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Old 06-21-2020, 07:00 PM   #1
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Lehman 120 cooling issue

So I have emptied and refilled the coolant in my port engine for the second time. The reason was because I was getting overflow out the cap (along with some odd coolant boogers). I had been getting some coolant collecting under the engine, and thought it was from the overflow tube (I haven't upgraded the cap/overflow). But after going through the Lehman 120 manual's directions on filling with coolant again, there is no coolant coming out of the tube.

I did everything up to running the engine with the cap off at 900rpm. I checked on the coolant every couple of minutes, when I saw the coolant was expanding and overflowing the neck. I shut down and of course the level dropped slowly over the next few minutes to about a half inch from the top.

So I ran the engine again, this time with the cap back on. After a couple minutes, coolant again started coming out of the cap - and still nothing coming out the overflow tube.

I've read that it's a good idea to clean out the overflow tube occasionally. Has anyone done that? I'm assuming it requires removing from the top front of the expansion tank, as opposed to sending a wire or something up through the end of tube to clean it out...
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Old 06-21-2020, 07:12 PM   #2
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Just as a matter of curiosity when you run it with the cap off do you see any bubbles popping up in the header tank when the thermostat opens? Particularly when you increase revs?
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Old 06-21-2020, 07:16 PM   #3
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It can involve drilling out the tube to remove solid blockage, and involves removing the tank. From memory, with the tank off you have access to the thermostat. Check the tube from the bottom of the tank, it corrodes and gradually disappears, it`s aluminum,my guy welded on an Al. tube he found somewhere. If the tube degrades the hose on it may not seal,coolant leaks at head/block joint level,mimics a head gasket leak. Which is why I have a not needed head gasket kit on hand.
ADC make an overflow bottle conversion, we fitted a Mercruiser overflow kit which does the job.
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Old 06-21-2020, 07:18 PM   #4
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Sounds like you need a new cap. Did you properly bleed all the air out of the tube running down the starboard side of the engine? To do this you need to open the petcock on the port side of the coolant tank mounted on the front of the engine. This will allow air into the system and allow the coolant to drain into the tube. Top off the coolant a couple times as you do this.

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Old 06-21-2020, 07:26 PM   #5
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Sounds like you need a new cap. Did you properly bleed all the air out of the tube running down the starboard side of the engine? To do this you need to open the petcock on the port side of the coolant tank mounted on the front of the engine. This will allow air into the system and allow the coolant to drain into the tube. Top off the coolant a couple times as you do this.

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Caps are about 4psi. It`s more likely a blocked tube than the cap imo, but a new cap won`t hurt. I`d expect overflow would prevent pressure overcoming the cap seal.
Topping up should always be with petcock open, engine not running. Lehman had a useful Manual for the engine, lots of info, a good read, expanded diagrams,and marinizing part numbers. Mine went with the boat.
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Old 06-21-2020, 08:08 PM   #6
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Just as a matter of curiosity when you run it with the cap off do you see any bubbles popping up in the header tank when the thermostat opens? Particularly when you increase revs?
It was bubbling somewhat, but I did not increase revs before it started overflowing.
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Old 06-21-2020, 10:48 PM   #7
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Hmm! Normally when you run an engine with cap off you will see the coolant begin to flow through the header tank as the thermostat opens. If lots of bubbles and it overflows, normally head gasket. If you rev-up and boils out certainly look at head gasket. Also can get the problem on a 2715e if the system is not bled properly and you have an airlock on the exhaust manifold, that's why there is normally a valve cock there on the water cooled manifold to ensure no air around #1 and#2 .
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Old 06-22-2020, 12:11 PM   #8
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did you bleed the system with the valve as per the manual? Buy the American Diesel overflow/coolant tank mod, no more coolant in the bilge. Its cheap and even a landlubber could install it.
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Old 06-22-2020, 12:30 PM   #9
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did you bleed the system with the valve as per the manual? Buy the American Diesel overflow/coolant tank mod, no more coolant in the bilge. Its cheap and even a landlubber could install it.
I think I will be getting the coolant tank mod from AD.

As far as bleeding, etc., I followed the manual explicitly. Which I've done before on both engines and not had any previous issues.

This afternoon I'm going to take the cap off the stbd engine and put it on the port engine and run it. If no problem, it's likely the cap (hopefully!). If problem persists, I'll clean the overflow tube first...
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Old 06-24-2020, 07:46 PM   #10
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Turned out my overflow tube was totally gummed up and blocked. Cleaned it out and now everything seems to be running normal!
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Old 06-24-2020, 08:19 PM   #11
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Turned out my overflow tube was totally gummed up and blocked. Cleaned it out and now everything seems to be running normal!
Now that's a happy ending! Good to hear it.
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Old 06-24-2020, 08:30 PM   #12
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Turned out my overflow tube was totally gummed up and blocked. Cleaned it out and now everything seems to be running normal!
Glad that resolved it. Now let`s ask why it happened.
Solid fallout from coolant? Something else contaminating the coolant? Wrong coolant or not changing it often enough. Not using distilled water for concentrate dilution?
There should not be solids to fall out of coolant. It is, as I posted, a significant Lehman issue. Possibly the same thing causes silting around no.6 in the coolant passages compromising cooling and that cylinder/piston, and the engine generally.
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