Is running at low RPMs for a long time "bad" for the engine

[mjfink]

I live in an area that's got extensive no-wake zones; there are lots of times that I'll have the boat out for hours and never crack 1500RPMs. Is this type of use bad for any parts of the engine? I use my boat almost like a trawler, operating almost exclusively at displacement speed, I'm just worried that my engine isn't made for this and maybe I'm not getting it hot enough or running it hard enough to "work it out" when I take the boat out.

Boat is a 260 Sundancer with a 5.7MPI engine. Raw water exhaust.

 

[79Merc80]

Re: Is running at low RPMs for a long time "bad" for the engine

When vollunteering for Seafair's boat races in Seattle, we run our boats at idle from Friday morning thru Sunday afternoon running all day with the possible exception of during the air show, and those of us that help set up, are running it like that for a week solid.

Not sure if it's good or bad for the engine, but they seem to be able to deal with it.

Hope others will chime in as I woulod like to know as well.

Craig

 

[Technorunner]

Re: Is running at low RPMs for a long time "bad" for the engine

You dont have to worry. Its not bad for the engine. As long as the engine reaches working temp its no problem at al!
And i think you should have full voltage from the alternater at about 1000rpm. So charging shouldent be any problem either.
What is less healthy is short runs with lots of coldstarts with the engine not reaching working temp.

 

[picklenjim]

Re: Is running at low RPMs for a long time "bad" for the engine

Just keep an eye on the gauges and it should be alright. What I have heard is with an I/O running under 1500rpm's for long periods is hard on the coupler.

 

[achris]

Re: Is running at low RPMs for a long time "bad" for the engine

Just keep an eye on the gauges and it should be alright. What I have heard is with an I/O running under 1500rpm's for long periods is hard on the coupler.

That's true. It creates a load/no load situation so the yoke is constantly switching between the drive side of the splines and the overrun side of the splines. Like constantly on and off the gas in a car (just like the Singapore taxi drivers do, and you should hear their diffs :facepalm...

As far as the engine itself is concerned, as already stated, as long as the engine's at normal temperature, AND it's been run in properly (not still in the run in period) you should be fine. You might find some of the carb engines might have a tendency to 'fuel up' a bit, just knock it out of gear, give it a rev with the fast idle lever, back to idle, pop it back in gear, good to go....

Chris............

 

[Technorunner]

Re: Is running at low RPMs for a long time "bad" for the engine

achris: when you run it at low rpm do you still get thet situation of load/no load or is it if you often go gear/ no gear that gives that wear on the yoke?
Just courios and it can be good to know .

 

[achris]

Re: Is running at low RPMs for a long time "bad" for the engine

achris: when you run it at low rpm do you still get thet situation of load/no load or is it if you often go gear/ no gear that gives that wear on the yoke?
Just courios and it can be good to know .

It's only when you're in gear and there's a bit of slop around. The boat tends to get shoved and that 'unloads' the drive line, then as the boat slows the drive line loads up again. When you're out of gear the only load on the drive is the gears themselves and the water pump. That's consistent and constant, so no on/off situation...

Chris....

 

[Technorunner]

Re: Is running at low RPMs for a long time "bad" for the engine

ahh thx then i get it

 

[cyclops2]

Re: Is running at low RPMs for a long time "bad" for the engine

achris
Are you saying that the loading & unloading of the drivetrain is possible at 1500 rpms ? Even it it did happen. That is a extremely small amount of torque compared to WOT. Also. It is a few thousandths at most. So the slaming under high torque loads does not occur. Shifting at very high high rpms IS hard on everything.

That same coupling, loading & loading, occurs in cars. It is no problem in either cars or boats, because of the few thousandths of gear teeth play & low torque at those constant rpms. As a matter of fact MOST cars are far rougher. Because the shift out of gear on light loads & then lockup as the rpms go higher than coasting speed.

I know what you meant. But it is not hurting the coupling.
In NO WAKES you would need a wave MUCH faster & more powerfull than the boat is running to push it foward faster to unload the coupling. Still, the very few thousandths prevent slaming & damage of couplings.

