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Old 04-14-2003, 08:29 PM   #1
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Default How many hours will my engine run? A Case Study

How many hours will my engine run? A Case Study

I find this topic being discussed very frequently among boaters and there seems to be a fairly large discrepancy among experienced boaters on how long a particular motor will last. The unit of measure most often is discussed is “engine hours”. I find fallacy with using engine hours as a unit of measure. Here’s why:

Joe Fisherman buys a new boat. He is strictly a bottom fisherman, and fishes the same bottom spots every trip. He fishes every Saturday (for the sake of argument will say 52 fishing trips per year). His weekend trip consists of 125 miles round trip. Since he only bottom fishes, his running time consists of basically “cruise” speeds only.

If Joe Fisherman “cruises” at 50 mph he only puts 2.5 hours per trip on his motor, or 130 hours per year. At 25 mph he puts 5 hours per trip or 260 hours per year. At the end of 5 years he would have 650 or 1300 hours respectively on his motor.

Using “engine hours” here implies that running your boat WOT is better than a reasonable cruise or it is better to run your motor harder for a shorter period of time. I think we all would agree that just the opposite is true.

So, would it be more reasonable to use “miles” instead of hours? In this case it would be better than “hours” because at least the ‘mileage’ would be the same. But it is obviously not practical to measure, and it would reason that the engine run at 25 mph would still be in better shape.

Engine hours of course has been used a unit of measure for a very long time. But, hours did not imply “clock hours” as it does today. Rather, engine hour meters where mechanical and based off the rpm of the engine. An “engine hour” was equivalent to the engine running a specified RPM for an hour. If the engine were run at half that speed it would take 2 hours for the hour meter to reflect 1 hour.

So, it would be more accurate to develop a way to use RPM and time. Lets look at my car for example. It is a 3.0 L V-6 producing 210 hp. Which is very close to specifications of some modern day outboards. I mainly use my car on the interstate and feel confident in estimating its life at 200,000 miles. I run 75 mph at about 2600 rpm. 200,000 miles / 75 mph = 2666 hours. So, all else being equal, if Joe Fisherman cruises his boat at 2600 rpm then should he expect 2666 hours life out of the boat engine as being comparable to 200,000 auto miles?

Well, all else is not equal. A boat motor is under greater load than an automobile motor. What if Joe Fisherman wants to run his boat at 3500 instead of 2600 rpm? What if he decides he wants to troll too? These things will obviously effect engine life hours. Due to the extra load a boat is under we could use 75% of the auto ‘mileage’ expectancy and use 150,000 hours. So our modified boat engine life expectancy at 2600 rpm would be 150,000 miles/75 mph = 2000 hours. At 3500 rpm my car is going 100 mph. 150,000 miles/100 mph = 1500 engine hours for the boat.

What about if Joe decided he wanted to troll between his bottom spots once he got offshore. Trolling distance would cover 25 miles at 1,200 rpm at 8 mph. These 3 hours worth of trolling time obviously has an effect life expectancy in that the engine is run ‘less hard’ and it would increase the “hours”. To use data from an actual boat, at 3500 rpm he can cruise at 25 mph, or would cruise 100 miles in 4 hours. He spends 3 hours trolling. Using the same rpm/speed estimation above, 1200 rpm equals about 34 mph on my automobile (assuming it doesn’t down shift – just trying to keep things simple). Or 3 hours of trolling equals about the same ‘mileage’ as 1 hour of cruise.

To see the effect, we must look back at our original estimation. At Bottom fishing only the trip consisted of 5 “hours”. To take away the 1 hour and replace with 3 hours of cruising to come up with an equivalent “mileage” we have 7 hours for the trip, or a factor or 1.4 more hours. 1,500 hours x 1.4 = 2100 hours.

Obviously the more you troll as a % of cruise the more “engine” hours one should expect.

