Where's my thermostat? And what is that knob?

[LordGothington]

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?

[Marian Claire]

Welcome to the forum.
My guess is that you do not have a T-stat at all. Not to worry. There are many set ups that will work. This post may help http://www.moyermarineforum.com/foru...ad.php?t=10248
The only way to tell is follow each line and let us know where it goes.
Can you give more info on all the lines running to/thru the muffler, and I assume you are referring to the red part in the second pic, and the valve assembly? Does the "uphill" black hose come directly from the manifold? Is there only one hose leaving the manifold? What exits the muffler and where does it go. I think I understand your set up from your first post but just want to clarify. Some folks have set up a system that allows them to divert some of the hot water coming from the manifold directly overboard and not send it all thru the muffler ect. I believe this is designed to reduce the exhaust system back pressure. You do not have to have full water flow to keep the muffler and exhaust hose happy.
Your system may be a modification of a modification.
Dan S/V Marian Claire
Edit: Another thought on the valve is that it could be a way to by-pass the muffler and wet/dry connection altogether. This would prevent water from backing up into the cylinders if she does not fire up quickly. Any history of water in the cylinders? Reason for rebuild?

[LordGothington]

I need to double check everything when I am back on my boat next week, but I believe this is how it works. Here is a picture I should have included before,

https://photos.app.goo.gl/VRaNcUXGusATyTUJ7

I believe the raw water enters the engine at the diverter. Unfortunately, we can not actually see that because it is hidden behind the alternator. But it *is* clear that I do *not* have a t-fitting with a bypass hose on that side.

On top of the manifold there is a t-fitting. On one side of the t-fitting is the sender. On the other side there is a right angle hose connector fitting. That hose runs from the manifold to the T-fitting above the red muffler. The output of that T-fitting then runs uninterrupted to the stern where it goes overboard. Only water exits that hole.

That is the only 'hose' that leaves the manifold. The manifold also has the insulation wrapped standpipe (?) that goes to the muffler. There is a large diameter hose that leaves the muffler and goes to the stern. That spits out a mixture of exhaust and water.

I believe the ball valve on top of the muffler is what controls the amount of outgoing raw water that gets mixed into the muffler to cool the exhaust. As you note -- too much water could cause issues like too much back pressure.

I do not know why the engine was rebuilt -- aside from the fact that it was at least 30 years old at the time.

I am thinking that I don't have a thermostat.

So my system would be most similar to the early model diagram in this thread,

http://www.moyermarineforum.com/forums/showthread.php?t=10248

Except with the thermostat and return line missing.

So -- I am curious how the early model works. Here is my guess,

When the engine is cool, the water is recirculated. This means the warm water leaving the manifold is mixed back into the input of the water pump. As a result the 'cooling water' is now not so cold and doesn't cool as much.

As that water gets warmer, the thermostat sends less warm water into the recirculation loop and so the water entering the cooling system is colder.

I've heard rumors of systems that had a ball valve instead of a thermostat. I am guessing that to add that to my system, I would need to restore the recirculation loop and add the ball valve in the recirculating portion?

The other question is -- how much does this matter? I've been running my engine for 8+ hours and it is still basically room temperature. It could be that my sender and gauge are working fine and the temp really is so low it is off the scale.

Is this going to cause issues long term? I typically boat it water that is 50-60°F, so it has quite a bit of cooling power. I think it leads to less efficient and incomplete combustion? Are there other side effects?

[Marian Claire]

"When the engine is cool, the water is recirculated. This means the warm water leaving the manifold is mixed back into the input of the water pump. As a result the 'cooling water' is now not so cold and doesn't cool as much.
As that water gets warmer, the thermostat sends less warm water into the recirculation loop and so the water entering the cooling system is colder."
Yes. That is my understanding of the early cooling system that has the after market Dole T-state added.

"I've heard rumors of systems that had a ball valve instead of a thermostat."
Not just rumors. That is how my boat, with 1965 A-4, is set up.

"I am guessing that to add that to my system, I would need to restore the recirculation loop and add the ball valve in the recirculating portion?" Yes. Just make sure you have descent access to the valve.

"The other question is -- how much does this matter?" That is a point of debate. I think most will agree that a engine running at "proper" temp is best.

I use my boat in all seasons, water temps, conditions and durations and have posted my thoughts on why this system works so well for me.

Dan S/V Marian Claire