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Old 05-20-2015, 05:43 PM   #1
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Genset overheats after coolant change

8KW Kohler on 2002 mainship 400T

Was running fine until I did a coolant change, now when I put it under load it overheats. I'm getting a reading of about 185 degrees on my laser gun before it shuts itself down.

This was the first time I have changed the coolant on this generator as we got the boat two years ago. To my knowledge the coolant has never been changed prior to this time. There are 430 hours on the genset, we put about 250 of those on it with no issues at all.

My first thought is that I had an air bubble in the system, so I let it run for a while with the cap off, but that did not help. There are two drains for the coolant, one high on the block and one at the bottom of the Heat Exchanger. I let about 6 ounces of coolant run out of the higher drain hoping to clear a possible bubble, but that didn't help either.

Any ideas? Is there another way to bleed it? Maybe the thermostat got some crud in it and is now stuck?

Anyone know how to access the T-stat on this genset?

Thanks in advance.
Doug
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Old 05-20-2015, 06:14 PM   #2
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Could be a coincidence. I would check raw water impeller and tubes on heat exchanger. On a 13 year old genset, I would be considering servicing or replacing raw water pump, heat exchanger, thermostat, pressure cap, fresh water pump, and anodes unless there is a maintenance record of those things having been serviced.

It could be the thermostat, but they usually fail open not closed.

Ted
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Old 05-20-2015, 06:16 PM   #3
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Start with the basics. Check flow at strainer. Is basket clear?

First thing that sings to me is the upper drain. I would let it flow and then let it flow some more. Antifreeze is cheap compared to an cracked block.
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Old 05-20-2015, 06:20 PM   #4
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Raw water impeller is fine, and the strainer basket is clear. There is a good flow of raw water. Also, there are digital fault codes on this genset that pop up when it shuts down. The code for no raw water is LOC (loss of coolant) which I have seen before when the strainer clogs. The engine overheat code is HE which is the code I am currently getting.

With the temp gun on the manifold it gradually heats up to about 155 degrees then quickly rises to around 180 where it shuts down.
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Old 05-20-2015, 06:27 PM   #5
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Was there a lot of crud in the old antifreeze? I had a chunk of something not allowing my thermostat to open fully. If its not a hassle, maybe change it out.
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Old 05-20-2015, 06:28 PM   #6
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185 deg. is not even close to overheating. 180-190 is normal operating temperature for many/most diesels.

Check your thermostat. Try tapping around the area where it's mounted if you can while the engine is running. You may pop it loose.
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Old 05-20-2015, 06:47 PM   #7
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OK, I bled about 20 ounces of coolant off of the upper drain and refilled. Still having the same issue.

The old coolant was not bad, much better than I expected it to be, not much crud in it. The PO owned this boat from new and barely used it. He had it maintained by a yard, some things they did and some they didn't. I don't know that they didn't change the coolant, it just doesn't seem like something they would do, as they neglected other things that are easier to change, like pencil zincs.

I'm not sure where the t-stat is located. there is a sort of bell housing just above the fresh water pump that has a sensor tapped into it, do you think that is where it is? My operating manual does not show the location of the T-stat.
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Old 05-20-2015, 07:01 PM   #8
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Could be the sensor?
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Old 05-20-2015, 07:02 PM   #9
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Go to your heat exchanger. There should be 2 hoses that go to the engine, 1 to the raw water pump and one to the exhaust elbow. Generally, of the 2 that go to the engine, the highest one has the thermostat under the hose connection at the block, or very near to it. The other lower hose usually connects near or into the fresh water pump.

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Old 05-20-2015, 07:35 PM   #10
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OK, a little more info.

The 175 degree reading I've been getting just prior to shutdown is coming off of the manifold at the top of the engine, the one that is connected via a hose to the air filter.

This time I measured the temp at the sensor on the fresh water pump, where I got 210 degrees prior to shut down.

There are 3 hoses on the HE, one from the raw water pump and two larger hoses that connect at the back of the motor. I tapped around both of the larger ones where they go into the block/coolant tanks. I also checked temps on theses two elbows, just prior to shutdown one read 94 degrees and the other about 110.

