318 Manifold question

Hello,

I've done my best to search old posts for the answer, but I'm not sure I've found it. I have a 1981 Silverton 31C with Chrysler 318s. The motors are fresh water cooled, but the manifolds are raw water cooled. I had some issues this past season, but replacing the mixing elbows did a world of good. I'm out of the water for the season, and I have my manifolds off to give them a good check. My question is, do I need to run with the copper distribution tube installed? I've seen posts that say they are only for raw water cooled motors, but since there are at least 3 configs I can think of, and all of them involve some raw water, I'm just curious if they are needed in my case. Again, the block is fresh water cooled but the exhaust manifolds are raw water cooled. It may not make much difference either way, but I just wondered if anyone has experience with it.

Thanks

Dave

I ran WITHOUT that tube in my raw water cooled motors for years without a problem. It began when I accidentally left one of the tubes out. The motor ran fine, so I left them out deliberately from then on.

Jeff

PS: On mine, the water entered the front of the manifold and flowed out the back--also the reverse of the 'accepted' method.

Thanks, They don't look like they serve much purpose. maybe they are there to get more water more quickly to the mixing elbows on engine startup. In any case, I want to maximize raw water flow through the system. Now that the boat is out of the water, when I go down to reinstall the manifolds, I'm going to dissasemble and inspect everything on the suction side of the raw water pumps. The only components that the raw water goes through before entering the pump is the raw water pickup, the strainer, and the V-drive. I've never inspected where the raw water goes through the V-drive. I'm curious if that can be a source of constriction if its clogged in any way. I will say that once the mixing elbows were replaced, I do seem to get pretty good raw water flow out the exhausts.

The Walter v-drives have an oil cooler mounted at the top. There isn't much to it, just some tubing over which the cooling water flows and then exits. Are you sure you don't have an additional oil cooler for the transmission (probably a BW 71C). I've never seen a installation like that without one. If you find one, take it out and see if there is any marine debris or old impeller pieces inside. That's a common place to find a restriction.

There is an additional cooler that receives raw water right after it exits the heat exchanger. from the top of that cooler, the raw water then splits and goes to the mixing elbows. the cooler is not much larger that a can of soda, and has 1" raw water lines going in and out. I never really looked at it closely, but I thought it was an oil cooler for the engine. It may be a transmission cooler, I never really traced the lines. I have definitely looked at the raw water plumbing since I replaced most of the lines this past spring. Starting at the Raw water intake, it goes from there to the V-drives, then raw water pump suction, raw water pump discharge to the heat exchanger, Heat exchanger outlet where it splits in 2. One line splits again and goes to the "low"side of the exhaust manifolds, and the other line goes through the cooler I mentioned before, splits and then to the mixing elbows and out the exhausts. I did look at the smaller coolers, and checked the tube side for obstructions, They seemed pretty clean. I suspect my raw water pickups may be causing some issues. They are the kind with hundreds of small holes like a cheese grater. They probably have been painted 20 times. if practical, I'm going to remove and inspect them, and what may be behind them.

Thanks

If it looks like this, it is the transmission cooler.You can see the transmission oil lines going to and coming from the cooler. This picture was taken when I was draining the heat exchanger, getting ready for winter layup.