What does a dry compression test showing a maximum reading of 150 PSI indicate?

A maximum reading of 150 PSI in a dry compression test typically indicates the condition of the engine's internals, particularly the piston rings and cylinder walls. When the reading is within an acceptable range (which can vary by engine design), it suggests that the piston rings are sealing properly against the cylinder walls, allowing for adequate compression.

However, if the reading is lower than expected or if multiple cylinders show significantly reduced readings, it can indicate potential issues, such as weak piston rings. Weak or worn piston rings may fail to create the necessary seal during the compression stroke, leading to lower compression readings. A reading of 150 PSI by itself could indicate a healthy cylinder, but if there are concerns about performance or other symptoms, weak piston rings should be suspected and further investigated.

The other options do not directly correlate with a compression reading of this nature. Faulty spark plugs would more typically manifest as misfiring or rough idling rather than affecting the compression test significantly. High oil viscosity doesn't usually affect the compression readings directly, and while correct oil levels are essential for engine operation, they have no bearing on compression testing outcomes. Thus, focusing on the condition of the piston rings is paramount when analyzing a compression test result like this.