1978 Johnson idle temps

Hey all,
Got a quick question..... so I have changed my t-stat and waterpump assy unit as per service manual. Water "seems" to be flowing fine as far as i can tell via tank test and not hose. Here is my question. When motor is at idle the t-stat housing seems fairly hot. However, when I throttle the motor to 1/2 -to- WOT I can tell water is flowing through the t-stat housing because it feels much cooler. So now my question:

1. Is there not enough pressure to open the t-stat springs to allow flow through an open t-stat until throttle is opened.
- or -
2. Or is the t-stat i have not opening until a fairly hot temp. (hot enough to not be able to keep my palm on the housing for long)

I understand there are diff temp sensitive t-stats, however the one I bought is OEM replacement. I would like for water to flow through the block sooner without the need to run the motor so hard.

thanks for the help

Re: 1978 Johnson idle temps

You don't say what hp this engine is. Hard to diagnose without that information. If it is a V4 or larger, your engine has thermostats which will open when they get to 143 degrees. In addition, it also has pressure relief valves in the thermostat housing(s). Once the engine gets up on plane the force of the incoming water causes these valves to open, flooding the powerhead with extra cooling water. It is very possible that your stats are stuck shut. Once they stick shut, no water will circulate through the powerhead, and it will overheat-at idle. If you bring the engine up on plane these pressure relief valves open and will provide enough water flow to keep it cool-as long as you are on plane.

Re: 1978 Johnson idle temps

Its a 70hp model, and has only 1 thermostat that I replaced. The thermostat should still open up at 143 degrees whether or not the boat is on plane or not correct. Im just wondering/worried that fishing at idle or just letting the motor run at a low RPM, the motor may overheat.

Re: 1978 Johnson idle temps

The motor should run all day long at idle rpm w/o overheating.