 

[achris]

Re: Is running at low RPMs for a long time "bad" for the engine

achris
Are you saying that the loading & unloading of the drivetrain is possible at 1500 rpms ? Even it it did happen. That is a extremely small amount of torque compared to WOT. Also. It is a few thousandths at most. So the slaming under high torque loads does not occur. Shifting at very high high rpms IS hard on everything.

That same coupling, loading & loading, occurs in cars. It is no problem in either cars or boats, because of the few thousandths of gear teeth play & low torque at those constant rpms. As a matter of fact MOST cars are far rougher. Because the shift out of gear on light loads & then lockup as the rpms go higher than coasting speed.

I know what you meant. But it is not hurting the coupling.
In NO WAKES you would need a wave MUCH faster & more powerfull than the boat is running to push it foward faster to unload the coupling. Still, the very few thousandths prevent slaming & damage of couplings.

Go back and re-read my posts. I think you missed something in translation.

 

[cyclops2]

Re: Is running at low RPMs for a long time "bad" for the engine

I was answering your posting of low rpms is bad for the coupling. What part of what I said is wrong ? What did I miss in your posting ?

 

[achris]

Re: Is running at low RPMs for a long time "bad" for the engine

I was answering your posting of low rpms is bad for the coupling. What part of what I said is wrong ? What did I miss in your posting ?

If you have any doubts about what I said, read the service manuals and owners manuals. They all say that low speed is hard on couplers. All I did was give the reasons.

Enough said!

 

[cyclops2]

Re: Is running at low RPMs for a long time "bad" for the engine

My Chaparral Mercruiser 5.0 L V8 owners manual does not state that anywhere. Only about excessive use of trailer trim angles at over 2,000 rpms.

What make & models are you referring to ? I ask because no one in our boating clubs has ever said.
" We can not due that speed. It will ruin our couplings on the several hour sightseen trips we do all summer. "

 

[Bondo]

Re: Is running at low RPMs for a long time "bad" for the engine

My Chaparral Mercruiser 5.0 L V8 owners manual does not state that anywhere. Only about excessive use of trailer trim angles at over 2,000 rpms.

What make & models are you referring to ? I ask because no one in our boating clubs has ever said.
" We can not due that speed. It will ruin our couplings on the several hour sightseen trips we do all summer. "

Ayuh,.... When trolling, the motor pushes the boat, then the boat pushes the motor, then the motor pushes the boat, then the boat pushes the motor, 'n on, 'n on, 'n on, etc...

That action, against the splines, Wears the splines...
Skip greasin' the splines a year, 'n you'll need a coupler, cause the splines wear out....

 

[cyclops2]

Re: Is running at low RPMs for a long time "bad" for the engine

I decided that there had to be a reason why some people sincerely say that the coupler / coupling / splines can or will be damaged by continous below 1500 rpm use.

There is a very good reason for that statement. It is commonly said at Mercruiser bull sessions. If they, staff, do not disagree then it must be true. Right ?

Not so. I called Mercruiser at 405-743-6566 & went to sterndrive tech support. He said he heard that it was the action of the pistons firing downward that caused the damage. ??

I then asked if this slow speed wearing out was ever put into a owners manual or a shop manual. He replied. No.
Did Mercruiser ever do a wearout test at any speeds ? No.
Is there anybody to say this was not a Christmas Party topic that made it all over some areas. He said it is called "tool box " talk. Sounds good, but no testing or proof it really does occur. I directly asked him if there is any verified evidence by Mercruiser that this damage can be done at slow rpms. No.

So everybody who says it can / will damage the coupling or splines at slow speed is not wrong. They were / are / just repeating what they had heard.

I am glad I have found out how this all started.

 

[achris]

Re: Is running at low RPMs for a long time "bad" for the engine

I decided that there had to be a reason why some people sincerely say that the coupler / coupling / splines can or will be damaged by continous below 1500 rpm use.

There is a very good reason for that statement. It is commonly said at Mercruiser bull sessions. If they, staff, do not disagree then it must be true. Right ?

Not so. I called Mercruiser at 405-743-6566 & went to sterndrive tech support. He said he heard that it was the action of the pistons firing downward that caused the damage. ??