Thanks for all your help guys, I'm stumped.
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Old 05-20-2015, 07:37 PM   #11
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Did as much coolant go in as came out? Try to compress the downstream hose "burp" them and see if the level of coolant falls at the fill site. If it does , you should keep refilling until it stops. Worked for me on one occasion.

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Old 05-20-2015, 07:44 PM   #12
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Hard to say how much coolant came out. Access on this genset is VERY poor. I had to cut a milk jug to create a sort of funnel under the HE drain and put an old towel under it in the bildge. The run off soaked the towel. There was no way to catch it all.
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Old 05-20-2015, 07:53 PM   #13
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Might be worth rigging something to completely drain the system and compare the collected volume with the supposed coolant volume on the engine specifications. At least it would rule that in or out clearly. I would make sure the volume of coolant being too little was not the problem before doing anything else. Could be that simple.

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Old 05-20-2015, 08:05 PM   #14
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This is compounded by the access to the pressure cap/fill. There is about 1.5 inches of space between it and the underside of the deck. The only way to check the coolant level is stick my finger in it, I can't see it at all. I have to fill it through a 24" hose attached to the spout on a funnel.

I "burped" the hoses and managed to get about 10 more ounces of coolant in. I'll do a test now and report back.
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Old 05-20-2015, 08:10 PM   #15
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Still overheating.

Also, the expansion tank is not filling.
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Old 05-20-2015, 08:43 PM   #16
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The fact that you got another 10oz in suggests to me that you may be indeed dealing with a lack of coolant volume. I could not believe how many times I had to "burp" the hose attached to the heat exchanger before I got the full volume replaced and I was in a fairly comfortable position and not so cramped as yours. If those fresh water hoses are compressible I would really work them still and keep adding. Even let it sit for a few hours and return. Since the only thing you did was change the coolant one has to believe that is the issue. Chances are it is a cause and effect situation and I would still do what it takes to make sure the volume of fluid is adequate.

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Old 05-20-2015, 08:50 PM   #17
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got to have air in it somehow. get a long vinyl hose and plug it in to the fitting on side of expansion tank filler neck. Get bottle up high a few feet and tape it to something to hold it. make sure exp tank is topped, put cap on, then put some in the bottle. Run it til it trips, then let it cool. Repeat. Eventually it should burp out the air.

Can also crack loose hoses near water pump and see what spews. 'Do this while there is head pressure from higher bottle.
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Old 05-20-2015, 09:23 PM   #18
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Quote:
Originally Posted by Ski in NC View Post
got to have air in it somehow. get a long vinyl hose and plug it in to the fitting on side of expansion tank filler neck. Get bottle up high a few feet and tape it to something to hold it. make sure exp tank is topped, put cap on, then put some in the bottle. Run it til it trips, then let it cool. Repeat. Eventually it should burp out the air.

Can also crack loose hoses near water pump and see what spews. 'Do this while there is head pressure from higher bottle.
I'm not sure if I follow you, Ski. My expansion tank (the little plastic tank that the coolant overflows into) has a single hose running from it to the neck of the coolant tank just below the pressure cap.

Are you saying to lengthen that hose, raise the expansion tank above the level of the genset, fill up the expansion tank with coolant, close both the pressure cap and the expansion tank cap and run it till it trips?

Thanks,
Doug
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Old 05-20-2015, 09:31 PM   #19
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Bottle: plastic coolant reservoir

Expansion tank: metal tank, part of engine with the pressure cap and the neck out the side
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Old 05-20-2015, 10:12 PM   #20
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Got it.

I had to burp the fresh water hoses like crazy....probably squeezed each one 300 plus times and kept pouring in more coolant as suggested. I got about 12 to 14 more ounces in.

Under load, in the same spot I was getting over 190 degrees before shut down I'm not holding steady at 154 to 157.

Like Blanche DuBois, I rely upon the kindness of strangers. I can't thank you guys enough.

Doug
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