74 Southwind Intake/Cooling Problem

I have a 1974 Southwind 18 that has developed a cooling issue. Last night while cruising up the lake, I noticed a strange engine sound. Upon lifting the engine cover, I discovered the cooling hoses were much hotter than they usually are, and the trans cooler, which is much oversized, was a lot hotter than I believe it should be. I have a rebuilt Chrysler 318, and new exhaust manifolds. I checked the impellers (dual pocket) and they seem to be in good shape, and they were pulling lake water at idle, judging by intake suction below and exhaust above. I took the boat to dry land and pulled all the hoses and ran water through everything, but didn't find any obstructions or debris or loose impeller pieces anywhere. That's important because...

...at the beginning of the season, a friend of mine drove the boat into a mud bank and grounded it. My boat has 24" of draft, and it took a 4WD on the riverbank and lots of cable to get it out. The mud was very soft sediment, and did not damage the prop or rudder. I started the engine and drove it back down the lake that night with no adverse indicators. I can't find any residual mud in the engine or hoses.

However, upon looking at the bottom side this morning after pulling the boat out of the lake, it seems curious to me that there's no strainer or scoop below the intake hole. The intake hole is just positioned in a shallow wedge-shaped depression. There are 4 small screws that look like they don't hold anything around the periphery. I wonder if there was a strainer/scoop that got pulled off and is now permanently residing in the river mud? Is that a scoop that's supposed to create a ram effect under high speed that isn't, so I'm not getting sufficient water flow under way? And/or, does the speed of the boat under way work against the impellers to create a reduced flow while moving such that the cooling capacity of the boat can't keep up?

Or do I have a different cooling problem I haven't considered yet?

Finally, does anybody out there have a replacement scoop/strainer if that's what I'm missing? Or even a pic to post or send so I'll know what I'm missing?

My '69 Barracuda had two tru-hull pickups, one with a tee like you describe. The '74 Southwind only has one. Both originally had 318's. I pulled the 318 from the Barracuda and dropped it into the Southwind. Obviously I had to change the cooling system routing because I pulled the hoses from the Barracuda, but I have no diagram for the Southwind. If somebody has a complete cooling water diagram for the Southwind, I'd love to see it or get a copy. Currently one half of the RWP feeds the top of the tranny cooler. That exhausts to two hoses that run to the bottom of the manifolds on each side. That's why I'm surprised the tranny cooler was so hot. It has no thermostat and can't get any higher pressure than direct off of the RWP.

I ran the new manifolds in the Barracuda and had no cooling issues. The 318 has been in the Southwind about a year and I didn't notice any cooling issues until this last trip. When I first installed the engine, I used an infrared thermometer to monitor the manifold, tranny cooler, hose, and head temps on a couple of trips and didn't find any alarming temps. My new replacement manifolds are Barr Marine. I did use the copper tubes that route the water to the front/top of the manifold before it runs out.

There's seal between the halves of the RMP. If it was bad, it would leak to the outside, right? I've seen chewed-up impeller vanes. I didn't see any of mine that look chewed up, even though the engine stopped in different positions several times.

So you're suggesting at higher rpm's it's sucking air, not water? I suppose I need to take it apart and look at it, but how can I tell? Wobble in the shaft? I suppose it's the pulley end of the pump you're concerned about?

I'd really be surprised if the mud damaged it, though. It was very soft mud. No grit to it at all.

tleed wrote: So you're suggesting at higher rpm's it's sucking air, not water? I suppose I need to take it apart and look at it, but how can I tell? Wobble in the shaft? I suppose it's the pulley end of the pump you're concerned about? I'd really be surprised if the mud damaged it, though. It was very soft mud. No grit to it at all.

It's a ceramic faced mechanical seal against a hardened and polished steel face. It doesn't take much to screw them up and then they start sucking air instead of water. Considering your potential suction side restriction, I first would figure out the plumbing and then sure would go into the RWP seal.

BTW, ALL mud has "grit in it!! The seal face, as mentioned, is polished!!!!!

I pulled the hose off the intake side of the trans cooler and looked into the cooler. Nothing there but clear water and the metal of the cooler.

Chady74 wrote: I have a 74 Southwind with the chrysler motor i can send you pics if you pm me your email

Chad,
I have a feeling you didn't notice that the last post was almost 9 years ago. Hopefully Thomas has got the problem solved by now.