Low oil pressure
 

Never seen this one before. I've got an 08 288 Sunsation with the HO. At about 25 hours or so I noticed low oil pressure on the gauge while running. Around 3000 rpm or more the gauge shows oil pressure between 20 and 25 lbs and the needle flutters rapidly between that range. Not a steady needle at all like is customary. Idling in gear at 800 rpm with warm oil the gauge shows a steady 20 lbs or more. I can bump up the rpm to 1000 to 1200 and the needle immediately jumps up to a steady 40 lbs. Which is what I would expect. Problem is as soon as I start getting up on plane and with the rpms increasing to 3000 or better the gauge actually shows the oil pressure going down and the more rpm the lower the gauge goes to it's lowest point of 20lbs at full throttle but again the needle starts fluttering rapidly between 20 and 25lbs.

This problem didn't start until I got about 25 to 30 hours on the engine. I now have 45 hours. Before then I had great oil pressure (40-50 depending on oil temp) and a steady needle at all times and at any rpm. I changed the oil at 20 hours with the recommended Merc synthetic blend and so far the engine doesn't use a drop. I've checked the connections on the back of the gauge and everything seems to be fine there. I'm hoping maybe a defective sending unit or a defective gauge. I'm also hoping it's not really running that low of oil pressure especially at the higher rpms which would make me think it's an internal problem with the pump. It's just weird how it worked fine for the first 25 hours though. BTW, this happens when the oil is cool or warm. The temp of the oil doesn't seem to affect the results on the gauge much.

Any help or suggestions is much appreciated.

check youre sending unit , ground ect

First thing I would do is hook up a mechanical guage. That will tell you if its an engine issue or just a gauge problem.

I agree with Checkmate. I have a mechanical guage permanantly hooked up to my engine in the engine compartment.

Good idea.
Any thoughts on where a good spot is to tie in the tube fitting on an HO?

Airation or pick up/pump problem?

I checked the engine oil level yesterday while on the water and it was just a hair over full, like a 1/16" or so. I may drain out a half qt or so just to see if it makes any difference. And also install a mechanical gauge to check to the factory gauge.

Drop it to the add line on the stick for a test. You most likely have too much oil and are foaming it! I've seen this DOZENS of times.

Thanks, I'll try that. I'm hoping that is it.
I'm assuming that the "airation" that has been mentioned is caused by too much oil also right or can airation also be caused by something else?

Thanks for all the help guys!

I'm betting its the oil filter. Change the filter and see what happens.:cool-smiley-011:

ya that's probably it. And replace the fuel filter too right? :D
If you were serious, sorry.
Hey I'm not ruling anything out just yet though.

Why take the cahnce of messing something up, take it back to the dealer. It has to still be under warranty if it is an 08. Just my 2 cents

It's caused by the oil in the pan being high to the point that it rises above the windage tray or if no windage tray, either way the crank whips the oil, aerating it and literally making it froth and/or foam. I know this because it's happened to me with inferior aftermarket oil pans that advertise capacities that are two quarts larger than they actually hold. Did I say Milodon????

I wasn't kidding. It happen to me last year. I could not figure out what it was so i called mercury racing and they told me it was the filter. I changed it and thats what it was. If anything goes wrong inside the filter than the oil will bypass the filter and dump the un filtered oil back into the pan. The pressure will stay between 20-25#. It scared the chit out of me when it happen. I was running about 80 when the pressure dropped. The oil temp will climb also because your than by passing the oil cooler. Its only 10 bucks. Change the filter first to see if that helps.

Got it. Thanks!

Are you getting a hard alarm and going into guardian mode? If your not your probly fine. The Smartcraft system has its own sensor that supplies info to the ECU. Your guage runs off the traditional sending unit off the back left corner of the motor on the oil gally.
I wouldn't mess with trying to hook up a mechanical gauge. Find someone with the merc scan tool or Diacom. Hook it up and go for a ride while it is recording. It will give you the actual oil pressure off the computer. My guage reads lower than what the computer does.

No alarms and no guardian mode. No change in performance at all when this happens. The pressure just slowly drops off from 40psi while getting on plane and as the rpms go up. Then it just flutters between 20 and 25. I thought the same thing about trying to hook up a scan tool but I don't know anyone than has one. I'd actually buy one if I could find one cheap enough. I'm sure it would come in handy to have one.

I drained about a qt out tonight and plan to get it in the water no later than the w/e. I'll check the oil level at rest in the water and make sure I'm in the range but not even close to over before I fire it up and run it. If it still happens I think I'll replace the filter and throw in new Merc synth blend and try it again. Again making darn sure I'm not over. If it still does it then I'll be forced to add a mechanical gauge just to make sure it's not a gauge or sending unit problem. A scan tool would make this much easier thats for sure.
Hopefully I'll have some answers soon and it will just be operator error. I could handle that even after 30+ years of boating. :)
I know it's under warranty and nothing against the dealers but I just hate to take my boats to the shop unless I absolutely have to. Especially a brand new one like this.
Thanks for input!

Any possibility that water is getting in the oil?
A "milkshake" in the top portion of the engine will also make a froth and cause the oil pressure to behave just as you indicated. You might check under the oil filler cap to see of any indication of this.

Closed cooling. Would have oil in the surge tank before coolant in oil.

No signs of any moisture but I'll double check.
Thanks

Sounds like your a do it yourselfer like alot of others on here. IMO Diacom is well worth the $400 in the long run. Nice thing is that it will also scan the early merc EFI stuff as well as be upgradeable for future merc technology. I was like you and held out for a couple of years, finally did it this year. Even if your not getting codes it's neet to be able to see everything that it can show you about the 496.

Well I eliminated two possibilities today. I changed the oil and filter and went out on the water. Same deal.
Oil level was right in the middle between full and add so I would think that takes care of the airation from too much oil possibilty and the new filter eliminates it being a bad filter. I have a new Merc sending unit on the way and also a new Livorsi oil pressure gauge. Hopefully I can get them installed next week and see if either one of those takes cares of it as I know I'm running out of weather here to get this diagnosed.

Today the oil pressure would run about 40 (steady) @3000 but much past that the pressure would start to drop and the needle would start to flutter. Idle was at 20 lbs but if I bumped it up to 900 rpm or more the needle would jump to 40. It did seam to get slightly worse the warmer the oil was on the oil temp gauge. If the new sending unit or the new pressure gauge doesn't do it then it goes to the Merc dealer. I have a mechanical oil pressure gauge but couldn't find a good place to tie it in on the block. Getting to and replacing the sending unit is going to be a challenge in itself. It's on the port side on the rear of the engine somewhat hard to get to.
I fear the worst. Almost ready to pop the $399 for the Merc scan tool from Rinda.

Looks my low pressure problem wasn't really low oil pressure. In the essence of time I replaced the sending unit and oil pressure both and took the boat out for a run Friday night. The gauge stayed steady and did not flutter at all even during a hard run at 5000 rpm and with oil temp a little over 200. Oil pressure ran steady between 40 and 50 psi at WOT and a hair over 20 psi at idle after the hard runs. As oil temp went down the oil pressure would come up at idle. Unfortunately I will never know whether it was the gauge of the sending unit causing the problem. I'm just glad it wasn't a pump problem or other internal issue.

Thanks for all the help and suggestions!
PK

first thing first>>> validate the problom, remove the oil
sending unit, screw in a manual guage on a short hose and
verify that you really have an oil pressure problom and not an
electrical prob with the guage or s-unit. Good mechanics always check the simple first before going to the complex.