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Background: Yanmar 240's, Issue with port engine only, oil is full. Wiring on port engine is starting battery and house charged off the port alternator. Batteries connected via a Blue Seas ACR (automatic charging relay). Alternator output is to hot side of starting battery. Hot side of starting batttery runs to ACR, and then to hot side of house battery. Relay is to open only when there is a charging source for more than 2 minutes, and thereby charges up the house battery too. Alternator belt is basically new - less than 30 hours. Negative side of the house battery is NOT connected to negative side of the starting battery or to the engine ground (as originally configured, it changes below).

Instrument panel is powered off the starting battery. Batteries are Odysessy (under Dia Hard Label now).

Current Problem - When you accelerate, the oil pressure drops.

Oil Pressure readings - warm engine:

900 - idle - 30lb.
2400 - 18
2700 - 60
pull back to 2400 - 18 or less (sometimes down to 10)
pull back more to 2200 - 50lbs.

Over all gauge seems kinda bouncy.

SB engine:

900- 40
2400 - 60
2700 - 70
(It always has been about 10 higher than port).


History of problem - about a month ago, we were heading out. Oil pressure becgan to drop as I powered up leaving the marina. At the same time, the volt gauge began to drop. Rather than 13.8 to 14, it was falling down to 12. Checked the belt tension, checked oil, checked engine for other signs of problems, nothing.

So, determined it was an electrical problem, ran boat 50 nm., volt gauge continued to crash. Finally dropped down to 8. Turned engine off. Disconnected house battery, disconnected ACR. Both batteries on that side were pulled down to nothing. Used SB battery to re-start engine. Ran home at 2600. Volts were 14, oil pressure 50, and only the starting battery was used to run home. House was completely disconnected from alt. output.

Back at the dock, the house battery was put on a charger. It came up to 60% then kinda hung there. As if it would not take the charge. It was more than 5 years old, so I replaced it.

Starting battery was 60% charged by the alternator by the time we got back to the dock. It recharged fine.

Initial conclusion - bad house battery. Reconnected ACR and replaced house battery.

Ran this weekend again. All batteries 100% when I left the dock. Same story. Power up, volts drop, and oil pressure drops. Return to dock, disconnect ACR, and wire batteries in parrall (spelling). Meaning, hot to hot, negative to negative. Crank engine, volts now look right. But, I still have the weird oil pressure drop in this 2350 to 2550 range.

This weird oil pressure issue happens in the slip with no load, and under load.

Efforts to cure - pulled the dash panel, checked all connections, nothing appeared out of wack. CX applied.

Also checked ground conections at engine, battery connections, and made sure nothing had become disconnected. Oil pressure sender wiring looks good. Volt meter is accurate.

Current conclusion - subject to input from the board brain trust.

This is an electrical issue, not an oil pressure issue.

I plan to put a manual oil pressure gauge in the engine compartment, but nonetheless, why would the oil pressure drop at this relative narrow band of rpm's and then rise when the rmps are above or below the band? Does not make sense.

Could this be an alternator issue - voltage regulator? I did not swap alternators. And, the ground for the instrument panel is a common ground off the engine wiring harness. At the dash, this ground is jumped from gauge to gauge. Water temp gauge is not acting up. Tach on that side is not acting up either.

What sayeth the board?

Many thanks in advance.

Put a digital voltmeter on the panel 12v feed and watch it as you run the rpsm up and down. Gotta be a voltage problem related to either a falty ground or the charging relay sticking....CX will fix it.

Never trust electrical pressure or temp. gagues without verifying with a mechanical or IR.

UV

if the 240s are like the 230s if the belt is loose your rpms will be all over the place, i had a oil gauge bounce around on me at the start of the season, tuned out to be a loose wire on the bottom of the oil pressure sensor, or try changing out the sensor cheap enough to replace, should be located by or under oil filter 2 wires running to it. hope this helps

Ernest: Can you take the sender wire loose from the good engine and add a jumper wire over the the sender wire for the bad engine to make sure that it is not a sender issue?

Good thoughts all. Appreciate the input.

Charlie - the 240's are the same as the 230's, they just changed the ratings. I have a relatively new belt, its tight, and its the good fat belt, not the skinny belts that originally came with the engines.

Vic - you know, as this was going on, I was kicking myself because the old gassers had mechanical pressure gauges in the engine area, and I simply failed to install mechanical gauges when I repowered.

Rawleigh - I did not think of that. Good idea, and that should show whether its a sender issue in short order.

