First of all, the rings might not be seated yet. That would explain the black soot. Don't use synthetic oil during the break-in process because it lubricates too well. Watch the oil level. If it drops over time, suspect a cylinder wall or ring issue. Did you have the blocked honed? The cylinders must be checked for out-of-round and taper, then bored if out-of-specs. Honing with an electric drill is not the preferred method as it can easily introduce cylinder taper.
Another cause of the black exhaust could be a rich fuel mixture. Check the hose to the MAP sensor. Anything that causes it to read low vacuum will result in too much fuel. A leak in the exhaust system at the manifold will draw in air. The oxygen sensor will see this unburned oxygen and the engine computer will increase fuel delivery to correct what it thinks is a lean mixture.
Fuel mixture is also affected by readings from the coolant and ambient air temperature sensors.
As for the temperature gauge, the first time you fill the coolant, you will have to burp the block to get the trapped air out. Do this by removing one of the 10 mm allen head plugs by the thermostat housing, then fill the coolant until it reaches the hole. If the plugs are corroded tight or rounded out, you can also unscrew one of the temperature sensors on the housing. Failure to do this will cause engine overheating. You can also remove the upper radiator hose from the thermostat housing and push on the center of the thermostat with a long thin screwdriver.
What can happen if there's trapped air is the engine will warm up, but the thermostat will not open because it only opens when hot liquid hits it, not hot air. If you're driving it, the hot coolant can splash over to the thermostat but not before the temperature gauge goes much too high. When the thermostat finally opens, there will be enough force from the water pump to circulate the coolant, and cold liquid from the radiator enters the block and the gauge goes down to cold. After a while, the temperature evens out and holds steady.
If you believe the system is free of trapped air but the gauge still goes up too high, drill a small bleed hole in it or install a thermostat with the bleed hole. The temperature sending unit for the gauge is a long way away from the thermostat. Hot coolant reaches the sensor but it takes a long time to migrate over to the thermostat. By the time it does and the thermostat opens, the gauge has gone up much too high.
After working fine for many years, my '88 Caravan started doing the same thing. After watching the gauge do that for over a year, I took the thermostat out and drilled a 1/16" hole through the center. Don't know what caused the change but the hole solved the problem.
Hope some of these suggestions will help.
Wednesday, March 25th, 2009 AT 1:14 AM