Oil Pressure Dropping

[hanleyclifford]

The problem with adjusting for higher pressure when engine is hot is that the pressure could be very high at cold start up which is not good either. IMO low pressure developing after extended running is caused (among other things) by high bearing clearances, especially cam bearings. In any case if you cannot keep engine temperature below 180 that problem should be addressed first since oil pressure is partly a function of temperature.

[Marian Claire]

Agree with the idea of addressing the temp issue first. Get the A-4 running at normal temps and then report oil pressure #s. Dan S/V Marian Claire

[geekeasy]

Agree with the idea of addressing the temp issue first. Get the A-4 running at normal temps and then report oil pressure #s. Dan S/V Marian Claire

The temperature stays at nearly exactly 180, until the pressure drops when it starts climbing. But I really don't really know the causation there -- pressure drop causes heat, or heat causes the pressure drop.

In related news, my boat is out of the water now, I just removed the grated cover for the raw water intake and found out that the water intake behind it was almost completely clogged. ***?



This could perhaps make a big difference when I put the boat back in the water.

[hanleyclifford]

The temperature stays at nearly exactly 180, until the pressure drops when it starts climbing. But I really don't really know the causation there -- pressure drop causes heat, or heat causes the pressure drop.

In related news, my boat is out of the water now, I just removed the grated cover for the raw water intake and found out that the water intake behind it was almost completely clogged. ***?



This could perhaps make a big difference when I put the boat back in the water.

You dodged a bullet. You were starving for raw water due to the clog. That looks like a 1/2" thru hull - way to small. Try replacing it with a 1" Groco and then reducing to 3/4". You'll always get good flow.

[geekeasy]

Agree with the idea of addressing the temp issue first. Get the A-4 running at normal temps and then report oil pressure #s. Dan S/V Marian Claire

I've run a bunch more tests. And it seems to me like it's an oil pressure issue, not a temperature issue.

I do not have an RPM meter, but if I give the engine quite a bit of throttle engine runs at 40 pressure and 180-185 degrees which seems perfect. That is for the first 45 minutes or so.

But then after 45 minutes, oil pressure gradually drops to 20 and the temperature starts climbing to about 195.

If I drop the throttle a bit, I can motor all day at 20 pressure, 180-185 temp, and 5 knots. But it would be really nice to be able to get up to hull speed.

I tightened the oil pressure adjustment valve as much as it would turn by hand. Should I try cranking it down harder from there?

Is there anything else I should try?

Thanks!

P.S. Removing the blockage from the intake didn't seem to make any real difference.

[hanleyclifford]

Your symptoms are actually classic for an engine nearing rebuild time. It takes about 45 minutes for an engine to thoroughly warm up including all it's oil. When cold the viscosity of the oil gives you the 40 psi but as the oil warms up it cannot maintain the pressure because the bearings are worn such that a lot of volume is being bled off at each station along the oil route. Look at your Moyer Marine Manual, the section dealing with the oil system. IMO it is important to replace the camshaft bearings and have the clearance set by a machine shop to .015". I had exactly the same symptons as you and this is how I solved it. Of course the mains and rods must also be within spec. In rare cases the oil pump itself can be implicated if the clearance for the gears gets too wide. Moyer Marine has that issue covered too. In the meantime if you can bring the temperature down by getting rid of the thermostat that will get some relief. Even a raw water cooled engine can run safely at 160. You can also go to 40w oil but watch your start up pressure so it does not exceed 60 psi.