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Old 06-01-2017, 08:23   #1
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Ford Lehman overheating

I've got a Ford Lehman 4 cylinder that has run at about 180-185 for years. A couple of months ago, it suddenly shot up to well over 200 and the over heating alarm when off. We dropped the anchor and waited a while checking the water(all fine). Restarted the engine and while it still ran hot, it didn't trip any alarms.
I checked the heat exchanger and it was nice and clear(flashlight shown through the tubes). Coolant was fine(maybe a bit low). I opened the pet cock on the top of the manifold and water came up the tube. I opened the fresh water cap on the tank and water was flowing though the system seemingly just fine.
A few days ago, when we were running into the wind, the engine again shot up and the alarm went off again. We dropped the anchor and a day or so later entered a main harbor where I could get parts and find a mechanic for advice.
His thoughts were that I was getting air into the raw water cooling system through a small hole in one of the water hoses and that I should check or change them as well as pull the impeller. The hose from the through hull had a "T" in the line with it going somewhere under the floorboards to God knows where. I took it out and replaced the hose. I got the impeller out and there were two vanes with pieces missing. Water was still going through the engine which is why I'd not taken the impeller off before. Out with the old and in with the new. This morning, we pulled up the anchor and started out for a "stress" test. Again, the heat shot up but we turned around and headed back to the anchorage doing about 1300-1400 revs(low-normally at 1500).
I figure to drain out the existing fresh water and flush the system and put in new along with a new thermostat.
Any suggestions of other things to try would be greatly appreciated. Mechanics run over $100/hour and they all want the boat in a marina while they are working on it and the cheapest is about $100 per night if you can find a slip available(US Virgin Islands).
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Old 06-01-2017, 08:55   #2
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Re: Ford Lehman overheating

It sounds like a sticky thermostat to me
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Old 06-01-2017, 09:52   #3
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Re: Ford Lehman overheating

Quote:
Originally Posted by mestrezat View Post
I got the impeller out and there were two vanes with pieces missing. Water was still going through the engine which is why I'd not taken the impeller off before. Out with the old and in with the new. This morning, we pulled up the anchor and started out for a "stress" test. Again, the heat shot up but we turned around and headed back to the anchorage doing about 1300-1400 revs(low-normally at 1500).

Where'd those missing vanes go? In some systems, they could be clogging the downstream flow, perhaps intermittently. Backflush? Or otherwise search them out and remove?

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Old 06-01-2017, 10:23   #4
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Re: Ford Lehman overheating

heading in tomorrow to drain the water, flush the system and change the thermostat. they put it in a very convenient place--right under the fresh water tank! No way to get at it without draining everything.
As for the broken impeller pieces, the hose goes from the water pump to the oil cooler. I took off the hose and didn't find anything in the cooler. No clue where they could have gone. I'm going to take off the hose that goes from the engine to the oil cooler tomorrow once the engine cools and see if they are still in it.
Running out of things to inspect and change. If it's not the existing water(three years old, or the thermostat, about the only thing left is the fresh water pump attached to the front of the engine. I already checked the fan belts to make sure they are good and tight so it spins the pump. But, hey, we are living the dream right?!?!
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Old 06-01-2017, 14:15   #5
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Re: Ford Lehman overheating

When you have an impeller go bad, you need to totally search out the salt water components. Usually water flow wedges the pieces into heat exchanger tubes.
Make sure you have no flow restrictions where water comes into the hull and goes out.
I have found mussels growing in intakes and strainers, blocking flow. Sea Grass and other marine life can block the intake.
Rust buildup can happen on the coolant side of the cylinders (acting like insulation) when the rust inhibitor in the coolant gets too old. If thermostat and other quick fixes don't work, do a proper flush.
With a heat gun, check to see if all cylinders are working equally by measuring the temperature at the exhaust port of each cylinder. Harbor Freight, Ebay and Amazon have inexpensive guns.
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Old 06-01-2017, 15:11   #6
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Re: Ford Lehman overheating

Work your way logically and linearly through the systems. Is the prop fouled? Otherwise start with the raw water system. Make sure the through hull is clear, clean the strainer, replace the raw water impeller, clear the heat exchanger, check the mixing elbow and all hoses and clamps along the way. If you are still overheating, move on to the fresh water circuit. Check coolant level, check thermostat, finally check fresh water pump. Don't assume anything, check everything systematically and you will isolate the problem.
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Old 06-01-2017, 15:23   #7
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Re: Ford Lehman overheating

I had some similar problems a while back and in was a combination of a worn impeller and a tiny bit of air getting into the input side of the system. The air leak was intermittent so hard to spot but I noticed at the times the temperature climbed I was seeing significantly reduced outflow of cooling water from the exhaust.

Is it possible to observe the raw water flow rate with your setup?

Also, I second the advice to find those missing impeller bits. I would not be relaxed until they were all accounted for.


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Old 06-01-2017, 15:25   #8
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Re: Ford Lehman overheating

Incidentally, your description of coolant flowing well past the coolant filler tends to suggest that both the thermostat and the coolant pump are working as they should.


