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Old     (CenCalLakes)      Join Date: May 2014       07-08-2015, 5:45 PM Reply   
'89 Ski Brendella with a PCM 351 Ford raw water cooled.

-last weekend running on the lake engine started to overheat.

on the water I let it cool and replaced the impeller on the sherwood raw water pump even though it seemed fine. I had one on the boat and figured it wouldn't hurt. Checked the screen under the boat and the screen on the oil cooler everything looked clean.

It was close to the end of the day so we headed back to the ramp, engine was running around 165 which I feel was fine but it is about 10 degrees warmer than it usually runs. I did at one point think I heard a strange humming sound coming from the re-circulating pump.

I changed the thermastat 'cause the local PCM dealer had one on the rack.

Ran it today with the fack-o-lake and it started to creep up again, i shut it down at about 200 degrees

I was getting plenty of water out the exhaust and water seems to be flowing well.

I just ordered a re-circulation pump overnight shipping b/c we want to be out on the lake this weekend.

Anyone have any other ideas what the overheat problem could be coming from?

I am the kind of person that likes to cover all my basis because I would rather spend the money now and just replace the old stuff before I get stranded on the water.

Thanks for the input and thoughts ahead of time.
Old     (you_da_man)      Join Date: Sep 2009       07-08-2015, 11:30 PM Reply   
No mechanical advice but those were sweet boats back in my college skiing college had 2 of them. Good luck with your trouble shooting.
Old     (Froggy)      Join Date: Nov 2013       07-09-2015, 3:41 AM Reply   
Are you sure the pump is on correctly? When installed the hoses should be on the engine side.
Old     (SWEC)      Join Date: Jun 2015       07-09-2015, 6:12 AM Reply   
Was it running 165 before you changed the Tstat? I'm wondering if you got a Tstat with a higher temp setpoint, I think the Tstats they use in cars run at about 190.
Old     (CenCalLakes)      Join Date: May 2014       07-09-2015, 7:15 AM Reply   
No at that point on the lake I had not changed the t-stat.
After changing the Tstat I ran it on the fake I lake and it got up to 200 before I turned it off.

The new one is a 160 b/c I was told if I am not running in salt water 160 is fine. I know these boats came from the factory with 143 because Brendella didn't know if it would be a fresh or salt water boat. I haven't checked the old stat to see if it was actually bad it was pretty corroded looked like it is probably the original to the boat.

I'm thinking it has to be the circulating pump won't know for sure till tomorrow when it comes in.

there really can't be any other part that could have failed that would cause this right? Except maybe a passage is clogged. Can I damage anything if I use a hose to blast out the engine water passages after I take the circulating pump off? Or if I shoot water through the exhaust manifold and risers through the front hoses to try and clear any debris? Would that not be advisable?
Old     (denverd1)      Join Date: May 2004 Location: Tyler       07-09-2015, 1:14 PM Reply   
hmm... did you try burping the system? temp sensor is usually the highest point on a marine engine.... on the intake manifold. could have an air pocket. although that wouldn't explain why it started overheating to start with.

blast water all through that puppy you aren't going to hurt anything.

only other option really is the circulating pump as you mentioned. you could also pull the t-stat to eliminate that part of the equation

Last edited by denverd1; 07-09-2015 at 1:18 PM.
Old     (CenCalLakes)      Join Date: May 2014       07-09-2015, 1:39 PM Reply   
Yeah i thought about leaving the tstat out but a new one was only $15 and I figured the engine is designed to have it in there limiting the water slightly. I might pull it if it still runs hot after installing the new pump and see what happens. I am going to blast out the passages and the oil cooler with the hose before installing the new circulation pump. Hopefully she will run good this weekend. This is my first boat and wanted to make sure there wasn't something else that could possibly be the culprit that I didn't know about.

