Yanmar engines: raw water pump design

Island Girl 34 · Jul 23, 2009

Stu,

I have a 1983 Hunter 34 with a Yanmar 3GMF, 20 HP, 3 cyl. The raw water pump on this engine is driven by belt (as shown on the bottom left of the attached photo.)

Ken

Maine Sail · Jul 23, 2009

Stu Jackson said:
I have a friend with a Universal diesel (M35-series). He has had some "issues" with his raw water pump seals. The pump is engine driven (not by the alternator belt). He claims the seals never leaked (neither water nor engine oil, and the pump seized up and took out his engine).

For those of you with Yanmar engines, what is the arrangement of your raw water pumps? Belt driven or engine driven? If different size Yanmars are different, then what engine? In the 21 to 35 HP range, 3 or 4 cylinders, 34 foot boat.

I'll be checking the Yanmar website, too (doin' my own homework!) but would appreciate your input.

Thanks,

Stu

Stu,

This pump could have seized if the shaft bearings failed. There are two bearings on that Johnson pump and they are of the sealed type. It's possible the weep hole got plugged and salt water passed through the sealed bearings, bearing seal. There is usually a weep hole that should prevent raw water contamination due to pressure pushing through the seals. I would think it is possible, having seen weep holes plug due to the "ignore it and it will go away factor" that the seals got penetrated by salt water. If they were penetrated by the oil side no big deal but salt water could cause a failure.. If his pump was weeping for a while the weep holes could have conceivably plugged enough with dried salt and caused an issue. Of course one would think it would make an awful lot of noise before getting to the point of killing the engine? Even without sufficient lube it is tough to kill a sealed type bearing let alone two of them back to back..

Rick2413 · Jul 23, 2009

On my old YSM12 and my 3GM30F, both are belt. However, I just rebuilt a dockmates older 1GM10 and it was engine driven. I thought it extremely odd. Although there was two oil seals, I think it is possible if both failed, raw water could actually enter the engine and cause serious damage if one didn't monitor his engine daily.

Don12364 · Jul 23, 2009

My 3JH2E (37 HP Yanmar in H376) has an engine driven pump which faces aft and it is particularly difficult to change the impeller.
Other raw water pumps have a small bleed hole between the pump shaft water seal and the engine oil seal so any leakage should not enter the engine - unless both seals have failed. Best I could do was to feel for such a hole to avoid the situation Stu refers to above, but I was never able to establish whether such a hole exists.
Anyone know for sure please?

kloudie1 · Jul 23, 2009

Man, I wouldn’t expect a pump to lock up without making a whole lot of noise.. and leaking for a while too before the lock..
My Yanmar is just like Ken’s (his engine box is cleaner) .. the seawater pump driven by the little dedicated belt in the bottom left of the picture..
I have cleaned from a Westerbeke and a Universal the gray mayonnaise oil/water emulsion that happens when the direct drive pump seals fail and drool water into the crankcase.. Not fun.. Many newer Yanmars have direct driven pumps, so they can have the problem too..

sailaway78 · Jul 23, 2009

The same setup

I have the same set up, on a 3GM. Belt driven raw water pump. Now that I have replied to that, I have a couple of questions. First off, when the pump froze up, and quit working, it had to be more than just a touch noisy. If it froze up, something had to break, as this is a gear driven pump. Was the noise totally ignored? Also how did this " take out" the engine. From overheating? When a fresh water cooled engine has the raw water pump quit working, the temp is going to come up rather slowly. Was there no temp guage or warning buzzer. Something about this just doesn't feel right.

Neil McDonald · Jul 23, 2009

Re: The same setup

Not wishing to high jack this thread, but I couldn't help comparing the Yanmar engine pics posted by Ken and Claude. On one engine the top of the coolant overflow bottle is approximateley level with the cap on the heat exchanger and on the other it stands half the bottle height higher. What is the correct height? I asked this once before without any response.

Mike Holibar · Jul 24, 2009

Neil, as the overflow tank works via the radiator (hex) cap which in turn allows for expansion and contraction of the coolant (pressure when hot, vacuum while cooling) it does not rely on gravity to feed coolant to the heat exchanger. Therefore I don't think the precise position of the overflow tank is all that critical.

kloudie1 · Jul 24, 2009

You are right, Mike.. The expansion tank would work a few feet higher or lower.. The radiator cap releases coolant to the tank at around 6-8 PSI (some caps are higher) so it could drive water uphill a bit .. When the engine cools, atmospheric pressure pushes the stuff in the tank back through the check valve in the radiator cap.

DougM · Jul 24, 2009

My boat has the Yanmar 2GM20F-YEU version. This version has the belt driven Johnson pump. Like any othe belt driven pump one has to be careful about the amount of belt tension. If the belt is too tight, it will cause premature wear on the seals, and they will leak. Too little tension and the belt will slip.

Yanmar engines: raw water pump design

Stu Jackson

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Island Girl 34

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Maine Sail

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Don12364

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kloudie1

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