02' BF225 gradual loss of oil pressure at higher RPM

Here's what I've got, oil pressure is initially within acceptable ranges (around 30psi at idle and 60-70 at 2500-3000rpms). When I get on plane and am going about 25mph (2500rpms) it will initially go for about 5min and then the low pressure (continuous) alarm sounds, green oil pressure light goes out, and guardian mode kicks in. I shut down the motor and restart. Pressure returns to normal. I can get about two minutes within 2500rpms before it repeats and if I hit hard and go up to 3000-4000 the alarm goes almost immediately.

I ran it with a pressure gauge attached and noticed that while pressure look good at the start it will gradually decrease to around 30-40 (while at higher rpm) until the alarm sounds.

interventions:
Changed oil & filter multiple times
Replaced both high & low pressure sensors (prior to running with the gauge and realizing it was a gradual pressure drop)

I'm a bit stumped on this one. I had rebuilt the motor prior to these issues and know all the bearings are in proper tolerances. I'm not familiar with the oil flow path so I'm lost as to why the pressure would be gradually dropping. it never drops below 25-30psi at idle which makes my believe the pump is fine.

Would a worn pressure valve spring or a clogged valve spool filter attribute to any of these symptoms?

Any ideas would be appreciated I'm chasing a dragon at this point.

What is your idle oil pressure with a cold engine, it should be close to 80psi and drop to 30-40 psi oil is at operating temp. Above 2000 rpm oil pressure should be constant and above 80psi
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Also, can you be more specific about work done, full rebuild, partial, was condition there before rebuild etc?

iang6766 said:

Also, can you be more specific about work done, full rebuild, partial, was condition there before rebuild etc?

Click to expand...

PSI at cold startup initially jumps to between 70-80psi at idle and then falls to 30psi after running and warming up for a few minutes.

Work done was a partial rebuild...I had replaced the tensioner pulley and mistook some paint marker for the alignment marker when position the crankshaft at TDC. Subsequently upon attempting to start it screwed up a valve stem. I immediately recognized my error and corrected it but the damage was already done and the next time I took it out on the water it ran great for 15min before the damage valve broke off in cylinder 4 and cracked the piston sleeve/power head. I replaced the power head, starboard head, #4 piston, rings, plugs bearings and quite a few other parts along the way. All oil seals have been replaced along with every gasket and O-Ring for any part I removed for the repair.
Also had recently replaced T-Stats, impeller, heat sensors, low pressure fuel pump and high pressure strainer for a previous issue...which has been fixed just prior to the tensioner pulley failing and the new set of issues arises...self inflicted issues unfortunately
Main and piston bearings were all within proper tolerances at install, checked with plastigauge, and there was no sign of shavings or bearing contamination residue/sheen floating on the surface of the oil I replaced when the low pressure issue began.

So you have answered my question, you clearly have an internal oil leak, where is anyone's guess. I have rebuilt a lot of these, let me have a think and I'll get back to you.

Just a far-fetched idea - is it possible you actually have an overheat situation that is thinning out the oil?

Also, in my part of the US, most folks with big Honda's have switched to the Merc 25W-40 oil, which is a bit thicker.

Overheat is a possibility, although it's not hot enough to trigger any alarm. Impeller, T-Stats, and heat sensors are all new so it would be a surprise. Trying a higher weight oil is a simple attempt that doesn't hurt anything so I'll give it a shot.

The only two possibilities is the oil pressure relief valve or missing oil flow restrictors in the block between the block and the cylinder head feeding the camshafts assuming your bearing oil clearances are correct as you say. Quite honestly, I have never come across an oil pressure issue with these motors, I have seen engines with up to .003" oil clearance that still had plenty of pressure.

Honestly I have no idea what the oil restrictors are so I could have easily missed that when putting the the parts into the new block. Trying to find a diagram for those parts/locations in the shop manual...any idea what part number those are?

15140-P8A-A00 is this it?

Ok I found what you're referencing, I recall replacing the O-Ring but I honestly can't recall confirming they were in when I reinstalled the heads. I'm going to have to pull the heads to have a looksie.

Here's the update:

I searched through archived pictures that I had taken while putting everything back together and was able to confirm that the Flow Restrictors are in place...so that rules that out. Unfortunately, that leaves only one other possibility according to your assessment.

I'm going to attempt the heavier weighted oil just to give that a good college try before going internal. Probably unlikely fix but if I get lucky it sure bear's breaking things down far enough to access the relief valve.

Also random thought, do y'all think there's any chance a clogged spool valve filter could affect things?

Clogged spool valve filter will not affect oil pressure.It's really hard to diagnose a problem like this, I'm pretty certain it's to do with something missed during reassembly. Oil grade will not change anything, I'm afraid all you can do is dismantle and carefully check everything again.I am certain you've left an o-ring out somewhere, an oil restrictor or you have a broken pressure relief valve spring ( highly unlikely). Let us know what you find
Get a factory manual and go through everything step by step, it shows all the components really well.

Sorry to leave y'all hanging it's been busy over here.
So one thing I gained to mention at the start (nothing ground breaking just as to the mystery), but when I had initially completed my "motor rebuild" and gave her a test run when I had put her in the water she ran for about 15min (mostly idle with and when in gear very low rpms because I never got it of the no wake zone from the ramp). Alarm sounded, never got on plane. I assessed the situation and decided perhaps the "break-in" from honing cylinders caused the oil filter to clog and so I changed the oil + filter. Repeated test in the same location/ramp. Got through the no wake zone and got on plane (2500rpms) for less then a minute. Changed oil again and repeated, worked for about 5min on plane. That was when I changed the oil sensors and found the procedure (oil location) to hook up a gauge and test actually oil pressure. And then came to you guys with my findings.

Current up date, haven't had time for a water trial, but for kicks and giggles I went ahead and changed the oil yet again. I used the Merc 25w-40. On hose pressure it appears to be running at a higher pressures. Previously my idle pressure had been between 25-35psi and it was running 40+. Couldn't sustain any higher rpms to see if they're was any change in sustained pressure at higher rpms because it was on the hose but hoping for a water test this week.
Not holding my breath but it's worth a shot. I'll keep y'all posted.

Hey gents,

Life got in the way of the boat for a while so I hadn't been able to get anything done until recently. The good news is it appears to have been fixed. Basically I continued chasing the oil pressure issue inspecting and testing different components. Each water test produced the same result. Green oil pressure light would go off, continues buzzer would sound, motor would go into limp mode...all signs consistent with an oil pressure issue. Last test I ran I had put in the oil Hawk had suggestion, 25-40merc, boat went a little further/longer but still gained. Got me thinking of something Hawk had mentioned early on asking about overheating. At the time I hadn't thought it was an issue as the impeller was beans new T-Stats we're six months and the heat sensors were all new... Nonetheless I decided to just pull out the T-Stats and try running on the water without them in. (Even though I tested then in hot water and they appeared to function properly, but after taking them out everything ran fine. I didn't the entire day on the water. Now I just have to figure out what long term affects running without thermostats would be. Now that it works I don't really want to put them back in... Crazy problem that led me down a ton of rabbit trails but hopefully if anyone else has similar issues this thread will provide done insight.

I really appreciate all the help and thoughts y'all shared.