Do you think it would be necessary after installing the new pump to pull a line off the tstat housing and start it to bleed the air out of the system?
Old     (denverd1)      Join Date: May 2004 Location: Tyler       07-09-2015, 1:45 PM Reply   
I would just loosen the bolts on the housing enough to make sure you get some water coming out of there.
Old     (SWEC)      Join Date: Jun 2015       07-09-2015, 11:09 PM Reply   
If she's sucking lots of water through the fakelake and dumping it out the exhaust it pretty much narrows it down to the cooling system through the actual engine block. You're probably on the right track with the circ. pump; she is an 89 after all!
Check and make sure the Tstat is installed the right way up as well.
Old     (cadunkle)      Join Date: Jul 2009 Location: NJ       07-10-2015, 3:49 AM Reply   
If you're getting plenty of water out the exhaust it sounds like your raw water pump and intake are functional and not plugged up. Does the PCM 351w have any sort of check ball/valve in the thermostat housing or elsewhere to restrict or regulate water into the exhaust? I know Mercruiser engines for many years had a threaded rod with a ball on each end and spring between that restricted and balanced flow to each exhaust manifold. If corroded or stuck it would allow too much water direct to the exhaust, bypassing the engine. Manifolds would be normal or cool temp but engine would overheat. Just something to check in your plumbing.

Also, when changing thermostat always good to check the number stamped on it, should be stamped the temperature on the copper lug. 160* should be fine, but if it's a 180* (doubtful, since you saw 160* and it came from PCM), 10*-20* higher than tstat temp is within the realm of normal. Mine always runs a little hotter on the hose than on the water.

Could also be corroded impeller on the circulating pump, you're on the right track checking that.
Old     (denverd1)      Join Date: May 2004 Location: Tyler       07-10-2015, 8:18 AM Reply   
were you missing any fins on that old impeller you pulled? they can get stuck in the block too
Old     (CenCalLakes)      Join Date: May 2014       07-10-2015, 9:13 AM Reply   
No it wasn't missing any pieces on the impeller. I pulled the circulation pump and that thing was corroded as all hell! It spins fine though. The new pump is arriving today. Although I haven't found any specific sign on what would have caused it. After replacing everything I feel it should be good to go. I'll let you all know

Thanks for the help
Old     (CenCalLakes)      Join Date: May 2014       07-10-2015, 6:25 PM Reply   
What would be the repracautions of running the boat without a thermostat? After replacing the thermostat, impeller and circulation pump it still started to overheat on the fake-o-lake. I pulled the thermostat and it stayed around 145 deg.

I put the thermostat back in but if it overheats at the lake I'm thinking about running it without the thermostat.

Is there any repracautions to running it without the thermostat?
Old     (lerg)      Join Date: Jul 2013       07-10-2015, 7:29 PM Reply   
Stupid thought. But have you checked the hoses? Are they in good shape? They do break down over time and can have an impact on cooling over time.
Old     (CenCalLakes)      Join Date: May 2014       07-11-2015, 1:27 PM Reply   
So new impeller ( raw water pump mounted correctly and feel cool to the touch when running), new circulation pump feels cool to the touch when running, replaced thermostat, all new hoses. Running on the lake overheating again and the thermostat housing was hot to the touch, PSI gauge read 60 psi so I pulled the thermostat To make it through the day just didn't run it hard just cruzed around the lake.

I'm Thinking the new thermostat is bad will check it in some boiling water later tonight but if that seems to work what the hell else could be the culprit I sprayed out the two engine passages, do I need to replace my slightly corroded exhaust risers and heat exchangers?

I'm pretty lost on why this is happening it gets up to 200 before I shut it down
Old     (CenCalLakes)      Join Date: May 2014       07-11-2015, 4:28 PM Reply   
So, I think I figured it out. Just got back from the lake heated up some water on the stove and the bran new thermostat I bought doesnt open until after the water is above 200. I am thinking with my luck the it was just a new bad thermostat and I didnt need to replace the circulation pump, I had a feeling it was the thermostat all a long.

