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  1. #1

    Default PCM gt40 runs hot

    Replaced raw water pump, head gaskets, removed thermostat, calibrated gauge and checked all hoses for blockage. Checked risers for blockage, checked engine water pump, engine is raw water cooled. Checked raw water pick up. Runs at 140/150 with no thermostat.

  2. #2
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    Default Re: PCM gt40 runs hot

    strainer cap on tight?

  3. #3

    Default Re: PCM gt40 runs hot

    Quote Originally Posted by makomark View Post
    strainer cap on tight?
    Yes, it is on tight. There is very good flow going through the engine. I am thinking there might be not enough contact time without the thermostat to restrict it.

  4. #4
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    Default Re: PCM gt40 runs hot

    not enough 'contact time' would like the block get hot which is contrary to what is in post #1...??

    Assuming your raw water pump is supplying plenty of unaerated water, there isn't much left on a RWC setup to go bad. You do need the correct thermostat to match the bypass scheme used in the housing....how did you check the risers/elbows? How old are they?

  5. #5

    Default Re: PCM gt40 runs hot

    Quote Originally Posted by makomark View Post
    strainer cap on tight?
    It runs between 140/150 w/o thermostat. We ran a garden hose through the risers and there are no restrictions. We have another boat with same engine and the engine maintains 140 with a thermostat. I have ordered a new marine thermostat and hopefully this solves it. I did put a new thermostat in and it ran at 180. I suspect the thermostat may have been sold to
    me as a marine thermostat and was not. Thanks for your feedback, hope this solves it.

  6. #6
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    Default Re: PCM gt40 runs hot

    A garden hose, especially one fed off city water makes a helluva lot more pressure than a floppy vane raw water pump, especially after the pressure drops in a RWC system. if the new t-stat you had in there was a 180 deg F version, you may be on to something....i've never seen a marine thermostat for a gas engine that was rated that high.

  7. #7

    Default Re: PCM gt40 runs hot

    Quote Originally Posted by makomark View Post
    A garden hose, especially one fed off city water makes a helluva lot more pressure than a floppy vane raw water pump, especially after the pressure drops in a RWC system. if the new t-stat you had in there was a 180 deg F version, you may be on to something....i've never seen a marine thermostat for a gas engine that was rated that high.
    The thermostat was a 143 degree, the risers are cast iron and 3 years old.

  8. #8
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    Default Re: PCM gt40 runs hot

    143 degree thermostats are usually marine so that isn't likely to issue.

    Have you checked the oil cooler?

  9. #9

    Default Re: PCM gt40 runs hot

    Quote Originally Posted by makomark View Post
    143 degree thermostats are usually marine so that isn't likely to issue.

    Have you checked the oil cooler?
    Yes and it is clear.

  10. #10
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    Default Re: PCM gt40 runs hot

    Thermostat outlet, where the exhaust manifolds are fed from - is it a poppet valve design?

  11. #11

    Default Re: PCM gt40 runs hot

    Quote Originally Posted by makomark View Post
    Thermostat outlet, where the exhaust manifolds are fed from - is it a poppet valve design?
    No it's not a poppet valve, it has three hoses and no valves.

  12. #12
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    Default Re: PCM gt40 runs hot

    Damn...not much left...is the raw water pump installed correctly? all hose clamps in working order and tight?

    might want to call the skidim shop and get their two cents

  13. #13

    Default Re: PCM gt40 runs hot

    Quote Originally Posted by makomark View Post
    Damn...not much left...is the raw water pump installed correctly? all hose clamps in working order and tight?

    might want to call the skidim shop and get their two cents
    All clamps are tight, now you understand our frustration!

  14. #14
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    Default Re: PCM gt40 runs hot

    ok...how bout you get an IR thermometer gun and take some measurements...

    I'd also MEASURE the output of the raw water pump to MAKE SURE it is adequate.

    The other item that is useful in finding the issue is a clear piece of tubing that you temporarily replace the black rubber hose with. lets you verify a solid stream of water is flowing between any two parts.

  15. #15

    Default Re: PCM gt40 runs hot

    Quote Originally Posted by makomark View Post
    ok...how bout you get an IR thermometer gun and take some measurements...

    I'd also MEASURE the output of the raw water pump to MAKE SURE it is adequate.