I then asked if this slow speed wearing out was ever put into a owners manual or a shop manual. He replied. No.
Did Mercruiser ever do a wearout test at any speeds ? No.
Is there anybody to say this was not a Christmas Party topic that made it all over some areas. He said it is called "tool box " talk. Sounds good, but no testing or proof it really does occur. I directly asked him if there is any verified evidence by Mercruiser that this damage can be done at slow rpms. No.

So everybody who says it can / will damage the coupling or splines at slow speed is not wrong. They were / are / just repeating what they had heard.

I am glad I have found out how this all started.

And Mercury don't make MILLION$ every year selling parts....

 

[mjfink]

Re: Is running at low RPMs for a long time "bad" for the engine

Wow, this turned out to be much more contentious than I expected. Sounds like the engine itself is fine running at low RPMs for long periods of time, perhaps there are problems on the drive side, but the engine itself doesn't much care. I was wondering if I would get bad carbon buildup by running at low RPMs, or other issues that used to happen to engines if you didn't "blow them out" occasionally.

Thanks for all the help, and I'll continue following this thread to see what others think!

And Mercury don't make MILLION$ every year selling parts....

 

[Technorunner]

Re: Is running at low RPMs for a long time "bad" for the engine

Since you have an MPI engine you will not have any problem with carbon buildup. The ECM will get just the right amount of fuel at any rpm,s and loads. So you dont have to wory at all about that.

 

[cyclops2]

Re: Is running at low RPMs for a long time "bad" for the engine

I can speak for my 5.0 L V8 with a carburator. No stumble, nocks, pings on 95 degree days. The plugs are a correct light brown all the time.

At 74 I have heard some ..."This is a fact"... in different machinery fields. We called some word of mouth truths..."Cocktail Party".....Engineering. Too much time, food, drinking & conversation.

If this is the worst we can do. No harm. Enjoy

 

[Fun Times]

Re: Is running at low RPMs for a long time "bad" for the engine

mjfink, What chris and the others are talking about goes beyond the water cooler talk, It's what's talked about while in a OEM manufacturer school as well.

Keep in mind there was a reason why the manufacturer had to come up with a better coupler for a "Work Application" environment much like you are doing at slow speeds in your bigger and heavier 260 Sundancer, For example only,

Item #24 861523A9 COUPLER ASSEMBLY, Engine - Short Aluminum Hub (Bravo and All Jackshaft Models) $533.25 $470.01.
Item #24 861523A11 COUPLER ASSEMBLY, Engine (Bravo) (Steel Hub for Work Application) $744.17 $655.91 OPT.

Also there is a reason why both the owners and service manuals say you should,
Lubricate engine coupler every 50 hours if operated at idle for prolonged periods of time.
Engine Coupler,
Lubricate engine coupler splines through grease fittings on
coupler by applying approximately 8-10 pumps of grease from a
typical hand-operated grease gun using Quicksilver Engine Coupler
Spline Grease. If boat is operated at idle for prolonged periods of
time, coupler should be lubricated Bravo Models - every 50 hours;
Alpha Models - every 150 hours.

Also there is a another reason why Mercruiser wants to know why the boat is used for "commercial business", So they can basically choose what to cover under warranty by the way the boat is used from experiences in the past.

• Product used for commercial business purposes, employment, amenity, or to generate income, even if only occasionally, must be properly registered as commercial use in order to apply the correct warranty duration.
• Product purchased for noncommercial use by Federal, State, Local and/or Municipal agency for official use must be registered as Government use. *Product sold to schools and universities or to nonprofit organizations may also qualify-Consult our Government Sales Office.

The bigger and heavier the boat is, the harder the on/off work load is applied to the coupler at slower speeds/RPM especially while in rough water, in return more maintenance is required to the engine coupler.

Unfortunately sometimes calling the Mercruiser technical "customer" support line for technical engine questions hardly result in the correct answers you need to hear as i have seen personally in the past.

Also agreed with the MPI engine, If everything is in normal working order (especially your engine temp @160*?) than your good to idle as long as you want/need with less fear of the engine loading up then a carb.

Have fun.