1999 Deville

[pcbres]

I just test drove a 99 deville today and was very impressed by that car. I was told that you need to run synthetic oil in it, do I have to, or is it just a good idea to do so? Does that car need premium fuel all the time? I know those Northstars had head gasket problems, was that year one in which the head gaskets were faulty, if so, when was a good year for a cadillac that didn't have engine problems?

[maxwedge]

You don't "need" syntheitic it is just a better oil. Head gaskets were an issue in 99 as well. Maybe 2004 forward.

[MagicRat]

I have owned a '97 Deville, which is virtually identical to yours.

No, synthetic oil is not needed. Just change the oil regularly using a high quality conventional oil.. Use the "oil life remaining" feature on the dashboard. Simply re-set it at each oil change.

I find with mine, the oil is getting a bit dark and stinky (from partly-burned hydrocarbons) at about 40% to 50% oil life remaining, so change the oil then.

These engines have an 8-quart oil pan, meaning they take 3 quarts more than most other V-8's, so the engine is pretty easy on the oil.

These engines do tend to consume oil, so check it regularly. Adding a quart every 1000 to 1500 miles is very common.

BTW it's not the headgaskets that actually have a problem, its the head bolt threads. The head bolts screw into threads cut in the block, like virtually all other engines. The problem is the threads are cut into the soft aluminum of the engine block. These threads eventually fatigue and break, allowing the head bolts to loosen and blow the gasket.

The repair is pretty straightforward. There is a Time-Sert kit, which allows you to replace the stripped aluminum threads with threaded steel inserts. An engine repaired in this manner will never blow the headgasket again.

This repair is expensive and time consuming, though. Both cylinder heads must come off, and, for some reason, mechanics doing this job like to pull the entire engine (for access, I guess.

IMO it seems like about one third of all Northstars, from 1995 through to almost the present day will eventually break in this manner, which is a shame. Otherwise, they are a flawless and long-lasting engine.

You can reduce the occurence of this problem by changing the coolant every 2 years and using AC-Delco cooling system stop-leak tablets. (Don't use any other brand). The manual calls for using 3 tablets placed in the lower rad hose when you change the coolant, but people in the know use 6 tablets.

Also, personally, I suspect lots of full throttle use can contribute to the problem, over time, because these are powerful engines. Personally, I tend to go easy on my car, and rarely use full throttle, but I am not sure if this will actualy help in the long run.

Finally, many people know these engines have HG problems, so their resale values are much lower than other luxury makes. I figure the $10,000 I saved in buying my Deville over a10-year-old Mercedes, Lexus or BMW can buy a lot of HG repairs.

EDIT: yes, use premium fuel ALL the time. My car gets 15% better fuel economy on premium, which more than offsets the extra cost.
On regular, the ECM retards the ignition timing, which decreases mileage, AND it still pings and rattles from detonation, quite a bit