In the helicopter's oil system, which component bypasses high pressure during cold starts?

• A. Oil cooler bypass line
• B. Oil filter bypass valve
• C. Relief valve in the fuel system
• D. Scavenge pump

Answer: (B)

During cold starts the oil is very viscous, which makes it harder for the pump to push it through the filter. If the oil must pass through the filter, the pressure can build up and the bearings may not get lubrication quickly enough. The oil filter bypass valve is built to handle this by opening when the pressure across the filter becomes too high, allowing oil to flow around the filter instead of forcing through it. This keeps lubrication available to critical components right away, even with thick, cold oil or a partially clogged filter.

The oil cooler bypass line serves a different purpose—granting oil a path around the cooler to heat up faster or to regulate temperature—so it’s not about relieving high pressure during cold starts. The relief valve in the fuel system is unrelated to the oil circuit, and the scavenge pump’s job is to return oil to the reservoir, not to bypass high pressure.