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Old 08-05-2013, 03:34   #1
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Kohler Generator Problem

I have a 6.5kW Kohler generator, powered by a three-cylinder 1500rpm Yanmar engine of about 1000cc displacement.

I depend on this generator very much as I don't have power on my mooring, and I spend quite a bit of time aboard there and at anchor.

Last year I got a big clot of seaweed in the seawater strainer, which caused the genset to overheat and shut down. I had a cascade of problems from this, starting with a burned up impeller, bits of impeller in the heat exchanger, etc., etc. In the course of sorting this out I understood that the overheat shutdown device is very effective, reliably shutting the engine down when the temperature at the upper coolant flange reaches about 95 C, a safe temperature.

Nevertheless, something was damaged which I have not been able to identify. I am losing coolant, enough to require adding a cup of water every 4 or 5 hours of running. Moreover, the coolant is rusty and nasty looking, and remains so despite dozens of flushes.

There is no coolant in oil, no oil in the coolant, and the generator runs and functions perfectly. Temperature at the upper coolant flange is steady at 80C under all circumstances. I have actually been using the generator for almost a year like this without any problems at all other than the bother of frequently topping up the fresh water cooling system. But obviously this can't be good and needs to be fixed.

When I was in the US at Christmas, I brought back a new heat exchanger. It seemed to me that the most likely fault was a hole in the 12 year old heat exchanger, allowing coolant to drain off into the sea water side. A little sea water infiltrating the fresh water side would explain the rust, I thought.

Well, to cut a long story short -- no. I replaced the heat exchanger and everything is exactly as it was before.

My next likely suspect is the exhaust manifold. This is just about the only other place I can imagine where coolant could be escaping. The exhaust manifold is combined in this engine with the header tank, so the exhaust pipes are surrounded by coolant. The exhaust elbow is attached directly to the manifold with no intervening pipe.

The exhaust manifold is not a very expensive part and I am tempted to just buy one and bang it on. But this approach failed with the heat exchanger, so I'm trying to be a little more analytic this time.

Does anyone have any hints?

I will in any case do another thorough search for leaks, but I really doubt that the problem is a simple leak, as this would not explain the rust in the coolant. I think it is probably a hairline crack in the manifold which is letting coolant leak into the exhaust, and is rusting. It's the only thing I can think of, but maybe someone else has some ideas, for which I will be, as usual, very grateful.
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Old 08-05-2013, 06:19   #2
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Re: Kohler Generator Problem

Pressure test the cooling system, then bypass (dis-connect) the exhaust and pressure test again. Also if you have been topping with plain water for a year, that in itself could be the cause of rusty coolant.
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Old 08-05-2013, 06:50   #3
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Re: Kohler Generator Problem

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Originally Posted by Zil View Post
Pressure test the cooling system, then bypass (dis-connect) the exhaust and pressure test again. Also if you have been topping with plain water for a year, that in itself could be the cause of rusty coolant.
+1 on the pressure test!
I had an elusive coolant leak on a 4cyl Yanmar once... It turned out to be a casting flaw in the exhaust manifold which allowed a pin hole leak directly inside an exhaust port... Was the pure devil to diagnose, as it only leaked under pressure (while the engine was too hot to tear down). Finally I parted the HE/manifold from the head and pumped it up to 14psi before the leak was apparent. Ground and welded the flaw and several thousand hours later, all is good!
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Old 08-05-2013, 22:49   #4
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Re: Kohler Generator Problem

We have one of these - slightly larger. We also just recently pulled the heat exchanger. The gaskets can be tricky - make SURE you don't have a leak there, as that would do exactly what you are having.