    The other item that is useful in finding the issue is a clear piece of tubing that you temporarily replace the black rubber hose with. lets you verify a solid stream of water is flowing between any two parts.
    Thanks. Great suggestions, will try after my vacation.

  16. #16

    Default Re: PCM gt40 runs hot

    if none of what you tried work and then the thermostat could be stuck in you need a new one

  17. #17
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    Default Re: PCM gt40 runs hot

    For a raw water cooled engine, the engine cooling demands will be predicated by the thermostat on an "as required" basis. IOW.... the thermostat holds back seawater, until the temperature causes it to open up.
    (you definitely want to run a thermostat in the system)

    Unless under extreme heavy loads.... this means that more seawater will be sent on to the exhaust system than what the actual engine cooling will demand.
    If the exhaust system is restricting spent seawater flow..... the engine cooling may suffer.


    Perhaps more info is needed:

    Which seawater pump? Belt driven.... crankshaft pump..... or other?

    There is an old issue with the large volume Johnson crankshaft pump impeller being inadvertantly used in a large volume Jabsco pump.
    The Johnson impeller measures 1.900" in depth....... Jabsco requires 1.990".
    Each impeller offers the same OD, same blade count, same spline...... but the depth is not the same.
    Parts counter staff occasionally get this wrong when selling an impeller.

    When you say that the elbows are clear...... does this included the seawater transfer ports?

    Have you looked at the hoses that feed spent water to the exhaust manifolds? Make sure that the interiors are OK.

    On many of these there is a mixing chamber within the T-Stat housing . Look at the exiting ports, and make sure that these are clear.


    Any small suction breach (from pump to pick up area) will affect the pump's ability to pull seawater in.



    .
    Last edited by RicardoMarine; 07-17-2014 at 08:46 AM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
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  18. #18

    Default Re: PCM gt40 runs hot

    I came across this thread as I too have a PCM GT40 (351W) running hot. Any help appreciated, especially if Danielm resolved his similar issue. I have a new 160 degree thermostat. Engine warms up normally to 160 then continues to slowly creep up to 185-ish. If I rev approx 1100-1200 rpm in neutral, it will drop back down to 180 I've done everything but the circulating water pump and the temperature sensor. The main pump runs quietly and no leaks, so it's hard to imagine that the brass impellers "wear out" like a neoprene raw water impeller.

    New impeller, new thermostat, new hoses, new exhaust manifolds, new risers. The water canister contents swirl rapidly with bubbles for just a couple of seconds, then runs clear with no bubbles so system seems tightly sealed. I actually switched the impeller twice thinking I had a faulty one, but water gushes from the feeder hose on testing and will fill a 2 gallon bucket in just a few seconds. Very baffled here. I will end up changing the main pump because that's all that's left.

    Boat is a 1998 Ski Nautique with 900 hours. I've owned it since new.

    Click image for larger version. 

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  19. #19
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    Default Re: PCM gt40 runs hot

    water canister = strainer in the suction hose, feeding the pump?

    was the previous thermostat a 160deg unit or a 143 deg unit?

    what type of water do you boat in?

    Have you verified the 'accuracy' of your gauge with another instrument?? IR thermometers are pretty cheap and easy to use...

  20. #20
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    Default Re: PCM gt40 runs hot

    another light bulb just illuminated....did you make sure the oil cooler(s) is clear, where the cooling water passes thru it?

    made sure the strainer lid gasket is in good shape and the lid is secure?

  21. #21

    Default Re: PCM gt40 runs hot

    Makomark,
    Thanks for the great tips. I called my local parts guy (J A Chamberlin in Longwood whom I like) for a new pump. He said exactly the same thing: Clean out the tranny oil cooler before you replace the main pump. The raw water seals are tight. bubbles disappear quickly in the cannister. The flow seems good from the feeder hose off the raw water impeller, but perhaps there's not enough pressure due to build up in the cooler. I'm due to change the ATF anyway so I'm going to remove the cooler and clean it out thoroughly, and report back. Much appreciated. Nick

  22. #22

    Default Re: PCM gt40 runs hot

    Makomark,
    Thanks for the great tips. I called my local parts guy (J A Chamberlin in Longwood whom I like) for a new pump. He said exactly the same thing: Clean out the tranny oil cooler before you replace the main pump. The raw water seals are tight. bubbles disappear quickly in the cannister. The flow seems good from the feeder hose off the raw water impeller, but perhaps there's not enough pressure due to build up in the cooler. I'm due to change the ATF anyway so I'm going to remove the cooler and clean it out thoroughly, and report back. Much appreciated. Nick

  23. #23

    Default Re: PCM gt40 runs hot

    Click image for larger version. 