Now, what about inboards? A 350 cubic inch (5.7 L) chevy block producing 225 hp is bound to last longer than a 3.3 L producing the same hp right? Well, you probably ought to also consider the estimations above take into account rpm. An outboard produces max hp at around 5,500 rpm while an inboard produces it at around 4,500. So where the outboard produces 25 mph at 3,500 rpm, the inboard would be able to achieve the equivalent hp at a lower rpm, say 3,000 for this argument (assuming a prop curve where %WOT produces equivalent hp). Using same rpm/speed variable above, 3,000 rpm = 85 mph. To keep it simple, lets assume the extra displacement on the inboard will only give you 10% more ‘mileage’, or 165,000. So 165,000 / 85 = 1941 hours. Or if going with the trolling scenario, 1941 x 1.4 = 2717 hours.

Now, what about diesel? Lets use a Cummins 6bt rated at 210 hp (5.9L) because a friend has one in his truck. Recommended overhaul is at 300,000 miles by Dodge on truck engine version with equivalent hp. A diesel is designed for running more loaded than a gas engine, but to keep things consistent we will also use 75% or 225,000 miles expected. At 2,000 rpm the truck runs 64 mph. WOT on the truck engine is 2,900, and on the marine version of the engine it is only 2600. Again assuming a prop curve where %WOT produces equivalent hp, our boat would only need about 1,850 rpm to produce 25 mph boat speed. Using the rpm/speed ratio for the truck, 1,850 rpm = 60 mph. 240,000 miles/60 mph = 4,000 hours. Or if going with the trolling scenario, 4,000 x 1.4 = 5,600 hours.

The point of this is to help people have an idea of how many hours to expect out of “their” engine. This data is in no way meant to be absolute. One can easily argue that some of the ‘assumed’ numbers should be different. For example, I have a Buick with 195,000 miles on it that still runs very well and has plenty of life left in it. But I wouldn’t want it in a boat running 50 miles offshore!! That’s just my preference. Yours may vary. Plug in your own numbers as to what makes you comfortable.

This was the result of a group of engineers sitting around a dock all day waiting for the weather to clear. This is what we came up with. We bounced it off data from all the boats we own (have owned) and it seems to compute for us. I have posted it on the hull truth for two reasons….to get some feedback in what others think, and maybe to help some new boater maybe ‘estimate’ what to expect out of his new boat.
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Old 04-14-2003, 09:24 PM   #2
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Default How many hours will my engine run? A Case Study

Huh, huh, pretty cool.

Only thing I can add at this hour is that it is quite possible that the hour/rotational life expectancy of a 2 stroke may be less than a 4 stroke.

Something about pistons swimming around in fresh, cool synthetic oil rather than having a quick squirt of very diluted oil injected for only a moment before being blasted in the inferno into a zillion razor-edged particles of carbon.

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Old 04-14-2003, 10:13 PM   #3
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Default How many hours will my engine run? A Case Study

Interesting topic. How about using fuel consumed. since each gallon of gas contains a fixed amount of energy that is converted to HP, it seems that an estimate of expected motor life could be determined by the amount of fuel consumed IE trolling uses less HP less fuel.... running WOT most HP most fuel.... to bad there's a reset on the flowscans. Then of course there's a proper maintenance schedule or maybe they shouldn't let engineers get together in groups with nothing to do ...
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Old 04-14-2003, 10:43 PM   #4
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Default How many hours will my engine run? A Case Study

Nice write up. Another element is weight. A heavy iron head will last longer than a thin light aluminum one trying to generate the same power.
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Old 04-15-2003, 02:21 PM   #5
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Default How many hours will my engine run? A Case Study

Boy, & I thought only Toyotas lasted that long !
Good going Any maintence tips for this kind of longevity ?

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Old 04-15-2003, 03:24 PM   #6
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Default How many hours will my engine run? A Case Study

I Want to go and get him .

I try but some how he ignore the ªSignsª.

