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Hi Bruce, my name is Jason.
Do you boat in saltwater or fresh? Are the exhaust risers running cooler or hotter than the engine?
The easiest and best way would be to use an IR temp gun and take the temperatures manually.
All engines overheat for the same 4 basic reasons.
1. Water is not getting in (Bad impeller)
2. Water is not circulating (bad circulation pump)
3. Water is getting airbound (typically bad head gasket)
4. Water is not getting out (clogged exhaust risers)
When the engine runs, the exhaust should always normally be cooler than the engine itself. If the exhaust is hotter, Out of those 4 items, the 2 that would cause hot exhaust is 1 and 4, either water is not getting in or water is not getting out, and not taking the heat with it. Since the impeller has been changed twice, what you would want to do next is pull both exhaust risers and see if the internal water jackets on both the riser and the exhaust manifold are clogged up with rust. Does that make sense to you?
I think that should do it. But I work for tips so I do want to make sure you are happy with my service before you go. If you had a further question on the issue by all means feel free to ask. If not, Just in case you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. To rate, you must select the star you wish and also confirm it. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, or if you can not see the ratings box which is at the top of the screen. Please reply back "I rate Jason's service _______" and fill in the blank.
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The belt doesn't effect the seawater pump. And if it's not squeeking or slipping, then it would not effect the circulation pump either. If it is slipping or squeeking, or if just showing signs of cracks you would want to replace it as just maintenance, but this would not effect your cooling.
On the thermostat.... Part of the reason I asked you if the exhaust was running cooler than the engine or not is because the exhaust manifolds get what they call bypass water. Bypass water is water that goes from the seawater pump to the manifolds, and it does not go through the thermostat first. If your engine was running hot, and the manifolds cool, then the thermostat would definitely cause that. But because they are both hot, the thermostat would not effect that. At the same time, if the thermostat housing is simply clogged up that would cause a lack of flow to the manifolds. So it definitely would not hurt to pull it apart and see if it's clogged up in there or not. If it is, clean and retest (and install a new thermostat). But if it's not, you are back to pulling the exhaust risers and inspecting them.
Was there anything else?
Hi Bruce, just checking in. Have you made any progress?