I love buying new broken parts

Can anyone re-assure me that it is okay to run a 160 t-stat if I run in fresh water, instead of the 143
Old     (SWEC)      Join Date: Jun 2015       07-12-2015, 8:06 PM Reply   
I've been running a 160 on my PCM351 all season so far; it's just a generic Tstat from the local autoparts store. That same block in a car would have a 190deg tstat or something in so 160 definitely isn't hurting it.
Old     (TTyler89)      Join Date: Jun 2015       07-12-2015, 9:46 PM Reply   
Since you discovered the new thermostat wasn't opening right, I would check that first. If it still over heats, on your raw water pump and cover was there any substantial grooves worn into either? If so, that's usually the culprit because they cavitate and can't pump the normal amount of water. Now if everything was fine there, it could be the manifolds and risers rusted internally being that old. You replaced the water circulating pump, did you order one for the correct rotating direction, or was it bi-directional. The other thing I would check seeing that you replaced and have checked most everything else would be the total timing to make sure the distributor didn't turn and advance the timing beyond about 28-30*. I know it's a long shot but I have seen it happen. Not saying this is what it is, but if everything else checks out, then that would be a next step. The first time it overheated, did the impeller chunk a blade? How old was the impeller?
Old     (denverd1)      Join Date: May 2004 Location: Tyler       07-13-2015, 11:21 AM Reply   
Test your stats folks! Often fail right out of the box!

To answer your question, the tstat makes sure the rings warm up and seat down properly before you get into any RPMs. I pulled it out the last boat and never had a problem with it. Still hanging on the wall in my garage actually. Once you get a few hours on the engine it's not nearly as big of an issue as it would have been in 1989 with 0 hours on it.

Definitely remove it to test things out
Old     (CenCalLakes)      Join Date: May 2014       07-13-2015, 8:20 PM Reply   
I believe the raw water pump is okay, it does drip slightly out of the front of the shaft, has anyone had any luck using the rebuild kits? I would rather spend $75 and rebuild it than spend $400 on a new one. The recirculating pump is a bi-directional. However besides some corrosion on the old one I believe that one wasn't bad.

I pulled the heat exchangers and the risers off, purchased the rebuild kit from skidim and have them soaking in vinegar right now to loosen up the rust.

I think it was just the tstat, when I ran with out it on the lake it ran Pretty much too cold so I didn't stay out for long or pull anyone.

I have had the boat for two years it has 1090 hours on it. The last two seasons it has run around 150-155deg. With the 143 tstat

With a 160 tstat what should I expect as optimal running temp? 175 possibly? I would think anything over 200 would be pushing it and considered overheat right since it is raw water cooled and water boils at 212 deg.
Old     (cadunkle)      Join Date: Jul 2009 Location: NJ       07-14-2015, 4:58 AM Reply   
You could measure up the seal and replace just that if the shaft is not grooved. Impeller would hopefully be brass or stainless and clean up nice. Backing plate hopefully stainless and not rusted through. Water pump is one of the few items that are worth spending extra for "marine" on any raw water cooled engine, close freshwater system with antifreeze you can run automotive parts.

Anyhow, What is the $75 rebuild kit you're thinking about and waht does it include? If everything is good aside from the seal I'd expect a seal to only be a few bucks.

Not sure where you're getting $400, here's a marine SBF pump for $150.

SkiDIM lists one for $120, but does not say the brand.

Another for $98, I've ordered from here before for misc parts and they usually have good prices.

For $100 or so I'd probably just buy a new pump unless I had doubts about the quality of what I was buying new vs the rebuilt parts. I do enough work on vehicles that I'd rather not spend the time going OCD on a water pump for my boat. Unless it's an original pump on an engine that you want to keep numbers matching correct parts on it, not worth the time when replacement parts are cheap.

160* is fine for fresh water, heck even 180* should be alright. Hotter is better (within reason) for engine longevity and efficiency, only reason to run a 145* is if you run in salt or brackish, otherwise my choice is a 160*. Generally operating temps on a stock cooling system will be 10*-20* hotter than thermostat depending on how efficiently the rest of the system is working and how hard you're running it.
Old     (TTyler89)      Join Date: Jun 2015       07-14-2015, 6:11 AM Reply   
Does yours for sure have a closed cooling system or is it cooled by raw water alone?
Old     (DenverRider)      Join Date: Feb 2013       07-14-2015, 7:21 AM Reply   
I think that the pump he was talking about rebuilding was the raw water pump, not the recirculating pump, cadunkle. Raw water pumps are a lot more expensive because they are a boat specific part that isn't shared by the boat motor's automotive cousin. The pumps I've seen for my PCM 330 are over 600 new.
Old     (CenCalLakes)      Join Date: May 2014       07-14-2015, 1:28 PM Reply   
I replace my circulation pump, and only paid $105 for it, I don't think that was my issue but it was cheap so I'm going to leave it on. I'm talking about re building the Sherwood raw water pump. It works but it drips out of the front just a couple drops per minute.

