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 Post subject: W50 Overheating Mystery
PostPosted: 15 Jul 2012 11:23 
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Midshipman

Joined: 02 Jan 2011 15:51
Posts: 53
This string is an off-shoot from my "How did you know when to repower" one.

I have had an overheating issue with my W50 since I bought #225 2 years ago. Now that most of my initial punch list projects are complete, I have been spending more time on her more AWAY from the slip. Every time has resulted from a high engine temperature alarm. The alarm continues to sound on a re-start even after shutting the engine down until the thermometer reads well under 180. I replaced the temperature sender, but that did not change the situation. On top of that, my tachometer becomes increasingly inaccurate as the engine RPM's increase (verified with a strobe tach). So, I have three issues that may or may not be related, but I'd like to hear from anyone who has advice on any of the issues.

My mechanic checked the raw water cooling loop for any signs of blockage but didn't find any. He looked in the heat exchanger, the exhaust elbow, and several of the other 'usual suspect' places. He told me it looks like there is plenty of water going through at idle, but the water flow decreases as the engine RPM's increase. He's been working on Westerbekes for a couple of decades, and he has never seen anything like this before. We've changed the oil, all filters, all belts, an alternator, coolant, the impeller, transmission fluid, and the prop (thinking the old oversized one on the shaft at the time of purchase was too much for the engine). Even the factory guys are baffled by this one.

Are we missing something simple, or is the W50 going into its death roll?


 
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 Post subject: Re: W50 Overheating Mystery
PostPosted: 15 Jul 2012 13:36 
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Skipper

Joined: 27 Oct 2006 10:32
Posts: 827
I now this is an over-the-top stupid question, but did you change the thermostat? You can always take it out and run the engine to see if it is the culprit.


 
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 Post subject: Re: W50 Overheating Mystery
PostPosted: 15 Jul 2012 14:12 
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Skipper

Joined: 21 Jan 2010 12:57
Posts: 168
How about a worn cam in the raw water pump? I believe that it (the cam) is replaceable.


 
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 Post subject: Re: W50 Overheating Mystery
PostPosted: 15 Jul 2012 16:00 
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Rail Meat

Joined: 24 Jun 2007 20:30
Posts: 19
Check the little spigot that is about two inches to the right and a little above the heat sensor. I think it helps break an airlock when you drain your coolant. On mine it is closed when it is turned to the right, but that actually causes the little stem bolt to go "up" which seemed wrong to me. Anyway, I must have left it open once and then it started spurting small drips of coolant that would short out the heat sensor sending unit. I noticed some coolant in the pan, and finally figured out that it was causing the false alarms. It didn't take much to set it off.


 
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 Post subject: Re: W50 Overheating Mystery
PostPosted: 15 Jul 2012 19:53 
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Midshipman

Joined: 02 Jan 2011 15:51
Posts: 53
Thermostat? I am going to have to ask my mechanic...because neither of us have ever said that word. Like I said, I am hoping it is something so simple that we just didn't think of it...like a thermostat. Thanks!

I thought about the raw water cam, too. It is on the list along with the thermostat of things to check.

I know the coolant petcock valve you are talking about. I checked that, and it was fine.

I really appreciate all of the input!


 
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 Post subject: Re: W50 Overheating Mystery
PostPosted: 15 Jul 2012 20:25 
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Skipper

Joined: 21 Oct 2006 15:36
Posts: 268
Scott-

I have a W50 on my boat, which I've owned now for 8 years. Like yours, I had some cooling issues I had to solve. The good news is that today, it's OK. I had most of the typical things wrong( e.g., blockage cause by impeller tips, fouled HX tubes, plugged line at the mixing elbow, etc.). But I would like to share some of mother major issues that may have been overlooked.

1. HX End Cap: This absolutely, positively needs to be installed correctly. To do this you need to make sure the HX divider plate is installed between the two ridges inside the end cap. If it isn't, significant flow will bypass the tubes, and will significantly reduce the cooling. The PO of my boat hadn't installed it correctly, and I could not run my engine greater than 1600 RPM without overheating. I actually had to replace my endcap because the two ridges were damaged. Westerbeke has a Service Bulletin about this. Some people say they can install the cap with the HX on the engine in the boat. I can't. I have trouble doing it with the HX on the bench.

2. Overpitched Prop: You mentioned you tried this, but here's some data from my boat. After I virtually rebuilt my cooling system, my engine would overheat at about 2200 RPM, but the boat was clearly at hull speed and any additional rpm was overworking the engine. I had the originally installed 2 blade 16" x 14" prop. My prop was clearly overpitched. I had it repitched to 11". Now I can get the boat up to 2600-2700 RPM, before the engine starts to overheat slowly. Again, the boat is clearly at hull speed. I have chosen to live with this configuration. But to be able to get my engine to 3200 RPM (design max.), I probably would need a pitch of about 8". So, if you are only getting your overheating when you are trying to reach max RPM, this may be the only problem you have.

