[Sentoa] oil change and oil pressure

Wrocklage, Hubert HWrocklage at lubriplate.com
Fri Oct 13 11:47:59 EDT 2006

Hi John,
Maybe I can help you out. The viscosity (how fast an oil flows at a
given temperature) gives the oil pressure gauge its reading. Example,
cold oil temp will have high viscosity (slow flow giving a high gauge
psi reading. Example, 65psi (pounds per square inch). As the oil
temperature increases, the viscosity becomes lower (higher flow giving a
lower gauge psi reading). What controls your initial gauge reading will
depend on a number of factors.
Example, is it the same oil maker, same viscosity selected,(SAE 15W-40,
SAE 30, or SAE 40). Was the engine temperature very cold, cool, or quite
warm since that is the best time to change oil & filter. What is the
engine's rpm,A 4psi increase with new oil and a cold engine is not a
problem. As the oil accumulates running time it will shear down some and
not show the same psi when first changed. You will notice after getting
engine upto it's normal operating temp. and throttle up to 2,000 plus
rpm you will see a higher psi (40-60 psi) and throttle down to 800 rpm
you will see a lower psi (10-20 psi). Two main reasons for this, oil
pump speed (high speed-higher psi, low speed-lower psi)and oil
temperature( high temp-lower viscosity and as oil temperature lowers so
the viscosity will regain it's initial SAE #.

When to get real concerned with gauge readings is when you see numbers
that are way out of range be they high or low. That's a whole long

Hope this helps. If you wish to e-mail me direct
(hwrocklage at lubriplate.com) , I will be pleased to share my 38 years
experience that I have with Lubriplate Lubricants as Special Projects

Butch Wrocklage
St. Louis, MO. 

-----Original Message-----
From: sentoa-bounces+hwrocklage=lubriplate.com at lists.samurai.com
[mailto:sentoa-bounces+hwrocklage=lubriplate.com at lists.samurai.com] On
Behalf Of John Kidwell
Sent: Friday, October 13, 2006 9:37 AM
To: South East Nordic Tugs Owners' Association (SENTOA)
Subject: [Sentoa] oil change and oil pressure

We changed our oil and filter10 days ago, in anticipation of hauling 
out. Before the oil change, our oil pressure at start-up was always 60. 
Immediately after the change, we noticed that it was more like 64. We 
added a little bit less oil (15 1/2 qts, rather than 16) than we thought

was actually called for, on the theory that it was easier to add a bit, 
than it would be to remove some if we overfilled. Any ideas about the 
change in initial oil pressure? Did we not get all of the oil out, 
before we added new? I confess I don't really understand how oil 
pressure is measured.

John Kidwell
Gayle Ann NT32-187
Madison, WI

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