Re: Are Sierra thermostats OK?

[DAN ANDERSON]

FrankR & pugentsoundboater. That is the way the water flows as I understand it on the 6hp. I just finished talking with Pappy & we spent some time looking in the service manuel to refresh our memory. We are pretty sure the water comes up on the starboard side of the powerhead thru the round tube up the side of the block. It then passes over the top of the block to the exhaust manifold. Water travels down the slot in the inner exhaust plate to enter the bottom of the cylinder head/cylinder jugs. After warming up the pellet in the thermostat to 145 (optimum) the thermostat opens and dumps the water down the center of the cylinder head out the midsection. The old (brass thermostats) had a cut vee in the top hat. You can see this by looking at a 18-3553 Sierra thermostat on ME. The newer BRP SS stat does not have a vent! We remember a small vent in the block, but could not see it in the manuel. If you were going to modify anything the smaller the hole the better. Any short circuit of the system can cause the motor to run cold thus defeating the whole reason for a thermostat. It has been a long time since I have studied the cooling system on this motor, but I have put many new style stats in them recently. No problems. Remember you just need to bleed the air in the system off not water.

Dan in TN