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Old 06-05-2018, 11:09 PM   #1
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Default Thermostat Install

I'm installing a new thermostat this weekend. I'm using Sierra 18-3647. It comes with more gaskets than I need, and I want to ensure I'm using the right gaskets. From manual and IPB, it looks like I just need the gasket, o ring, and thermostat on the right side of the picture, and the gaskets on the left side are extra. Let me know if I got that right. thanks, Randy
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Old 06-06-2018, 12:45 AM   #2
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Not sure if you need the o-ring but I agree that’s the gasket. See if there is one when you take it apart.
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Old 06-06-2018, 05:27 AM   #3
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You need only the termostat and the gasket, no O ring.
Be careful when you remove the thermostat from the housing. Is a plastic tube what hold the thermostat in place. Take your time and don't break it.
Good luck
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Old 06-06-2018, 10:48 AM   #4
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You are correct, no 0-ring. I got to stop watching youtube.
I had overheat last weekend, hopefully this will fix it. Impeller was replaced at the end of last season.
thanks
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Old 06-06-2018, 03:56 PM   #5
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Quote:
Originally Posted by jrsick View Post
You are correct, no 0-ring. I got to stop watching youtube.
I had overheat last weekend, hopefully this will fix it. Impeller was replaced at the end of last season.
thanks
How hot was?
Can be your exhaust manifold to....hard to say from here.
Check, when the engine is hot, if the two manifolds are even hot.
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Old 06-06-2018, 06:21 PM   #6
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Quote:
Originally Posted by jrsick View Post
You are correct, no 0-ring. I got to stop watching youtube.
I had overheat last weekend, hopefully this will fix it. Impeller was replaced at the end of last season.
thanks
I seldom hear that the t-stat was actually bad. Was the old impeller missing any vanes? Use an IR temp sensor to search for the hottest spot as this is most likely where the issue is.
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Old 06-06-2018, 06:36 PM   #7
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Great info, I appreciate it.
My son was driving the boat so I don't know how hot it got. I'm assuming the worst. I replaced the oil. The old oil didn't seem burned and was relatively clean.
I replaced the impeller at the end of last season, and am making initial assumption that impeller is good. But since I replaced it, there's always possibility of install error.
I smelled rubber when we got the boat back. I can see on starboard manifold that the upper rubber exhaust tube shows signs of overheat where it contacts the exhaust riser - a little shiny. No bubbling or distortion though.
At end of last season I replaced the port manifold gasket. I removed the port manifold and riser and they both looked near new.
What could be the problem with the starboard manifold or riser? possibly clogged?
IR temp sensor is good suggestion. I don't have one yet but will get one for when I start engine after replacing thermostat.
Keep the troubleshooting tips coming, thank you.
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Old 06-06-2018, 11:50 PM   #8
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The burnt exhaust hose is a sign of reduced to no water flow. The water gets mixed into the exhaust stream at the end of the elbow/riser to cool the exhaust gases. Without water the hot exhaust temps will burn the rubber.
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Old 06-07-2018, 12:51 PM   #9
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Your comments have me thinking that new thermostat will not fix my overheat.
I'm going to remove and clear the hoses going from the thermostat housing to the manifolds.
Some questions:
- Manifold and riser should not overheat regardless of condition of thermostat, correct?
- Would it be safe to use a garden hose to flush water through the manifolds and risers? I would disconnect the cooling hose at the thermostat housing and flush manifolds using a hose. I think this would replicate normal operation but don't want to do anything dumb.
- Would it be safe to backflush the seawater pickup line? I would disconnect the seawater inlet hose at the thermostat housing and use a garden hose to send water through the hose and out the impeller housing. See above comment on dumb.
- Where does the temp gauge measure engine temp? I'm sure I have a water flow problem with at least one manifold/riser, but not sure if there is also flow problem in engine block.
- Have you ever heard of an impeller failing in its first underway after replacement? I guess I got to take a look at the impeller, but I replaced it at end of last season. Hopefully I will turn up problem in other checks.

thanks for the excellent advice and comments. This is first overheat for me so I am learning the cooling system.
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Old 06-25-2018, 10:31 PM   #10
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Update on overheat.
I removed the lower unit (and what was left of my exhaust shutters) and impeller was good. I checked the hoses going to the manifolds and risers, and all were clear. No obstruction in the seawater intake where it enters the thermostat housing. I also noticed there was no water in any of the hoses.
Now that I see how the cooling water flows, I think my problem was that the water tube was not seated properly. Can you think of anything else that would cause the manifolds and risers to overheat? Any other troubleshooting I should do?
I've got my IR Thermostat gun ready.
I'll start it tomorrow and let you know what happens.
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