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Old 20-07-2008, 07:55   #1
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Yanmar running hot

OK, First I know I have said on this board I have 35 years experience in the service end of this industry but I am by no means an engine mechanic, although I do know the basics. So down to my problem. we are about 1800 miles into our 2000+ trip along the coast and most of it has been motoring. The engine is a Yanmar 4JH3E and has performed flawlessly for years. The last few weeks the engine seems to be running hotter than usual. I only have idiot lights so I have no idea how much more the temp is rising. The problem shows up by the fresh water overflow tank filling while we are under way during the day. It will fill to the point of overflowing and when it cools I pour the coolant back into the tanks and the next day the same thing happens. It does not over heat, YET, to the point that the warning buzzer and light goes off. In the last week I have flushed the fresh water system and replaced the coolant with a premixed 50/50, replaced the raw water pump impeller and pretty much checked the hoses in the fresh water system, pulled the thermostat and put it in a pan of boiling water and it opened. The flow on the raw water side seems to be strong and what comes out of the exhaust appears to be normal for the engine so I don't think it could be the heat exchanger although I have not yet pulled it apart. Since we are under way the access to resources are limited right now. Any one see something I might have messed. Can't tell much about the fresh water pump except that it is spinning. Thanks in advance.
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Old 20-07-2008, 08:25   #2
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At what temperature did the thermostat open? It should be open well before boiling point...

Also what condition is the fresh water cap and gasket in? I presume the overflow tank requires the cap pressure to be overcome before it can "puke" to the overflow tank. Bad gasket or weakened spring in the fresh water cap could attribute. Most caps have a pressure rating as well.

Without a temp gauge it is diffucult to say it is really getting/running hotter.

BTW - Are you headed south? Ambient temperatures are probably hotter too...


Do the simple - replace the thermostat and replace the cap. Cheap medecine that does no harm...
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Old 20-07-2008, 08:32   #3
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Dan, Don't know the temp that the thermostat opened. One cap I have is new and it leaks when the pressure builds up in the tank, and I mean leaks on the top of the tank. So I put the old one back on and it was fine for over a month then the problem began. we are in north Floriduh south of St. Augustine right now. This will be the third cap I have put on the engine that leaks after the engine has run a bit. The engine should increase the water in the holding tank when run but it should also draw the water back into the FW tank when cool and it is not doing this.
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Old 20-07-2008, 08:49   #4
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The replacement caps are designed for a closed vent system, right?

Basically the cap should blow open at the specified pressure - usually 12-15 pounds and then as the water temperature drops in the fresh water system the vaccum created is relieved by the cap as well, exposing the overflow tank to the vaccum draws the coolant back into the fresh water system.

I am sure you have check the condition of the overflow tank, the plumbing to/from the overflow tank (leaks will make it inop) and the the tube in the overflow tank goes to the bottom of the tank.
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Old 20-07-2008, 08:58   #5
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Dan, That is the dilemma. I don't know if the engine is truly overheating or something else is going on. The overflow tank and hose is fine and has worked for years. No leaks and yes it goes to within a 1/2" from the bottom. The water is not being drawn back into the coolant tank. The newest cap will not even blown the coolant into the tank, instead it leaks around the very top and runs all over the engine. The old cap will at least let it run into the overflow tank.
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Old 20-07-2008, 09:33   #6
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Just a question, when the engine is cold, how much coolant is in the overflow tank.

When you get to a port of any size, see if you can buy a small infrared temperature gun. You can get them at NAPA, Sears, most chain auto stores. They will let you find the hot/cool spots. First place to check would be at the temp sending unit
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Old 20-07-2008, 09:41   #7
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Chief, That is on my list to get anyway but thanks. When the engine is normally cold the tanks holds maybe and 1 1/2 to 2 inches of fluid. It now fills to the top and is even overflowing and the tanks is about 5 inches tall. It is a standard plastic overflow tank and installed according to Yanmar specs as far as height to the FW tank.
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Old 20-07-2008, 10:04   #8
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Wanted to add I plan to run without the thermostat from here to St. Augustine which is about 25 miles and see how it goes. There is a Yanmar service shop there that I hope will have the thermostat. I think we are going to try and find a cap at an auto parts store since Yanmar's caps are $35.00 to $40.00 and they seem to have a problem.
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Old 20-07-2008, 11:53   #9
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Chuck,

The cap on my 4JH3E (vintage 2000) was leaking coolant onto the top of the engine. I went to the Yanmar dealer to replace the cap, and learned that the whole "cap assembly" needed to be replaced. The assembly consisted of the filler opening that the cap screws down on, which is part of a base that bolts onto the engine block. The new cap was much smaller than the original. That solved my leak.

If your cap is the larger, original variety, maybe changing out the filler cap assembly will solve your problem, too.
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Old 20-07-2008, 15:36   #10
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Hud, I have suspected that for a while when 3 caps failed but the Yanmar people in Houston said, no it is the cap.
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Old 20-07-2008, 16:19   #11
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If you can get to an auto parts store. See if they loan tools. Get a radiator pressure tester. Pump your cooling system up to the pressure rating on the cap and see if it holds pressure.

If the tank is over flowing it can be one of two things.

Overflow tank has too much water in it.

Or the engine is "making water" i.e. leak in heat exxchanger allowing seawater intrusion into freshwater side.
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Old 20-07-2008, 16:21   #12
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Also...in your original post, did you say the oveheat alarm was going off?

or did you say you "think" it was overheating because the expansion tank was overflowing.
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Old 20-07-2008, 17:17   #13
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Cheif, Not making water because the FW tank is less the water in the overflow tank and if I pour it back in the FW system it will just fill it up. Overflow tank can start out empty and will fill up. Then I can dump it back into the FW tank on the engine and start all over again. No the overheat alarm does not go off, at least not yet. Not able to get to a parts store here. I don't think it is overheating as much as running hotter than it should be or a problem somewhere with the overflow system. Either way I need to figure it out and correct it since we still have over 200 miles to go.
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Old 20-07-2008, 17:34   #14
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If the water is expanding into the overflow tank but not returning to the engine when it is cold then there is a problem with the cap. If the water that does go into the overflow is returned to the engine after running ( and allowed to cool down) then the engine probably isn't over heating.

I have seen yanmars run w/o overflow....much like cars....the fluid may look low when cold i.e. below the top of the filler neck by an inch or so....when it heats up it comes right to the top.
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Old 20-07-2008, 17:40   #15
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The water is not returning to the engine at any time hot or cold and that is part of the problem. It keeps filling the overflow tank until the overflow tank overflows. This started about a week ago and has not been an issue in running the last 1800 miles.
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