View Full Version : Cooling issue PCM 351??

08-26-2008, 06:09 PM
I've got an older (~1990) PCM 351.
It's got this Sherwood raw water pump:

Not sure if I've got a cooling issue or not.
Here's the facts:
When the boat's underway the temp seems fine, steady around 140-150 (don't remember the exact number).
When we're just idling on the water the temp rises (don't remember how much but maybe 10-20 degrees).
When the boat's run on a fake a lake, the right exhaust is noticeable cooler than the left, and there's more water coming out the right exhaust. (the boat is parellel parked in the street, so it's tilted to the right). I don't think the temp gauge gets higher than when we're running in the water.
When I'm running it in the driveway, water pours out around the fake a lake (i.e. where it seals against the hull). On my friend's boat, the suction from the impeller is strong enough to actually pull the plunger up against the boat.
When I've changed the impeller, it comes out very easily (but I read stuff about people having a terrible time getting it out, and they make a tool to do this. Mine's not even close to fitting that tightly).

Any thoughts on if this is a problem or not? Everything's pretty much fine, mostly I'm a little worried it's getting too hot when it's running out of the water, or that this may be indicative of something that's going to be a problem later.

08-26-2008, 06:16 PM
Something doesn't sound right. I've never had an impeller come out easy. I don't have to fight it all the time, but it should fit tight. Are you sure you have the right impeller?

The fake a lake isn't always a great indicator. Try taking the intake hose, and putting it a 5 gallon bucket, then use the hose to try to keep the bucket full. It should suck pretty hard when you put your hand near the hose in the bucket.

08-26-2008, 06:29 PM
mine runs around 140 all the time. Just replaced the sea water pump and impeller due to overheating, or rather just running too hot for my liking. Once I replaced the pump and impeller, I had a lot of water running out the back and no more steam. If you're having a heat problem, you're gonna have steam out the back too......just something to keep an eye on the next time you run the boat. Be careful w/the fake a lakes........I use the inline device by perko. It attaches on the intake hose just past the clamshell and goes in line. Just screw the garden hose into the unit and you're done. Much safer and easier to use. Takes about 30 minutes to install costs around 45 bucks, and you leave it in there permanently.

08-26-2008, 07:30 PM
You need an impeller. If the one in it is new, you have a blockage. Try the impeller first and see what happens. Actually, clear out the oil cooler first.

08-27-2008, 01:52 PM
You need an impeller. If hte one in it is new, you have a blockage. Try the impeller first and see what happens. Actually, clear out the oil cooler first.
If the boat stays cool at speed (140-150), it doesnt sound like an impeller or blockage problem to me. If it were one of those issues, it would heat up the faster he goes.

If you heat up 10 degrees when returning to idle after running hard, thats normal. If you heat up 10 degrees just idling, tighten all of your hose clamps between the intake grate and RWP. Use a socket and ratchet, not a screwdriver.

A *little* bit more flow out of the starboard exhaust is normal- notice that the thermostat housing is not perfectly centered on the engine- its closer to starboard. A big disparity in flow side to side can be indicative of a blockage or ineffective RWP (bad impeller or seal), but if youre not overheating while loaded (running fast on the water) then I wouldnt worry about it.

Ive never struggled to remove the impeller from the RWP on any of my PCM's, though they get removed and stored inside every winter per the PCM lay up instructions.

08-27-2008, 02:16 PM
I am with Benj. The temp usually climbs while running at speeds then goes drops after idling for a moment.

08-27-2008, 02:23 PM
sounds more like some kinda blockage in your cooling system, are you running in fresh water ??
sometimes the risers get clogged with sediment which reduces the flow of water and can cause an overheat at idle but will be fine at higher revs due to the increased flow/pressure .

08-27-2008, 02:40 PM
If your boat is a 1990 and has a PCM, it must not be a MC.;)
I think 85 or maybe early 86 was the last of PCM before MC switched to Indmar.

PCM impellars are much easier to replace than Indmars,

Since you boat does cool somewhat this probobly isnt the problem. Maybe the exaust manifolds are somewhat plugged? Or as others have said the impeller is worn or maybe the oil cooler is plugged or maybe broken pieces of impeller are in the system.

Edit/ OK, you have a Brendella with a PCM........ I am guessing partial pumg in the system.

08-27-2008, 05:19 PM
Being off-center shouldn't make one side cool better than the other- it's the water flow that counts. In every motor I worked on that had one side cooling better than the other, something was causing it. If one side of the motor cools better than the other, I would look into why.

Partial cooling is better than none but it's still not enough.

08-28-2008, 12:05 PM
My 1976 Pro-AM is a Mastercraft clone. Just purchased it and am working thru many defferred maintenance items. Previous owner said heads were replaced about 1 yr ago, follows as they're not painted. Boat runs good but temp gauge barely moves under load. Suspect thermo is stuck open? I'll check the temp sender in a pan of hot water today.
What is the correct thermo for this engine? Where to learn more about the 4 barrel carb?

08-28-2008, 02:35 PM
140 is probably the right thermostat. It could be open or it could be missing- you never know when some people work on motors. Could be the wrong intake manifold gasket, too.

Make sure the oil cooler isn't clogged and the impeller is good. If there's no water getting in, the indicated temperature won't be accurate.

09-27-2008, 01:59 PM
Thanks fro the responses. Impeller I'm using is from PCM - RP061015, which I'm pretty sure is the right one. So my guess was that the impeller/pump isn't doing it's job quite well enough, thus the higher temp at idle, but when the boats at speed the thru-hull is forcing water up into the system and that makes up for it.
Doesn't really explaing the left-right difference, though...
I've taken the exhaust risers off and they looked pretty good, but I've never taken the manifolds off. The manifolds have a fair amount of rust around them, so I'm sort of afraid the bolts will be a problem, i.e. I might end up shearing one off in the engine, in which case I think I'd need to take it into a shop to fix. I don't really like the thought of going from a working boat to a non-working one due to my "maintenance":)
Pretty sure for now I'm going to not do anything, if I ever find a set of risers cheap