3.0L OMC Engine

[gtaeza]

I noticed that only 3,500 rpm I got and the engine is aalready noisy. Timing is o.k it seems to me everything is okey. Is there anymore things to do to improve the rpm. and what is needed to be change. You advise is greatly appreciated.

 

[cuzner]

Re: 3.0L OMC Engine

Hey george, what size boat do have and what pitch prop do you have? is 3500 rpm at wot?<br /><br /><br /> Jim

 

[Boatist]

Re: 3.0L OMC Engine

I agree need to know your speed at 3500 also. Has it always been WOT at 3500 RPMS or is this something new. also as Cuzner said size boat and pitch prop.<br /><br />It could be too much or not enough fuel, loss of compression on one or more cylinders, valves not adjusted correctly, too much weight in the boat, dirty bottom of the boat.<br /> <br />Start by giving as much info as you can and then someone may be able to help you.

 

[TwoBallScrewBall]

Re: 3.0L OMC Engine

What do you mean by noisy?

 

[gtaeza]

Re: 3.0L OMC Engine

1. The timing is O.k<br />2. The compression test is ok. 150+ all cyl.<br />3. The boat is 1979 OMC.<br />4. The noise is like whistling at WOT.<br />5. The pitch is 13-1/4 X 17"<br />6. The boat is free and I chaged the manifold,<br /> circulating pump, thermostat, sending unit,<br /> valve grinding, etc, <br />7. I still got 170 deg. when I go to full throttle

 

[gtaeza]

Re: 3.0L OMC Engine

By the way it's a 140 HP GM engine.

 

[cuzner]

Re: 3.0L OMC Engine

Doesn't sound like a prop issue, what speed are running at @ 3500 rpm,if your over 30 I'd look at your tach to see if its working properly.<br /><br /><br /> Jim

 

[gtaeza]

Re: 3.0L OMC Engine

Jim <br />I installed a new teleflex tach. the other day <br />also if I accelerate higher the tach seems remains<br />at 1000rpm at half throttle. It looks like the<br />tach is not indicating the correct engine rpm.

 

[cuzner]

Re: 3.0L OMC Engine

Hey george, looks like we may found your problem(tach). I'm not much with electrical problems,someone else should be able to help you there. I had 17p prop on an 18ft cuddy with a 3l engine,and was almost 5000 rpm @wot (34 mph).Thats well above recomended rpm.The noise may be from over reving engine. Any idea on the speed your going?<br /><br /> Jim

 

[Boatist]

Re: 3.0L OMC Engine

Ok Now we know you have a 3.0L 140HP OMC stringer with 150 PSI in all cylinders and you have a 17 pitch prop. <br /><br />Your tach is bad so have no idea of your WOT RPMS.<br /><br />Still do not know your speed and if motor is in a aircraft carrier or a 14 foot car top boat.<br /><br />First you need to get the tach fixed and give us your WOT RPMS. Then need boat size, type and speed.<br /><br />At that point someone may be able to help <br /><br />The 170 degrees at WOT is pretty normal for that engine. Should return to 150 at slow speeds.

 

[Bondo]

Re: 3.0L OMC Engine

4. The noise is like whistling at WOT.<br />

Vacuum Leak......

 

[gtaeza]

Re: 3.0L OMC Engine

Hello my friends,<br />The tach. setting wa set to 6p that's why the<br />reading is incorrect now it was set to 4Cylinder<br />and the rpm reading at full throttle 5500 rpm. So,<br />it seems the rpm is ok. Thank you guys for helping<br />me float my old boat.<br /><br />It seems to me there's no vaccum line.

 

[cuzner]

Re: 3.0L OMC Engine

Hey George,5500 rpm is WAY to high for that engine!!!! I think the max is around 4600.Unless you own an oil well you should keep your rpm at around 3200 while cruising. This won't slow you down too much and will save alot of gas.<br /><br /><br /> Jim

 

[gtaeza]

Re: 3.0L OMC Engine

Jim, thanks for your advise. I appreciate it.

 

[Boatist]

Re: 3.0L OMC Engine

Max WOT RPM range for a 1979 3.0L OMC Stringer is 4200 to 4600. You need to change from that 17 pitch prop to at least a 21 pitch prop and maybe even a 23 pitch prop. The 21 pitch prop should gain you about 6 MPH and better fuel mileage. You should still have a good hole shot and turn 4700 RPMS. 4700 RPMS is still a little too high. A 23 pitch should put you at 4300 RPMS and it would be my choice. A 22 pitch would be even better if you can find one.

 

[cobra 3.0]

Re: 3.0L OMC Engine

I dunno, I have a 17" pitch on my 16 ft bowrider 3.0 OMC Cobra and get no where even near 4800 rpm with no gear aboard, hardly any gas, going with the current, and naked!<br /><br />A 19" pitch is as high a pitch as my boat can handle as it revs 4200-4300 and I get around 37-38 mph measured by GPS.<br /><br />5500 rpm? No way! Unless you have it rigged on a large bathtub!??? Don't you mean 4500?<br /><br />What is your boat? 16,17,18, 19 ft? What kind? Bowrider, cuddy cabin, etc.

 

[gtaeza]

Re: 3.0L OMC Engine

cobra you're right 4500rpm. I don't know my speed<br />yet due to have no speedometer only last week that<br />I installed the 17" pitch from 15".

 

[Skipster1]

Re: 3.0L OMC Engine

All this debate about maximum RPMs can best be summed up with one basic rule: Keep it at, or under, 4,000 RPMs.<br />The engine may be able to handle more but the attached equipment - fuel pump, oil pump, etc. - are not designed to handle higher RPMs .... unless you have heavy duty equipment installed.<br />Operating at, or under, 4,000 will assure you longer life on all parts as well as better mileage.

 

[gtaeza]

Re: 3.0L OMC Engine

Skiph: Thanks a lot for your recommendations.

 

[Boatist]

Re: 3.0L OMC Engine

If you are turning 4500 at WOT thats perfect, go out and enjoy the summer.