145 to 180 degrees, cycling up and down

[lost in translation]

Hi. I noticed recently that my engine temp is cycling between temperate ranges of around 140 or 145 F and about 180 F when run at speed (2000 rpm is about max with my folding prop on my C&C 36).

My motor is raw water cooled in a fresh water lake. I have not flushed it in the three years I've owned it and it stays in the water year around and is used regularly.

I replaced my water pump with a Moyer earlier this year and am very pleased with the pump. It moves a lot of water and reduced the slower speed work of the boat by about 10 degrees F as my prior impeller in the old pump was pretty worn.

I read in the FAQ I could crimp the bypass hose a bit to see if this solves the problem and take other steps if it does. https://moyermarine.com/faq-3-2-2-2-2/.

Wanted to check and see if there are other thoughts as well.

thanks.

[sastanley]

LIT,
180 is a *little* bit high, but not too bad. Most of the RWC folks will see it drop to 140° or so until the t-stat closes, and then it will rise again until the t-stat opens. (the temp sender is on the hot side of the t-stat)

Other variables (besides crud/blockages) are the type and temperature of t-stat that is installed. The OEM 3 spring Holley was a 140°F if I remember, and back in the day, my RWC'd motor fluctuated between about 145°-165°F before conversion to FWC. Due to the scarcity of that OEM t-stat, there have been a few different additions of t-stats to the field over the years.

[joe_db]

I would do an acid/vinegar flush first off and then install the Moyer valve in the bypass line.
EDIT - my old engine would do this, it started out going 140-180 and eventually got to 140-240
A yearly acid flush fixed it for the most part, salt is not the only thing that precipitates in the engine block.
I would maybe first off try removing the thermostat and putting a valve in the bypass, this gives you a way to baseline max possible cooling effort. I can run hours at 100% throttle in 80 degree water and not hit 140 degrees at full-cold on the valve.

[Sam]

Good advice received. I have a 66 early model w/ old std 140 degree Tstat and the temp stays at solid 140 and maybe 150 after running hard in warmer water . Every few years I dis assemble the T state housing - check for debris and clean the T state in a vinegar soak. On later model engines like yours the std temp is 160 and it sounds like yours may be both sticking "closed and open" at times. I'd do a simple Tstat cleaning first and then see how it runs. After that a flush would be my second task

[JOHN COOKSON]

A bit of reserve cooling capacity is good to have. IMO you are on the right track.
If after confirming good water flow through the engine*, and a acid flush you are not happy with the result try removing the thermostat and balancing the water flow through\around with a valve on the bypass.

*Start at either end of the cooling system checking for any blockages. There may be a piece of crud in the inlet strainer restricting the water flow to a blockage at the end of the manifold or something in-between.

Even thought you have a new water pump it wouldn't hurt to check to be sure the impeller is in good shape.

ex TRUE GRIT