Lehman 120

[10Benjamins]

I have a couple issues. Was out crushing yesterday. Port engine buzzer (alarm) sounded. Oil pressure was good and water temp was fine. I shut it down and limped home on one main. Came back the next morning and started it up. No alarm sounded. Exhaust Water was flowing and everything seemed fine. This is the second time this has happend. I replaced the raw water pump Which I don't believe has anything to do with this issue.
The othe issue i have is. I replaced both water fill caps I purchase from Napa. After running both mains, up until the port main buzzer went off. I came back the next day and the starboard main was down 2 liters of water. There was 1/2 that amount of coolant in the drip pan under the engine and the port was down about a quart. No coolant in the drip pan of this engin. What's up with that? Do you have any in site as to how I can resolve these issues. I'm mostly concerned with the buzzer. I'm thinking I'll have to ditch the new fill caps unless there's something else I can do about loosing coolant.

[SV THIRD DAY]

So first when you say "buzzer" are we correct to assume you had a "High Temp Alarm"?

[10Benjamins]

Yes if I lost oil pressure or the water temp exceeded 205 degrees. The buzzer/alarm should sound. The oil pressure and water temp were both within operating conditions when the buzzer sounded.

[neptunesjester]

On my 120's, the alarm sensors and gauge sensors are separate. You could have a sensor going bad or a bad connection.

As for the expansion tank caps, you may want to check with American Diesel to see if the Napa cap is a suitable substitute. My expansion tanks only stay a quarter full. Fill past that, and the excess is blown out once the engines reach temp. While discussing this with American Diesel, the explained some differences made to the expansion tank neck over the years and different caps needed.


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[10Benjamins]

So I'll eyeball the alarm and gage sensors. Can the alarm sensor work fine for a while then sound then the next day seem to be fine again?

I chatted with Brian at AD and he thinks I may have a 14# expansion tank cap as opposed to what it's supposed to be 4#. I'm going to score on the right caps. I just hope using the wrong ones didn't cause any damage.

1/4 full you say... Shooooot man I'd be afraid to do that... but maybe that'll keep the top of the expansion tank from puddling up around the caps after a few hours of running at about 1400rpms.

[Xlantic]

The problem may not be the temperature alarm sensor going-off when it shouldn't but the temperature gauge sensor not registering the correct temperature. An infrared temperature gun may help determine the actual engine temperature and which sensor, if any, is malfunctioning.

How old are the heat-exchangers?

Make sure you purge the air from the coolant circuit after you fill it and warm the engine. There is valve at the top of the engine for this.

[10Benjamins]

Xlantic, I think you nailed it with correct gage sensor temp. I did not bleed the air and plan to tend to that today. Thank you so much for the help.

[10Benjamins]

There was a tiny bit of air on top of the exhaust manifold. I'm still at a loss. I plan to go out today and put the laser pyrometer on the block and see the difference between actual temp and gage temp. What a drag.... I'm sure it's somthing easy it's just escaping me.

[10Benjamins]

I know there is no such thing as magic but I went out for a four hour cruse and no problems. This doesn't give me much confidence. I took laser pyrometer readings all over for vital signs half way into the cruse and Everthing checked. WIERD.

[Xlantic]

On these engines the temperature gauge sender may not operate correctly when there is a loss of coolant. Maybe that is why the temperature gauge reading was fine when the temperature alarm went off.

But the question remain, why was there the loss of coolant in the first place. It could have been the wrong caps, as you mentioned. Or it could have been clogged up heat exchangers. These need to be replaced or at least cleaned every few years. (You can check them by removing the end caps.)

Clogged-up heat exchangers may only lead to overheating when running above a certain speed for some time. Were the RPMs the same when the alarm went off as when it didn't?

[omc]

Originally Posted by 10Benjamins

I know there is no such thing as magic but I went out for a four hour cruse and no problems. This doesn't give me much confidence. I took laser pyrometer readings all over for vital signs half way into the cruse and Everthing checked. WIERD.

Don't know if that could help but I still have the FL 120 technical manual of my former GB 42' classic.