PCM 351W fresh water cooling (FWC)

Wrapping up this thread: the impeller change did not change much as far as engine temps or bucket test results go. I've decided to live with the slightly high (by marine standards - but seemingly acceptable by automotive standards) operating temps.

Do you still have the lower thermostat housing R025004? Mine is cracked and I'm searching!

SNobsessed wrote: The housing only goes together 1 way, as the holes are not exactly 120 deg apart. I would just scrape off the crud, put a new PCM impeller in it, & not look back.

To me, the cam looks good, it's symmetrical and can go in either way.

8122pbrainard wrote: I really don't feel it would help the cooling problem.  Have you double checked how you have the engine plumbed?

Yes, I'm confident the plumbing is correct. I'll change the impeller and report back.

As I noted in this thread, my boat's ventilation system was totally butchered at some point. As part of this process, the front vents were sealed off, so it seems to me there is very limited flow of fresh air getting to the engine under normal operating conditions. Could improving engine ventilation improve engine temperatures in any meaningful way?

Logically, if you have no idea what the Raw Water Pump impeller or the inside of the pump  looks like or how old it is, that would be a good place to start.

Wilhelm,

TRBenj wrote: I’d like to see how the cooling passages line up on those risers. Never seen that style before, though they are handsome. Manifolds look like normal PCM.

Finally figured out what manifolds and risers I have: link. They are the Chevy ones though, hence the adapter plate as mentioned in some of the later posts.

Interesting mix I have here: New Zealand manifolds on an American boat in South Africa.

Up to you if you change them Correct Craft seems that now days they only use that grey plastic. If your in salt,which I think the reason you have the fresh water cooling, and you want to change you don't want brass you'll want bronze

I know you have a few issues you are working on. Agree with KENO to simplify what you have until it is working. Get an infrared temp gun.
1. Create a block diagram of your system.
2. Your heater should be on the antifreeze circuit. (Warmer heat, ability to help cool your engine using it).
3. Have you been able to verify both of your pumps are working?
a. Part number for your engine mount water pump is a bi-directional marine pump?
b. Raw water pump has sufficient flow.
4. Your path should be water inlet, strainer, trans cooler, raw water pump, heat exchanger, tee, exhaust manifolds.

Pg55.
https://www.marinepartsguys.com/wp-content/uploads/ILLUSTRATED-PARTS-MANUAL-PCMcompressed.pdf

Gary S wrote: 8122pbrainard wrote: Wilhelm, Getting back to the high temp issue, if your bucket test proves the RWP is doing the job AND if your manifolds are running cool, I'd see if a raw water restriction to the manifolds will do anything. The restriction may put more raw water through the heat exchanger to make a difference. I'd like to know where the water comes from before that T to the manifolds i.e. Is the raw water making a full pass through the exchanger not tapped off half way down it or something. I just cannot see where it is coming from in the pictures

The pictures below shows the detail. Raw water leaves the heat exchanger to the T circled in blue. From there I assume it is supposed to flow to the next T circled in green (more clearly visible in the second photo). This T sends water to the exhaust manifolds and the trans oil cooler. From the trans oil cooler, water is sent to a heater I have mounted in the front of the boat. Water from the heater comes back to the blue T via the red elbow connector.

Upon looking at this setup, a few things here don't make sense to me the way the guys who did the installation for me did things:

1. Water coming out the heat exchanger and water coming back from the heater will be 'fighting' each other at the blue T, not so? Surely this will create flow issues somewhere? The heater never heated up properly despite the engine running hot - a symptom of this perhaps?

2. Having raw water pass through the heat exchanger before going to the trans oil cooler must surely mean the trans oil cooler is not getting particularly cool water? The standard placement would be before the heat exchanger, right? Even though this means the trans oil cooler is putting some heat into the water going into the heat exchanger?

Thanks for any help here!

So if it is reverse rotation it may actually need a bidirectional circulation pump to work correctly, Something has to move that water through the heat exchanger. Considering the number of automotive parts needed to make things work over there I would check to make sure a standard rotation automotive pump wasn't used.   

It is important that the heat exchanger is plumbed in the correct location to get full capacity out of the heat exchanger but near as I can tell it is.   I would love to see how they got a chevy manifold to fit a ford.

Gary S wrote: TRBenj wrote: Just 1 connection, rather than in/out? Risers are dry? Tim the raw water from the hull pickup follows the normal PCM path until it exits out of the Sherwood pump. Instead of running to the thermostat housing it goes to the heat exchanger cooling the block coolant then exits out of exchanger via 1 outlet into that T and then like a raw water cooled engine into each exhaust manifold through the risers and out. They put the water in the back of the manifolds only because the way the exchanger is mounted its outlet is near the bellhousing thus keeping the hose length short. The only real difference here is that he has the exchanger mounted across the rear of the engine rather than PCM's length wise mount behind the Sherwood pump. This is why it is called a half system in the sence that only the block is protected- the manifolds still being raw water. I'm not sure but I think a full system has the manifolds cooled by the block water with block off plates at the manifold to riser joint but the risers are still cooled by the exit of the raw water

I know how it’s supposed to be plumbed, I’m asking how he has it plumbed since there appear to be a number of inconsistencies to go along with the described cooling problem.

8122pbrainard wrote: Wilhelm, Getting back to the high temp issue, if your bucket test proves the RWP is doing the job AND if your manifolds are running cool, I'd see if a raw water restriction to the manifolds will do anything. The restriction may put more raw water through the heat exchanger to make a difference.

I'd like to know where the water comes from before that T to the manifolds i.e. Is the raw water making a full pass through the exchanger not tapped off half way down it or something. I just cannot see where it is coming from in the pictures