Recommended normal and minimum continuous duty oil pressure for
the Atomic 4?
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