No thermostat OK? 15HP 1976 Evinrude

Hello

I finally get the kicker going and we recall HEY! The thermostat was removed long ago (in a galaxy far away) so is this kosher? Or are we in for an afternoon of wrenching?

OMC would not have gone to all the trouble to design one in there if it wasn't useful. You can run it for a few days like that but the benefit of having a T-stat is that it keeps your motor running at an optimal temperature, a temperature which dictates the spark plugs you are using etc. If you run your motor without a t-stat, it will run colder and that will carbon up your piston rings and eventually foul your spark plugs over time. One of the design flaws of spark plugs is that they foul only when you are farthest away from your dock.

Anyway, short term, your motor will run fine without one, longer term, you should put one in there.

the motor gets warm in less than 2 minutes. And I was told that many thermos don't work anyway in vintage salt motors. I was hoping we could just fish and clean the plugs when necessary rather than mess with the head.

I've worked on a ton of the 74-92 vintage of those motors.

The politically correct answer is thermostat - always.

The reality is those early versions had less than ideal cooling designs - and the 15's were high strung.

If you're in salt, cooling passages can become narrowed - making things worse.

We always tried to get them to run on thermostats, but sometimes they ran too hot for our liking , but not worth dumping a boat load of money for a $500 outboard.

Why was the thermostat removed to begin with? Was it tested after removal and found to be working properly?

Waterpump needs to be in good shape( there's no telltale), including the center seal.

No urgency here, it won't blow up yesterday.

Only the thermo cover (not head) needs to be removed, but the earlier covers(74-76) use a different gasket from the later units.

Well I really think it is a 76 (Red White and Blue) but naturally I will check. The guy originally removed it cause he thought it was restricting the water flow. It just needed to have a new impeller. There is a full pee stream currently.

I heard it was a real PITA to change them. If its not too bad, I'm up for it. Otherwise, some of the other guys around here have had them out for years to simply prevent restriction I guess. I know its not good to listen to everyone though.

If this is a "kicker", you will get a much better idle if you run a thermostat - or troll in water that's about 110 degrees

If you've got a pee hole it's 77 or later - that's a better vintage from a cooling perspective.

Shoot me your model # and I can tell you the year.

"Galamb" is right on the money. Much easier to reliably dial in the idle speed/mixture when a consistent temp... I presumed yours was functioning acceptably.

77 and later have cdi ignition(no points), so the plugs don't tend to load up.

TCW-III doesn't tend to coke up pistons. If you run a little "Engine tuner" through the carbs once a season, that will work.

As you can see I'm not jumping on the band-wagon to torture you into tackling the job. It all depends on your expectations. Those are VERY tough motors to kill.

Since the thermo cover has been off before, the risk of breaking a bolt(a big concern) is minimal.

7/16" wrench. Pull the latch bolt (7/16") and a good scraper is needed. Get the correct gasket, thermostat, and thermo rubber gasket. 1st time 2hrs..

It would help to have a thermo stick or infrared heat detector to ensure it's not overheating at WOT.

Hope this helps.

(Thermostat Purpose)
(J. Reeves)
Many engines are considered high performance engines and demand a thermostat(s), and many smaller hp engines also require a thermostat for the following reason. The pistons actually distort/twist off round when running. The thermostat is required to keep the outer wall surrounding the steel cylinder, and the cylinder wall itself at a temperture to compensate for the distortion.
With the thermostat removed, the difference in temperture between the inside the cylinder and the water jacket quickly reaches a point whereas (in effect) you have a oblong piston running up and down a round cylinder, or vice versa. Bottom line is without the thermostat, the piston and cylinder wall could be damaged in a short period of time.

The thermostat in your car isn't there simply to have the heater function properly..... think about it.