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Lehman fresh water drain

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  • #16695

    Evening all,

    Anyone know where the FRESHWATER drains are on the Lehman engine block ?
    Mine’s probably not had the drain / flush / new coolant treatment for many a long year.




    Hi Ned, Theo, I have a MkII 1981 Nauticat with the Ford Lehman 80hp engine. I located the drain on the port side of the engine at the rear of the engine it is tucked under the curve of the engine casing. The drain has ‘wings’ so that you might be able to undo it by hand. I found it from the Nauticat diagrams I have for the boat rather than the engine manual. Hope that is helpful.


    Once drained, how do you refill ?


    Richard ?

    David Babsky

    Richard! ..You undo the “radiator cap” on top of the fresh water coolant tank, right at the very front of the engine and just on top of it, and refill with a mixture of fresh water and anti-freeze.

    Pour in the coolant (water + anti-freeze) till it appears to be full, then run the engine, so that the coolant gets pumped around the system and the level in the tank drops, and while running it, keep topping-up the tank till it’s full. You can “dip” that header tank by just putting your finger into it – while it’s cool – and checking that the coolant comes up to the level of the vertical metal rod which stands inside the header tank, about half-an-inch below the open filler ..or just use a pencil to dip the tank, and make sure that the watery coolant is up to about half-an-inch below the open filler neck.

    I can’t remember if the coolant hose to the gearbox-oil-cooler is LOWER than the engine’s own drain cock, or if the engine drain cock is lower, but to draw the whole system – INCLUDING both the engine and gearbox oil coolers – you MAY need to disconnect their rubber coolant hoses, too. Can’t hurt.

    Incidentally, I just – last year and this – replaced my twenty-five-plus-year-old gearbox oil and engine oil coolers, as the gearbox oil cooler had spring an internal leak, and was bleeding water into its oil ..and thus into the gearbox! I replaced the gearbox oil cooler last year, and as the engine oil cooler was of the same vintage I replaced that one this year ..just to be safe!

    It’s also worth REMOVING the ENGINE HEAT EXCHANGER and cleaning out the pipes inside it with a very thin long-handled artist’s paint brush, to remove all the gunk which gathers inside the coolant tubes. My engine (..1989 NC33 Mark II Lehman..) had been overheating, and removing and cleaning the engine heat exchanger has dropped its running temp down from 90 degrees (ouch!) to 70 degrees. The heat exchanger was cluttered with multiple old scraps of zinc anode which had collapsed into the heat exchanger for-ard section. Well worth removing and thoroughly cleaning – but it’s VERY TRICKY to replace onto the side of the engine, as the metal bands which hold it onto the engine are a very tight, very snug fit!




    Here are several pictures of drain-cock, both for the seawater circuit and for the fresh (eg. water and glydol) water circuit.
    My engine (NC33 1977-1978) is a Ford 2712E marinizes by Gustavson of Stockholm.
    – Chauffe-eau vanne moteur_10023.jpg shows one drain at the bottom of the coolant water (fresh water) tank. This tanks exachange heat betzeen fresh water and seawater.
    – Purgeur_1478.JPG is taken from port side, front side of the engine, the alternator being removed to show one drain (green arrow). One can guess the beaing axis for the alternator at the opposite side of the arrow, very rusty at that time. And the alternator belt too.
    – Purgeur_1490.JPG is shot from port side toward the rear of the engine. One can guess the stainless steel exhaust elbow. The drain will certainly remove saewater for the top of exaust manifold and the marinistation part by Gustavson
    – Purgeur_1497.JPG is another view of the drain that lies behind the alternator.

    Hope it helps,
    Yves 5Naïla of Burnham, NC33 MkII #484)


    While you where at it did you replace the calorstat that lies at the front and port side of the engine ?
    This is the calorstat that prevents the fresh water that circulates in the bottom sides of the engine from circulating at the top of the engine until the water temperature stabilizes at around 70 °C ?


    @ Yves, hank you for the photos, now I have an idea where to look for the fresh water drain.

    @ David, good idea about cleaning out the muck but I think your heat exchanger his different from Gustavson / Lehman, will in any case investigate as last year’s new Stbd side anode in the header tank (Bosomotor) has disappeared completely.

    @ Richard, the original ? Seems to have stirred things up a little ! all good stuff and very necessary. My response to your ? does not seem to have got through but I concur with David ref refilling. I would just add that leaving the low down drain taps open during the early stages of refilling until a bubble free stream of fluid comes out of them will reduce the possibility of an air lock in any lower galleries.

    N33 521

    David Babsky

    Oui ..yes, Yves, I replaced what you call a ‘calorstat’ and what I call a ‘thermostat’ ..same thing, I think.

    That was the 1st thing I thought of when the engine was overheating, so I did change that by removing the fresh-water header tank, and – on my engine – the ‘thermostat’ is directly beneath that header tank. (I may have replaced it twice in 12 years, I think.) After changing the thermos it’s easy to replace the fresh-water header tank ..just two bolts, I think.

    I also checked the fan belts – to make sure that the raw-water pump was pumping properly! – and checked the raw water strainer ..the whole water system, in fact. The problem was the clogged engine cooling heat exchanger. When I’d removed all the old junk inside it, and cleaned out the narrow copper tubes with a SOFT, WOODEN, LONG-HANDLED artist’s paintbrush handle, everything ran perfectly and cool again.

    Thanks for asking!


    you are very right, Gustavson heat exchanger is quite different from Lehman’s stuff that – according to David – is easy to remove and inspect.

    I did it 15 years ago on a volvo 2040. very esay task.
    Thus I tried on the Ford Gustavson and never came to an end as I became too frightened to break something.
    Of course
    I started with the 3 bolts on the starboard side of the fresh water tank. This is the place where both seawater and engine oil pipes enter the heat exchanger. The 3 bolts themselves were easy to remove and then everything went too dificult for me and too dangerous with that old engine and its hard to find spares.I never succeded removeing the cover held in place by the three bolts.

    For your information I vaguely remember I passed along to Richard a diagram of Gustavson water tank I got from someone on Nauticat USA forum. Very helpfull.

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