FAQ: Oil System
9. Recommended normal and minimum continuous duty oil pressure for the Atomic 4?

Early Universal manuals recommended oil pressures between 35 and 40 PSI. Our own manual recommends 40 PSI (fully warmed up) at your favorite cruise setting, and our oil pressure troubleshooting section suggests readjusting the pressure if it drops below 35 PSI at normal cruise.

In terms of idle pressure, Universal manuals allowed pressures as low as 10 PSI (fully warmed up), while our own manual is somewhat more conservative, suggesting that pressure at idle should be no lower than 1/2 of the pressure at normal cruise (17 to 18 PSI).

It is very important to clarify two issues regarding oil pressure: 1) The intent of all the above recommendations is to provide a range of oil pressures below which you should attempt to readjust the pressure by adjusting the regulating valve, not necessarily to establish a threshold below which you would have to pull the engine for overhaul. 2) It is our understanding that the recommended oil pressures shown in the original factory manuals (and certainly in our own manual) were intended to apply all the way to the rated maximum (theoretical) output of 30 horsepower at 3500 RPM.

These two issues prompt an important secondary question: What is a reasonable minimum (continuous duty) oil pressure when operating below maximum rated power and RPM? We are told by several different sets of experts (engineers and race car drivers) that they use 10 PSI per 1000 RPM as a minimum oil pressure for continuous duty operation. For example, at 3500 RPM, minimum continuous duty oil pressure would be 35 PSI. As a point of reference, specifications relating to continuous duty operation mean that if the specifications are violated, the engine won't self-destruct within the next 5 minutes, but it does mean that its life expectancy will be significantly reduced.

While this rule of thumb equates rather well to the factory recommendation of 35 PSI at 3500 RPM, the same 35 PSI seems somewhat conservative if your favorite cruising power setting is down around 2000 RPM, where you could (by these experts' rule of thumb) look at 20 PSI as your lowest pressure for continuous duty.

In summary: We recommend that you try, to the extent possible, to adjust your oil pressure to maintain a minimum of 35 PSI at your normal cruising power setting (whatever that setting might be). If you cannot maintain an oil pressure of at least 10 PSI per 1000 RPM, we recommend that you consider serious corrective action, including pulling the engine for overhaul, particularly if you are contemplating using the boat for anything other than pulling in and out of your slip. - Updated: November 4, 2003


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