Any drawbacks to running a cooler thermostat (180 to 140)

[Erik]

I had some impeller & cooling issues this weekend when we launched the boat, so I changed the impeller and things seem to be ok... The boat cools properly at speed, but gets pretty warm at idle, one-click "blub" speed and in general the cooling issue isn't fully resolved in my mind. However I did notice some of the same issues about which people have posted over the past few days regarding their GT40's running hot at idle. I will check my strainer, as has been reccomended. The boat is 30 miles from me right now.

But I am thinking about also changing the thermostat to a cooler temp (140). I am pretty sure I have a 180 degree thermostat in there now, but I am not positive of that. Whatever is stock, is in the boat now.

So I am just wondering if there are any major drawbacks to running a cooler thermostat on that GT40 engine. Also with my limited technical knowledge of this new (to me) boat's inner workings, a little bit of schooling would also be appreciated.

Thanks,
Erik

[NautiqueJeff]

While running a cooler thermostat may mask the issue, the real cause of the problem will still be there. I'd recommend keeping the factory thermostat (or replacing it with one of the same type) and digging deeper to find the true cause of the problem.

If you have a heater in your boat, it won't work nearly as well with a 140 in there.

[Erik]

Good point Jeff. Thank you. I will stick with what is in there now.

[richard]

180-140 thermostat

I had one time experience last year exactly same you situation, after try many check,(impeller,clean heatexchanger,hose camps,stainer,...),the temp.still shift up and idle high, the last way I change a 140 thermostat,it solve the problem,the old one was 170, and had a test to hot water it will open, the boat than runs fine at 160f, and the heater works normal, my area water temp. around 22-32C in summer. However do this last way,as Jeff said,this may mask the true issue, confirm there are no suction air leak in the raw water intake side first.