View Full Version : question when draining block and replacing thermostat how to prevent air lock?

10-30-2011, 10:05 PM
quick question guys when i drained my engine block and also replaced the t-stat and after you fire it up and hook the garden hose up to it how do you avoid the engine from getting an airlock in it .has anybody put a small hole in the t-stat to prevent this or does it not happen on a boat .i would think once you drain the block the engine would get an air lock in it .

this is for a 1988 351 ford indmar engine. just curious i am new to all this stuff i just purchased the boat last month . i don't see how the air can escape the system .water can come in the impeller pump and go through the water pump .but it will get stuck jammed up at the t-stat .and how will the t-stat open if the water can't get to it because of the air bubble. and all this i am thinking is because you can drain the block, giant air bubble in the motor now .

just curous. any info would be great .

10-31-2011, 12:45 PM
You don't need to worry about it because it's not a sealed system. The force and volume of the water past the thermostat will ensure any trapped air is forced out. You can see this for yourself by running it and then removing the thermostat cover - there will be water in there again.

Think about it this way - did you have to do anything special to get water in there in the first place? When it was new, or when you drained it last year? Is there a procedure in the book for 'first time starting' regarding purging air from the cooling system? There isn't, so don't worry about it.

10-31-2011, 01:24 PM
Agreed, you do not need to worry about it.

10-31-2011, 02:23 PM
Yup - I agree...the water pressure forces the water up from the scupper... in an open system the exhaust is like the vent on your home....it takes work to drain and prep the system...but no work at all to refill it in the spring...I like these systems....

10-31-2011, 06:08 PM
thanks for the reply's everyone no worries then