Perkins 4-108 0verheating

Discussion in 'Diesel Engines' started by jimisbell, Sep 28, 2006.

  1. Joe Breshears
    Joined: Oct 2006
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    Joe Breshears New Member

    Jimisbell: Have you cleaned the transmission cooler? If the heat exchanger was stopped up, then the trans cooler and engine oil cooler-if you have one- is subject to being stopped up as well. I've seen the trans cooler stopped up And full of impeller blades, if it is directly after the salt water pump.
     
  2. jimisbell
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    jimisbell Junior Member

    I dnot think there is a problem with raw water as there seems to be about a qt of it coming out the exhaust every 2 or three seconds. Also I did some temperature testing with a laser thermometer. The raw water going into the heat exchanger is 77F and coming out it is 86F while the fresh water going in is 165F and coming out it is 125F for a 40 degree drop (at fast idle at dock side). I am getting a 40 degree drop in fresh water temp for a 10 degree rise in raw water temp. I dont know if that is up to design or not. BUT....I cannot see any circulation of water when looking down into the HE tank and I was told I should see it flowing???

    I have also noted a hose that does not appear in photos of the engine I find elsewhere. It runs from a fitting on the head next to the thermostat housing to a "T" on the HE output line. It seems to be by passing the thermostat and the HE. I will check that out today. Perhaps someone added this for some unknown reason and it is preventing some of the engine water from circulating thru the HE.
     
  3. Frosty

    Frosty Previous Member

    jimisbell,-- I take it you had no help from Perkins then?
     
  4. jimisbell
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    jimisbell Junior Member

    No, they were helpful the first time I contacted them. They agreed with everything I had done and said they couldnt think of any thing else to check except the tranny cooler. When I contacted them the second time they did not return the contact. Maybe on vacation.

    I have not gone after the tranny cooler though because I have plenty of raw water flow and the raw water temp is only rising 10 degrees (from 76F to 86F) so I am sure that is not the problem.

    The problem seems to be in the fresh water circulation, and if that hose isnt supposed to be there, as I suspect, then that would account for the lack of cooling. It is my estimate that that hose is diverting OVER half of the fresh water flow around the heat exchanger. But it might be there for a reason so before I take it out I would like to hear if someone else has it and what its for. Friday I plan on putting a clamp on the hose while leaving it connected so I can evaluate what happens when its not there.
     
  5. alex fletcher
    Joined: Jun 2006
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    alex fletcher Junior Member

    from my expiriance it sounds like curclulation pump problem or your themostate may be installed back to front or in the wrong position, also a hole in the heatX baffle or chamber will give the same symptom can you pressure test CW system and is there flow and pressure from eng curc pump test by removing a hose.
    if you run your raytech over all the hoses you may find the prob sea water into the heat Ex should be cloder then the exit water clear water into theEx should be hotter than the exiting water a sudden change in temp along o hose may nean a bloked hose etc good luck
     
  6. Frosty

    Frosty Previous Member

    On some older british engines they had a strange thermostat that had a nother opening valve underneath. This meant that when the main large one opened the smaller underneath closed off a bypass port. I did mention this on page 9.
    A normal type thermostat can be fitted and no one would know the wiser exept that it would overheat.
    This was definately the case on the old Austin Maxi ( the first English car to have 5 speed gearbox in Uk)---- 1970's.

    There must be dozens of 4108 here --I will take a walk around this morning and have a chat.
     
  7. jimisbell
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    jimisbell Junior Member

    Alex

    I am going, next, to check the freshwater pump. As to the thermostat, it cannot be inserted backwards.

    Jack

    The thermostat came out of a box with the Perkins logo on it and the correct part number so unless someone swapped the boxes, I have the correct thermostat....which by the way, matches the old thermostat which has also been tested and found to be working.

    Now a report on the results of clamping the "extra hoase":

    Took her out for two hours today and the heating is less. Its not cured, but its better.

    As I said above, the next step is the fresh water pump, then the Tranny cooler, and on the 15th she is being hauled for a bottom job so we will look at everything that up to now we could not get to.
     
  8. Frosty

    Frosty Previous Member

    Your obviously a very gifted engineer. I am sure you will be able to solve the problem yourelf with out having any more interference from us here and suggesting stupid ideas.

    It is very kind of you to take the time to type out your results of your experimentation and explain to us what you are doing and your conclusion, We are glued to this thread.

    I will not take up any more of your time. I have been asking around the marina this morning for you but--- well never mind, its not what you want to hear.
    I am sure that Perkins could be of the same opinion,--but naa,-- I think your are correct they must have been on vacation.

    What I cant understand is that you have all the right parts and checked every thing over and over, and done every single little thing,--then why does it still overheat, Strange one that?
     
