overheating question

Discussion in 'Diesel Engines' started by tropicalbuilder, Oct 2, 2012.

  1. tropicalbuilder
    Joined: Jun 2010
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    Location: costa rica

    tropicalbuilder Junior Member

    hulls are perfectly clean as are the props that are folding ones and in perfect conditions.
    I'll try to check the whole raw water system including the elbow, and then i'll try the FW pump swap ….
     
  2. tunnels

    tunnels Previous Member

    ok lets back up a little . how long has this been happening ?? was it ok before you did the work on the motors ? is eack motor identical to the other ?? are the hoses to and from the heat exchanges identicall ? ;like in the same possition in and out . the thermostats have you tried changing them ? dont leave the thermostat out !!! its there to slow the flow of water going through the exchanger if you take it out the water will circulate to fast and wont have time to cool , hence the temprature going up when the reves get up and happens slowly and when the rpms come down so will the temrature slowly come down !!!
    In a car if the radiator had been repaired and slow driving is ok and as the speed increases the temprature comes up the first thing you check is the number of rows of fins in the radiator are they the same as what was there before . in both cases the number of fins was less ! fit the new core with the right number of fins and problem fixed each time !!
    Have had this happen twice in my career over a few years ! first time was a fluck we found it as the care was a v8 auto and noticed a space at the front of the radiator , the core fitted was for a 6 cylinder not a v8 , second time a 2 litre car and the same thing core had been replaced with a 1600 cc motor Core !!!so went straight to the source !

    So all indications i would think point to the heat exchanger !! what did you do to the heat exchanger ?? what has happened if it wasnt doing this before ?what have you done or changed ?? it will be something small for sure have you checked the water supply to the pump and from the pump ?? do you have a gate valve ? is it operating like full closed and full on ?? is the handle loose ?? blow water back the opposite direction and see what comes out !! has it got a strainer on the outside of the hull over the water pick up ?? is it partly blocked ? plastic bags love getting stuck half in and half up the pipe !! Is the water pump the same size as the other motor ?? measure the width od the casting !! did you take the impelleres out of the pumps ? all the fins maybe there but did you check the key is not stripped ?? if its stripped the in the impeller it could still be going round but slipping , causes are water pipe restriction ! water to the pump is partly blocked !!
    its a complete process of elimination ! you have changed something !! some thing small something that you havent paid attention to .:?::idea:
     
  3. Red Dwarf
    Joined: Jun 2012
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    Location: USA California

    Red Dwarf Senior Member

    What is wrong with FF's explanation? Makes a lot of sense to me. Have you checked the props and verified they are correct for your boat?
     
  4. tunnels

    tunnels Previous Member

    Get real people one motor is ok the other is not !! why ????
    In the case of a emergancy and a need to operate both motors at max it could cost a life maybe . engines should be able to operate at max with out cooling problems !!!! come on get real stop skirting around the problem !!
     
  5. tropicalbuilder
    Joined: Jun 2010
    Posts: 49
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    Location: costa rica

    tropicalbuilder Junior Member

    raw water intake was my first suspect, so i checked and cleaned the strainer, followed by the impeller (no broken fins or stripped key) and the HE that I opened and cleaned even if there was no obstruction.
    Beside this, the strange thing is that the raw water coming out of the exhaust is similar to the other motor at the same rpm (already tried different RPM from idle to high rev).
    At that point I checked the belt to see if it was tensioned properly, and it was.
    I tried the thermostat, put it in a container with water and brought to the temperature it was supposed to open .. and it did … to make sure i swapped the thermostat between the two motor … still the same overheating …
    At this point i will try to swap the FW pumps and see what happens
     
  6. tunnels

    tunnels Previous Member

    question !! how long have you had this boat for and has it had this problem all the way along ?? :confused:
     
  7. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    "At this point i will try to swap the FW pumps and see what happens"

    Might check if the gear boxes have the same reduction ratio. Some will be slightly different to reverse the prop on twins.

    In that case a shaft tach might be of interest
    .
    IF the gear boxes are identical rotation, swop the props , two different builds or repairs may have changed pitch.
     
