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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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  #11  
Old 04-25-2012
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Re: Yanmar 3GMF Overheating

Quote:
Originally Posted by smurphny View Post
4000 rpm is very high for this engine. I have a 3GMF and run it at less than 3000, usually around 2700 which seems to be its sweet spot at hull speed which for me is around 6.5K. ...
You are right, I meant full at 3000. A few months on the hard and the memory goes a little. Last season I could motor for hours at around 5.5K (she has a hull speed of 7K) but when I pushed her beyond that the alarm would go off after about 10 minutes. The season before I had no trouble motoring all day at hull speed.

So I was at the yard today with these suggestions in hand and made a few discoveries. The first is that the coolant I used was supposed to be diluted and I hadn't - not pleased with myself on that count. The other is that the belt for my raw water pump was cracked and loose. I am still going to flush out the coolant system and check the mixing elbow as per the recommendations here and believe that my engine will be back to her full potential this season. Thank you again for the responses. This forum is indispensable.
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Old 04-26-2012
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Re: Yanmar 3GMF Overheating

#1 I'd check water flow out exhaust pipe, easiest way to see if you're obstructed.
Mixing elbow is another good one. they say they need to be changed every 4-5 years which is probably too frequent but they do rust up inside.
I too have a 3GMF & sweet spot is 2800 for my hull.
Coolant may not be proper but I believe the issues with that would be levels of corrosion protection not hot & cold.
Loose belt would certainly do it.

Last edited by Shortman; 04-26-2012 at 09:59 PM.
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Old 04-26-2012
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Re: Yanmar 3GMF Overheating

Today I checked the mixing elbow - a little rusty but not clogged - cleaned the coolant system with Prestone Super Flush - pretty gungy - replaced the RW pump belt and replaced the coolant with the proper mix and ran the motor for for a good hour with the RW intake in a bucket with a hose. I'll update this post once she's back in the water and I can see if we've solved it.

I also happened to look in my Don Casey Bible (don't ask me why I didn't do this before I tackled the coolant) and according to Him full strength coolant gels up at high temperatures and clogs the hoses causing overheating - thought I should post that.
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Old 05-18-2012
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Re: Yanmar 3GMF Overheating

Did you get the overheating solved? Sounds like you had several items working against you, but mainly the coolant change. What is the correct tempature the Yanmar Diesel should operate at? I was constantly cleaning my mixing elbow to keep the engine cooler. It did not run the past two months and now that it is running again I wonder if it has rusted on the inside again. Last cleaning, I took it off and soaked it in a bucket overnight full of cleaning solvents. Maybe I'll do that again. Currently, it runs about 250 degrees after an hour....too hot to leave your hand on so I kill it when this happens. Mine is a YSM 12 so it is cooled by raw water. Impeller sprays out great on the input side....I know cause the line slips off from time to time. Most likely another clog. I'll follow the advice given here and post an update.
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Old 05-18-2012
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Re: Yanmar 3GMF Overheating

Quote:
Originally Posted by gordofloats View Post
I also happened to look in my Don Casey Bible (don't ask me why I didn't do this before I tackled the coolant) and according to Him full strength coolant gels up at high temperatures and clogs the hoses causing overheating - thought I should post that.
Full strength antifreeze also actually 'loses' its freeze protection (ie the freezing point comes back up from the 'low' peak at about 60% concentration.)

Something to be aware of for your truck up north, maybe not so critical in a boat but still...
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Old 05-18-2012
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Re: Yanmar 3GMF Overheating

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Originally Posted by Sailingking22 View Post
Did you get the overheating solved?
So far so good. I'm pretty confident that my issue was coolant mix and a loose impeller belt. As far as it's actual running temperature, I don't know how to get that figure. I have a temperature alarm but no thermometer. Is there a handheld instrument that we should have on board?
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Old 05-18-2012
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Re: Yanmar 3GMF Overheating

Quote:
Originally Posted by gordofloats View Post
So far so good. I'm pretty confident that my issue was coolant mix and a loose impeller belt. As far as it's actual running temperature, I don't know how to get that figure. I have a temperature alarm but no thermometer. Is there a handheld instrument that we should have on board?
An infared thermomitor is a really handy tool to have. Just shoot it at the engine (pick a spot on the block) and you can get a good sense of the temperature.

Amazon.com: Raytek MT4 Non-contact Mini Infrared Thermometer: Automotive Amazon.com: Raytek MT4 Non-contact Mini Infrared Thermometer: Automotive



I just wanted to add a couple things in regards to things that were said:
1) Yes this forum is a tremendous resource, it's great you came back to give the conclusion. It's a pet peeve of mine when people don't. I routinely do google searches for "blah blah site:sailnet.com" (if you don't know this trick you should try it) which is great at digging out old threads.

2) It's really really hard to judge the amount of water coming out of the tailpipe. I dealt with overheating on my 1gm10 (google search "overheating 1gm10" and my thread will come up) which turned out to be a lodged impeller blade from the previous season. But there was seemingly plenty of water coming out and after it was fixed the difference was still hard to judge.
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Old 05-18-2012
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Re: Yanmar 3GMF Overheating

Quote:
Originally Posted by Sailingking22 View Post
Did you get the overheating solved? Sounds like you had several items working against you, but mainly the coolant change. What is the correct tempature the Yanmar Diesel should operate at? I was constantly cleaning my mixing elbow to keep the engine cooler. It did not run the past two months and now that it is running again I wonder if it has rusted on the inside again. Last cleaning, I took it off and soaked it in a bucket overnight full of cleaning solvents. Maybe I'll do that again. Currently, it runs about 250 degrees after an hour....too hot to leave your hand on so I kill it when this happens. Mine is a YSM 12 so it is cooled by raw water. Impeller sprays out great on the input side....I know cause the line slips off from time to time. Most likely another clog. I'll follow the advice given here and post an update.
Normal cooling water temps for raw water cooled engines is about 140F or so and for fresh water cooled engines its 160-180F. What temp are you saying is 250F? MUCH too high for the cooling water!
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Old 05-18-2012
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Re: Yanmar 3GMF Overheating

I have read that full strength coolant does not dissipate heat as well as 50% mix. Changing to 50% may be an easy fix? Let us know how it comes out.

Paul T
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Old 05-22-2012
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Re: Yanmar 3GMF Overheating

I agree with smurfny, 4000 rpm is too high for the 3GMF for any length of time. I never go over 3000 on mine and the boat won't go any faster anyway.
If you have flushed your coolant, when you fill it back up, you will need to run the engine for a few minutes, then stop it and add coolant and repeat as necessary. That engine takes a lot of coolant. The problem with the mixing elbow that everyone mentioned is usually due to running the engine at anchor to charge the battery. When the engine runs under load, it should not be a problem. You may want to check that the elbow is free of obstruction at the end of the season, though..
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