Low oil temperature can cause loss of flow or diminished flow rates.  As oils get colder their viscosity increases which in turn increases the friction on hose walls, and the oil becomes increasingly difficult to pump until at -40 degrees the oil “freezes” solid and flow rates drop to near zero. As an example, think of honey, which flows easy when heated but not when cold. The longer the hose the greater the friction. We can cause “frozen” oils to flow slowly in the ROS suction hoses until warmer oils work their way from the engine to the tank where they accumulate and become available for the return to the engine. Thus, you can establish system operation at very cold temperatures, which is a safe practice if the engine is started with a full crankcase, but it may take an hour or two. For this reason, the engine must always be checked before starting, to give the system time to accommodate the slower starting flow. In all cases the time to establish flow in the ROS system will be correspondingly more rapid as shorter hoses are used. We recommend routing hoses in the most direct fashion without up and down legs whenever possible, to minimize friction in the hose. Routing hoses on locations less exposed to ambient temperatures are preferred as even a few degrees warmer temperatures can greatly improve oil flow at cold temperatures. For extreme arctic temperatures self regulating low wattage ribbon cables on the hoses can establish oil flow very rapidly at temperatures below -40 degrees.

The pumps are rated as operational down to specific temperatures. The -17 degrees C is the range when the R2000K style #1 pump, which is the basis of all the ROS withdrawal pumps, begins to see greatly diminished oil flow.  The -28C is the point when the #2 cold weather side of the R2000CK or the DF2000 will begin to see a severe drop in flow. -40 degrees is the same for F. or C and is the point when oil goes solid state and resists flow altogether.

It is important to use a dual function pump such as the DF2000 or the D8 at the temperatures approaching -28 degrees C, as if the oil tank is overfilled, such as by oil being added to the engine and being drawn back to the tank, the tank can “freeze” solid and the R2000CK style pump will not be able to sense air anymore and the system will fail to operate. With the dual function pump flow will establish anyway.

The reserve tank is vented by the air relief normally and the tank will rise to a 1 lb. pressure which is the loading of this valve. It is a minimal restriction to the pump outlet pressures to deliver to this tank. However, when the return oil line is “frozen” the tank can pressurize higher. Using the dual function pump will establish flow in the return oil line faster and help prevent this pressure gain in the tank. Tanks can be vented to atmosphere at the risk of causing an oil spill. if the issue of overfilling tanks is not there. The air relief is still needed on tanks higher than the engine to prevent a siphon.