Yanmar 2GM20F – Upgrade Raw Water Intake Seacock from ½” to ¾”?

[testingthewaters91]

Hi all,

I’ve got a Yanmar 2GM20F (16-18 HP) with a ½” raw water intake seacock. I’m hauling out soon to redo my thru-hulls, and I’m considering enlarging the intake hole and installing a ¾” seacock instead.

My current setup has run fine—engine runs for hours without overheating—but I’ve heard from a few people that ½” might be a bit undersized for this engine.

Has anyone upgraded their intake size for a 2GM20F? Is it worth opening up the hole and going to ¾”? Or should I leave it as-is if it’s working fine?

Looking for any firsthand experiences or best-practice advice.

Thanks!

 

[Don S/V ILLusion]

No clue what pump flow rating is but it makes no sense to enlarge the hull fitting only to keep the same small hose restricting flow rate.

 

[testingthewaters91]

No clue what pump flow rating is but it makes no sense to enlarge the hull fitting only to keep the same small hose restricting flow rate.

I would of course upgrade to a larger hose!

 

[kloudie1]

Not at boat now, but I think those raw water hoses are 5/8" on my 3GMF.. A 5/8" thru-hull gives ya a smidge more than 50% flow area, so if the 1/2" is not causing a problem a 5/8 should make the non problem better

 

[BigEasy]

Fairly certain that I have 5/8” fitting & hose on my 3YM30 Yanmar. Had a scoop strainer thru hull fitting from factory; however, I removed it & installed a straight fitting. Too many barnacles made a home in the strainer portion of thru hull with no provision of cleaning.

 

[Clutch Cargo]

FWIW, my 3GM30F has a 3/4" induction valve and matching hose.

 

[testingthewaters91]

FWIW, my 3GM30F has a 3/4" induction valve and matching hose.

Is 3GM30F comparable to 2GM20F?

I imagine the lower horsepower may require quite a bit less water to cool.

 

[testingthewaters91]

Fairly certain that I have 5/8” fitting & hose on my 3YM30 Yanmar. Had a scoop strainer thru hull fitting from factory; however, I removed it & installed a straight fitting. Too many barnacles made a home in the strainer portion of thru hull with no provision of cleaning.

That's a great set up. I'm already on the hard and have power tools available. One thing I'm nervous about is screwing the basket stainer into the hull. It seems like an odd way to go about attachment. I also have the fresh water strainer, albeit a plastic housed one.

 

[dlochner]

I would of course upgrade to a larger hose!

A larger hose won't help if the pump intake is only ½".

 

[Rich Stidger]

Don't "fix" something that is working fine.

 

[BigEasy]

Don't "fix" something that is working fine.

In other words, Don’t fix it if it ain’t broken!

 

[mermike]

3GM30F owner here. When I bought Tosca the diesel survyor said the 1/2" throughhull was undersized. When I redid my throughhulls a few years later I increased it to 3/4".

 

[Allan12210]

Here is a link to a write-up I did a few years ago upsizing my raw water through hull to 3/4". I also upsized the hoses from the valve to the strainer. It reduced the frequency of getting obstructions clogging the path to the strainer.

Hunter 34 Owner Modifications and Upgrades

Hunter 34 Owner Modifications and Upgrades

hunter.sailboatowners.com

 

[Ward H]

I upgraded from 1/2" to 3/4" thru hull for my engine water intake for a different reason. Hose barbs for 1/2" hose have smaller ID's than 1/2". I had a couple of small clogs of fine grass restrict the water flow. I went with a 3/4" thru hull and hoses to my 3/4" Groco Strainer intake. Then reduced to 5/8" to the pump.
That lets the grass and other crap reach the strainer where it is removed.

 

[testingthewaters91]

I upgraded from 1/2" to 3/4" thru hull for my engine water intake for a different reason. Hose barbs for 1/2" hose have smaller ID's than 1/2". I had a couple of small clogs of fine grass restrict the water flow. I went with a 3/4" thru hull and hoses to my 3/4" Groco Strainer intake. Then reduced to 5/8" to the pump.
That lets the grass and other crap reach the strainer where it is removed.

What engine do you have? This is an interesting idea. Allowing a larger flow area into the strainer but keeping the water intake size into the engine.

 

[Tally Ho]

I checked my boat today, O’Day 322 with a Yanmar 2GM20F, and I am running 5/8” hose for the water intake.

FWIW

Greg

 

[Ward H]

What engine do you have? This is an interesting idea. Allowing a larger flow area into the strainer but keeping the water intake size into the engine.

I have the Universal M25XP. 23hp.