One of the first signs that a vehicleâ€™s engine is worn and may need to be replaced is blue smoke from the tailpipe on start-up or when accelerating after coasting. Blue smoke is caused by oil leaking past worn cylinder bores and piston rings or through worn valve guides and into the combustion chamber where it is burned along with the air and fuel mixture. By the time the cylinder bore or valve guides are worn out on a modern engine, many other components are also likely to be worn out Car Diagnostic Tool, so completely rebuilt engines are a good alternative to just performing a valve job or re-ring.
Unlike blue smoke indicating a worn out engine, a sudden plume of blue smoke from the exhaust pipe accompanied by significant loss of power is a sign that one or more pistons have developed holes or have broken into pieces, allowing oil to escape directly into the exhaust port. This sort of catastrophic engine damage typically results in the owner seeking engines for sale.
More serious signs that an engine needs to be replaced are unusual noises from within the block that increase with crankshaft speed rather than road speed. Most engines feature a crankshaft with plain journal main and rod bearings. Knocking is a sure sign that the connecting rod bearings are worn and in the process of failing, the noise itself being caused by excessive clearance between the crank journal and the bearing, or the wrist pin is failing. Rumbling noises from within the block are likewise caused by too much clearance on the main bearings. Operating under these conditions would also cause low oil pressure gauge readings or the oil pressure warning light illuminating while the motor is running above idle.
Repeated overheating can be both a cause and another sign of an engine needing replacement. Cracked castings and worn deck or cylinder head mating surfaces allow hot combustion gases to enter the coolant system, over-pressurizing it while displacing coolant from where it is needed. While a blown head gasket can cause a similar situation, the effect of overheating by any means potentially warps the cylinder heads, leading to the same problem happening repeatedly until the problem is remedied.
Coolant leaking from anywhere on the engine other than from the freeze plugs or hose connections strongly indicates a cracked block, and, whether it is cast iron or aluminum, this generally means replacement is in order autel ds808, as remanufactured engines are usually less expensive than the labor and parts involved with welding up a cracked block.