What?s with these Volvo thermostats and housings?

[further]

Noticed today that my temp was reading low after being fine all season long. Usually run between 150-170 and today was no different until about an hour in, temp wouldn?t go above 120. This happened to me two summers ago and I removed the tstat housing, replaced the tstat and cleaned out all the passages and still couldn?t get it to warm up right so replaced the housing with an oem and that worked until today. Used an infrared thermometer and temp at tstat is close to gauge at 125, manifold was 165-170. Freshwater only boat so don?t understand why this keeps happening. Any thoughts? Guess I should remove housing and clean it out again? Tstat could be stuck?

 

[Scott Danforth]

most likely its a hunk of rust that flaked off and is holding the t-stat open.

 

[further]

Ok to remove and reinstall without new gaskets? Or should I replace gaskets again? Don?t remember what I did last time.

 

[Lou C]

Most likely as Scott said. I had this happen many times. Its because the cast iron engine in your boat was designed by GM, to run antifreeze in it with a pressurized cooling system. The companies who modify these GM engines for marine use in their short sightedness think running raw water through them is all good. And this and other problems are the proof that yes its cheaper than closed cooling, but this, and other corrosion related issues is the down side.

If you don't clean off the old gasket and use a new one it will leak.
I keep a bunch of thermostat gaskets and either OMC gasket sealer or Permatex aviation sealer on hand. One time I tried this: got the engine good and warm from running on plane so the temp read normal (160) then tapped lightly around the T-stat housing with a small hammer to jar loose any rust flakes in there and believeit or not it worked. No low temp readings for quite a while after that. One of the down sides of open or raw water cooling. All inboards should be closed cooled at least a half system.

 

[BRICH1260]

Your "bypass" passages are probably getting clogged with debris from the pump or engine block. They are much smaller, about the size of a pencil and are up inside the housing unit. You really have to look for them. I suggest taking the housing off and giving it a good cleaning, especially these passages.

 

[further]

Thanks. Got a few gaskets on order and will pull it off (AGAIN...) and give it a good cleaning.