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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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Old 06-26-2018, 01:27 AM   #11
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So the exhaust shutters melted?

Can you explain “water tube was not seated” , what tube?

How old is the exhaust? Risers have internal passages that inject the cooling water into the exhaust and these can become clogged with scale and block water flow. Use a hose on low and insert it to the hose going to the exhaust to see if water comes out the back.

Have you pulled the water hose going to the t-stat housing that comes from the raw water pump to see if water is flowing with the engine running for a minute?
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Old 06-26-2018, 01:44 PM   #12
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If you truly overheated the manifolds, risers, and elbows you would have smelled the paint burning and paint would be a flat black, rather than shiny.

I agree with Mike, the two most common cause of overheat is either a bad impeller or clogged passages on the exhaust manifolds and risers. Are these the traditional or dry joint exhaust?
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Old 06-26-2018, 10:56 PM   #13
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Thanks for the replies.
Shrew, the manifolds are flat black. The shine I was talking about was where the rubber exhaust tube meets the metal exhaust pipe.
This exhaust is a 2006 dry joint.
Mike, I think the exhaust shutters melted because I found crumbled black rubber in the bellows and sitting on top of the impeller housing when I removed the lower unit.
I will take your suggestion and run water through the hoses coming out of the thermostat and going to the risers and manifolds.
I'll also try pulling the raw water inlet hose going to the thermostat and see if there is water flow with the engine running. The serpentine belt is right there which will make this challenging.
Water tube. I'm referring to the tube connections that attach to the top of the impeller housing and carry water up and through the transom. The coupler connects to the top of the impeller housing, then the guide tube, then the black hose that runs up into upper unit.
I'm going to check the system as per your suggestions then start it up and check with IR thermometer. Can you tell me what temps I should be looking for on risers and manifolds? If manifolds got to 160 degrees F would that be time to shut down the engine?
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Old 06-27-2018, 01:31 AM   #14
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Exhaust temps I typically see range between 110F to 125F.

Disconnect the water hose to t-stat housing prior to starting the engine.

Ok the guide tube that aligns the upper water tube into the bushing on the top of the water pump housing.
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Old 06-30-2018, 07:57 PM   #15
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I've checked water flow through the risers and manifolds, and it seems normal. I've confirmed that the seawater impeller is pushing water to the thermostat. I did not measure gallons per minute, but did see flow. I also replaced the thermostat.
I started the motor today in my driveway. I used basic muffs, and had the garden hose full open after the engine started. During the run, the engine sucked in all the water the hose could give it and there as not much leaking out the side of the muffs. Exhaust water was exiting both transom exhaust ports normally.
Both risers and the starboard manifold stayed cool, around 115 or so. The port manifold temp rose steadily to 150 degrees then I shut down the engine.
The boat is level fore and aft, but has about a 12 degree list to starboard as it sits in my drive. The starboard trailer tire is 3-4 inches lower than the port tire.
Do you think the low side manifold would get more water in this situation? I know I need to do test on water, I just want to be sure I've tried everything before putting the boat in the water. Let me know if you can think of anything else I should be checking. thanks, Randy
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Old 06-30-2018, 10:01 PM   #16
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The water hose to t-stat housing should be gallons per minute. The steam of water should shoot out a few feet with the hose disconnected.
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Old 06-30-2018, 10:59 PM   #17
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Thanks Mike, my hose can't put out the volume of water needed for a good test. I'll put it in the water on tuesday. I appreciate your help.
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Old 07-10-2018, 11:01 PM   #18
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I mentioned earlier that my port manifold got warm when testing on the muffs. I put the boat in the water and got enough water to do a reliable test. I found a crack in the rubber lower exhaust tube on the port side. It was shooting water everywhere so I know I'm getting water on that side.
I took a look at my muffs to see how large the water flow opening was, it was less than a half inch diameter.
I"m going to replace the upper and lower exhaust hoses on both sides, as well as the exhaust shutters.
Has anyone bought exhaust hoses online? I found a set of exhaust hoses and shutters for $100, a great price but I wonder about the quality of the off-brand products. Good ratings on Amazon though. I just want to do this one time.
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Old 07-11-2018, 01:30 AM   #19
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I have only use OEM or major name brand parts.
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Old 07-11-2018, 11:15 PM   #20
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I agree and went with Sierra brand. I've used Sierra parts before and they were fine. Some other brand names I had to choose from were "no!no!" and "Youen". I got the upper and lower exhaust hoses for both sides, flappers, and exhaust manifold gaskets. I'll post my progress.
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