Big picture - the "kinda sorta" electrician that was with me on Saturday kept saying, its a faulty ground someplace. Check your grounds. So, thats what I started doing on Sunday with respect to the dash panel and battery and engine.

No takers for the bad alternator/voltage regulator? That was my guess going into this post.

Alternator is possible.

If it is not charging properly or working properly but intermittently than that can cause issues with your gauge readings.

This alternator is doing the house battery as well and can be compunding your problem.

I assume your wiring is OK so I would possibly switch alternators to see if it fixes problem.

I agree that your oil pressure is OK and its the signal to the gauges that is getting whacked out.

You can hook a mechanical gauge up to be 100% but like I said its prob OK.

Further more, if your batteries are that drained by time you get back then I would have to agree that the alternator is not charging properly.

A bad ground could cause that but I suspect the alternator.

Ernest,

My oil slingin' dump truck motors are a completely different beast, but I had the exact same problem about 5 years ago.

After doing a lot of swapping and trouble shooting, like you are doing, I traced the voltage drop to the flybridge. Removed the flybridge instrument panel and inspected it.......green corrosion on the under side gauge connections from condensation.

R+R all the connections on the problem gauges, cleaned and re-tightened.

Sprayed all with corrosion x.

Problem went away.

Paul

Thanks for the additional comments.

The time it drained the batteries, I had turned off all the electrical stuff except only the plotter when the problem first arose. So, I had the engine running and the plotter. Maybe the B pump came on a few times, but all the radar, sounder, auto p., and the like was turned off. Ran something close to 3 hours/55 n.m.'s.

Nevertheless, it drained both batteries.

I would assume, if the ACR fails, it is designed to fail in the closed position. Meaning, no juice flows from the house to the starting battery.

Unfortunately, when I was initially troubleshooting this issue over the weekend, I did not appreciate that the charge had to hit the ACR for some two minutes before it opened up. Thus, I cranked the engine, put the meter on the output to house side of the ACR, got low readings - as in basically zero - and assumed it was bad. So, I just wired the batteries together.

This weekend I will go at it again. Check sensor, install manual gauge, and even swap alt's.

And, I'm kinda pizzed cause I'm trying to keep pace with that fish thug Tom P. Last weekend, he is just raping the fish. Had a white, had a sword, had a sail, had a blue, and some bottom fish to boot. I figure, had I been there in my boat, just the change from that Hatt to a Bert hull means I would have at least doubled his fish count. If I was running a 31, triple his fish count, easy.

Thanks again.

Tom P. is a member of the Thudd club?

Come on Walter, at least my little Hatt is running, usually. One day, when I get rich, move to a deep water area and fish a day boat, I will have a 31. I promise. Until then, I can at least hang with the cool guys.

Ernest is so tight, virgins point and laugh as he passes. I suggest he spend a couple of bills and have it diagnosed by the local yanmar guru. I'm way over the joy of self diagnosing electrical issues.

Man he has one good day of fishing and it goes straight to his head.
Maybe if you came and helped me work on mine you could ride in run haha

"Tom P. is a member of the Thudd club?"

Yes, and he owns a Hatt.

Update:

1. Swapped alternators. No change in oil pressure issue.

2. Swapped oil pressure sensors. No change in oil pressure issue.

3. Began inspecting wire from oil pressure sender on engine with problem. Connector to sendor looked good, but connector from wire to wire end was suspect. Cut and re-wired. Oil pressure issue appears to be resolved.

I say appears, because I can't run under load at speed. Dinged up one of the props, so I can't run it up. At the dock, no load, oil pressure reads normal with no drop along its range.

Still messing with the volts issue. Maybe that was just a battery going bad. Maybe cured by the the work on the dash. Still a bit of an unknown.

Thanks for all the thoughts and comments.

Maybe I'm wrong but rpm's and their correct oil pressure would/should be related, load or no load, no?

Walter - I would think so, but I was also thinking my oil pressure issue has an electrical source/origin for the problem, as opposed to a mechanical source/origin.

Ernest - I had the same problem with my gear pressure gagues - the wires from the senders on the gear to the FB had a few splices in them and those got corrosion & went bad - both of them back to back.

All these senders - oil pressure, temp, etc. - are nothing but varibale resistors that change resistance as pressure or temp changes....higher pressure, less ohms & vice-versa for example. The gague itself is nothing but an ohmeter that is reading the resistance in the circuit.....so, any corroded connection that increases the resistance in the circuit affects the accuracy of the reading on the gague.

UV