Also, ours, when we did the flush, took MANY cycles to get clear water out of the system. If it hadn't been flushed in a long time, or if there wasn't enough coolant in the water mixture, you WILL have this above mentioned problem. For about $5 you can get a tester, from an autoparts store - make sure you have just water and coolant (no seawater).
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Old 08-05-2013, 23:07   #5
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The fresh water coolant could still be leaking into the sea water side of the HE. Since you replaced the HE it most likely is somewhere else. If you are actually filling the plastic overflow tank and not the radiator cap itself then you could have a leak in the tubing or the filler neck where the tubing attaches to the radiator. Small leaks are a pain to find because the coolant often evaporates before you can spot the drip. Talk to a local radiator shop to see if there is some kind of tell tale die that is safe to use. It might leave a trail you can find.
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Old 09-05-2013, 05:24   #6
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Re: Kohler Generator Problem

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The fresh water coolant could still be leaking into the sea water side of the HE. Since you replaced the HE it most likely is somewhere else. If you are actually filling the plastic overflow tank and not the radiator cap itself then you could have a leak in the tubing or the filler neck where the tubing attaches to the radiator. Small leaks are a pain to find because the coolant often evaporates before you can spot the drip. Talk to a local radiator shop to see if there is some kind of tell tale die that is safe to use. It might leave a trail you can find.
Thanks -- I am filling the header tank cap (to the exhaust manifold tank, not the overflow tank).

I do have a replacement radiator cap which I will fit and try, just in case.
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Old 09-05-2013, 05:30   #7
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Re: Kohler Generator Problem

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Originally Posted by bstreep View Post
We have one of these - slightly larger. We also just recently pulled the heat exchanger. The gaskets can be tricky - make SURE you don't have a leak there, as that would do exactly what you are having.

Also, ours, when we did the flush, took MANY cycles to get clear water out of the system. If it hadn't been flushed in a long time, or if there wasn't enough coolant in the water mixture, you WILL have this above mentioned problem. For about $5 you can get a tester, from an autoparts store - make sure you have just water and coolant (no seawater).
Probably the same generator! Mine produces 8kW in 120 volt/ 60 cycle form, at 1800rpm. At 1500 rpm (for 50 cycles and 230 volts), it produces 6.5kW. It's a 8/6.5EFOZ, I think.

A tester to see if there is sea water in the coolant? Never seen one of those.

The fresh water is so nasty, that it could hardly be residue from back then.

I'm excluding the heat exchanger (for now, at least), since it is brand new and I didn't mess with the gaskets, and since the symptoms were exactly the same with the old heat exchanger.

I'm still considering the exhaust manifold as the prime suspect.

By the way, the fresh water level seems to go down when the generator is not running, too -- provided the cap is left open.

All this seems to point to the exhaust manifold.

I am excluding a cracked head or block so far because of lack of any oil contamination, although I realize that it is conceivable that a crack in the head just at an exhaust port just might leak coolant into the exhaust without any oil contamination. This seems pretty unlikely to me.

I considered a pressure test, but the equipment is expensive, and what will it accomplish? I know I have a leak -- the question is where!
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Old 09-05-2013, 11:58   #8
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Re: Kohler Generator Problem

The water could also be leaking into a cylinder and be getting burned off, not just into the oil or an exhaust port. After an overheat, a leaking head gasket wouldn't be out of the question. The advantage of a pressure test is that it will accelerate the leak and hopefully lead you more quickly to it. For example, if it's a manifold leak, you might be able to see water accumulating through a disconnected exhaust hose or fitting. Also, if you drain the coolant and do the pressure test, the leaking air may be audible when leaking water seldom is.
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Old 09-05-2013, 12:28   #9
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Re: Kohler Generator Problem

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The water could also be leaking into a cylinder and be getting burned off, not just into the oil or an exhaust port. After an overheat, a leaking head gasket wouldn't be out of the question. The advantage of a pressure test is that it will accelerate the leak and hopefully lead you more quickly to it. For example, if it's a manifold leak, you might be able to see water accumulating through a disconnected exhaust hose or fitting. Also, if you drain the coolant and do the pressure test, the leaking air may be audible when leaking water seldom is.
I think if it were leaking into a cylinder, I think I would have a knackered engine by now, considering that quite a bit will drain off if the engine is left standing with the cap off.

