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Old 23-01-2013, 17:12   #16
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Re: Yanmar Engine Overheating?

Couple more thoughts. We have essentially the same engine (earlier model, and turbocharged).

***** From what you describe, I would first replace the thermostat. It's a cheap solution - and very possibly your problem. ****

In addition:

1) Replace the impeller. If you don't know how old it is, it's time to change it. I change ours every year. It's not difficult, and you NEED to know how to do this. Learning in a seaway is not fun. Much better to learn this one at the dock. You will also need a gasket.

2) Check your coolant. It should be no more than 50% antifreeze. 30% is just fine. The testers are about $5. 100% coolant has about 1/2 of the heat capacity of 30% coolant/70% water. Water is a MUCH better conductor of heat. This is a common problem with boat engines.

3) Remove and clean the heat exchanger. Usually not a hard job on a non-turbo engine. We just did ours, and it wasn't bad nor difficult. You will need new gaskets from your Yanmar dealer. Remove the 2 end caps. If needed, tap the exchanger out with a block of wood. If it's at all logged, or it has deposits on it, take it to a radiator shop and for a very nominal fee, they will make it look like new ($100). Note that if you do this job, you will lose some of your coolant. So, don't fix number 2 until you do #3, if #2 is a problem.

None of these tasks is at all complex. Usually the single biggest issue is access.

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Old 24-01-2013, 09:05   #17
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I've no experience with your type engine, being diesel I assume it's freshwater cooled, have you checked the coolant level & the pressure cap?

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Old 24-01-2013, 21:16   #18
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Re: Yanmar Engine Overheating?

Niel, 9 to 1 you simply have a bad connection. Check where the wire connects to the sender for looseness, corrosion,or a chafed wire. Even if it looks good, remove the wire and spray with electrical cleaner(carefully, it is flammable). If you can trace the whole length of the wire for damage, it would be a good idea. While the wire is off, turn on the ignition and see if the gauge pins? It probably will. That will indicate if the circuit is designed for the resistance in the sender to go up as the temp goes up. A loose/disconnected wire is the ultimate high resistance and will give you a pinned meter. If the gauge stays at zero, I will order a pound of crow to eat, and go back and review my old electronics books. Good Luck with it._____Grant.
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Old 24-01-2013, 21:39   #19
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Re: Yanmar Engine Overheating?

I agree on sender, gauge, or related wiring - "bounce" is usually something electrical.

But - your engine gets a lot of horsepower from a small block. You need to maintain the cooling system more carefully than a less stressed engine. Overheating can really damage an engine.

Replace the coolant and impeller now. I believe Yanmar specifies every two years for coolant. I also wouldn't be surprised if a few vanes have broken off your impeller and are somewhere in the heat exchanger.

And next time the engine is having maintenance, have the heat exchanger pulled and cleaned and the exhaust injection elbow checked.
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Old 24-01-2013, 21:50   #20
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Re: Yanmar Engine Overheating?

I think several folks have touched on it. The raw water impeller is essential and should be changed religiously. Just a few seconds of running without water will destroy it. Cheap, and you should know how to change it with ease. You should have more than one as a spare on the boat
Thermostat is almost as easy to change but is pretty reliable, and I don't understand why it would change following a haul out.
Lastly is the exhaust elbow where the raw water once again cools the exhaust. Failure here usually includes steam but if the boat is new to you, you don't really know how much water is actually supposed to be exiting the exhaust. I sold a boat and this piece came up in the survey. The boat was blowing just as much water as when I bought her but I was forced to replace the part. The change was dramatic and I would estimate the blockage at about 70%.
The problem could be the gauge but I would check all of these pieces first because this could kill your engine. It's like when the oil pressure alarm goes off and you blame the gauge and don't check the oil level

I vote impeller in the ballroom with the candlestick. When you went into the water again the lapse in raw water caused you to loose lobes on the impeller.

Good luck
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Old 24-01-2013, 22:49   #21
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Re: Yanmar Engine Overheating?

Getting any boiling water in the expansion tank? Most likely sending unit or wiring as stated above because other temperature sensor does not indicate overheating. You cound also check belt tension.
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Old 25-01-2013, 05:55   #22
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Re: Yanmar Engine Overheating?

