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Old 05-23-2022, 09:13 AM   #1
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Coolant Problem

So I had to change the exhaust elbow and when I put everything back together I refilled the coolant. I made a mistake and did not close the bleed on the manifold. So I was running yesterday and everything seemed normal as far as temps, etc. I went to WOT and after 4-5 minutes there was a loud pop, like a gunshot. I stopped the motor as all the coolant was now going out the aforementioned open bleed valve. There was NO fluid coming out of it before the pop which is why I didnít catch that it was open. After cooldown I filled the system with water and bled the system. Everything seemed normal and I fast idled back to the dock.

I called AD and will talk to Brian tomorrow. I just canít figure out why nothing was coming out the bleed before I even left the dock and what that pop was. I was thinking maybe the thermostat had a ton of pressure behind it? Just real happy no cracks in head/manifold and no bent rods, etc.

Jeff
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Old 05-23-2022, 06:02 PM   #2
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It's not uncommon for an air bubble to form under the thermostat if it doesn't have a small hole to allow air to pass. Some engines don't completely fill places where air pockets form without some effort. Larger better designed engines have a bypass circuit that allows some coolant to bypass the thermostat so there is always minimal circulation.

When I fill an empty engine, I start with the known capacity and if necessary work out the air until I've added near that amount of liquid.

Finding the source of the gunshot will require careful inspection of cast parts. I guess there's a crack somewhere if the engine was the noise source. If there were air pockets stopping circulation, some coolant could have turned to steam. Water expands 16x when becoming steam, building pressure rapidly. In an enclosed space it can cause an explosion like a boiler.
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Old 05-23-2022, 07:00 PM   #3
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Maybe the bleeder was plugged with rust or gunk and it broke free under
pressure making the noise.
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Old 05-23-2022, 07:21 PM   #4
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The bleeder valve is in suction when open and the engine is running...you are introducing air into the system, not expelling coolant.

The bleeder valve is to get the air out of the top of the manifold when not running and adding coolant into the expansion tank.
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Old 05-23-2022, 07:28 PM   #5
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The bleeder valve is in suction when open and the engine is running...you are introducing air into the system, not expelling coolant.

The bleeder valve is to get the air out of the top of the manifold when not running and adding coolant into the expansion tank.
Apparently under pressure in the OP's case.
Also begs the question of why the coolant has a pressure cap?
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Old 05-23-2022, 07:43 PM   #6
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Apparently under pressure in the OP's case.
Also begs the question of why the coolant has a pressure cap?
If it is a Lehman 120...it is NOT under pressure at the bleed valve when the engine is running.

There are warnings in the manuals about opening it when running.

This is ASSUMING it was an engine running normally when the valve was left open.

When you shut down and there is enough coolant in the system....because it now is hot and maybe super hot from air pockets, it does come out the bleed valve.

Quote from the OP...... " I just can’t figure out why nothing was coming out the bleed before I even left the dock ......"
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Old 05-24-2022, 04:08 AM   #7
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Iím surprised to learn that a Lehman engine runs a vacuum in a section of the cooling system when running. I would of expected various pressure gradients but a vacuum I find unexpected. It would lower the boiling point somewhat in that area.
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Old 05-24-2022, 06:51 AM   #8
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Iím surprised to learn that a Lehman engine runs a vacuum in a section of the cooling system when running. I would of expected various pressure gradients but a vacuum I find unexpected. It would lower the boiling point somewhat in that area.
It's described on page 19 of the operator's manual which you can download from the library.
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Old 05-24-2022, 07:02 AM   #9
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Lepke mentioned the small hole in the thermostat. That hole is there for a reason on Lehmans. When I refill my block I open the manifold bleeder and pour in the coolant until coolant begins flowing out of the manifold bleeder. At that point the level in the header tank is about one inch below the top. I have never found an excess of air in the system after running the engine. It's the hole in the stat that lets air to bleed out naturally on both sides of the thermostat as the system is filled. The stat is a common 53mm stat, maybe $8. Simply drill a 3/16 hole in the horizonal surface of the body. Or purchase a $35 stat from Fred Warner or American Diesel with a ready-made hole.
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Old 05-25-2022, 12:00 PM   #10
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Test
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Old 05-25-2022, 12:02 PM   #11
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Originally Posted by catalinajack View Post
Lepke mentioned the small hole in the thermostat. That hole is there for a reason on Lehmans. When I refill my block I open the manifold bleeder and pour in the coolant until coolant begins flowing out of the manifold bleeder. At that point the level in the header tank is about one inch below the top. I have never found an excess of air in the system after running the engine. It's the hole in the stat that lets air to bleed out naturally on both sides of the thermostat as the system is filled. The stat is a common 53mm stat, maybe $8. Simply drill a 3/16 hole in the horizonal surface of the body. Or purchase a $35 stat from Fred Warner or American Diesel with a ready-made hole.
All tstats without a small hole 1/16" in size or so when i install them ill do so to allow air purging when filling
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Old 05-25-2022, 12:09 PM   #12
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Ok, so I spoke with Brian at AD. Iím doing a pressure test. To address a couple of comments which I very much appreciate:

Yes, I know the bleeder was supposed to be closed. It was not expelling any fluid.

I was interrupted and forgot where I was at in bleeding process. I ran the boat at the dock several times checking everything with no leaks or fluid seen.

I know the bleeder needs to be closed for fluid to move through the system. It was a mistake.

Since no fluid was coming out of it until the pop and then all the fluid was coming only from there I believe it was blocked. I was watching my temps during my test run when this happened. I was shooting all parts of the motor with temp gun and everything in all aspects was normal.

This happened 2-3 minutes at 2475RPM which is my WOT. I know it is rated at 2500. Brian wants me to simply pressure test it and then if thatís good do an operational. I normally run anywhere from 2,000 to 2,200 RPM cruise. Running like this has eliminated smoking and other problems with an over propped setup and glazing.

Iíll update the thread after my testing. Again, thanks for all the input.
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Old 05-25-2022, 08:15 PM   #13
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I know the bleeder needs to be closed for fluid to move through the system. It was a mistake.
Finally, I have met someone who has made a mistake. One time I also thought I made a mistake, but of course I was wrong.

You are on course now, we can learn from the adventure
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Old 05-30-2022, 01:03 PM   #14
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I need to remove the cap to bleed on my 120. Then if still nothing comes out, time to add just a bit more fluid.
I was distracted once and left the cap off. Learn from the mistakes. Good thing these engines are pretty tough
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Old 05-31-2022, 06:54 AM   #15
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Quote:
Originally Posted by Lepke View Post
It's not uncommon for an air bubble to form under the thermostat if it doesn't have a small hole to allow air to pass. Some engines don't completely fill places where air pockets form without some effort. Larger better designed engines have a bypass circuit that allows some coolant to bypass the thermostat so there is always minimal circulation.

When I fill an empty engine, I start with the known capacity and if necessary work out the air until I've added near that amount of liquid.

Finding the source of the gunshot will require careful inspection of cast parts. I guess there's a crack somewhere if the engine was the noise source. If there were air pockets stopping circulation, some coolant could have turned to steam. Water expands 16x when becoming steam, building pressure rapidly. In an enclosed space it can cause an explosion like a boiler.
I am not familiar with the thermostats on an FL, but many others have a small bleed/vent hole in them to relieve that air bubble. I have drilled a small hole (1/8") in the body of the t stat if they don't. If the t stat is mounted vertically you need to install it so the vent hole is at the top.
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