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Calling all small block Merc owners - Specifically 6.2 liter
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Author:  Berger [ Mon Aug 13, 2012 2:48 pm ]
Post subject:  Calling all small block Merc owners - Specifically 6.2 liter
Well, my new boat has been running great. However, I noticed that when I run at high RPMs (4,000-5,000) for a period of time, my oil pressure crashes at idle. The alarm doesn't go off, but I cannot remember if an alarm even goes off when I start it or not, so that may not even be functioning. When I'm running at 3,000 or so RPM, the pressure is at 40, but the more the engine warms up over time, the pressure drops below 10 at idle.

How concerned should I be? The oil is full and unless I cannot hear it over the exhaust, I do not hear any valves tapping or anything.

Thanks
Author:  RedRocketSS [ Mon Aug 13, 2012 2:53 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 liter
General rule of thumb that for every 1,000 rpm you have, your oil pressure should rise by 10 psi. With that being said, I never did like that rule.

I would have it looked at for sure though. Could be something simple like the oil pressure sending unit or the gauge being faulty. Hook a mechanical gauge to it and see what it says.
Author:  Paul I. [ Mon Aug 13, 2012 3:26 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 liter
What wight oil are you using. Nerver had the problem, but I do remember seeing post to this. They were running 10-30W oil.
Author:  ric [ Mon Aug 13, 2012 3:34 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 liter
My boat did that with a KN oil filter after a little bit, something happened to it and it went into bypass mode most of the time. Switched to a mobil 1 oil filter and all went back to normal.
Author:  Hodge [ Mon Aug 13, 2012 3:38 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 liter
What weight oil are you running?

When oil warms up it becomes thinner and running at the high rpms is warming up the oil. thinner oil is easier to pump and therefore creates less pressure. Think of maple syrup out of the fridge compared to after it is warmed up in the microwave.

Boats don't typically need a thin oil like 5W-xx because they tend to turn higher rpms(and run warmer) and are usually only run when it's warm out.
Author:  Berger [ Mon Aug 13, 2012 3:58 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 liter
I honestly have no idea what weight oil is in it. Given the oil appeared pretty clean and full, I didn't consider changing it until I winterize the boat.

My main concern is that I have a work "off-site" meeting scheduled on the boat for tomorrow night, so I'm just worried about causing any potential damage if we go out.

Once it dipped below 10 psi this weekend, I revved it up a little to bring it back up to 10-15 psi at about 1,300-1,500 rpm. It just made me nervous seeing it so low, unless that is normal after running it at 5,000 rpms for a small stretch of time...
Author:  ric [ Mon Aug 13, 2012 3:59 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 liter
You should be at least 20 psi idle. I'd change out the oil/oil filter.
Author:  Walt [ Mon Aug 13, 2012 4:13 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 liter
according to the manual, 6 psi is the minimum required oil pressure @ idle.
Author:  Graham R [ Mon Aug 13, 2012 4:47 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 liter
ric wrote:
You should be at least 20 psi idle. .



I can't really believe that; admittedly, my current boat's engine (5.7 GXi) does run something like 20 psi at idle if the gauge is to be believed. There again, the voltage on the dash is never indicated to be above 12V, usuallty less; the fishfinder wired seperately indicates 13.9 V ! I really must rerwire the dash with a proper fuse panel/ breaker panel !The engine in my previous boat ( 5.7 GSi, less hours), felt like a much more powerful engine but oil pressure dropped to about 5 psi or even less at idle. No bearing knocking sounds. Maybe it was the VDO cluster ( no other issues with it !) or a sender.
Author:  NiagaraChillin [ Mon Aug 13, 2012 5:00 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 liter
Hodge wrote:
When oil warms up it becomes thinner and running at the high rpms is warming up the oil. thinner oil is easier to pump and therefore creates less pressure.


+1 to that. While my boat knowledge is weak, I am a gearhead from way back and 4-5k rpms will thin oil quickly, leading to low readings. But, low pressure doesn't mean no oil is circulating and doing its job. How long does it take for your psi to come back up after you go back to idle?
Author:  LouC [ Mon Aug 13, 2012 5:25 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 liter
Oh Oh an oil thread....
well here we go...its a Merc engine and Merc, never recommended a 10W or 5w anything so lets start right there. You should be using either, Merc's 25/40 sterndrive oil, or straight 40 if you listen to Merc.
I've used both straight 30 (OMC's rec) and straight 40 (my preference for a 24 year old engine of unknown hrs) and I can say that my hot idle pressure is usually around 20. Cold idle is about 40, at 3500 on plane its about 55, maybe 60 tops.
The issue with using multi vis oils (conventional oil) that span a 10-30 or 10-40 range is that they need VI improvers to do that. They eventually break down and then the oil can shear down to a lower viscosity. So change the oil n filter and use Mercs stuff and report back.

If I put a new motor in my boat, I will probably use the Merc stuff, it's the only easily available oil that meets their sterndrive specs. But in truth I have had no lubrication or oil pressure issues using Chevron Delo 400 straight weight conventional.
Author:  Technologic80 [ Mon Aug 13, 2012 6:16 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 liter
((waves hand!)) I was one of the members here who had problems running a 10w-30 oil in my boat. At the time, it was my 99 Vista with a 5.7l engine.

After coming off plane, the oil pressure would drop like a rock and the alarm would sound. Verified with a mechanical gauge. Cruising around I had 50psi. Cold starts I had good oil psi too. But after running for a while, apparently the 10w-30 thinned out too much.

Changed to 15w/40 conventional and never had a problem again.
Author:  Berger [ Mon Aug 13, 2012 7:13 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 liter
Thanks for all the great and quick feedback. I do feel much better now. I had no idea oil pressure could drop so low and not necessarily be an issue. I will change my oil and filter ASAP and will run straight 30 or 40 weight oil going forward. I can only assume that there is currently some thinner oil in it now, and as long as I avoid any 5,000 RPM runs tomorrow night, I should be ok. I'll just watch the gauge like a hawk.
Author:  bigvander [ Mon May 13, 2013 1:42 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 l
Berger, love the graphics on your 260. Sharpest scheme I've seen yet. Anyway, I am wondering how you like the 6.2 in a 26' boat. I am looking at a 2001 260 with that engine. All of the other 260s either have 454 or 496. How's the hole shot, planing, and top speed? What outdrive and prop are you running? Any info would be greatly appreciated, thanks.
Author:  pet575 [ Mon May 13, 2013 2:54 pm ]
Post subject:  Re: Calling all small block Merc owners - Specifically 6.2 l
I've had this issue as well but have never verified that it was anything other than a faulty gauge or sending unit. Took it back for temp sensor/sending unit checks when under warranty and it went away. I've never changed a thing and have always run the 25W40 in it.
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