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Old 04-15-2003, 04:16 PM   #7
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Default How many hours will my engine run? A Case Study

I agree with the engineers and especially with finadict. Fuel consumption is a better measure of wear, than hours, but I'm suprised that nobody mentioned a maitanance factor in there.
Unless we are assuming that maitanance of engines is at least average or above. I have a viking w/ two, twin turbo charged 3208 cats. The turbos are after-market, so I try to not to push them too hard. I cruise at an rpm just below where the turbos really kick in hard. I spend almost as much time below decks, as I do fishing.
When cruising, I spend as much time scanning the gages as all the other equipment put together. I've known many people who didn't hear the low oil alarm on the out board until they slowed down and the had no idea how long they ran that way. Friends with inboards that didn't know they lost a water pump unti they heard the valves pinging And a good friend who didn't notice the temp gage in a bertram was pegged till I yelled up to him, that I could smell radiator steam in the salon. All these engines still ran fine afterwards, But I wonder how much engine life was lost.

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Old 04-15-2003, 04:22 PM   #8
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Default How many hours will my engine run? A Case Study

I run about 15-48 gals a day When I go!!
Thats how I measure !
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Old 04-15-2003, 06:10 PM   #9
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Default How many hours will my engine run? A Case Study

a good outboard will go a 1,000 hours,any more and you are on borrowed time. IMO You can not relate marine gas engines to any other motor because no engines certainly not car engines cruise at 4,500 rpms in a saltwwater environment cooled by Saltwater and running thru bumpy weather. I guess if you took your car, left it in first gear at 4,500 rpm and drove over speed bumps constantly in the kmart parking lot for a thousand hours that would also be the end of it too.
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Old 04-15-2003, 06:17 PM   #10
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Default How many hours will my engine run? A Case Study

There is a set of 3208 Cats (TA) in my boat with 1500 hours on them. At a cruise of 24 knots,they consume 12 GPH. (IT will be less when I get the new injectors in them).
With 200 hours a year useage, at @ 10 GPH (That is an average, combined cruise and slow stuff) I have 2K gallons used per year.
Cat Certifies these engines for 40,000 gallons of fuel. That means 20 years on the engines, before Major Overhaul.
I am the third owner of this boat. That means that my current 1500 hours on these engines is less then 1/2 of their economic life. That is IF I take excellent care of them. Oil, Minding the temps, and keeping antifreeze clean and changed.
air filters have a enormous impact as well.
It is all in the numbers.

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Old 04-15-2003, 06:25 PM   #11
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Default How many hours will my engine run? A Case Study

Gas I/O 2000 -2500 with good maintance PS don't have to decarbon @ 50 hrs. Fresh Water A no Brainer I/O V8
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Old 04-16-2003, 04:57 AM   #12
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Default How many hours will my engine run? A Case Study

Don't forget, an inefficient engine or one running in an inefficient part of the rev range, can consume plenty of fuel while much of the fuel is producing zero power.
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Old 04-16-2003, 06:23 AM   #13
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Default How many hours will my engine run? A Case Study

Big Bone,
The study was for 4 strokes. I agree about the 2 strokes and would only add that you could reduce the % (was 75% for 4 strokes) more for 2 strokes...

Fin Addict,
Actually, you are absolutely correct. Diesel engine manufacturers base overhaul on fuel consumed. If you compare same blocks (3208 for example), an industrial lower hp version and a recreational higher hp version, the industrial will have a longer "hours" between overhaul. But the fuel consumed between the two will very close if not identical. I use to work with CAT engine division and am very familiar with this process. But GAS engine manufacturers do not provide this information.

Double Action,
The weight issue sort of falls into the inboard or outboard categories doesn't it? Outboards have aluminum heads don't they and are inboards cast?

yeah, my Buick really has 195,000 miles and really doesn't burn any noticeable oil between oil changes. I only do routine maintenance and change the oil every 5,000 miles. It is a '94 Buick LeSabre with the 3800 V-6 engine and it has been a very good car. The only problem I have had with it has been the transmission. It's for sale by way as I just replaced it with a Toyota Camry....which I also expect to get 200k miles out of...

fidhhook54, huh?

In a minute,
already agreed(see above). I was a big fan of the 3208's and hate to see CAT discontinued production. That version you have was put together by the CAT dealer in S. Fla.

