For anyone else out there with a diesel that runs too cool, especially a Universal 5432, I am happy to report that I have solved this sort of problem on Aeolus. In short, the factory thermostat is rated 160, which as many will know is fine if you are raw water cooled to prevent salt crystals forming, but for those many of us with fresh water cooling, 160 is way too cool. This can dramatically shorten engine life and produces carbon build up in the usual places.
The engine manual says the optimum temperature is 170-185 and yet Universal only provides a 160 thermostat. Go figure. Without giving a dissertation on the things that influence engine temperature, suffice to say here that Aeolus ran a steady 160 no matter how hard she was run, and that this was controlled entirely by the 160 thermostat setting in my case. She has an extremely efficient cooling system.
After a lengthy search involving all the usual steps, I found my answer. Car Quest makes a 180 and 195 degree thermostat that is an exact match. They are actually made by Stant and just rebranded by Car Quest. I put the 195 degree in Aeolus tonight and ran her up to temperature and she parked herself on 190!!! Perfect.
Car Quest part number 31979
I could just see the carbon burning off the piston rings and the valves. In my case this is especially important because I run a high % biodiesel for all the mechanical and environmental benefits, and it has a slightly higher flash point which is helped by the higher operating temperature.
As only someone who really knows their boat can appreciate, I noticed a distinctly quieter and smoother sound to her tonight while running at the higher 190 temperature.
For pictures and more of the story see my boat blog at
Stories of Aeolus- Our Gulf 32 Pilothouse
I hope this helps anyone else out there who has an efficient cooling system and who worries about carbon build up with an engine that is running too cool.