Evinrude 18hp temp

[bluehaze]

I’m working on a 1964 Evinrude 18hp, model 18402.
New impeller, new thermostat.

At idle it seems to be running rather warm. With a non contact thermometer, it reads around 160 to 167 degrees. Checked on the starboard side, on the side of the cylinders and top.
My other thermostat motors usually read in the 140’s.
What do others with this type of 18hp get for idle temps?

Also, when watching the spray out of the mid section relief at idle, I can watch it go back and fourth from a light spray, to a heavy flow as the stat opens and closes. It goes repeatedly from open to closed, and steaming hot water comes out when opened. Again, this is at idle, in a barrel, plenty deep in the water. Haven’t tested it on a boat yet.
Wrong temp thermostat perhaps?
Is this cycling normal for this motor?

One other question. The stat is in the grommet groove, but which way does the thermostat rubber grommet face? Does the extended part of the grommet face up or down? It will fit both ways. I think I remember putting it on facing down.

[fisherman6]

My 1959 Evinrude Fastwin 18 runs at between 162 and 168 in the barrel at high idle. It runs a little cooler at WOT on the boat. Seems to run 158-164 after a blast around the lake. Also measured with an infrared non contact thermometer. I think your temp is OK and it sounds like your thermostat is functioning as it should.

I though that was pretty warm when I first got my engine running as well but it does not overheat and it is a great runner. It will run fast or slow for as long as you want it to without issue. I trolled the whole lake for hours and then made a couple hot laps around the 860 acre puddle and the old girl never missed a beat.
-Ben

OldJohnnyRude on YouTube

[dan-in-tn]

You would normally shoot the thermostat pocket for consistent temp readings. That is assuming the motor has a thermostat. You will get the temp the thermostat opens at most closely that way. Shooting other places can lead you to errors as to powerhead temps. I believe the old OMC #378065 stat was 135 degrees, but the new stat it SS to is 143. Not that big of difference. Sierra still makes the brass stat (with slot in the top hat #18-3553, but shows it to be 143). The seal #310058 that fits around the head of the stat fits with the skirt down. Sierra & Mercury also make this same seal. Check ME for part numbers. Hope that helps.

Dan in TN

[fisherman6]

I’ll have to test mine again, but I know at the top of the head near the thermostat pocket mine was running at about 152 degrees F in the barrel.
-Ben

OldJohnnyRude on YouTube

[bluehaze]

I did check the temp on top, and it was in the 160’s. I don’t remember what it was on the thermostat itself though.
I just find it odd that it runs 15-20 hotter than every one of my other thermostat motors…..and I have a "few" !

Now I’m having ignition problems too, so further investigation on the temperature may have to wait. Cylinders cutting out, on and off. 👿

Thanks for the replies.

[david-bartlett]

Is this a new motor for you, or one you have had for a while? I will assume the old impeller was intact when you took it out. What is the condition of the intake screen behind the prop? They can plug up and you will not notice it unless you really look. Sometimes they get painted and partially plugged.

Just something else to check.

[bluehaze]

Yes, it’s a new motor to me. The old impeller was intact, but took a set, so it was replaced. Overall the motor is in nice shape. Pumps water like a fire hose when the stat opens, with lots of steam, and stays warm.

I may eventually pop off the head and take a look inside.

[fisherman6]

One other thing to check is behind the water bypass cover plate on the side. The place where the water comes in at low speed. I doubt this is related to your current temperature concerns but check it to be safe. I overheated my ’54 SuperFastwin due to the area behind that plate being clogged. It would pump lots of water standing still but starve for water when the boat was moving. I ALWAYS check behind there on new to me motors now.
-Ben

OldJohnnyRude on YouTube

[johnyrude200]

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.

[fleetwin]

What year is this engine? Many of the low tension ignition engines that had a funky idle/plug fouling problem were modified a bit to get the temperature up….If you pull off the thermostat cover, you will see a black rubber plug actually blocking the bypass water passage on top of the head….This modification will result in the higher temps you are seeing and the funky water spray….
To me, I would only use the modification on an engine that is idled/trolled extensively in a colder climate. Definitely wouldn’t do this on a Florida motor. So, you might want to remove the rubber plug if it is there to be on the safe side….
If there is no rubber plug present, I would go through the cooling system as Johnny advises, starting with the water pump….

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