I have a 2006 Larson 208LXI with a 5.0 MPI Mercruiser (seven blue drain plugs) and Alpha 1 drive. On each of the first spring trips after w
I have a 2006 Larson 208LXI with a 5.0 MPI Mercruiser (seven blue drain plugs) and Alpha 1 drive. On each of the first spring trips after winterization I notice that the port exhaust manifold is cold while the starboard exhaust manifold is at normal temperature. The temperature gauge reads 165 (normal for this boat) at this time and no water leaks around engine. After I shut down the engine for several minutes, restart the temperature on the port exhaust manifold heats up normally and boat operates fine. Just concerned?
I ran your question by Steve Schroeder, Mercruiser's engineering guru. While there may be a small difference in temperature between each manifold, they should each be cool enough to touch by hand. A difference of 15-degrees or more is cause for concern.
In your case, its recommended to first check the poppet valves on the thermostat housings. These little nylon balls can jam, or partially jam, and if they do, water will follow the path of least resistance and cool one side more than the other. If the poppets are jammed, replace them.
If the poppet valves check out, the next thing to do is remove the elbows and inspect the inside to see if they are clogged with scale. If so, you may be able to use a coat hanger and scrape out the blockage, or your may need to replace the elbow. You wont know until you pull them and have a look.
In any case, your concerns are justified, and it is this type of "thinking ahead" on your part, knowing your boat, and recognizing something slightly out of the norm, that helps avoid a big repair bill and a catastrophic failure. Good on you!