Thermostat

[Chad.Lawie]

Ok. so stupid question here.
The manual says the thermostat should be fully open at 175 degrees.... well how do I know? what is fully open? right now at 185 degrees my thermostat opens about 1/4 of an inch.

My engine heats up to about 185 when it is just idling. It's getting water. So i'm guessing that means i'm going to be doing an acid flush, unless you fine people tell me that my thermostat is barely open.

Thanks for the help!
Chad

[Kurt]

Assuming that you checked the thermostat by putting it in a pot of water while heating it up and monitoring the temp with a thermometer while observing the thermostat action? If so, opening about 1/4 of an inch sounds about right in terms of fully open to me. From my understanding, thermostats are pretty resiliant and, provided they are clean, either work or don't. If your thermostat is opening, then it is likely working correctly. Just make sure it is fully clean. Sounds like it is time for that acid flush - pressure flushing is helpful too if you haven't done that in a while.

[Chad.Lawie]

I put the thermostat in a pot of water. It was a little red from minor rusting. but it looked to be in good shape. so yeah. time for the acid I guess. based on the way the hoses are setup, and the way my thermostat housing looked,
I don't think the engine has ever had an acid flush or a pressure flush.

Thanks for your response.
Chad

[Don Moyer]

A normal thermostat will move approximately 3/8" between fully closed and fully open.

Don

[Chad.Lawie]

I flushed with vinegar twice. I'm not sure if it helped.
My temperature gauge has gone bad, while i'm waiting for the new one I've been putting a thermometer on the exhaust pipe to try to get an idea for how hot the engine is running. The exhaust pipe reads around 200 degrees. The top of the engine is much cooler. Just warm to the touch.

How hot should I expect the exhaust pipe to be?

What is the purpose of the thermostat in the engine? If the idea is to keep the engine cool, why not just always have the water flow through the engine as it would with the thermostat all the way open?

Thanks,
chad

[Don Moyer]

Chad,

It's difficult to relate exhaust pipe temperature to engine temperature, but the fact that the top of the engine is warm to the touch is good indication that it's operating a bit too cool (less than 130 degrees).

The purpose of a 140 degree thermostat in a late model engine is to keep the temperature in the range of 160 to 170 degrees, where it will operate very efficiently. Early model engines with Dole 140 degree thermostat systems tend to regulate a bit closer to 160 degrees.

Don

[Dana Paterson]

Don,

You wrote that “A normal thermostat will move approximately 3/8" between fully closed and fully open.”

I have purchased the new thermostat housing with the shoulder nuts, gaskets and what I assume is a Volvo-type thermostat. I like to see how things work, so I but the thermostat in water and used a calibrated digital thermometer to measure the opening, fully open, and closing temps. The thermostat works well opening at 140 degrees, fully open at 163 degrees, and closing fully at 140 during cooling.

An unexpected observation was that the thermostat opens quite a bit farther than 3/8”. In fact, it opens about 3mm farther than the clearance that the housing provides below the water pump inlet.

This means that when the engine heats up to a bit less than 163 degrees; the thermostat will like a gate valve and positively close off the water pump inlet. This will literally force every bit of the water pump outlet through the engine.

I think that’s good engineering but; (and this is my question) does it hurt the thermostat to be compressed in this way?

I noticed that the underside of the water pump inlet has been machined. So, I’m guessing that you’ve already taken all of this into account. Let me know if I’m just being a curious cat or if this bit of engineering needs to be told to those who might consider drilling their own thermostat housing without machining the WP inlet too. Thanks.

[Don Moyer]

Dana,

The 3/8" specification to which you are referring was written when the primary thermostats in use in the Atomic 4 fleet were the ones with 3 small coil springs around the outside of the operating mechanism (which were made by Holly). The operating mechanisms of the thermostats made by Westerbeke and the ones that we use in our aftermarket kits do move a bit further than 3/8". There are separate small springs built into the mechanism of these thermostats which compress as the valve presses against the bypass inlet in the bottom of the thermostat housing.

Don