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Old 10-28-2018, 04:36 PM
LordGothington LordGothington is offline
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Where's my thermostat? And what is that knob?

I have a 1965 Tartan 27 Yawl with an Atomic 4 that was rebuilt a decade ago. The rebuilt engine appears to be mostly early model, but has the oil fill tube on the front typically only found on a late model engine.

My water temperature gauge always reads minimum and the engine always feels pretty cool to the touch - even after 8 hours of use. There are three things that could be going on:

1. bad gauge. I removed the wire from the sender and when I touch it to the ground, the needle jumps to max temp. So I think the gauge is fine.

2. bad sender. I have not tested this yet.

3. bad thermostat causes the engine to always receive maximum cooling. I am in the Illinois River at the moment, so the water is pretty cool. Before that I was in Lake Michigan.

Because the engine does always feel cool to the touch, I am tempted to believe it could be #3. But looking at my engine -- I am not even sure where the thermostat is. You can see photos here:

https://photos.app.goo.gl/RmGAgJLqmnRorGEv8

In the late models, the thermostat would be in a dome at the front of the engine. In early models, it would be attached to a t-joint at the rear of the engine where the sender is.

But I seem to have neither of those things going on.

But there is a T-valve on top of the muffler. And, my boat seems to have two hoses that run to the stern. One is the normal hose that carries exhaust and water from the muffler. The other one is smaller and is hooked to the output of the t-valve on top of the muffler.

So I am thinking maybe the thermostat is in there, and instead of recirculating the water, it just spits it out the back?

But, what is that knob for between the t-valve and the muffler?

There is a third option. I have heard rumors of some atomic 4 setups that had no thermostat at all -- just a manual valve. Maybe that is what I have going on?

I guess the next step is to test the sender?
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