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Old 15-11-2015, 17:36   #1
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Fresh Water Pump Overheating on Yanmar 3HM35

Engine was making strange noise, Brian realized the alternator belt was slipping.

Replaced belt.

A couple hours later, running in calm waters @ 2500 RPMs, the engine began to overheat. Cleaned all filters, plenty of water coming out of exhaust.

Turned off to let engine cool down. After cooled down, he started the engine and it would quickly overheat. Every time after cool down, as soon as he started it, it would peg to high heat.

Next Brian replaced the fresh water pump with new Yanmar pump( after a 5hour dinghy ride to get the part:-) )

But the engine temp gauge still pegs high as soon as you start it.

Upon closer examination, the engine does not get hot, the new fresh water pump does, which is where the sender unit is.

What the hell???

Hope this made sense, we are a little fatigue and hoping there is a glaring obvious error on our part( like installation error)

Thanks for any feedback.
Erika
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Old 15-11-2015, 17:57   #2
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

Air blockage in the FW cooling circuit? Bad thermostat?

An IR temp gun is very handy for these types of problems. It can tell you if the gauge is bad, where the engine is getting hot, etc.

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Old 15-11-2015, 18:00   #3
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

Any chance you know if it was the same problem with the old pump? Same problem 2 different pumps..
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Old 15-11-2015, 18:24   #4
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

Do have bubbles at Heat exchanger header tank?? Did it get Spit and Sizzle Hot ??
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Old 15-11-2015, 19:03   #5
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

Thermostat not opening ?
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Old 15-11-2015, 19:05   #6
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

www.j30.us/files/yanmar-cooling-system-chapter8.pdf
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Old 15-11-2015, 20:27   #7
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

I don't think it has anything to do with the thermostat because it happens too fast. Thermostat normally does not open at idle for at least ten minutes. This gets hot and pegs the thermostat in under a minute. The engine block and heat exchanger are still cool. Just the fresh water pump is hot. It almost seems like it must be friction, but I hear no noise that sounds like metal on metal.
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Old 15-11-2015, 20:29   #8
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

Quote:
Originally Posted by Guy View Post
Any chance you know if it was the same problem with the old pump? Same problem 2 different pumps..
I don't. Old pump started gushing coolant. Seals were blown. It could have been the overheating that ruined the seals. That seems most likely.

Another possibility is the new pump is just defective, but that seems less likely.
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Old 15-11-2015, 21:37   #9
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

The belt slipping means something is freezing up. Take the belt off and make sure that the pump and the alternator turn freely.
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Old 16-11-2015, 03:53   #10
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

Quote:
Originally Posted by RainDog View Post
I don't think it has anything to do with the thermostat because it happens too fast. Thermostat normally does not open at idle for at least ten minutes. This gets hot and pegs the thermostat in under a minute. The engine block and heat exchanger are still cool. Just the fresh water pump is hot. It almost seems like it must be friction, but I hear no noise that sounds like metal on metal.
Seems it could be one or a combination of only six things.

Excessive belt tension.
Airlock.
Incorrect assembly blocking bypass flow. (Flipped gskt, etc.)
Bad thermostat.
Internal cooling passage blockage.
Defective or incorrect pump.

I lean toward 2, 3, or 4, but it's just a crapshoot to try and guess which, so a process of elimination, from easiest to most difficult, seems indicated...
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Old 16-11-2015, 09:51   #11
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

Start with the raw water intake, remove, clean and inspect each piece, reassemble or replace and move on. This has worked when all else failed a couple times.
be patient and careful.
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Old 16-11-2015, 09:57   #12
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

engine cold but pump hot ? what does your temp gauge read.if you have one installed , if temp raises fast, on temp gauge, I would try to bleed air from cooling system, first, if no help, look for kinked or collapsed hose in fresh water system.
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Old 16-11-2015, 10:51   #13
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

You say the engine is cool (not overheating) but the temp gauge reads high. I guess I'd double check the connections to the sending unit and check the sending unit itself. Could something have happened with the sending unit/wiring when you replaced the water pump? If the pump itself is actually getting hot, it could be defective (bad bearings) or maybe installed incorrectly (e.g. missing spacer plate or gasket). Is there anything different now from the old pump installation?
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Old 16-11-2015, 11:22   #14
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

Since you have plenty of water flow out the exhaust, what else can it be but a bad pump, most likely bearings?
If you didn't have good water flow then of course we go to vapor lock, clogged / collapsed hoses etc, but all that is eliminated with good flow.
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Old 16-11-2015, 11:26   #15
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Re: Fresh Water Pump Overheating on Yanmar 3HM35

No, my mistake I was thinking raw water pump.
First see if there is a bypass, sometimes it's just a small orifice and if it's clogged what your describing will happen.
If it's the bypass clogged, removing the thermostat will eliminate the overheat and will be a trouble shooting step.
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