Re: Normal running temperature of outboard engines?
Trust me, on at least the V6 motors of the late 70's to early 90's, even on lower HP motors of that time frame. The overheat sensor is anywhere from 240F to 285F in some cases. This sensor measures the Metal temp of the head just near one of the top cylinders. Underneath the cylinder head cover, not far away from the combustion chamber. It never touches water.<br /><br />Water temps will never get that high however. But 180F-190F metal temps is not out of the question. And is normal for those motors.<br />The problem is, you can't measure the metal yourself where the overheat sensor or temp. sensors are located. They are fixed against the head, underneath the water jacket cover . And the cover has water flowing through them which cools them down to a lower temp, compared to where the sensor is measuring. <br /><br />Just because a thermostat is rated for 143F does not mean that the water will not exceed that. It has to go over 143 to open it, at higher rpms and increased metal temperatures that water can get hotter, how much I don't know as I've never been able to measure it at high speeds. But my numbers of 180F+ refer to aluminum head temps. near the combustion chambers. There is a big difference between water and metal temps! Especially where the sensor is located.<br /><br />Boatster, I thought you had a Merc 200hp... On that 20hp you need to see what type of overheat sensor you have and what temp it is rated to go off.