Overheating indicator for Ski Twin 33

[wetwillie]

My boat came with an old Engine Overheat indicator mounted in the dash. I have no idea what make or model motor the indicator is for. Its just a metal plate with a red light but I like the way it looks and thought it’d be great if it were functional.
However, I’m now running a ’66 Evinrude 33 hp Ski Twin.

So my question is, is there a way to connect a sensor of some type to my Ski Twin that would turn on the indicator lamp if the motor overheated?
Thanks,
Willie

[Mumbles]

Here’s something which was on the market years ago. I believe it had a sending unit which fastened to the motor under a head bolt. Check with aviation stores as aircraft engines use a similar system to monitor engine heat.

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[vintin]

I’m not sure what temperature you need but a switch like one of these under a head bolt would turn on a light. Guessing 160°F is a guess. A single wire shorting to ground at the switch to complete the circut should work.

https://www.google.com/#tbm=shop&q=12+v … p+switches

[fisherman6]

Not sure what the temp should be for that switch either. I’m guessing it may be a little higher than 160 F. Maybe closer to 180 – 185 F. Still cool enough that it shouldn’t damage anything at that temp. My ’59 Fastwin runs at about 170 – 175 F at the cylinder head according to my infrared thermometer. That engine has a thermostat. I believe the Ski Twin 33 does as well. It does seem to run a little cooler than that WOT on the boat. I have no idea what temp the built in overheat alarms are supposed to go off.
-Ben

OldJohnnyRude on YouTube

[wetwillie]

Great ideas. The indicator that I have consists solely of a painted red light bulb and a pigtail lead. I like the ideas presented here and appreciate every one of them. I’ll do some searching and see what I can find that is small enough to mount properly.
Thanks.

[wedgie]

Here’s one mounted on a Gale 35 hp. I believe it is a Mercury product, but not certain of that.

[frankr]

That looks like the one that came with the OMC Temperature Gauge Kit. We used to sell quite a few of those kits back in the day. Whenever possible, I tried to mount the sender under a head bolt on the exhaust side where it is the hottest. Not much point in monitoring the temp on the cool side. On some motors, you could screw it right into the cylinder block water jacket.

http://www.marineengine.com/parts/johns … &sid=36287

[frankr]

While you are looking, be aware that there are two kinds of senders. The one for a light or horn is an on-off switch, but one for a temp gauge is a thermistor whose resistance varies according to temperature.

[wetwillie]

I understand the application for the two types of senders and don’t recall seeing a plug that can be removed to thread a sender in on my 33 but will take a closer look. I can also see the importance of monitoring the temp downstream. Personally, I’ve always felt that an on/off type indicator wouldn’t give you much notice before its too late. On the other hand, I doubt the average boater monitors a temp gauge very often either. In my case, its like keeping an eye on my water pressure gauge. I like having it but look at it only from time to time. I doubt I’ll be lucky enough to catch it before the damage from overheating has happened. But, I’m sure that’s just me. 😉

[frankr]

I agree 100%. It only takes a few seconds to cook an engine if in case of total and sudden pump failure. I’d be much more likely to be checking the bikini in the passing boat than looking at some stupid idiot light.

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