I've recently noticed what might be some coolant coming from the upper portion of the back cylinder near what appears to be what would be a freeze plug on cars. Whatever it is, goes down the upper groove of the cylinder fin and then onto the heat shield of the rear exhaust pipe. It appears to be a white colored substance. What is it, and more importantly, how expensive to fix?

There are cylinder block core cleanout casting plugs back there, one or more could be rusted out. Also make sure the coolant is not coming from up top like at the rear of intake manifold.

check that the upper basket is the correct one for the unit. some one may have just put in a basket to sell it

THE CADILLAC HAS A COOLING SYSTEM THAT IS A LITTLE COMPLICATED.. YOU HAVE TO FOLLOW THE HOSES AND CHECK FOR LEAKS.. BUT THAT CAN ALSO BE FROM A SEAL ON THE ENGINE. THEY ARE CALLED. FREEZE PLUGS. THOSE CAN ALSO LEAK.. A HOSE, NEAR THE RIGHS,WATER PUMP OR FREEZE PLUG. THAT IS ALL.

time to get a new one then go to sears

if you have a freeze plug leaking oil you've got major problems....freeze plugs or expansion plugs are for engine coolant only, they are there in case the coolant freezes it will pop out one of those plugs before it cracks open the engine block. at least in theory. you should probably start with the valve cover gaskets and then do upper and lower intake gaskets...

1. Write down your radio code if it has some anti-theft device.
2. Allow the engine to cool down for about 3-hours before the start of this operation.
3. Open the hood, and disconnect the battery negative terminal. Tuck the negative terminal aside so it won't flip back.
4. Locate the radiator drain-plug (plastic wing-nut) on the lower back side of the radiator, and turn it backward to remove it.
5. Place a container under the radiator to catch the anti-freeze coolant.
6. Remove the radiator cap.
7. Once the coolant is drained, trace the upper radiator hose to where it ends on the engine(thermostat housing), and remove the hose with a medium size plier.
8. Loosen the three bolts holding the thermostat housing. Gently take out the housing.
9. Notice the position the thermostat was previously installed.
10. Replace the old thermostat, and the o-ring around it. Clean its mounting area. Notice that the o-ring fits around the thermostat.
11. Replace the thermostat housing and torque the three bolts to 78-inch pounds. Replace the upper hose.
12. Replace the radiator drain-plug.
13. Re-use the antifreeze coolant and be careful no dirt goes in with the coolant into the radiator.
14. Return the radiator cap.
15. Reconnect the negative battery terminal.
16. Start the car and check for leak.

Important: Anti-freeze coolant harmful to the environment. Return unwanted anti-freeze coolant to collection areas.

i think you should check the radiator fan ,if its not working then check the sensor on the engine.

Have a look for a heater control valve that may be leaking in area near firewall on passenger side, just follow your heater hoses.

unplug each injector one at a time and use a multimeter to check the resistance between the terminals on the injector. they should read 10-14 ohms

Check the spark plugs. If it is coolant getting into the combustion chambers the plugs in the affected cylinder/cylinders will have a gray or clean appearance to them.Normal plug color is tan to brown.