come here with little and BIG problems. NO ONE normally comes here to post "My engine has 125,000 miles on it, runs synthetic blend oil, Widget filters and Sparko plugs and gets 32 mpg in the city. I love the car. What can I do to make things break ?"....:rolleyes: