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Discussion Starter · #1 · (Edited)
I have been under the impression I had a 2GM20(f) (because thats the manual I got with the boat from the PO) and now I think I have a 2GM20 (because I bought a part that didn't fit, and finally looked at the ID plate on the engine (DUH!). I looked at the manual again and it only confused me more. I think the (f) is for freshwater, but can someone explain the difference. My engine is raw water cooled, and I can tell you the water pump shaft on the (f) is larger, as the bearings I bought (thinking it was an (f)) were too large for my pump. Anyway, whats the difference?:confused:
 

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F does stand for Freshwater

My 3GM30F has the same manual as the non-freshwater version. If you have a anti-freeze reservoir tank, then you have the Freshwater version motor.

DrB
 

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Discussion Starter · #3 · (Edited)
My 3GM30F has the same manual as the non-freshwater version. If you have a anti-freeze reservoir tank, then you have the Freshwater version motor.
DrB
So they are referring to "fresh" vs. "raw" water, and if you have a closed cooling circuit (with heat exchanger, etc.) it's an (f)? The lady at Yanmar made it more complicated than that. Well, if so, that clears that up. Sadly, I definitely don't have an F. Terrible thing to do to a diesel:( !
 

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Although I don't like the thought of my raw water cooled block (2GM)corroding away, as part of it's normal use.. it has been doing so for 25 years, and is still going strong!

They did build them well, knowing they would be raw water cooled. There are alot of threads on here about clogged heat exchanges, etc. On ours it's KISS!
 

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Just a question. Does the raw water cooled motor use internal zincs as opposed to the F that does not?
 

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Yes, Heres your Yanmar part numbers

2GM20 (18 H.P.)​
2GM20F (18 H.P.)​
Raw water cooled​
Fresh water cooled​
Oil Filter119305-35151Oil Filter119305-35151
Fuel Filter104500-55710Fuel Filter104500-55710
Fuel Filter Gasket24341-000440Fuel Filter Gasket24341-000440
Air Element128270-12540Air Element128270-12540
SWP Belt104511-78780SWP Belt104511-78780
Alternator Belt128670-77350Alternator Belt25132-003700
Zincs27210-200300 (2)ZincsNA
Zinc Gaskets123210-09310Zinc GasketsNA
Impeller104211-42070Impeller124223-42092
Impeller Gasket104211-42090Impeller Gasket124223-42110
SWP Rebuild KitK28270-42000SWP Rebuild KitK28670-42101
Thermostat105582-49200Thermostat121750-49800
Therm Gasket104211-49160Therm Gasket129350-49541
Starter128170-77010Starter128170-77010
Motor Mounts Front124772-08341Motor Mounts Front124772-08341
Motor Mounts Rear128270-08340Motor Mounts Rear128270-08340
 

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Yes, Heres your Yanmar part numbers

2GM20 (18 H.P.)​
2GM20F (18 H.P.)​
Raw water cooled​
Fresh water cooled​
Oil Filter119305-35151Oil Filter119305-35151
Fuel Filter104500-55710Fuel Filter104500-55710
Fuel Filter Gasket24341-000440Fuel Filter Gasket24341-000440
Air Element128270-12540Air Element128270-12540
SWP Belt104511-78780SWP Belt104511-78780
Alternator Belt128670-77350Alternator Belt25132-003700
Zincs27210-200300 (2)ZincsNA
Zinc Gaskets123210-09310Zinc GasketsNA
Impeller104211-42070Impeller124223-42092
Impeller Gasket104211-42090Impeller Gasket124223-42110
SWP Rebuild KitK28270-42000SWP Rebuild KitK28670-42101
Thermostat105582-49200Thermostat121750-49800
Therm Gasket104211-49160Therm Gasket129350-49541
Starter128170-77010Starter128170-77010
Motor Mounts Front124772-08341Motor Mounts Front124772-08341
Motor Mounts Rear128270-08340Motor Mounts Rear128270-08340
Excuse My Ignorance Please by SWP I presume you to mean Salt water pump?
 

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If the zincs are changed regularly, and the engine occasionally descaled, raw water cooled diesels can last a very long time. The principle disadvantage to RW cooled diesels is that they run cooler than their FW cooled counterparts (to keep scale build-up to a minimum), and therefore are not quite as efficient and a bit more prone to gunk building up in the cylinders (i.e., they don't get hot enough to burn everything off).
 

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My 3GM is raw water cooled and 30 years old. I think I like the raw water cooled. Very simple and fewer parts to break. If I had to repower, I would install the same if it were available- 30 years or more use not bad.

The zincs on mine were corroded away and I had real trouble getting the zinc plug out of the block (2 GM will have one in the block and one in the head). You remove the zinc plug and then unscrew the zinc (or what is left of the zinc). I had to use a small propane torch to heat the plug to get it off. And even then I must have had 400 ftxlb force to get the plug to unscrew.
 

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On our old boat we had a 2GM20F and loved it.

On our new boat, we have a 2QM20H raw water cooled engine, and other than being older it runs just as well. The PO wasn't the best on maintenance (bad news) but whomever he used for engine work was (good news). I replaced the zincs and everything (so far) that I have taken off (metal to metal) had had traces of "Never-seize" and has come apart easily.

One nice thing about the freshwater cooled (someone mentioned) is they run hotter - that translates into hotter water in hot water tank for the domestic water or hotter air in the hot water cabin heater.

The full engine repair manual and parts lists are online somewhere.

Rik
 

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I had a 2GM18 Yanmar diesel. Do you have any fotos of the stuffing box/stern gland I would be very interested to see them as my stuffing box was removed and a Volvo stern gland fitted in its place and not very well I might say.
 
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