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Old 04-06-2015, 19:15   #1
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Lehman Overheating

I have a Lehman 80hp that had overheated and I found that the fresh water pump had blown. After replacing the (original) pump I ran the engine and it was still overheating, so I replaced the (original) thermostat with a new one rated at 179.5 degrees and still it was overheating.

The system temp is supposed to be at 175-190 degrees.

Long story short I have replace all the original FW cooling components, including the Heat Exchanger and Expansion tank. Its ALL NEW!

However, after again starting the engine it is still overheating so I took the new thermostat off and took it home to test. I tested it 3 times in a pot of water on the stove using a thermometer to see when it opened and all 3 times it started opening at 190 degrees and was fully open at 205 degrees.

Do I have a bad thermostat or do I allow lag time or...?

BTW, I'm a complete newby.

Thanks in advance.
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Old 04-06-2015, 19:28   #2
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Re: Lehman Overheating

Dan, The thermostat on my FL120 opens at about 170 degrees. The engine runs at about 175 at our normal cruising speed. I suggest you contact Brian Smith at American Diesel. Chuck
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Old 04-06-2015, 19:38   #3
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Re: Lehman Overheating

Woe is me, you may have a blown head gasket .
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Old 04-06-2015, 20:01   #4
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Re: Lehman Overheating

Hi AG,

Thanks for the contact info, I'll try him in the morning. BTW, I referenced your site when this problem started back in early May.

I suspect thermostat is 1.) defective and 2.) not the correct one for the engine. There is another that is rated at 170 degrees that I'm going to take a look at tomorrow.

And I HOPE it isn't a blown HG.
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Old 04-06-2015, 20:22   #5
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Re: Lehman Overheating

Good luck. Brian will surely give you some insight. They are the experts on the Ford Lehman. Chuck
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Old 05-06-2015, 08:23   #6
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Re: Lehman Overheating

Have you checked the injection elbow?
Edit: and you don't mention servicing or replacing the raw water pump.
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Old 08-06-2015, 22:35   #7
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Re: Lehman Overheating

Update:

I checked in with Brian at AD and after going through the issue he recommended to change out the thermostat to one rated at a lower temperature. He also recommended to check to ensure that the sender unit was operating correctly.

I had replaced all the old SW gauges with new ones, and they require you to use their branded senders. Given that, I checked and, sure enough, I had a different brand sender.

So after putting in the new sender and thermostat I ran the engine and everything worked exactly as it should. The temp was solid as a rock!

Thanks all for the input!
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Old 09-06-2015, 04:06   #8
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Re: Lehman Overheating

So it really was not overheating just the gague was wrong?

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Old 19-07-2015, 00:47   #9
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Re: Lehman Overheating

Update II

After many weeks of thinking I had this problem whipped and moving on to other projects, I finally got chance to move the boat from its slip at a boatyard back to my dock.

Everything was a-ok water temp-wise until I had pulled out of the marina and put a load on the engine. The temperature very quickly climbed to ~230 at around 1600-1700 rpm. No steam; no cap pop-off; no leaks; raw water exiting exhaust as normal.

To recap: I've replaced nearly every fresh water component (heat exchanger, pump, expansion tank, thermostat, sender unit and gauge. Ensured no air bubble when putting in new fluid. Cleaned raw water strainer and verified that good flow RW flow out of the exhaust.

I suspect I'm not getting good FW flow through the system but don't know where or how to check?

Any ideas out there?
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Old 19-07-2015, 04:36   #10
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Re: Lehman Overheating

It sounds like you have an air lock. Try pumping coolant in or pulling it it with a vacuum. Can you burp the system while it's operating and building pressure?

I have a keel cooled system and had to install valves on my hot and cold side to burp out air after I work on any part of the coolant system.

It doesn't take much air to lock up the pump.

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Old 19-07-2015, 05:44   #11
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Re: Lehman Overheating

Quote:
Originally Posted by DanSFB View Post
Update II

After many weeks of thinking I had this problem whipped and moving on to other projects, I finally got chance to move the boat from its slip at a boatyard back to my dock.

Everything was a-ok water temp-wise until I had pulled out of the marina and put a load on the engine. The temperature very quickly climbed to ~230 at around 1600-1700 rpm. No steam; no cap pop-off; no leaks; raw water exiting exhaust as normal.

To recap: I've replaced nearly every fresh water component (heat exchanger, pump, expansion tank, thermostat, sender unit and gauge. Ensured no air bubble when putting in new fluid. Cleaned raw water strainer and verified that good flow RW flow out of the exhaust.

I suspect I'm not getting good FW flow through the system but don't know where or how to check?

Any ideas out there?
You must be pulling your hair out.

Loosen hose clamps slightly at each high point while running (before it gets too hot) and check for air.

Also you may want to check hoses for internal delamination. They sometimes peel off an internal layer and it folds over & restricts flow.

Maybe invest $30 in a cheap infrared heat gun and look for uneven temperatures in your cooling circuit.

As mentioned above, it is possible that a head gasket was blown during the initial overheating when the pump failed. You may pick that up with your heat gun.

Check also for possible a kinked hose on an auxiliary line such as to/from your hot water tank heat exchanger.
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Old 19-07-2015, 06:59   #12
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Re: Lehman Overheating

If you have opened the air purge petcock on the top of the manifold when you filled up the FW coolant and leave it open until air is gone and nothing but coolant came out, you should not have air in the system. It is still possible. If that isn't the problem, you will next need to look at the head gasket. We just replaced ours in our FL 120. Also, check all of your hoses while underway and at cruising speed. Make sure none of the hoses have collapsed and are blocking the flow. They won't show at low speed or when not under load. Chuck.
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Old 19-07-2015, 09:32   #13
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Re: Lehman Overheating

Sounds like a possible air lock.
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Old 19-07-2015, 10:02   #14
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Re: Lehman Overheating

Thanks all for the answers.

I've read in other threads that I can confirm a blown head gasket by opening up the expansion tank and watching for air bubbles, or something like that.

Anybody have specifics?

Thanks in advance.
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Old 19-07-2015, 11:17   #15
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Re: Lehman Overheating

Dan, there are a lot of different signs of a blown head gasket, depending on where it's blown. Yoy may see bubbles and maybe not. Overheating is a sign. If your FW coolant increases, that's another sign. You can have the coolant tested for exhaust, but you need the proper tool. Water in the oil, or no other signs. It might be time to call the mechanic.
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