  8. Aliboy
    Joined: May 2011
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    Location: New Zealand

    Aliboy Junior Member

    As previously mentioned, buy one of those cheap IR thermometer guns and shoot the whole cooling system on both engines for comparison. I think you can get the basic but reasonably accurate guns for around $50. Useful tool for keeping track of engine temp problems. If you shoot the raw water pipe after the HE, and then again at either side of the elbow you will have some better idea of what is happening. When you checked the HE did you actually acid wash it, rod it out, or just pull an end cap, or pull both end caps? If your raw water flows are really the same, then you either have a heat transfer issue (HE) or a coolant issue, or perhaps a boost/fuel issue. One other thought - do you know if you have the correct coolant ratio in your engine(s)? Wrong coolant to water rations can lead to poor heat transfer.
     
  9. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Is the HWH tied into the one that overheats first? A HWH loop can add backpressure.

    Idea #2 you have feathering props with the pitch stop dialed in too high. Talk to other owners of your boat. You've got warm water down there. You may need to take it a bit easy when sea temps are above 75 degrees.

    The two fixes are bigger heat exchangers or less prop. Um, before I say bigger heat exchangers, it would be nice to know the output temp of raw water with the engine pretty hot.

    Some basic performance info would help also. What boat? What weight in cruising trim? What speed at 2400 rpm? Tranny ratio and prop if you know it?
     
  10. jonr
    Joined: Sep 2008
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    Location: Great Lakes

    jonr Senior Member

    As tunnels said, if a prop causes overheating, you have an engine cooling problem that needs to be fixed.
     
  11. tunnels

    tunnels Previous Member

    when you had the exchanger apart you didnt think to count the number of tubes by any chance did you ??
    SOMETHING to check is the number of tubesinside the exchanger in the motor that over heats !!, then to the number of tubes in the motor that dosent over heat . has one more than the other ??? its all to do with heat transfer from one to the other ,x number of hp will produce y amount of heat and z lenth of tube is needed to cool that water !! so if z is less than it should be then theres your problem its needs more tubes .
    So is this classed as observe !, evaluate and find the solution to a problem ?? :p
     
  12. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    jonr, that might well be true in the great lakes, but not in the tropics where raw inlet temps can be pushing 90 degrees. Some engines just aren't set up with the flow rates to produce rated power at those temps. My old dinosaur is one of them. The book on it is to derate by 30% in the tropics (ie, size the prop based on 70% rated hp.) Or, you can modify the cooling system to get some of it back. But new heat exchangers cost around $700. That's a lot of dough to regain maybe 4 hp. The other fix involves fiddling with the HWH, which I chose to do. That costs about $10.

    Does anyone know any spec sheet limits for raw water inlet temps applicable to modern motors?
     
  13. tunnels

    tunnels Previous Member

    the things we do !

    I been awake for hours this morning found these !,theres lots in here answers to questions etc etc
    http://www.orcamarine.com/faq_and_tips.html#tips7


    http://fluiddynamics.com.au/fluidex/

    http://fluiddynamics.com.au/2012/wp-content/uploads/2012/03/3_FluidEX_Shell_Tube_Specs.pdf This has lots info and drawings and pretty graphs etc etc

    more info http://fluiddynamics.com.au/2012/wp...luidEX_Shell_Tube_Installation_Maintenace.pdf

    even a forum to look through http://forum.woodenboat.com/showthread.php?3295-heat-exchanger-cleaning

    http://www.practicalboating.com/forums/showthread.php?t=5233
    Didnt have time to read anything as yet !



    something else to add to the collection need to go looking !! http://www.eldoradocountyweather.com/climate/world-maps/world-sst.html
     

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  14. jonr
    Joined: Sep 2008
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    Location: Great Lakes

    jonr Senior Member

    > Some engines just aren't set up with the flow rates to produce rated power at those temps.

    Say 130F rise vs 110F (90F to 200F) rise. That's about a 10% decrease in cooling system performance. Not sure where they came up with a 30% derating, but if one engine had such a deficient design, I'd fix it.
     

  15. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    Many of our engines were truck or car engines to start.

    On a vehicle the radiator will drop the coolant only about 20degF .

    So the inlet temp of a boat engine could easily be 160+ , IF the heat exchanger is as good as on a vehicle , able to actually reduce the temps by 20F at full loading .

    Usually only a keel cooled setup will have the required cooling for full throttle operation.

    To keep from an over cooling situation most keel cooled boats require a bypass thermostat to send 160F water back to the engine.

    Warm engines (proper temp) are more efficient than too cool engines.
     
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