I have a water crossover and never had a thermostat, today I put a 140 degree thermostat on and drilled 4 -3/16" holes on the sides. Ran it on the hose the temp gauge never moved over 100 degrees, did I drill to many holes? I ran it for 7 to 10 mins.

You really need to put it in the water and run it. Temps when running of the hose are usually different. Mine temps cycle a lot from about 100* to 160* on the hose, but are rock steady at 155* when idling in the water.

I drilled two holes in mine. Like Griff said run it on the water first then see what it does.

do you have the bypass?

if you are using a x-over with a 5/8" bypass - is it a neccesity to have any holes in your t-stat? say with a 140 deg. stat....

any help on this subject would be greatly appreciated.

You need to run it and experiment to find out what works best.

Yes it is still best to have the holes. The holes are to allow air out from around the thermostat when it is closed. That way it reads the temp of the water more acurately. Raw water cooled systems are always pulling air along with the water into the engine.

5/8 is a pretty small bypass. Mine is 1". Does it cool the manifolds ok?

i am just finishing the project. i am going to be running it outside the boat this weekend just to check for any leaks etc. i knew the bypass was a little on the small side however if i drill 3 - 3/16 holes in the stat i would think that would do the job until the stat opens. like griff said it's trial and error. i can always go a little larger on the bypass size.

thanks for helping out. the holes for the air also makes good sense. i may even pull the stats out all together for the prerun in the shop. then dial it in next spring.