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    Well the transmission oil cooler was clean as a whistle though I was hoping it would be clogged. I boat exclusively on a very weedy lake, but the raw water strainer is apparently doing its job well. On to the main water pump......

  24. #24
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    Default Re: PCM gt40 runs hot

    The circulating pumps usually have issues with the bearing or seals.....rarely do you see an impeller issue.

    How was the cam in the raw water pump when you changed the rubber impeller?? any wear on the faceplate?

  25. #25

    Default Re: PCM gt40 runs hot

    None. I always run my fingers around the metal inside and along the brass cam to be sure it's smooth and there's nothing that would prematurely wear the impeller out. I changed out the impeller anyway to be certain it didn't prematurely fail as I always carry a spare, and the prior one was still in new shape. The neoprene vanes do hold in a slightly bent position from the direction of rotation, but no wear and function is fine. The boat is on a lift, so I drop and run it for a moment to be sure water has run through the entire system, but without allowing the engine to warm up. I then disconnect the raw water feed hose at the thermostat housing, stick the open end in a bucket, and turn over the engine letting it idle for 3-4 seconds then shut down. In that amount of time, there's about a gallon of water pumped into the bucket so I'm confident my problem is downstream of the raw water supply.

    Before I change the main pump I'm going to take off the thermostat housing that includes a pipe that feeds to the water pump and make sure there are no obstructions. It's easy to do if I'm going to remove the main pump anyway. BTW, I agree with you that there's little to go wrong with main pump impellers as they are brass and only touch water. The bearings are quiet with no play, and their seals are tight. The 160 thermostat is new and I tested it on the stove in a pot to see that it opens as the water heated up to proper temp - all good there. The temp gauge would indicate it's OK too because warm up is steady to 160, then the progressive rise in temp above that level is slow.

    If it turns out the pump is OK, I've got blockage somewhere, and I'm hoping it's not in the block. Unlikely as the boat has never sat more than 2 weeks without running to full operating temps. Thanks for your input.

  26. #26

    Default Re: PCM gt40 runs hot

    Blockage found! Click image for larger version. 

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    This is inside the thermostat housing itself. I have a rat-tail file inserted from where the raw water enters the housing adjacent to the thermostat. At first I couldn't fit a small screwdriver through this portion where it joins the main water channel as it was 80%+ blocked with built-up rusty scale that is like a hard clay mud. Likely 21 years of silty sediment from the lake accumulating in this narrow opening. I scraped then rinsed it out without too much resistance. It's evident that the blockage was preventing sufficient quantity of raw lake water to enter the engine. I'm putting in the new pump anyway given that the boat is already apart. I'll confirm success when all is back together and cool running.

    Thanks for the member input. I hope this helps others as it's a cheap fix......good thing to check when changing your thermostat.

  27. #27
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    Default Re: PCM gt40 runs hot

    I wouldn't have expected that when you said lake.....but most of everything around here has salt.....and build ups like that usually occur long before 20 years on the poorly maintained boats (they usually get sold after a few years....)

    Anyhow,glad you found the likely culprit.

    FWIW, there have been a few post on flushing the blocks with a muratic acid bath or one of the newer 'magic bottles' marketed for a de-scaling purpose....may be worth the effort in the fall.

    Finally, I can't believe you haven't had to replace the cam yet...guess there isn't much abrasive content in the lake....and that's a good thing!!

  28. #28
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    Default Re: PCM gt40 runs hot

    How's it cooling???

  29. #29

    Default Re: PCM gt40 runs hot

    Quote Originally Posted by makomark View Post
    How's it cooling???
    Excellent results. Changed pump and went old-school on the thermostat which was the 143F variety until mid 90s. The gauge indicates this temp and doesn't budge. If I really crank it up (took cousin tubing yesterday), it maxed out at 160F only after immediately slowing to idle and quickly dropped back to 143F in a couple minutes.

    As an antidote, PCM doesn't manufacturer the same thermostat housing anymore. The new version requires different hoses.
    Thanks for checking in!

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