Another vote for changing the impellor.
You need to know how to do this anyway. Don't wait to discover how hard this exercise is until the excrement hits the oscillating cooling device. Same thing happened to me after a haulout. Engine (Yanmar 3GM30) stopped pumping water when I was put back in. Luckily I have another engine so was able to get off the lift but was a hassle. Anyway the impeller had self destructed during the 4 week dry out.
Welcome to the world of boat maintenance.
PS wait til you have to rebuild your water pump in the middle of nowhere. Changing the impeller will seem like a piece of cake.
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Old 30-01-2013, 19:01   #23
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If sufficient water is batching from the exhaust, that tells you that your impeller is in good shape and the circulation is good. Your problem is almost certainly in the 'fresh water' side. Possible causes are: dirty heat exchanger, failed or failing fresh water pump, air lock in the fresh water side, thermostat. I'd go after the airlock first since its likely and cheap.

Disconnect and fill the water heater with coolant. Use head pressure to evacuate any air. Reconnect. With the pressure cap removed, rapidly squeeze the hoses on either side of the FRESH water pump like when you prime an outboard motor. This will force air bubbles past the coolant and out the filler opening. If you see a dramatic drop in the coolant level and bubbles, thats a good sign. You may even want to remove the upper hose and pour coolant into it. Reconnect and start. If the problem goes away, great. If not, remove and test the Thermostat. If the thermostat isn't the problem, disassemble and clean the heat exchanger core. If none of that works, the fresh water pump begins to look like the prime suspect.

If you really know your engine and how heat propagates through the fresh side as it warms up, an infrared pyrometer is a great diagnostic tool. Otherwise, it will only tell you whether or not your engine is actually overheating. They're only about $100 so go ahead and get one. I use mine to spot cold cylinders and to verify thermostat function.

Good Luck
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Old 30-01-2013, 19:38   #24
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Re: Yanmar Engine Overheating?

Originally Posted by neilacarter View Post
- I may look into the impeller, but since that is kind of a pain (from what I've read) to get at, I'll only do that if replacing the temp gauge doesn't resolve the issue.

You best get use to it!
This should be changed every year whether you use it or not. You could have a cracked vain right now, which could possibly be not allowing the proper flow. And you don't want those pieces getting into the heat exchanger tubes.
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Old 30-01-2013, 21:12   #25
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Re: Yanmar Engine Overheating?

I doubt it is the gauge. Likely the sender unit threaded in the block. I had a 4JH in my Ingrid 38. Great engine. I had my Tach do the same thing. Finally traced it down to the main harness plug to plug connection. As far as the fuel leak. Yanmar has a common problem with their copper crush washers on the diesel banjo connectors. I have a friend with a 4JHT on his Peterson 44 and has the same issue.
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Old 05-02-2013, 18:23   #26
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Re: Yanmar Engine Overheating?

Hey everyone,
Let me say a huge thank you to the community for helping me out. I've gone ahead and swapped out the water pump impeller and voila, no more overheating... at least so far. I've only tested the engine in the marina and have yet to really put her under load, but she's back to only heating up to proper temperatures. I'm heaving a tentative sigh of relief.

On another note... I have determined that there is a very special level of hell (8th or 9th) for the person who designed the engine access on my Catalina 440. It took me 7.5 hours of lying belly down in my bilge with my arms wrapped around my engine while working blindly and completely by touch to change this out. There was much swearing... especially since the first o-ring I installed got fubared when I was (blindly) putting the pump housing back together.

Here's to hoping this solves the overheating issue and she'll be back to normal.

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Old 05-02-2013, 18:30   #27
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Re: Yanmar Engine Overheating?

A good thing to do is plumb in a mechanical temp gauge into the system. That way you will know for certain that it is an overheating problem or an electrical issue .
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Old 05-02-2013, 19:02   #28
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Re: Yanmar Engine Overheating?

Have similar access problem to my water pump on my Yanmar change impeller I remove entire water pump and then
change out impeller while sitting at settee like a human.
Highly recommend, as boat is new to you, follow additional advise in previous post (#16 bstreep) inspect and have heat exchanger cleaned.
Also besides replacing filters and belts, you really want to learn
to be comfortable bleeding your motor.
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Old 05-02-2013, 20:11   #29
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Re: Yanmar Engine Overheating?


Before you get too enthused...

How did the old impeller look? That will tell you if you've at least taken a good hit to your problem.

You need to add a yearly replacement to your schedule - you don't want to be doing this repair at sea.

Also, you might invest in one of these - they are cheap - an exhaust temperature sensor. It will go off way before the water temp sensor:
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Old 06-02-2013, 04:07   #30
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Re: Yanmar Engine Overheating?

May want to install a SpeedSeal for next time. May make the job easyer and faster.
I have one installed on both engines and I check the impellers once a year.
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