Cadillac Northstar Engine Problemsby Richard Rowe
Built as an answer to Ford's 4.6-liter modular engine, introduced the same year and carrying the same displacement, the greatest of Caddy's little V-8s made history for two reasons. It was the first GM production V-8 built for overhead cams, and the last of the "non-corporate" V-8s the company would ever use. The Northstar never reached the epic levels of popularity of its Ford cousin, thanks largely to its phenomenal repair costs and disposable everything. The Northstar is a fine engine if you find a good one -- but woe to those buyers who don't know to spot a bad one.
Far and away, most of the Northstar's issues have to do with oiling. GM fixed a lot of these problems in the 2000 model year, but earlier engines are known to develop leaks around the main seals and valve covers. Oil pressure can disappear entirely on early 1993 to 1994 engines, as a result of debris caught in the the finicky oil pressure relief valve. The former requires replacement of the affected seals and gaskets, but the latter is much easier to deal with. These engines use external oil pumps mounted to the front of the block; if you see low oil pressure, remove the oil pump and clean the debris out of the assembly. It's a pain, but at least it's fairly cheap.
It's not unusual for pre-2000 engines to go through as much as a quart of oil every 500 miles. It's not leaking, it's just burning off in the combustion chamber. The problem goes back to the piston rings, which can get stuck in the ring lands as a result of carbon buildup in the ring grooves. When the piston rings get stuck in the grooves, they can't seal or wipe the cylinder walls. That allows blow-by to go into the crankcase -- resulting in a loss of power and fuel economy -- and oil on the cylinder walls to burn in the cylinders. GM is aware of the problem, and has a ring-cleaning procedure that involves filling the cylinders with a solvent via the spark plugs. After two -- and not more than three, hours -- the solvent will dissolve the carbon. Some people have done the same thing at home with Mopar Top End Cleaner, Seafoam or equivalent; running a high-detergent oil or cleaning solvent like Marvel Mystery Oil may solve the problem over a long enough period of time; but it will take so long, you may end up damaging the rest of the engine in the process, It might be best to have someone experienced in the GM procedure take care of it.
Carbon in the Cylinders
GM solved the ring carbon problem by the 2000 model year, but somehow wound up creating a different carbon problem in the process. Engines built in 2000 and 2001 have a tendency to build up carbon in the cylinders. The resulting carbon deposits heat up and act like glow plugs in the cylinders, causing the engine to knock and ping under hard acceleration. It's a simple enough problem to solve -- Seafoaming the engine or using top-end cleaner should get rid of most of it, and you should be able to dissolve the rest by using a quality carbon-dissolving fuel system cleaner in your gas for the next ten tanks or so. The quick solution is to fill the cylinders with solvent like the ring-cleaning procedure, but this carbon buildup usually isn't severe enough to warrant that. After the carbon is gone and your plugs are clean, run a carbon-dissolving fuel system cleaner every third tank or so to keep the gunk at bay.
Blown Head Gaskets
Say what you will about Cadillac, but they practically reinvented the market for top-end cleaners, fuel system cleaners and head gasket sealers. In addition to the aforementioned problems, Northstars of all years have a nasty habit of blowing head gaskets. Especially after any kind of overheating event. One of the big selling points of the Northstar was its resistance to overheating, and it certainly has that. But overheat it once, and you'll find out how little margin of error GM engineered in for excess metal expansion. Part of it has to do with the engine's basic design, but a good bit of it has to do with the awful, single-use, torque-to-yield head bolts Cadillac used. TTY head bolts are a bane to all mankind; once tightened, they permanently stretch. That's nice for assembly purposes, but overheating a TTY-bolt engine -- especially one with aluminum heads -- stretches the head bolts further than they were meant to go. And being TTY bolts, they don't shrink back to size when the heads contract. That causes the head to sit loose on the engine, and the head gasket to blow. Forget head gasket sealers; the only lasting option is replacing the gasket and The Devil's Bolts.
The Northstar is a perfect example of an engine that was slightly over-engineered for its own good. It's finicky, high-maintenance and expensive to repair if anything breaks. Fortunately, its most common problems are easily dealt with -- and savvy buyers have been known to get great deals on engines sellers thought were toast, but were really just in need of a good cleaning. That's the up-side of all this. The down-side is that if you judge wrong, you just made a very expensive mistake. You can avoid most of the Northstar's more irritating idiosyncrasies by using a carbon-dissolving fuel system cleaner every other tank, and running high-quality synthetic oil. General Motors gave a 7,500- to 10,000-mile oil change interval on this engine, and programmed later oil life monitors to reflect that. Forget them; change it every 5,000 miles, whether it seems necessary or not. The Northstar was a sophisticated, European-style powerplant designed for 'premium buyers," engineered like a Swiss watch. If you treat it like a BMW or Audi engine instead of like an old iron-block truck lump, the Northstar should prove as sweet, smooth and powerful a partner ten years from now as it was 20 years ago.