8.1 Low Oil Pressure

Tacoma290

Tacoma290

Active Member
Oct 5, 2006
498
Tacoma, WA
Boat Info
340 Sundancer 2007
Engines
Twin 8.1 V-drives
Hoping to see if I have missed something to look at regarding low oil pressure.
At the beginning of the week, a hose clamp failed on a hose between the engine and the pump. Shut the engine down on alarm. Replaced the clamp. The exhaust elbows got hot enough to crackle some of the paint, but after allowing a full cool down, the engine started and ran. I have been checking the oil condition and levels, and all seems to look good.

Later that day, the engine would stall and die after 10 minutes of idle following a long cruise. Replaced the Idle Air Control, and all seemed to be well for the rest of the week.

After a week of cruising with no other issues, I was headed home and noticed the oil pressure on that same engine steadily dropped at cruise. I saw the pressure drop on the smartcraft gauges to around 30-35 psi on plane (normal is around 55psi), and as I slowed to an idle, the alarm went off, so I shut down the engine. I was able to run at about 1500 rpm and the pressure started at 37 psi and dropped to 34 psi after 2.5 hours of running at 1500 rpm.

It is possible the oil pressure sensor is bad. So I could swap the sensors from each engine.

It is possible the oil pressure sensor is good. The next logical step is to change the oil and filter, thinking that the the overheat condition may have damaged or thinned the oil. Is there anything else I should be checking?
 
Start simple first, oil change. Verify oil pressure is correct.

Then it gets stickier from there. Is the engine making any knocking, rattling or rapping noises.
If no, then probably not a main, rod bearing or a lifter tossed out of the hole from a bad pushrod or rocker arm.

That would leave possible suspects of "decreasing oil pressure" to lead to oil pressure relief valve in the oil pump or possibly a spun cam bearing.
 
You say the riser got hot enough to blister the paint? How hot did the engine get - what was the temp guage reading?

I would do as mentioned, change the oil and filter then get a manual gauge on it to verify what the true oil pressure is.
 
Thanks for replying. The sensor was reading correctly. I changed the oil. The old oil looked normal, but boy was that old filter heavy. Put in new oil, and started up. Oil pressures are back to normal. Ran the boat home on a 90 minutes cruise. Oil pressures stayed normal. I think I will change it again to be on the safe side. Issue appears to be resolved.

Regarding the overheat, I didn’t explain the paint very well. The paint on the stainless elbows crackled. The paint on the manifolds is fine. Now that I have the boat back home, I can go over the enough room in better detail. I noticed a piece of wire looming that got brittle. Perhaps I was lucky in that regard.
 
Glad it is ok - I would have been sweating on that one! I have always heard you should change the oil first thing after an overheat - I know the heating/cooling cycles contributed to breaking down oil over time, but not sure exactly why a one time overheat accelerates this. The filter being heavy is curious, I would almost cut it open to have a look.
On a side note, I had an uncle that had the house next to my parent's lake cabin - he had a newer but still wooden Chris Craft - @1965 or so - he ran that thing hot one day to the point it just quit. I still remember the hot smell of the wood and paint in the bilge. Funny enough, he let it cool down, fixed the water pump and off he went - never heard of any other problems from that overheat!
 
I want to cut that filter open so much (in the interest of Science). But I don't have a band saw at home.

In any boat there is a normal accumulation of sludge that is a film on all the oil passages. The trick is doing enough oil changes to keep that to a reasonably thin layer.
My hunch is that the overtemp event made some of the normally accumulating solids (sludge) became suspended. Over the course of the week after the overtemp, none of my runs were longer than 30 minutes, so they stayed suspended, and the filter only saw a handful of turnovers of the oil volume with load. The start of loss of pressure started after an hours cruise home on plane, and the filter saw a number of turnovers with load. The filter did its job.

I thought about where the pressure sensor is installed at, and this makes sense. Oil starts in the pan, then goes to the oil pump, which discharges to the filter adaptor, them out to the remote filter housing, then from the remote filter housing back to the filter adaptor and to the engine. The pressure sensor is located right there. So the oil pressure we see on the gauges is the available pressure to the engine after the filter. If the filter consumes pressure (in other words is clogged), then the available pressure is less.