A new Sherwood raw water pump is around $350-400 when I can get the rebuild kit for about 85 that comes with the seals/races/clips

"T" it is a lake cooled or raw water cooling system not a closed system.
Old     (TTyler89)      Join Date: Jun 2015       07-14-2015, 3:36 PM Reply   
Ok that answers that. What heat exchangers are you referring to? Is it the transmission or oil cooler? There shouldn't be any heat exchangers other than an oil or transmission cooler. That was throwing me off. You made it sound as if you had a closed cooling system. Back to the pump, if it's got any grooves worn into the housing your wasting your time on a rebuild kit. If it is fine and the cover is flat, you can either sand the side with the grooves in it (basically surface the plate) and then do a rebuild kit or flip the cover over and also do a rebuild kit. But that is only if the housing doesn't have any wear grooves in it. Once they get to a certain point, you just have to bite the bullet and buy a new pump.
Old     (CenCalLakes)      Join Date: May 2014       07-14-2015, 4:49 PM Reply   
Sorry I guess heat exchanger is the wrong terminology, I am speaking about the exhaust manifold and risers with which I would consider a heat exchanger because that is what it does.
Old     (cadunkle)      Join Date: Jul 2009 Location: NJ       07-15-2015, 4:19 AM Reply   
Ah, misread that and thought you were talking about circulation pump. For the raw water pump check for scratches in the housing. Anything particularly deep and you'll need a new pump. Absolutely rebuild with new bearing and seal if the housing is in good condition. You can polish out minor scratches if you're worries but don't distort the housing out of round.
Old     (meathead65)      Join Date: Sep 2006       07-15-2015, 7:04 AM Reply   
I still think your core issue may be 26 year old manifolds and risers.
Old     (denverd1)      Join Date: May 2004 Location: Tyler       07-15-2015, 2:41 PM Reply   
I had to replace the original risers and exhaust manifolds on an 86 MC w 351W because PO didn't winterize them and they cracked. If they're not cracked, I can't imagine why on earth they would need to be replaced.

You could make the same argument that the heads would need to be replaced as well. Pretty thick cast steel we're talking about here
Old     (CenCalLakes)      Join Date: May 2014       07-15-2015, 6:14 PM Reply   
I pulled them off and first soaked them in vinegar then used ACF-50 stuff that I use on aircraft to clean corrosion. Got a lot of crap out of there haven't had a chance to run it yet but I think water will be flowing better.
Yeah those are a thick cast wasn't prepared for the weight and dropped the manifold right on my toe working barefoot wasn't a smart choice but I recently redid the floor and carpet so I don't allow shoes in the boat.
Old     (denverd1)      Join Date: May 2004 Location: Tyler       07-16-2015, 7:11 AM Reply   
ouch!! those babies are HEAVY too! Have fun getting them back on by yourself shoes recommended!!
Old     (meathead65)      Join Date: Sep 2006       07-16-2015, 8:01 AM Reply   
Manifolds and risers are "consumable" items. Rust and scale build up eventually restricts water flow enough that the engine no longer cools correctly. On salt water boats, we tend to replace them every 5-7 years depending on the owners flushing routine. Depending on how the cooling hoses are routed, the manifolds typically get a healthy percentage of the raw water flow. If they cannot evacuate that water as designed, two problems arise: the manifolds themselves overheat and transfer that heat to the heads, or the restricted water flow causes the cold water flow to the rest of the block and heads to "back up" and not move thru the cooling passages fast enough to carry heat out of the engine.
Old     (TTyler89)      Join Date: Jun 2015       07-16-2015, 7:20 PM Reply   
Yes manifolds and risers are consumables, but that issue doesn't just show up over night or a day out on the lake. You'll see temps continuously rise over the course of a summer which is an indicator. As old as that boat is, I'd start with a new thermostat and most likely a new raw water pump being that what's on there may be original and wore plumb out.


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