Engine hours interpretation ?

[rickwat]

Are engine hours when metered calculated straight off time or is account taken of revs ? To make further sense I have been trying to compare with a vehicle's mileage reckoning on 2000rpm average roughly equating to 40mph in a car. From this a boat with 4000 hrs is equivalent to a 160,000mile car/van. Is this fair or has anyone a guide for engine life expectancy given proper servicing?

 

[snowleopard]

most engine hour meters are run straight off the 'ignition' circuit, i.e. they clock up the time the engine is running. 100 hours equates to around 5000 miles in a car. wear should be less as marine engines normally run at constant revs for long periods so suffer less stress and have less cold running. (service intervals for oil changes are to get rid of acid combustion products which dissolve in the oil.)

 

[adarcy]

Re: Where do you lot drive?

Sorry but I can't agree with your average speeds.

Considering engine hours are "switch-on" time, I doubt if many average 30mph except a few rep's cars. My own has a trip computer and I average 24 mainly urban but usually not at busy times. Sure a long trip via motorway with quick on and off it will be better but you have to drive bl***y fast to average 50mph anywhere off motorways over a whole trip. That's the point, try timing with a stopwatch your true time and distance on a routine run from switch on to switch off. We have a motorboat used mainly around the solent so it is not entirely typical but I reckon that > 30% of the time is used starting up, warming up, manoevring out and trundling down the river and then off the plane wherever we go.

I agree constant revs/load is v much easier on an engine than motoring ( see how well generators last) and the most important thing with wear is the number of cold starts and hard load when cold (props like torque converters slip unlike geared cars/trucks) rather than hours run. On light use as in pleasure boats time between oil change is more important than time run.

Use 20mph as rule of thumb, 4000 hrs = 80K miles = nicely run in diesel not shagged

 

[Jacket]

i was told by a mechanic that the life epectancy of an engine has more to do with how an engine is used rather than engine hours.

Someone who uses their engine for long spells will have an engine thats in good condition for the number of hours its done, as the engine will be running at operating temperature and constant revs for most the time.

An engine that is used just for getting in and out of the berth (so rarely used for more than 15 minutes at a time) will be in a fairly poor condition for the number of hours, as the engine will never reach operationg temperature, and to make matters worse, getting out of a berth generally involves fairly rapid changes from full ahaead to astern etc, which puts a lot of load on a cold engine.

 

[colinroybarrett]

Most, but not all hour meters

There are several types of ‘hour-meter’ around, some are simple clocks, powered by the ignition, others, non-electric will only run when ‘rattled’ by a good old diesel. Both the above will record running hours, not related to revs.

Early ‘Icknield’ rev-counters (and probably others) with built-in engine hour counters were actually modified car speedometers, the ‘hours’ would only then be true at a constant speed, say 2000rpm, so they would ‘sort of’ take into account the speed of the engine.

Our last boat was 32 years old and both engines were fine, despite the hour meters having long since packed up working.

I would agree that neglect; infrequent oil changes and simply rotting away are much more of a problem to marine engines than the long hours run.

Cheers,
Colin Barrett
<A target="_blank" HREF=http://www.kahawi.co.uk>http://www.kahawi.co.uk</A>

 

[Guest]

Kwoyt royt

Cold engines getting hot also cause condensation to form inside the oilways - so water in all. Therefore the more they are started from cold the more water you get in the oil.

Thats why cold engines give off a lot of steam on cold days - although this is condensation in the combustion chamber.

Geoff

 

[chriscallender]

Re: Kwoyt royt

I have trouble believing that this is true - to get condensation you need moist air to begin with. Since the oil system is going to be sealed from the atmosphere most of the time (unless you do an oil change or top up), there can be no new moisture being added to the oil system on a regular basis so only a small amount of water ever gets to the oil no matter how much cold running you do. Of course there will be possibility of plenty of other damage with a cold engine.

Unless of course my understanding of engines is wrong and the oil system isn't sealed from the atmosphere.

 

[Robin2]

Re: Kwoyt royt

I have to protest

There is no condensation in a combustion chamber the temperature is too high.

The products of combustion are mainly water and carbon dioxide. The water will come out as steam. On cold days the steam is visible as water vapour - usually only while the exhaust pipe is also still cold.

 

[lauradee]

Re: Kwoyt royt

the prob with amateur engineers is that they know a few urban myths and a few engineering terms and usually make prats of themselves.
1: water is formed when fuel burns and shows up on a cold day as it condenses on exiting a cold exhaust system and hitting cold air. as the exhaust and the engine warms up the steam is hot enough to not condense immediately on exiting the now hot exhaust and so is not so visible.
2: the air inside a crankcase is saturated with vapour the same as your cabin (air gets in thru the crankcase vent) when you start an engine up for a short time the block doesnt get really hot and the water vapour in the air inside the block can condense on it the same as it does in the saloon, this prob is exaserbated by a small amount of blow by from the cylinders and this condensed water vapour will then start to form the milky sludge that we are familiar with in engines that are not run up to temperature or those that have faulty thermostats that do not allow them to reach working temperature, that is why it is important to get an engine up to working temp quickly to "boil" off unwanted condensed water vapour. that is why the london taxis leave their engines running continously and are famous for doing 250000 miles without a new engine. on a slightly different note i have never done any research but am slightly sceptical about what i consider to be an urban myth that you shouldnt leave a diesel ticking over because it is supposed to glaze the bore. see above about london taxis for an unscientific proof

 

[ean_p]

Re: Kwoyt royt

am I missing something here ,but dosn't vapour require a 'chill' in order to condense out in any given environment.....that is to say that given a condition then you need a drop in temperature either of the ambient air or of a surface for vapour held in the air to condense.....how can this situation ever exist within any part of an engine at or after startup when temperatures can only get higher?....after shut down sure!......enlighten me please....

 

[Sybarite]

Can you tell if the meter was ever disconnected or out of order?

I would use other criteria to determine its state.

 

[vyv_cox]

Re: Kwoyt royt

The prob with new user amateur engineers is that they forget that this is a boat forum, not a car one. 90% of boat exhausts are water cooled, so steam is generated at any time the engine is running. Ask any Bukh owner - they almost universally steam when running, regardless of the ambient temperature. Moisture that condenses inside crankcases is removed in seconds by the crankcase breather system that draws everything into the inlet manifold. The milkiness that can be observed in engines is mostly generated in the rocker cover. It is very much related to lub-oil formulation and engine design, some being far more prone to it than others.

Bore glazing is very temperature dependent. Leaving an already hot engine running on tickover is far less harmful than doing the same thing to a cold one.

 

[Spacewaist]

Re: Where do you lot drive?

We drive regularly between North London and Petersfield. 75% of the journey is on dual carriageway; 50% derestricted. Black box on car says we average 29.5mph and have for nearly 2 years.

A pontification from the Panjandrum of orotund bloviation AD2002