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Old 09-01-2017, 19:14   #9
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Re: Ford Lehman overheating

Here's an update on our plans. We'd thought to drain the coolant and change out the thermostat while we are doing it. If the problem still contines, we'd planned on changing the fresh water pump(original to 1982) and that would mean that everything we did today we would have to do again, so instead, we ordered in a replacement fresh water pump and will wait for it to arrive before draining the system. No point in doing it a second time and with the pump being so old, we don't think it's a bad idea to change it. Yes, I can see water flowing past the hole in the top of the water tank but if the pump isn't pumping enough water, the engine would over heat.
Tomorrow, we plan on taking off the mixing elbow and see if it's clogged. I ordered in a spare for it also as I've already had one blow and I used my spare to replace it. Can't have too many spares on board. Yes, we do float lower in the water than other boats but hey, if I need a part, I've probably already have it on board(now all I have to do is find it)
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Old 10-01-2017, 03:51   #10
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Re: Ford Lehman overheating

Good morning. I'm figuring that you are in St.Thomas although you never mentioned which island. If so, go see Bob at "Above and Below" in the Lagoon . He helped me with my SP135 Lehman in October. I had a cooling issue pretty much as you described but there is one detail lacking. Does the color of your coolant change? Does it get a little lighter in color? If so, I'd suggest that you remove the heat exchanger and do a pressure check on it as well as check the oil cooler for good flow. It's an easy thing to do. Also, look up American Diesel Corp. in Virginia. They are the go to guys for Lehman and have all the CORRECT parts you will need on hand as well as offering up good free advice on how to solve your issue. These guys know Lehman's. Also, if you need a place to anchor in the lagoon while this work is going on, I can help there too. My spot is open as I'm in Anguilla now, so you just have to let me know. You can have your stuff shipped via USPS to Red Hook Mail service @ 6501 Red Hook Plaza. It's everybody's address there. Go see the ladies first..
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Old 11-01-2017, 04:25   #11
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Re: Ford Lehman overheating

Thanks for the help. No change with the coolant though it's four years old. I alrady have new on board to replace once the new fresh water pump shows up. Figure to take off the alternator to get at the drain, drain it then take off the tank and change the thermostat and then take off and replace the water pump since it's original equipment from 1982(I think). Hitting each area starting at the through hull. All seems fine there though I'm going to take off the oil cooler though the last time we used the engine, I infrareded the filter and it showed 145 if my memory is good. Replaced the impeller and the line from the through hull. I opened the heat exchanger and it was clean enought that I could shine a flashlight through it's tubes. Lots of water coming out the exhaust but I'm going to take off the mixing elbow just to check that it's clear.

What caused the overheating on your FL? I always order from Brian or Dave at American Diesel. Tried Bomac once with some problems. Brians been great with suggestions of what to do. And yes, we are in Charlotte Amalie out at anchor watching all the cruise ships come in and working on our boat. Hey, we're living the dream right?
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Old 19-01-2017, 14:38   #12
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Re: Ford Lehman overheating

Everyone, please put on your thinking caps. I need some help. Running out of ideas as to why I'm constantly overheating.
So far, I've changed the thru hull, the impeller, checked the heat exchanger(clean), changed the hose from the water pump to the oil cooler(had a small kink). Today, we drained the coolant, changed the thermostat as well as the "fresh water pump" and refilled with a 50/50 blend of Prestone coolant.
I checked the old thermostat--opened at about 192 degrees but it opened. "Fresh" water pump spun like crazy with no wobble in the shaft. We ran the engine for about 7 minutes at anchor and all seemed fine. Pulled up the anchor and took the boat for a test run. Normally we run at 1500 to 1700. Today, we kept it down to just about 1300. Gauge in the cockpit showed us getting up to close to 200 after about 15 minutes. I used my infrared gun and shot the tank--showed just 178 degrees, well within normal. In the past when we were over heating and the alarm went off, it read about 205(at 1500 rpms). Didn't push it that hard today and still we were going up in heat.
OK, anyone have any suggestions??? I'm going crazy trying to figure out what the heck is going on. Already have a bald spot and I don't want it getting any larger when I start tearing my hair out!!
Put your thinking caps on!!! PLEASE!!!!
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Old 19-01-2017, 14:58   #13
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Re: Ford Lehman overheating

You did not mention if you found the broken bits of the Impeller. in my opinion finding the rose is critical. They did not dissolve. there is the possibility that your temperature gauge is reading incorrectly. Perhaps use the infrared gun right on the area for the temperature sender
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Old 19-01-2017, 15:13   #14
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Re: Ford Lehman overheating

Have you made a reasonably accurate measurement of the rate of flow of raw water through the system? In ours I was able to put a bucket under the exhaust outlet and measure how much water came through over about 15 seconds. In doing so I discovered the total rate of flow was too low which helped isolate the fault.

Edit: I note that in post 11 you say there is plenty of water coming out the exhaust but I honestly thought the same in our system before I made a proper measurement. It turns out my impression of "plenty" was less than one quarter of what SHOULD have been coming through.

Second edit: I was getting around 10 litres per minute, which looked ok at the time but now there is about 45 litres a minute it looks a LOT more ok.
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Old 19-01-2017, 15:32   #15
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Re: Ford Lehman overheating

OK, you've now replaced or checked everything in the raw water system from the through hull to the mixing elbow as well as the fresh water pump and thermostat. What's left is the mixing elbow and exhaust system. Remove the mixing elbow and check for deposition, clogging, corrosion, etc. and replace if required. if the mixing elbow is good check the water lift muffler and exhaust hose to make sure all is clear. You can also measure the pressure just downstream of the mixing elbow. If it is more than a couple of psi you have a problem with the exhaust system.
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