* Blown head gasket: This is a very common issue in these engines, especially with age. A blown head gasket can allow combustion pressure to enter the crankcase, pressurizing it and forcing oil out the dipstick. The oil consumption is a result of combustion gases blowing past the rings and contaminating the oil.
* Worn piston rings: Worn or broken piston rings allow combustion gasses to escape into the crankcase, similar to a blown head gasket. This leads to excessive oil consumption and crankcase pressure. This is less likely at 91k miles unless the engine has been seriously neglected or over-revved.
* Valve seals: While less likely to cause this *level* of oil consumption, worn valve seals can allow oil to leak into the combustion chamber, contributing to burning oil and potentially crankcase pressure.
* Cracked block or head: A less common but more serious problem. A crack in the block or head can allow coolant and/or oil to mix, and pressure to escape. You'd likely see other symptoms like milky oil or coolant loss if this is the case.
How to diagnose:
You absolutely should not continue driving the truck. Further damage is highly likely. A professional mechanic is needed for accurate diagnosis and repair. However, some things you or a mechanic can check:
* Compression test: This will check the integrity of the cylinders and rings. Low compression in one or more cylinders strongly suggests a problem with the rings or head gasket.
* Leak-down test: This further assesses cylinder integrity, determining if compression is escaping past the rings, valves, or head gasket.
* Visual inspection: A mechanic should visually inspect the engine for obvious leaks or damage.
* Oil analysis: Sending an oil sample to a lab can reveal the presence of combustion byproducts in the oil (like soot or fuel), confirming internal combustion leaks.
How to fix:
The fix depends entirely on the diagnosis. It could range from relatively minor (if it's just a valve seal issue – unlikely given the symptom severity), to major engine overhaul (head gasket replacement, ring job, or even engine replacement in the worst-case scenario). The cost can range from hundreds to thousands of dollars.
In short: Get this truck to a qualified diesel mechanic ASAP. Ignoring this problem will lead to catastrophic engine failure. The cost of repairs will likely increase significantly the longer you wait.