  9. jimisbell
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    jimisbell Junior Member

    Jack, I dont understand your anger. All I did was report what I had done as it was applicable to your suggestions. I was looking forward to your report on the thermostat.

    Just what did I say that you missinterpreted? Two people offered suggestions and I offered the results of what I had done along that line. It was in no way a rejection of ANY of your offerings.

    Sorry if something I said was not read with the proper iinflection, but I dont know what else I should have done to show that I was taking your suggestions seriously and trying them out ???

    Its very dificult to work on a program if I dont report the results to you. Up till now that is what I was doing and the suggestions were coming in and I was trying them or reporting that I had already tried them.

    If you are frustrated because none of the suggestions are working, think how I must feel, its my engine that is not working properly.
     
  10. jimisbell
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    jimisbell Junior Member

    By the way, what makes you think I am obviously a very gifted engineer? My engine is still overheating!
     
  11. sunseekeroi
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    sunseekeroi New Member

    Perkins overheating...

    Not sure if I can offer much however, here goes....
    I too have 4-108 that overheats above 2200 rpm. Like you I have tried it all in the past several years. I have a friend who own's an identical boat and engine. He added a larger heat exchanger and can now run up to 3000 rpm... no heating problems. Also, he changed pitch on his prop to 16in. Mine is 14". Hope this helps...
     
  12. jimisbell
    Joined: Jul 2006
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    jimisbell Junior Member

    Thanks for the comment. And you are spot on. I solved the problem and it will now cruise all day at 2600 RPM at 6.2 knots at 170F. Re-pitching the prop did the job. Its now an 18x13. When I hauled the boat last week I found the old prop was 19x18....too big and too much bite. Between that and the several little things like the "bypass" hose, the problem has been solved. I have not tried running it at the limit speed, which is now 3600 (90% of full throttle unloaded) so I dont know its limitations, but I suspect it will hit hull speed just under 3000 RPM so there would be no reason to push it any harder.
     
  13. 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 least once push up the throttle to find the Max rpm.

    Then cruise at least 300 rpm below that top number.

    Sounds like the prop you removed was a "cruising" prop,, designed to get the boat to cruise speed at well reduced rpm.

    6.2 K might have been normal cruise at 1800 rpm with the cruising prop , with less noise and better engine life.

    AS most boats with cruising props , the Mfg peak hp and rpm can never be achieved , but the advantage of quiet cruising can be enjoyed.

    If the previous owner had informed you , it could have been a choice to continue with the 19x18.



    FAST FRED
     
  14. jimisbell
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    jimisbell Junior Member

    That would have been nice to achieve. But changing props mainly allowed the engine to go to a higher RPM and to do so without overheating there was a reduction of speed with the newer prop at any particular RPM but to reach hull speed required an RPM (on the old prop) that could not be reached. Following is a table of the speeds and RPM before and after the prop change:

    Before with the 19x18 prop:

    Approx. Speed at 1800 RPM 4.5 Knots.
    Approx. Speed at 2000 RPM 5.2 Knots
    Approx. Speed at 2200 RPM 6.0 Knots (overheating began)
    Throttle wide open 2300 RPM speed 6.2 knots (major overheating)

    After with 18x13 prop:

    Exact Speed at 2000 RPM 4.8 Knots Temp 175F
    Exact Speed at 2500 RPM 5.8 Knots Temp 175F
    Exact Speed at 2600 RPM 6.2 Knots Temp 175F
    Throttle wide open is 3500 RPM

    Red Line is 4000 RPM

    As you can see the speed decreased approximately one half knot at any RPM with the new prop but Full throttle with the old prop did not reach hull speed nor did it reach max HP for the engine which is reached at about 3600 RPM

    Based on this latest data on the 18x13 prop it is my estimate that it will reach "Hull Speed" of 6.8 Knots at about 2900 RPM and without overheating. I have not yet tested it at these higher RPM s yet. I was just so happy to see the overheating go away I didn't do all the testing I should have.
     

  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

    Approx. Speed at 2000 RPM 5.2 Knots
    Exact Speed at 2000 RPM 4.8 Knots Temp 175F

    Sailboats are NEVER powered to cruise at "hull speed" under power as most operators wont stand for the noise and vibration for a 1/2 k.

    The SQ Rt times 1.1 is a normal cruise for most sail boats.

    Approx. Speed at 2000 RPM 5.2 Knots
    Exact Speed at 2500 RPM 5.8 Knots Temp 175F

    So for an added 500rpm you get a half K.

    On a 10 hour ditch day , you may get to the anchorage 50 min faster , but with 50% more fuel used?

    FAST FRED
     
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