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Old 07-04-2021, 18:16   #1
coz
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Yanmar 3gm30f raw water hose routing

Hi friends. I would like a little help on getting my cooling in order. The engine has been over heating and I have changed the impeller within the last few months (I really cannot tell how much wear is on the brass pressure hill or whatever the hell you call it). The strainer was very high and seemed to be airating, so I lowered it and put teflon on the threads. I have blown out or cleaned all the hoses. There is free flow when I open the 3/4" raw water seacock all the way to the pump. Last week we overheated. I wonder if the raw water hose/strainer is routed right. I have the hose coming off the cock under the engine, then it travels oil pan level to the strainer which sits above the transmission....then to the water pump">raw water pump. My questions are: what is the preferred routing height (above or below water pump impeller and level?) and since this engine is about 10 years old (2000hrs) with mostly fresh water but some heavy salt use each year for a couple of offshore races, could the thing be worn out? On a good day there is quite a bit of spray coming out of the exhaust but lately it seems to need to "recharge" even at higher RPMs. OK, to wrap up, is it poor routing or should I invest in a new pump?
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Old 07-04-2021, 19:03   #2
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Re: Yanmar 3gm30f raw water hose routing

Hi Coz...You might be better off posting this in the Engine and Propulsion system category.
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Old 07-04-2021, 20:44   #3
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Re: Yanmar 3gm30f raw water hose routing

ok, thx tech is the future, I'll look.
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Old 07-04-2021, 20:53   #4
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Re: Yanmar 3gm30f raw water hose routing

Have you checked your mixing elbow.....

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Old 07-04-2021, 21:06   #5
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Re: Yanmar 3gm30f raw water hose routing

Quote:
Originally Posted by coz View Post
....On a good day there is quite a bit of spray coming out of the exhaust but lately it seems to need to "recharge" even at higher RPMs. OK, to wrap up, is it poor routing or should I invest in a new pump?
Coz
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Have you checked your mixing elbow.....

Greg
+1. If the impeller is good and flow through the sea cock is good then the symptoms you describe are consistent with a plug someplace on the discharge side. The mixing elbow (where the water gets injected into the exhaust) is the most likely culprit. And if the “spray coming out” is not a steady stream....
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Old 07-04-2021, 21:08   #6
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Re: Yanmar 3gm30f raw water hose routing

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Have you checked your mixing elbow.....

Greg
What am I looking for? I don't see any pressure before the manifold, I mean a little, but not much. I have taken apart the manifold and it is clean. But if I need to rebuild that too, let me know. ****, I know you guys are gonna say it is the impeller but I just checked it and it looked great today and I just replaced it in November.
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Old 07-04-2021, 21:15   #7
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Re: Yanmar 3gm30f raw water hose routing

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+1. If the impeller is good and flow through the sea cock is good then the symptoms you describe are consistent with a plug someplace on the discharge side. The mixing elbow (where the water gets injected into the exhaust) is the most likely culprit. And if the “spray coming out” is not a steady stream....
OK, so I will tear into that in the morning. Other than purging and scraping crud, is/are there any tips?
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Old 08-04-2021, 01:50   #8
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Re: Yanmar 3gm30f raw water hose routing

Depending on age...... when I had my 3HM35f in last boat (similar engine) I never bothered cleaning the mixing elbow, I would just replace it. My opinion it’s a small price to pay. Second time I changed I was getting fair water flow (50% blocked) but exhaust side of elbow was 80% blocked. And hard as a rock.

Pull it off and inspect.

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Old 08-04-2021, 20:12   #9
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Re: Yanmar 3gm30f raw water hose routing

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Originally Posted by NYSail View Post
Depending on age...... when I had my 3HM35f in last boat (similar engine) I never bothered cleaning the mixing elbow, I would just replace it. My opinion it’s a small price to pay. Second time I changed I was getting fair water flow (50% blocked) but exhaust side of elbow was 80% blocked. And hard as a rock.

Pull it off and inspect.

Good lock
Greg
Thank you! I blew out everything and then ran water through the mixing elbow via a tube/funnel. It flowed but I agree it is probably the weakest link in this system. ordered part from local co. (HDI Marine, Van, WA). It is running well enough and putting out exhaust water so we can race this weekend but before offshore work I will install the new mixer elbow. Incidentally, I searched this site for these terms and couldn't dial it down but when I searched Google it found a CF thread from 9 years ago on this topic. I am digitally inept, so here we are.....Thank you!
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Old 08-04-2021, 20:56   #10
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Re: Yanmar 3gm30f raw water hose routing

Mixing elbow would top my list of suspects (I am 4+ years with a 316SS copy from ebay, OK so far). I also pull the front cover of my heat exchanger and use a brass pistol cleaning brush on an extension/ battery powered drill every 5 or so years. The heat exchanger covers are configured for a 3 pass flow before injection into elbow. Don't forget there is a thermostat but it resides in a lot friendlier environment.


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