increase engine heat for better efficiency?

Discussion in 'Powerboats' started by sdowney717, Nov 19, 2013.

  1. sdowney717
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    sdowney717 Senior Member

  2. michael pierzga
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    michael pierzga Senior Member

    Dont know...marine engines run cool because they are in engine boxes, not under the hood.

    The higher the engine room temp, the higher the air intake supply, the less efficient the motor.

    You should ask a marine engine engineer for his thoughts.
     
  3. PAR
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    PAR Yacht Designer/Builder

    There are a few reasons for this and less obvious then you'd think. Marine thermostats open at 160 degrees and are fully open at 180 degrees. A new, clean engine generally operates at the lower end of this scale, though as a raw water cooling system gets dirty, rusts, scales up and gets partial blockages, it'll operate at the upper end. Of course as Michael suggested, engine box/compartment temperatures are also a concern, but so are fitting temperatures. For example, if the raw water comes into the pump at 60 degrees, it'll dump into the exhaust elbow at 120 degrees. The elbow is one of the "choke" points in the system, because of it's small orifices, which tend to plug fairly quickly (within a few years).

    The subject can get complex, partly because of the different types of cooling. The higher temperature stats, used in cars are often to optimize emission control systems, such as the catalytic converter and to prevent a rich combustion charge. A raw water cooled block is unpressurized, so a lower temperature is employed so it doesn't boil at the top of the cylinder jackets and the head. Other things to consider are the fact that cars maintain a 15 PSI pressure on the coolant, yet a boat engine will be lucky to hold 2 PSI at 4,000 RPM, which means the coolant can flash to steam in areas of the engine (exhaust port passages, head/block interface, etc.), which wouldn't help the cooling situation very much. There are other considerations, such as designing a system that will offer an overheat alarm, before you cook the head gaskets off the block.
     
  4. gonzo
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    gonzo Senior Member

    On open cooling systems, the operating temperature is lower to prevent excessive corrosion.
     
  5. jonr
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    jonr Senior Member

    > Would that help my inboard fresh water cooled boat that has heat exchangers?

    I ran a slightly higher temp thermostat in a boat that saw only fresh water. Oil lubricates noticeably better at 180F than at 160F.
     
  6. sdowney717
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    sdowney717 Senior Member

    I wonder if moving to 180* thermostats would cause any troubles. I think one engine has 160* and the other maybe 170*.

    Higher temps won't they increase system pressures? Currently have 7 PSI pressure caps.
    This is closed cooling system with antifreeze and uses raw water heat exchangers. All manifolds and risers on my boat are in the antifreeze closed cooling circuit.

    IF you switch to Evans antifreeze which uses no water, then you can run higher temps, and I think since it has higher boiling point so mean pressures are lower than water mixes. May not be worth the cost to switch if the fuel efficiency does not increase. I emailed them to ask what they think.

    The 'box' of the bilge, the air temp would go higher, so there are perhaps some negatives in that area.
     
  7. dinoa
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    dinoa Senior Member

    Open cooling systems should operate at lower temperatures because scale deposits are greatly reduced below 160 degrees.

    Dino
     
  8. powerabout
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    powerabout Senior Member

    if the coolant gets too hot the salt will come out of the raw water side and coat the heat exchanger thats why you cant let a boat engine get too hot.
    Anyone that has worked on a overheated boat engine will know what I mean
     
  9. jonr
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    jonr Senior Member

    > Higher temps won't they increase system pressures?

    Not until you exceed ~212F (at atmospheric pressure, a little more at higher pressures).
     
  10. powerabout
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    powerabout Senior Member

    only if you use water based coolant
     
  11. jonr
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    jonr Senior Member

    While not very applicable to the 160 to 180F temps being discussed, how far you need to exceed 212F depends on the liquid. And in theory (not practice), some could boil at less than 212F. And of course hot spots within the engine mean you want some margin.
     
  12. sdowney717
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    sdowney717 Senior Member

    If I go from 170* to 180* thermostats, is that going to cause trouble?
     
  13. fredrosse
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    fredrosse USACE Steam

    "Oil lubricates noticeably better at 180F than at 160F."

    jonr, I think you are saying that there is less engine friction with the higher temperature oil. The higher temp oil has lower viscosity, so less friction for moving parts. However the lower temp oil (with higher viscosity) would provide a greater margin of safety in keeping machinery from wear or internal scuffing. So what constitutes "better" is a matter of definition.

    The EPA made all the auto manufacturers switch to lower viscosity oil for automobiles to save gasoline, but using 15-40 Diesel oil (CI Rated) in your crankcase will keep your engine running far longer than using the 5-30 (SI Rated) stuff that is now recommended for automotive service.

    The Diesel rated oils also have some anti-wear and anti-scuffing additives that further protect the machinery, and they are needed to protect Diesel engines because they generally have bearing loads that exceed the capabilities of the SI rated oils. However some of these CI oil additives can interfere with the functioning of catalytic converters.
     
  14. jonr
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    jonr Senior Member


  15. Barry
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    Barry Senior Member

    Do not use diesel oil in a gasoline engine
    1)normally diesel oil has many more additives in the oil to rid the engine of soot and broken down hydrocarbon molecules as diesel fuel is a higher chain hydrocarbon. This increased viscosity will produce more heat due to the heat generated from internal fluid friction within the engine.
    The higher heat reduces the ability of the oil to maintain a film on the pressurized oil wear surfaces
    A 8 to 10 degree increase in temp can result in a reduction of 40 % of the oils life
    2) An increase in the engine operating temperature will also contribute to a higher engine oil temp which, as above reduces the life of the oil, don't mess with higher temp thermostat
    The main reason that a marine engine runs cooler is that you have a raw water coolant to cool the water in the engine water jacket, whether heat exchanged or raw water cooled.
    3) Cold starts are hard on engines as the bearings are not supported by a film quickly with a thick viscosity oil,( because it is cold) and the oil when thick cannot lubricate the lifter bores as fast. Do not increase the viscosity of the oil of the winter rating of the oil
    (an aside, multi viscosity oils are normally rated for two set of conditions
    example 5w40, the 5W stands for 5 Winter, not 5 weight as many have come to believe.
    So for the first "W" rating, a given volume of oil at 40 degrees C is allowed to pour through a specific orifice, and the event is timed and if the time is the same as pouring a straight rated oil of 5, then the oil is designated 5W
    Then the same volume of oil is poured through a specific orifice at 100 degrees C, and if the time it takes is equivalent to a straight 40 grade oil, it then is designated 40
    The two are put together and you get a 5W30 5Winter 40.

    I assume that you have a gas engine, so do not change 5w30 SI rated,Spark, oil and use 15w40 diesel rated oil as Fredrosse suggests. As your engine will spend most of its life under high loads due to the marine environment, as compared to a car running down the road and using say 50 horsepower or so, and if you feel that you need more viscosity to deal with the high loads, there are many gasoline engine oils with a higher viscosity on the summer scale. 5w40, 10w30 etc.

    The engine will be more efficient if you can keep the engine running at a cooler temperature
     
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