Hey.
Thank you for coming back and letting everyone know what the fix was. I'm sure many others do and will appreciate it as well.
Glad you got her going well.
Sean
It was a long and confusing road but as a courtesy I'll try to distill this for others:
Symptom: motor was overheating sporadically.
- went for the obvious stuff first. Checked the thermostats which were both bad. Replaced them. Still overheats. Messed around with IR gun but could not figure it out. Tested the thermostats. Both didn't open until 155 (I mean cracked) and fully open higher. Sent them back and ordered two more.
- Took the bad thermostats out and ran the motor, temp readings were very cool (like 120 or less) as expected. Ran at 4K, all good. Ran at 5K, got an overheat, and unplugged the sensors to be sure. WTF?
- Took out the overheat switches and tested. They were totally jacked up, one didn't close until like 270 and the other didn't ever close that I could tell. Ordered two more overheat switches.
- Received more thermostats. Now I test everything when I take it out of the box. Both were bad.
- Back to the temp switches... received two new ones and installed them (I didn't test them!).
- Received two more (we're on six now) and tested them and finally they operate as designed. Put them in and ran and overheated within 3 minutes on a plane. WTF again! Swapped the overheat switches between port/starboard and the overheating followed the sensor. Tested the sensor and it closed way too early and the other was good. Ordered another overheat switch, tested and installed. No joy still overheats.
- Removed the heads, cleaned them up, replaced O-rings, and thermostat seals. This is where the broken head bolt happened. Once the heads were back on I'm back in business, no overheats.
Here are my takeaways:
- test your stuff when you receive it. This leads to the next point.
- Only buy OEM parts or at least stay away from Chinese knockoffs. But back to point #1, test it no matter what even if OEM, they're still shipping bad parts.
- a blown head gasket (degraded O-rings) seems to be the root cause of this investigation, however it could be possible that the thermostats caused overheating not caught by bad sensors in turn causing a blown head gasket. The perfect storm of issues.
- My new dry stack marina does not automatically flush my motor when they retrieve my boat. This makes a huge difference, just rinsing the thermostats with fresh water will prolong their life.
- The fact that this motor still runs well, and hasn't had any repairs other than service items (sensors are now considered service items), speaks to the sheer toughness of these old Johnson/Evinrude motors. I love 'em but the fuel economy will turn the next major repair into a re-power.
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