The Northstar V8 engine family is General Motor's top-of-the-line luxury power plant. Introduced in 1993 in the Cadillac Allante, Eldorado and Seville STS, the 4.6L 32-valve dual overhead cam all-aluminum V8 engine was a quantum leap forward for U.S. automakers. Initially rated at 295 horsepower, the Northstar V8 has been ranked as one of the "10 Best Engines in North America" by Ward's Auto World. It also beat out both Mercedes-Benz and BMW in horsepower per liter of displacement, fuel economy and required maintenance.
Like most other engines, the Northstar V8 has evolved over the years. In 1994, the first Northstar V8 (L37) was joined by a second version (LD8) with a different cam profile that lowered peak horsepower slightly to 270 hp but increased torque output in the lower rpm range for improved throttle response and quick acceleration.
In 1994, a downsized and somewhat less powerful version of the original Northstar V8 was introduced in the Oldsmobile Aurora. The L47 4.0L V8 was essentially the same engine as the larger 4.6L V8 but with a smaller bore size (87mm vs. 93mm). The L47 4.0L V8 was rated at 250 horsepower.
In 1995, the power rating of the L37 4.6L V8 (VIN 9) was bumped up slightly to 300 hp, and the LD8 4.6L V8 (VIN Y) was upped to 275 hp.
The two basic versions of the 4.6L V8 (275 and 300 hp) are still being used in model year 2003, and there are no plans to replace this engine in the immediate future. So it looks like the Northstar V8 will continue to enjoy a long production run.
GM recently unveiled its Northstar XV12 concept engine that is physically about the same size as the existing V8 but is capable of producing up to 750 horsepower! The engine uses cylinder deactivation technology to keep fuel economy manageable, but there are no productions plans yet for this exotic power plant.
The Northstar V8 has a die-cast aluminum block with a bottom end girdle that splits along the midline of the crankshaft bearings. This takes the place of the main bearing caps. In model year 2000, GM began using a new high pressure "squeeze" casting process for the lower crankcase to reduce porosity in the aluminum, which may allow oil to seep through and leak (this has been a problem on some engines).
The cylinders have cast-in-place iron cylinder liners that are not replaceable. Compression up to model year 2000 was a relatively high 10.3:1. It was lowered to 10:1 in 2000. Each head has two camshafts (one intake, one exhaust) and four valves per cylinder (33mm intakes and 29mm exhausts). Direct-acting hydraulic lash adjusters are positioned over each valve. The overhead cams are all chain-driven, and use an intermediate chain sprocket under the front cover to connect to the crankshaft. Three separate hydraulic tensioners are used to keep the cam chains tight.
The Northstar V8 is an interference engine, which means if a chain fails or is disconnected when the engine is cranked over, the valves will hit the pistons. That's something you don't want to happen with an expensive engine like this!
The intake manifold is Nylon 66 thermoplastic, which helps cool intake air by conducting less heat from the engine. Fuel delivery is by sequential fuel injection with separate injectors mounted under the engine's top cover. Under the top cover you'll also find the MAP sensor, intake air temperature sensor and fuel pressure regulator.
If the fuel pump relay fails on a Northstar V8, the engine should still run because the fuel pump also can be energized through the oil pressure sending unit.
A four-coil distributorless ignition with a waste spark set up provides spark to the plugs. Two crankshaft position sensors are used plus a camshaft position sensor to provide timing inputs. Both crank sensors are mounted in the block and the cam sensor is located on the rear head in front of the exhaust cam. There's also a knock sensor on the rear head between cylinders 1 and 3 to retard timing if detonation becomes a problem under load.
The ignition system has two modes of operation: "module mode" and "ignition control mode." In ignition control mode, the PCM controls ignition timing using sensor inputs. If there's a problem in the PCM or with its sensor inputs, the module mode takes over and runs the engine with a fixed 10 degrees of advance. The engine continues to run (essentially a limp-in mode) but with reduced performance.
In model year 2000, the DIS ignition system was changed to a coil-on-plug design, which eliminates the spark plug wires and waste spark. Each head has its own ignition module that fits in the middle of the valve cover.
Another feature of the Northstar engines is a "limp home" mode that allows the engine to continue running if all the coolant is lost. If the PCM senses an overheating condition, it temporarily disables up to half of the cylinders. This pumps enough air though the engine to keep temperatures from getting hot enough to cause any damage. Even so, GM says the vehicle should not be driven more than 50 miles in the limp-home mode.
- Precisely because the Northstar was a high-performance engine, in many ways it behaved like a delicate flower. It was an engine much like the high-performance Mercedes-Benz S-Class and Italian-made roadster motors. It could be temperamental with special needs. The Northstar featured a die-cast aluminum block. The bottom end girdle bisected the bottom of the engine along the center of the crankshaft bearings. There were no main bearing caps found on other engines. However, the engine was prone to oil leaks because aluminum was porous. GM in 2000 developed a new process that "squeezed" the lower crankcase casting to reduce leaks.
- In the 1990s, the Northstar V-8 had four primary problems: head gasket failure, oil leaks, high oil usage and oil burning. Cadillac enthusiasts generally dismissed high oil use as a problem, noting that it's not uncommon for high-performance engines to use a large amount of oil. GM noted that one quart of oil per 1,000 miles was not unusual since 32-valve tubes must be adequately lubricated. What's not normal was the buildup of carbon in the rings that also led to high oil use. A GM-made cleaning kit usually solved the problem.
- Common among the 1996 to 1999 Northstar V-8s were oil leaks originating at the rear main crank seal. Part of the problem was due to the aluminum block but also the seating of the oil seal in the block. GM solved the problem by developing a rear main oil seal that pressed into the block. It could only be removed and replaced by a special GM service tool.
- Head gasket problems also plagued the Northstar. Burning oil and the resulting buildup of debris in the engine caused it to overheat and blow a gasket. In other instances, the heads may have been serviced or replaced and then re-installed with a new head gasket using the original head bolts. The threads of the original head bolts were weakened after removal and no longer secured the head and gasket properly. New head bolts were required. Replacing the head bolts out of sequence and at the wrong torque values could also lead to a blown head gasket.
Read more: Cadillac Northstar Engine Problems | eHow.com http://www.ehow.com/about_6637955_cadillac-northstar-engine-problems.html#ixzz0s7WXnb94
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