Capt Bone,
If you reread the post, what we are saying is 1,000 hours at 4,500 rpm is not the same as 1,000 at 2,600 rpm. Also, a 1,000 hours at cruise is not the same as 1,000 hours trolling. So what we were trying to do was come up with a "general" way to estimate a life expectancy out of an outboard. What actually started this whole thing was me telling a guy(fellow engineer) not to expect more than 1,500 hours out of an outboard. He started asking questions like will it last longer if? why? thing you know we (2 other engineers were also at the dock) came up with what I posted...

Trader Vic,
Interesting you should bring that up. Most engines do have a "sweet spot" where the BSFC is the most efficient. However, it actually doesn't vary a whole lot between best to worst in actually producing power. Where the real inefficiency comes in is where the props are inefficient (or are slipping) like just before the boat gets onto plane....

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Old 04-16-2003, 06:52 AM   #14
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Default How many hours will my engine run? A Case Study

Interesting analysis. One more variable - what about non-use? A five year old outboard with 100 hours may be a lot worse off than a five year old outboard with 1000 hours. I guess "regular use" has got to be one of the assumptions made. I would love to know the difference in hours one could expect where one engine was used twice as often, with twice as many hours (assuming maintenance was otherwise appropriate). At what point does using the machinery more often offset more hours?
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Old 04-17-2003, 08:32 PM   #15
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Default How many hours will my engine run? A Case Study

Duty cycle is the proportion of time during which a component, device, or system is operated. The duty cycle can be expressed as a ratio or as a percentage.

The more a machine or component is used, the sooner it will wear out. Therefore, the higher the duty cycle, the shorter the useful life, all other things being equal.

(The more times the thing goes roundy round, the quicker she goes)


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Old 04-18-2003, 05:09 AM   #16
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Default How many hours will my engine run? A Case Study

This reply isn't very scientific, but IMHO, the more you use an outboard the longer it will last, as long as it's properly maintained. I owned my last boat 13 years, at the 10 year/3400 hour mark,I decided my luck was about to run out and repowered. Only repair that engine ever needed was a starter. Sold the old engine to a friend in the Keys, and it's still going today. Most of the problems I read about start with "the boat sat for a long time."

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Old 04-18-2003, 08:04 AM   #17
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Default How many hours will my engine run? A Case Study

Dag gone I must be lucky. I have got atleast 2500 hrs from my last 3 OBs and I run them at 4500 if I can. 2 of the 3 are still running with different owners. I know many com fisherman that dont trade theres in until they have 4000 hrs. Where does this 1000 hr thing come from. Must be from abused, pos from the start engines or lack of use engines. I have had 2 engine blow up prematurely but both were from factory defects and were covered under warrenty.

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Old 04-18-2003, 08:22 AM   #18
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Default How many hours will my engine run? A Case Study

If I only get 1000 hours out of my new Merc, I'm gonna be pissed!!!! At the rate I'm going, it's going to be 300 by the end of this year. Amazing how much more I use my boat now that I don't have a broken motor!??!?!

195,000? C'mon, that's chump change.... My '88 Cherokee has 209K on the original 4.0 inline six and auto trans. My goal is to roll the odometer over at 300K. It looks really sh*tty and rides like a Carolina Skiff in five foot seas, but it was free.... When the motor goes, I'm putting a 4.7 liter stroker in it!!! Bring it on you high school rich boys and your $5K Civic with $15K in upgrades!!!!
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Old 04-18-2003, 08:27 AM   #19
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Default How many hours will my engine run? A Case Study

And we think 200k is a lot. Several years ago the local Mercedes mechanic told me he had one coming in to get certified for the 1 million kilometer medal that you put on the grill. Not sure how many miles that is but I would bet it is a lot.
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Old 04-18-2003, 10:16 AM   #20
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Default How many hours will my engine run? A Case Study

It's interesting you did oil changes @ 5k & still got awesome life out of your engine.. I once read from a major oil co.'s website that was offering an extended warranty if you used thier oil that changes must be done @ 4000, the point being the 3000 mile mark when most people change thiers now a days might be overkill in the average vehicle..

I think a lot depends on driving habits & if your burning off the impurities & doing changes within 4 months no matter the mileage ect..
Oh well always looking tips on making my vehicles last longer, thanks..

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