Marelon thru-hull – oversized or right-sized?

[4arch]

I plan to replace my thru-hull valves and fittings this winter and have decided to go with the Forespar Marelon OEM 93 series. On my current 3/4" engine intake thru-hull valve there is a Groco engine flush fitting that allows me to connect a section of garden hose for antifreeze intake when winterizing. I like having this capability and very much want to preserve it going forward.

I’ve found that Forespar makes an engine-flush version of the 93 series but the smallest size available is 1”. Are there any potential downsides to using the 1” valve and a 1” hose to the engine strainer and then using reducers to step down to 3/4” at the strainer intake? Alternatively I could keep the Groco fitting and adapt it to work with a 3/4” series 93 valve – but then I’d be mixing bronze and Marelon.

 

[Maine Sail]

I plan to replace my thru-hull valves and fittings this winter and have decided to go with the Forespar Marelon OEM 93 series. On my current 3/4" engine intake thru-hull valve there is a Groco engine flush fitting that allows me to connect a section of garden hose for antifreeze intake when winterizing. I like having this capability and very much want to preserve it going forward.

I’ve found that Forespar makes an engine-flush version of the 93 series but the smallest size available is 1”. Are there any potential downsides to using the 1” valve and a 1” hose to the engine strainer and then using reducers to step down to 3/4” at the strainer intake? Alternatively I could keep the Groco fitting and adapt it to work with a 3/4” series 93 valve – but then I’d be mixing bronze and Marelon.

When using the 93 series it is best to go one size larger anyway. The thru-hull fittings on these are where a large part of the strength comes from. As such the wall thickness is MUCH thicker than a normal 3/4" bronze or 3/4" Marelon thru-hull. This extra wall thickness makes the ID smaller. A 3/4" Marelon 93 series is roughly a 1/2" ID. A 1" OEM/93 needs to replace a 3/4" of other styles if flow is to remain the same...

 

[4arch]

Thanks Maine Sail. I was in a chandlery today that happened to have some of the 93 series on the shelf and the reduction in ID was very noticeable. I was also surprised how much smaller the 3/4" valve body was compared to the 1" model. I'll definitely upsize to 1".