Re: Are Sierra thermostats OK?

[Casey Lynn]

Nope…not bass ackwards. He was 90% correct. Directly from the flow diagram in the service manuals.
The water enters the block on the forward side of the exhaust and flows up and through the exhaust passages. There is also a small passage that places some water on the top of the thermostat which would then flow down the back of the cylinder head independent of the thermostat. Forget that part for now although this would be why I could not see the relief in the casting I was looking for in lieu of the hole in the thermostat. This small passage would serve the same purpose as a hole in the thermostat. Okay….back on to the path of water flow.
The water, once it has flowed through the exhaust enters the cylinder jackets from the bottom and flows upward, around, and to the bottom of the thermostat. Once the thermostat opens the water then flows through it and then down the back side of the cylinder head through its passages and exits the block.
This particular engine is one of the few OMC engines ever designed to run totally on the thermostat for temperature control. This makes it even more important to have it installed and in place. I was off by 10F on the temp last night. This particular thermo is fully open by 145f. For this reason I would not substitute……….
As the thermostat opens and flows water down the back side of the cylinder head more high flow raw water from the pump is utilized to keep the block full and pulling heat away.
On a fully thermostatically controlled engine the recommendation for a washer with "The right sized hole" could very well spell disaster at high RPM and load.
I have emphasized in the past that if you are not very sure that what you are writing is fact….just don’t write it.
There are folks in here that are new and just learning and we would like them to learn correct service procedures and tips vs. theory and wives tales. Just my .02 but I will darn sure stick by it.