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  1. #1
    Join Date
    Sep 2011
    Currently Docked in Hamilton Ontario

    Default Ford Lehman 120hp Over Heating

    Hi, am new to this forum and hope some one can help.
    My stb engine over heats and the coolant ends up in the bilge. I figure I had a bad hose or something so,topped up the tank and started the engine to look for a leak. After about 5 minutes of running at 1000 rpm the coolant started coming out the tank overflow. I swapped the cap with the one from the port engine and the same think happened but it took awhile longer. I can replace both caps but it does not seem logical that they would both be bad. The port engine does not over heat. Can anything else cause this?

  2. #2

    Default Re: Ford Lehman 120hp Over Heating

    Check this forum , page 2 for a posting around 7-18-2007 , there is lots of helpful info there as he had 38 replies


  3. #3
    Join Date
    Sep 2011
    Currently Docked in Hamilton Ontario

    Default Re: Ford Lehman 120hp Over Heating

    Thanks, will do.Dave

  4. #4
    Join Date
    Apr 2008
    vancouver, bc, canada

    Default Re: Ford Lehman 120hp Over Heating

    Is your thermostat upside down? or faulty?

  5. #5
    Join Date
    Sep 2011
    Currently Docked in Hamilton Ontario

    Default Re: Ford Lehman 120hp Over Heating

    Thermostate is OK. Problem seems to be with the keel cooler. It either has a leak or there isw air trapped inside. WhenI fill it, the coolant shoots out the overflow once the engine is hot.

  6. #6

    Default Re: Ford Lehman 120hp Over Heating

    Hi dave, have you bled the air out of the top front exhaust manifold petcock ?? Also do you have a heat exchanger on th back of the engine or is it a keel cooler ?? Try flushing it out. Also could be partially blocked oil cooler restricting water flow.

  7. #7

    Default Re: Ford Lehman 120hp Over Heating

    Ford Lehman OVERHEATING.
    Damn you guys are good!!!
    You just saved me best part of a grand….
    It’s an old Lehman, lots of rust and crud even been underwater…

    So here are the symtoms:
    So for apparently no reason it started to overheat.
    Check the header tank and its empty. Check all the usual, water pumps both fresh and salt water, plenty of water out the exhaust. No leaks or drips anywhere but the header tank empty.
    Fill it up and try again.
    Few minutes running OVERHEAT, check header tank EMPTY.

    Gotta be the heat exchanger or worse cracked head…. Right?
    Otherwise where is the fresh water going?
    Thermostat, emm maybe!

    Read through a few blogs and plenty of people say PURGE the FRESH WATER SYSTEM.
    What is Purge the Fresh water system? I’ve never heard of it.

    So I find the purge valve and eventually with plenty of blaster, get it moving without snapping it off.
    Loads of air comes out, the header tank empties, fill it again until there is only water coming out of the purge valve.
    It’s been running for almost an hour and guess what….? No Overheating!
    Using a laser temperature gizmo thing the temperature at the header tank where the temperature gauge sender is, the temperature reads 140 exactly the same as the gauge.
    If it hadn’t of been for you guys I would have attacked the heat exchanger and oil cooler.
    Thanks guys, I owe you a beer.

  8. #8

    Default Re: Ford Lehman 120hp Over Heating

    Hi Dave:

    1.- Look to clean the little drain metal pipe coming out from the overflow tank collar in front of the engine. The purpose of this pipe is to exhaust excess coolant at high temperature, therefore it should be clean to exhaust the overflow quantity when the pressure pushes the refrigerant. Otherwise temp is not properly regulated.

    2.- Do not fill the tank full to the cap, leave 10mm below the cap.

    3.- Check the cap - The pressure should force the cap spring as to exhaust the coolant through the pipe described in 1.-Change it if required. There is a Volvo truck compatible black plastic, much better and modern in quality.

    4.- If not solved you should check /change the thermostat - If not solved, later the cleaning the coolers.

    I would be sure that is point 1.-

    GHood luck

  9. #9

    Default Re: Ford Lehman 120hp Over Heating

    I have been in the same situation for the past few months my engine (ford lehman hp 120)has been over heating when it crosses 17 rpm. Just aa every one else i did everything possible to solve the problem,I flushed the engine,checked the water pump, took out the tomostart but nothing worked. I decided to changed the impeller clean the heat exchanger but the problem still wasen't solved.so I came to the conclusion that the jabsCo pump was too small so I altered a bigger jabsco pump to fit and replace the smaller one the impeller in the new pump is twice the size of the old one
    I also replaced (cut out) the smaller pipes on the heat exchanger with larger ones which is about a inch and a half as well as change all the lines to inch and a half. I then took her out for a spin I ran up to29 rpm for a least 45mins and there was no over heating in which case I have never run that high before

  10. #10

    Default Re: Ford Lehman 120hp Over Heating

    Hi, It should not be necessary to change all your piping and pump. You have another issue, possibly electrical. did you check antifreeze temp with a mechanical gauge? Your engine should not turn up to 2900 rpm in gear which makes me believe your gauges are wrong. If there was an overheat problem I would remove the exhaust elbow and check for rust clogging the cooling passages.
    Charlie W

  11. #11

    Default Re: Ford Lehman 120hp Over Heating

    Hi.. can anyone provide more information or even better the part number for the "much better" black Volvo truck compatible expansion cap tank please?

  12. #12

    Default Re: Ford Lehman 120hp Over Heating

    Hi Ematty, on the front top of your exhaust manifold should be an air bleed petcock. always bleed the air out at this point when filling the expansion tank. a larger tank should not be necessary and the pressure caps were 4 pounds.
    charlie w

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