HEX flow direction

I backed myself into a hole by not taking enough pictures, and don't have allot of experience with fully closed system.

Long story short, moved from rear to front mount and ended up with a front mount Seakamp 63107 which has slightly different ports than the original Crusader HEX.

My questions are, in this diagram, is the in and out water and coolant flow correct? And out of curiosity, can water flow in the opposite direction, in through the out door? I thought I saw something about parallel vs. cross flow, which one are marine heat exchangers?

Thanks again, the knowledge and willingness to help on this forum is awesome.

The coolant flow indicators appear correct, but I'd suggest the 'full' configuration. this means the exhaust manifolds are in the 'closed' side of the system. you only have to change the hose barb on the outlet end of the manifolds....and of course, you'll need to make sure the blockoff plates are installed.

as far as the raw water side arrows, I really don't believe it matters much. I would reverse the arrows as shown so one doesn't fight thermodynamics. in other words, let the 'cold' water enter at the bottom and then exit out the upper port as it absorbs the heat..

I am certain that HX has a multi-pass core for the raw water to flow thru...you can tell by removing the 'drain side' end cap...there will be 'pie cut' separators to direct the water flow from one group of tubes into another. it will have to be an even number of passes with the inlet and outlet on the same side.

If you know the Mercruiser application(s) it very likely I can find the factory flow diagram if you want it...

Thanks Mark! Yes, this is a fully closed system with block off plates installed. In the diagram, where I indicate the "y-split", (most say T) that's where the raw water-out will split and connect to each exhaust elbow, beyond the block off plate.

Next mystery, the previous owner had one 1-1/4" fitting on the port elbow, the starboard elbow had a 1" fitting. Do you think they just used what they had, or is there a reason for two different sizes on the elbows?

your pic had the coolant returns labeled as 'from t-stat' so that's the root of the 'full system' comment.

ideally you'd want equal flow to both elbows....why they are different sizes is hard to say...could have been what was on hand, could be what 'fits'...I'd go with equal sized fittings as a default.

FWIW, when my first Crusader HX rotted out, we got Mercruiser closed conversion kits (I could get the kit cheaper than the wholesale on the CRU HX)....the big difference noted was the size of the coolant hoses to and from the manifolds...Crusader used 1.25"ID and the Merc's were 1.0"ID...
we kept the t-stat hoses at 1.25" (less work) and used the kit hoses from the manifold to the HX...and things worked out just fine...

Mark, you are absolutely right. My fault. I labeled that part wrong, it should say coming from Exhaust manifold fittings. Sorry, been doing way too much work on the boat and my brain hurts as much as my back!

The T-stat flow goes to the front of the manis!

For the past few I have been pulling just over 400 lbs (true story) of soaked foam from under he deck, re-pouring foam and closing the deck back in and painted. New engine beds shaped and re-bedded and glassed in... the fiberglass grinding and epoxying have gotten to me!

Looks schweeet! pretty work...hope you have a good breather - that 'glas dust' can rip up lungs...and throat and eyes...

Thanks! Yes, respirator most of the time when grinding, that stuff is nasty!!

different barbs for raw water dump:.... 90% of FWC systems have different length hoses to port and stbd elbows due to routing and distance resulting in one elbow typically running hotter than the other. Perhaps the P/O used different diameter barbs ( and hoses) in an attempt to equalize flows to the elbows.
:..