My line of thinking was based on expansion of metal. If it is run in cold water (which it is here in the northeast at this point…say 40° barrel water outdoors), it is going to take a lot more than just idle speed in forward gear to get the thermostat to open. So rev it up in a test barrel to 5,000RPM, hold that steady for 5-7 minutes, and that thermostat is going to open/cylinders are running at a temperature between 135-155°.

Then you throttle back to idle and evaluate based on your recommendations.

If I just turn the motor on and run at idle in gear, wouldn’t everything still be cold (in terms of metal expansion) and not give an accurate assessment?

I will say though, that my 2014 30hp Etec took about 30 minutes at idle in neutral to get up to temp a week ago, when I went to flush it with fresh water after the last day of the season running it in brackish/salt water on the charles river (boston). Easy to observe when the thermostat opens on those motors because the bottom telltale starts spitting water and there is plenty of steam that starts to exit the overboard water indicator/2nd telltale. I ran the motor for about 45 minutes because I wanted to see the thermostat open and get a full flush of fresh for at least 8-10 minutes to minimize salt effects (along with getting some fuel with stabil through the fuel system…this was the final run of the year and I was winterizing it too).

Basically they are like the older motors, but things are separated out a little bit more. My ’78 35hp has no steam coming out of it until 2-3 mins into run time, unless I throw it in gear and drop the hammer to about 3/4 throttle. Then 90 seconds in I get steam. I try to avoid going up to near-max RPMs on all my motors (depending on time of year/ambient temperatures) until I know all the internals have had time to expand/adequately warm up. Same thing I do to my personal vehicles (generally GMC’s/Chevy’s).

LOL! More learning lessons for me 🙂

You know, I’ve heard a few people talk about pressure relief thermostats, but until just the last couple of months, have only been working on small motors and nothing much newer above 25hp than 1993.

I did hold a couple of ‘newer’ thermostats in my hand over the summer, and I admit it, I was itching my head wondering how the heck those things worked. And to re-hijack this thread, how does that pressure relief thermostat work? Based on water flow pressure?

All sounds good. I suspected water pressure was what influence operation by the name, but again, always nice to hear it from folks who have/are living it.

I appreciate the info, insight, and assessment tools. As time moves on Ill continue to develop my knowledge base for these older motors, so the contributions of folks here are keeping these things alive for others to enjoy.