In hindsight, BillK is spot on. I should have changed the oil at the end of the day after the overtemp event. It would have saved drama on the run home. Lesson learned.

The other hindsight lesson is that as soon as I saw that the bilge pump was running, I should have stopped the boat immediately. I lost a few seconds slowly powering down, and looking at gauges for the source. 370 hp with no cooling water is a ton of stored energy; seconds matter. Shut the engines down immediately if it is safe to do so. Another lesson learned.
 
I don't believe the sludge theory, unless you never change your oil, there's allot of detergents in oil. You don't need a band saw to open the filter. Inquiring minds want to know what's in that filter.
 
Scoflaw, interesting...I trust your experience over mine. I'll open it this weekend and report back.
 
That outer skin is very thin, I put them in a vise and use a hammer and sharp wood chisel. Of course they make a special tool for that also but I'm too cheap.
Best of luck with the outcome
 
Thanks for the helpful push in the right direction, Scoflaw. Yesterday I opened the filter the that was changed after the low oil pressure. Inside was grit. I ran a magnet through it; the grit was not magnetic. Looking for opinions on the source that will determine the next steps. Given that overheat event was caused by lack of seawater flow, could be the filter breaking down, or it could be breakdown of one of the high pressure flex hoses (to remote oil filter or to the oil cooler; I believe one of those is near the exhaust manifold). There may be other sources. Your thoughts?

Below are pictures of what I saw. For curiosity, I also pulled a spark plug. Oil, filter, and plugs were new in April 2022. Filter was about 13 hours of running after the overheat.

Closeup of the filter media. On the top is sloppy glue.
Filter-1-Close.jpg


Filter media a little further away.
Filter-2-Far.jpg


I tapped the filter media and swirled the bucket. Very fine grit. Non metallic.
Filter-3-Oil-Debris.jpg


For my own piece of mind I pulled a plug.
Spark-Plug-2.jpg
 
Try to get enough oil for an analysis at a lab. Engine bearings are non-magnetic. If the grit is silver colored it's probably the bearings. I wouldn't use the engine until you figure this out
 
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I have two oil test kits coming from Blackstone:
  • One for the oil in the photo above (13 running hrs after overheat),
  • Second is for the oil that is now in the engine (14.5 running hrs after overheat). It will be interesting to see whether I can pump the oil with it being cold.
 
Not the best day today. Test kits came in on Friday so I drained the oil in the engine. Took over an hour since the I left the engine off and the oil was cold. Filter look great but I noticed a small amount of water in the oil; Not good. Will send both this and the previous change oil samples to Blackstone. Any one know if they can tell if the water is fresh or salt?
 
Here are the results of the oil tests. I am curious about the amount of iron wear on the first sample. And if I read this correctly, it seems I need to be dealing with head gasket, and check out the oil cooler. I need to talk the tech but they are east cost time and I am west coast.

First sample, from oil change 13 hours of running after the overheat.
07-SEA-RAY-220921-Sample-1-Publish.jpg

Second sample, this was fresh oil put in after the first sample. It had 1.5 hours of running on it:
07-SEA-RAY-220925-Sample-2-Publish.jpg
 
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I'm not an expert on oil analysis. But your early on issue of an overheat followed by low oil pressure screams blown head gasket(s). You could do a compression check to determine if it is one or both. Head gaskets can seem daunting, but it's not really an enormous deal, if that is the extent of the damage.
 
Thanks for the input from both of you.
I spoke with Blackstone this am:
  • Grit may be gasket material, or a reaction of the oil and the coolant.
  • The origin of the iron number was harder for them to pin down. Could be from the exhaust manifold, could be from cast iron head, could be from the cylinder liners. Likely not from the crank or cam shaft since the bearing metal numbers are so low.
At this point, it is possible the engine will live (its also possible it may not...); We won't know until the head is opened. I suppose I should hold off on ordering a gasket kit until we open it and get a chance to see the condition of the block.

All this drama over one failed hose clamp.
 
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