Cadillac Repair: Cadillac Northstar engine knock, cadillac northstar, northstar engine

Question
I have a 1996 Deville Concours which I bought used in 1999 with 24,000 miles showing.  Initial oil consumption was REALLY high but I found a loose fitting on the oil cooler and now it is only high (quart every 1000-1500 miles).  There is now a lower engine knock when the engine is cold.  At first, the knock only occurred for a short time on the coldest winter days.  This year, I have begun to hear it in the summer.  The knock only occurs when the engine is cold - by the time the temp readout reaches 190 degrees the knock has ceased.  The car now had 76,000 on it, and I have always babied the engine - Castrol Syntec blend changed every 3000 miles, new filter at oil change, etc.  I fear that the previous owner may have let the oil level drop too low, and that it has taken 5 years for the problem to surface.  It does not sound like it is a ticking lash adjuster/lifter.  The knock is too far down in the engine and toward the middle of the block.  Suggestions?

Answer
Hi Robert, Cadillac has known that this engine slidges up in the oil ring area and when it does the oil consumption increases. What they recommend doing is remove all the sparkplugs and pour 3-4oz of top engine cleaner into the cylinder and let that sit for 8 hours or overnight. Then with the ignition coil unplugged, there are 3 connectors to remove, so it can't spark crank the engine over 7 or so revolutions to remove whatever TEC is still inside the cylinder. You will want to place an old towl or sheet over the holes to deflect the TEC otherwise it will damage the paint if not washed off right away. Then comes the cool part if you like smoke shows and that is after putting the sparkplugs back in and plugging in the coil start the engine up and drive it down the road until the smoke clears out. It will probably be hard to start and might require cranking the engine with your foot to the floor to turn off the gas but it should start. Try to be away from the garage and house or close the garage door with the car outside before running the engine. Sometimes a second application might be required depending upon how sludged the piston rings are. As for the knock it might be what GM calls piston slap in that the piston skirts are alittle narrower than they should be when cold and as they reach opperating temperature they expand and the noise goes away. You can live with it or have the engine disassembled and replace the pistons that are causing the noise. Personally since the noise goes away and if it isn't too loud or annoying I would just let it go. However to give you peace of mind you could take it to a Cadillac tech and have the noise evaluated and then you would know for sure what to do...fix or ignore. Hope that helps. Bill