I have to consider the cost of the pressure testing equipment, which I would likely use only once, and might well not pinpoint the problem, compared to the cost of just having a professional tear it down. The cost is similar. I'm starting to lean to the latter solution.
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Old 09-05-2013, 18:29   #10
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Re: Kohler Generator Problem

Hold on - you said you didn't "mess with the gaskets"??? You DID replace the gaskets on the heat exchanger, right? Those are what keeps the sea water away from the cooling water. They are pretty cheap - and not replacing them is a no-no.

As for testing - just a cheap coolant tester from the autoparts store. If you are getting salt water into your coolant, the ratio of coolant will drop over time. BTW, NEVER use more than 50-50 coolant. Enough to prevent freezing and corrosion. Glycol has about 1/2 of the heat exchanging ability as water.
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Old 12-05-2013, 16:03   #11
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Re: Kohler Generator Problem

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Hold on - you said you didn't "mess with the gaskets"??? You DID replace the gaskets on the heat exchanger, right? Those are what keeps the sea water away from the cooling water. They are pretty cheap - and not replacing them is a no-no.

As for testing - just a cheap coolant tester from the autoparts store. If you are getting salt water into your coolant, the ratio of coolant will drop over time. BTW, NEVER use more than 50-50 coolant. Enough to prevent freezing and corrosion. Glycol has about 1/2 of the heat exchanging ability as water.
The heat exchanger is brand new! I just replaced it, at considerable expense.

Update: I am back on my mooring and using the generator intensively, two or three hours a day. It runs like a top and I'm now not actually sure that it is losing coolant. It seems to have stabilized. 10 hours of operation since I added water last, and even then it was just a cup or so. Possibly it was burping air out little by little?

I'm off the boat for a few weeks. If the header tank is still full when I get back, I might try to flush it and put some coolant into it.

It sure does run nicely when the sound enclosure is on it. A friend was standing on my pontoon today while I was charging batts, and simply could not believe that a generator was running.
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Old 13-05-2013, 01:12   #12
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Re: Kohler Generator Problem

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The heat exchanger is brand new! I just replaced it, at considerable expense.

Update: I am back on my mooring and using the generator intensively, two or three hours a day. It runs like a top and I'm now not actually sure that it is losing coolant. It seems to have stabilized. 10 hours of operation since I added water last, and even then it was just a cup or so. Possibly it was burping air out little by little?

I'm off the boat for a few weeks. If the header tank is still full when I get back, I might try to flush it and put some coolant into it.

It sure does run nicely when the sound enclosure is on it. A friend was standing on my pontoon today while I was charging batts, and simply could not believe that a generator was running.
Dockhead,

You're ...such a PollyAnna!.

Except when, you're a WorryWart!

hehe
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Old 13-05-2013, 01:47   #13
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Re: Kohler Generator Problem

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Dockhead,

You're ...such a PollyAnna!.

Except when, you're a WorryWart!

hehe


Is it possible to be both at the same time? Oh yeah, it's called being a cruiser

If you don't worry all the time, you miss 50 life and death issue every month. If you're not a total Polly Anna, always looking at the bright side no matter how hopeless, you'd quite within the first three weeks!
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Old 13-05-2013, 01:54   #14
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Re: Kohler Generator Problem

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Is it possible to be both at the same time? Oh yeah, it's called being a cruiser

If you don't worry all the time, you miss 50 life and death issue every month. If you're not a total Polly Anna, always looking at the bright side no matter how hopeless, you'd quite within the first three weeks!
hehe,

ya know, I'm just poking at ya.

Lloyd
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Old 13-05-2013, 11:25   #15
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Dockhead,

From your description it appears your generator does not now have an expansion tank. It must be very old if it did not come with one from the original manufacturer. You may have an issue where the water you are adding is simply replacing what has been forced out the expansion type pressure cap. I would recommend that you verify whether or not the generator requires an expansion tank and proper expansion type pressure cap. If it was designed to have an expansion tank then seriously consider restoring that feature.
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