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  #1   IP: 73.163.125.21
Old 09-02-2015, 09:54 PM
macgyro macgyro is offline
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Cooling system troubleshooting

Hi everyone, I know this has been discussed before, but I need some advice.

My engine went from operating at a normal 160-180 degrees depending on if the thermostat was open or closed, then somewhere in between trips it started going above 200! I think I saw 210 at one point before I pulled it back and got the bypass hose clamped off which only lowered the temp slightly to around 190.

I've installed the bypass shutoff valve, which kept the temperature around 190, but I was still getting some steam mixed in with the exhaust water.

I pulled out the thermostat and motored around today at 150 degrees. The water out the back was still hotter than I think it should be, especially with the bypass open or closed (doesn't affect the temp now) and the thermostat removed. Still plenty of water out the back.

My next step is to remove the exhaust and either replace or keep it depending on condition.

I think my engine is a 2006 Moyer rebuild. Not sure of the water pump brand.

Any advice?
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  #2   IP: 107.0.6.242
Old 09-02-2015, 10:32 PM
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hanleyclifford hanleyclifford is offline
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Question

Is your engine FWC or RWC?
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  #3   IP: 67.232.91.39
Old 09-03-2015, 08:15 AM
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Marian Claire Marian Claire is offline
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Any history of cooling system maintenance? Acid/vinegar flush, pump rebuild/replaced, etc.
Dan S/V Marian Claire
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  #4   IP: 73.163.125.21
Old 09-03-2015, 08:44 AM
macgyro macgyro is offline
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maintenance

It's a RWC in what is mostly fresh water/slightly brackish.

Did a vinegar flush last fall before winterizing the engine. No acid flushes that I know of.

The impeller may be original. I think I'll check that today before dismantling the exhaust.
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  #5   IP: 107.0.6.150
Old 09-03-2015, 09:51 AM
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hanleyclifford hanleyclifford is offline
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Check the output fitting on the manifold.
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  #6   IP: 161.213.49.150
Old 09-03-2015, 11:26 AM
JOHN COOKSON JOHN COOKSON is offline
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Quote:
Originally Posted by macgyro View Post
I pulled out the thermostat and motored around today at 150 degrees. The water out the back was still hotter than I think it should be, especially with the bypass open or closed (doesn't affect the temp now) and the thermostat removed. Still plenty of water out the back.
Did you check the theromstat in a pan of progressively hotter water to see if it is opening correctly? What you have reported is consistent with a thermostat that is stuck in the closed position.

One way to check water flow through a RWC engine is to run a hose from the manifold water outlet to the cockpit or bilge, start the engine and rev it up. You should see a lot of water - like a garden hose. Anything less indicates a blockage somewhere.

As far as hot water out the back of the boat, IMO that's a good thing. It means heat is being removed from the engine and going out the back of the boat. This assumes good water flow through the engine (not the bypass) of course.

You might try an acid flush to see if you can open the cooling passages a bit more.

TRUE GRIT
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  #7   IP: 32.211.28.40
Old 09-03-2015, 10:09 PM
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Al Schober Al Schober is offline
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mac,
I'm going to say that running at 150F with no thermostat is too hot. I'm going to agree with hanley and recommend you check the flow through the manifold. Probably the outlet elbow. With no t'stat and the bypass closed, you should barely see the gauge move off cold peg.
Oh yeah - do you trust your temp gauge? I compared my temp gauge to an infrared thermometer and finally realized the sender at the front of the head was probably reading head temperature rather than water temperature. I moved my sender to a tee fitting that I added at the outlet of the manifold.
Doubt if it's anything in the block. Block is a recent rebuild and should have been cleaned out at that time. Those passages by the valves are known trouble spots, but should have been opened up during the rebuild.
One good trick is to try blowing through the various pieces of the system. Disconnect them from the system, attach a hose to one end, and just blow by mouth through the piece in question. If your cheeks puff out, you've found the problem.
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  #8   IP: 73.163.125.21
Old 09-04-2015, 09:39 AM
macgyro macgyro is offline
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sounds like good advice

I did check the impeller and it looked okay. One of the fasteners was loose, but after tightening it, it did not resolve the problem.

I pulled the thermostat out while the engine was warm and it was open, but It was only open a little. I'm not sure how far it's supposed to pop up, but with it removed, I agree that there may be some type of blockage.

My next step will be to use Hanley, John and Al's ideas to check for blockages in the system.

On a side note, I now know that the exhaust wasn't the problem. When I tried to get the exhaust hose off the pipe, the pipe broke in half. So I now have new exhaust pipe and new hoses. There was a lot of exterior rust, but nothing blocking the flow of water or gases.

It will probably be a couple weeks before I can get back to troubleshooting. Thanks for your advice and sharing of knowledge.

-Dean
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