Home › Forum › Ask A Member › Evinrude 18hp temp › Re: Evinrude 18hp temp
To add to what everyone else has mentioned, the obvious thing you probably have already done is make sure you have the right heat range plugs (J4/J6). I’ve seen a lot of motors come in with J8’s (I surmise for extended trolling, but not for WOT applications), which I usually switch to the lower heat range ones.
If you’ve already checked through everyone’s suggestions, I would pull the cylinder head to check for a clog as you mentioned, especially if it was a salt motor. But even fresh water ones can get clogged up if used in shallows/sandy water a lot. The clogs are usually in the cylinder head, occluding water flow. Hopefully all 10 of those screws come out easily for you! There should be a large amount of water spitting out of the exhaust housing (not the behind prop – no way to see that!). If it’s a small amount of ‘spit,’ well then you know there is some sort of clog. Even at idle in neutral or forward in a barrel, there should be a good amount of water. Also on the topic of in a test tank/barrel, the water level has to be very high as an air pocket can form from the under water exhaust, which will give you false positives and inconsistent evaluations.
The only other odd ball thing I can think of is make sure the little orifice holes in the impeller housing isn’t clogged. There is one next to the driveshaft orifice, and another under the rubber grommet which the water tube inserts into (have to remove the grommet to see it). There isn’t any mention of either of these in the service manuals but they are both very important.