SmurfOnABoat

Ok here is the deal:

I was out boating today, and on our way in, cruising with the engine at 3500rpm, I noticed that the oil pressure was fluctuating between 0-30psi, brought the throttle down instantly and pressure came back, 3000rpm had 40psi, idle had 20psi (HOT).

Here is my thoughts:

-Wiring from switch is bad, or bad connection
-Oil switch has taken a crap
-New livorsi oil pressure gauge has taken a crap
-pickup fell off oil pump (dont know how these pumps come from mercury, if that is even possible, not sure if they are still press fit, or tack welded)

Going to take the boat out tomorrow night with a mechanic oil pressure tester and see if the problem continues... Just wondering if anyone else has some ideas that I might be missing.


Oil is maximum 15hours old. Rotella T 15w-40 with Amsoil filter.

stevesxm

your analysis of the possible causes essentially covers all the bases but your proposed diagnostic procedure of "taking the boat out to see if the problem continues" may very well be the dumbest thing ever suggested on this forum. you may as well have written " gee ill run it until it blows up and then find out what was wrong"

if the thing really had zero oil pressure at any time during that 3000 rpm run then there is great likelyhood that there is already damage and the very last thing in the world you want to do is run it under any sort of load. the first thing you do is take the filter off and cut it up and see if there is anything in it. assuming thats clear, then you drain the oil into a clean pan and look at that very very carefully. then you pull the plugs and with the feed line to the filter off, start putting oil in it a couple of quarts at time, and spining it over on the starter to see when oil starts getting picked up... if it happens at 2 or 3 quarts then the pick up tube is still in place... if it doesn't happen until 5 quarts or there abouts then the tube is probably off. don't treat those numbers as authoratative because your pan might be subtly different but its going to be quite obvious one way or the other...

only after you have done all that and confirmed all good should you even consider strating the motor with a mechanical gage.

its important that you understand the difference between starting the motor at the dock and discovering low oil press versus looking down at speed and seeing the gage on zero. at the dock at idle i would have no qualms about sticking a gage on it and starting it to check the gage first... but knowing as a matter of litteral fact that the boat the motor was in a severe load condition when the thing was going to zero means that IF the gage wasn't bad then you have some sort of damage already. the only question is " how much ? " and the next 10 revs could be the difference between a new set of rod bearings as opposed to a crank and rods and block.

maybe its the gage. maybe you'll get lucky. it will be great if thats the case but now is the time to be conservative and smart...

ezstriper

ck oil level, sounds like sucking pan dry...

SmurfOnABoat

now I did not say I am going to go WFO with the thing on zero psi and see what happens did I?

I have SOLID oil pressure under 3k RPM, so I start the engine, pending good pressure, take the boat out for a ride, if it fluctuates at all on the mechanical gauge, get out of it immediately and return to the dock.

1 second of zero oil pressure isn't going to do anymore damage than starting your motor that has been sitting for a few weeks without priming.


So technically that isn't quite the dumbest thing you have ever heard of on this forum. If it had fluctuating oil pressure at idle and all RPM range, then yes I would say dumbest thing ever.

My plan was to already change the oil, check the filter and with the empty oil pan, tap on the side of it with a hammer and see if the pickup is laying in there.... you will obviously hear it banging around if it did come off and install a new switch with a tee so I can put the mechanical tester in there and see if the gauge is faulty.

eztriper - Oil level is right on the money.

lake speed

Not to be pessimistic but my old motor did the same thing and unfortunately that why I have a new motor lol. spun main bearing and destroyed the block.

stevesxm

well... i could be wrong but it seems to me you said "fluctuating between ZERO and 30..." now admittedly my formal education was centered around the sciences and engineering disciplines but i do remember some of my basic english and it seems to me that a resonable person might surmise that since the motor was at 3 grand and IT wasn't fluctuating from zero revs to 3000 every time the oil pressure did that there were some times when the motor was under load at 3 grand with ZERO oil pressure. never mind when you wern't looking...

but hey... since you are the one with the ultimate responsibilty, then you get to assign whatever level of importance to that ugly fact that you care to.

and yes... if take that boat out and run it under load to check the gage before you do the rest then you are, in fact, the dumbest person that has ever posted here.

Expensive Date

Could it be overfull if so the crank throws could be airating the oil.The sensor will think the bubble is zero had that happen on a DT466 once.

Double Down

hey smurf you are coming across like an arrogant a$$hole who just happens to be asking for advice on this tread, if you don't want help then delete your post and take your chances...just sayin".

I am interested in the diagnostic points which stevesxm and others may kindly offer you in solving your dilemma, lighten up a bit!

Scarab28

Chased similar problem for two years only it happened at 5k rather than 3500. Believe it was bad relief valve in oil pump but not 100% sure. Yes it will eventually hurt the bearings. Also could be pickup too close to floor of pan sucking air at higher rpm or oil level too high, wipping oil and sucking air.

SmurfOnABoat

Not trying to sound arrogant at all, sorry for coming off that way. Just didn't realize that it wouldn't be assumed that I would check the basics without stating it. I didn't ask for everything to check and exactly how to look for what I was looking for, I was asking to see if there was anything I was missing (reread the original post)

Kind of like talking about starting a motor, I don't see someone coming out of the blue saying make sure you put oil in it, that should be assumed.

If I see zero PSI on the gauge I am not going to run right back out and run the boat the same way again. I guess I just need to write a complete novel so everyone knows that. I just wanted to know if there were any problems with the mercury or hp500 specific oil senders, or oil pumps. That I myself was not aware of.

Filter was removed, cut open, no metal, clean oil. Pickup still intact.

Taped with mechanical line tester, 62psi @ idle on mech gauge, fluctuating 52-58 on Dash gauge. Cold

Idle hot, mechanical gauge and dash gauge both 24psi +/- 1 psi of each other.

Over 3000rpm, mechanical gauge 45psi and climbing, fluctuating dash gauge between 0-25psi.

Suspect bad sender or gauge.

BTW, if someone wants to give helpful information, it doesnt help much when you criticize the other person as Steve did to me. Instead of wording "the dumbest thing ever suggest" or "dumbest person on this forum" you could act a little more like a damn adult and treat people with a little respect. God help me if I am not as smart as he is. (now I am being arrogant, maybe you can see my point of view).