3. Thermostat: As Tortuga's Lie suggested, you may have a thermostat issue. You may know this, but the temp. switch, which sets off the alarm is above the thermostat. The temp. sender (device that controls the gage) is located below thermostat. This may be causing the lag time between the alarm and the gage.


Your mechanic mentioned that flow seemed to reduce as RPMs were increased from idle. I don't think he meant that it actually decreased. He probably meant that it didn't appear to increase proportionately (i.e., doubled flow with doubled rpm). This is probably normal. The raw water pump acts as a positive displacement pump at low rpms (flow increases linearly with rpm). But as it speeds up, it acts more like a centrifugal pump which will have its flow diminish from the proportional nature based on the system's resistance. My engine appears to have great flow at idle, but comparatively at full rpm, the flow appears wimpy and I don't overheat as explained above. As an aside, I have thought about increasing the pulley size on my raw water pump to increase its flow, but haven't done that yet and probably won't because my system now is very livable.

Regarding your tach, I need to check mine. I have a strobe and I calibrated my tach at 1000 RPM, but I didn't check it out at any other point. I'll do that next time I'm on my boat. Your situation may be normal.

Hope this helps.

Jim
#191

_________________
Jim Voelxen
Odyssey #191
Home Port: Osterville, MA


 
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 Post subject: Re: W50 Overheating Mystery
PostPosted: 16 Jul 2012 19:06 
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Midshipman

Joined: 02 Jan 2011 15:51
Posts: 53
Jim,
wouldn't you want a smaller pulley to increase flow? I am trying to wrap my brain around that one with a cycling gear analogy, but am still coming up with nothing more than a headache.

Has anyone upgraded their raw water pump to a 24102?


 
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 Post subject: Re: W50 Overheating Mystery
PostPosted: 16 Jul 2012 19:26 
Offline
Skipper

Joined: 21 Oct 2006 15:36
Posts: 268
Scott-

You're right. The pulley should be smaller.

Jim

_________________
Jim Voelxen
Odyssey #191
Home Port: Osterville, MA


 
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 Post subject: Re: W50 Overheating Mystery
PostPosted: 16 Jul 2012 20:30 
Offline
Midshipman

Joined: 02 Jan 2011 15:51
Posts: 53
I actually had to look at my bike. I wish I paid more attention in physics and mechanical engineering. I also wish I took a shop class in high school. While we're at it, there's that whole PowerBall...thing.

Either way, your post was very helpful. Thanks!


 
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 Post subject: Re: W50 Overheating Mystery
PostPosted: 16 Jul 2012 23:21 
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Skipper

Joined: 14 Jul 2012 20:36
Posts: 495
Location: Norfolk, Va
The cam plates do wear down on the seawater pumps and I've rebuilt them many times and even had Jabsco rebuilt one. It takes a major kit to do a proper rebuild +$250. It should be good as new, but a new pump is so sweet. There is a new pump on ebay for $449 w/free shipping.
http://www.ebay.com/itm/Jabsco-Pump-5320-0011-/140748506896#ht_500wt_1156

One thing to remember is to not to overload the belt, the seawater pump's belt never slips. The pump only requires about 1/8hp of power to operate, verse the alternator which requires almost 4hp at 100amps.

My experience, the big things to check in overheating:
1) The Seawater pump. Like some have said, it's a positive displacement pump, if it's turning it's pumping water with a good impeller and cam plate. Inspect pump's impeller and cam.

2) Blockage (heat exchanger, seawater flow to the pump) When troubleshooting, break things down. Start at the thru-hull fitting. Shut the hull valve and disconnect intake hose and open the hull valve. Verify flow, it should rise about a foot above the valve. Shut valve and reconnect intake. Go to the seawater pump remove the discharge hose and disconnect hose leaving the heat exchanger. Now connect a hose and shoot water thru the heat exchanger. How does it flow, should be a nice stream. If it seems restricted remove Heat exchanger and take to a radiator shop. Have them rod it, clean and test. Or do a white vinegar flush of the system, it works for me every time. DO NOT INJECT WATER INTO THE SEAWATER PUMP DISCHARGE HOSE WITH EVERYTHING ELSE CONNECTED YOU CAN FLOOD THE MOTOR.

On my T-37, I don't have a seawater strainer and I don't have the oil cooler (oil to seawater heat exchanger). Best thing I ever did was remove that. It was done under the advisement of Marcus at TransAtlantic Diesel.

If you think it's the thermostat, watch the temp gauge/ While running if it stops and hangs around 185-200F for a while then goes up, my bet it's ok.

_________________
Hull #208, Puff Card
Southern Chesapeake Bay


 
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