Changed tach now overheat alarm

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Was running fine....as soon as I changed my digital tach it now has alarm after running 4000 or more for a few minutes.

Coincidence?

[99yam40]

more than likely, unless it is a false alarm.
You need to chase it down and see if it is real, and then see what is causing it.

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Other than heat temp gun what would be a good way to determine which engine is overheating and then which head? I was thinking of removing head heat sensors one by one and retesting to isolate which head......

[99yam40]

testing temp switches and thermostats would at least make sure they are working properly and then cleaning checking PRVs and looking at the cooling passages while opened up would be a good thing to do if not done lately.
also change water pumps if not done lately.
To find which switch is coming in would be easiest done by disconnecting them one by one while alarm is going off to see which one will quite the alarm, but a temp gun would be nice to see if one head is hotter than the others

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I tried to disconnect the temp sensors while overheat alarm is on but it goes off before I can get the cover off and disconnect.
Would have been nice if the over heat indicator would at least show which motor it is that's overheating. Water temp doesn't go up much over 1/4 way.

Maybe running lean and super heating the heads? It will do it in 15 seconds at WOT. Takes 10 min at 4000.