One head cool

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On my twin 89 200s, after running a good while one head is cool and you can hold you hand on it and the other 3 are good and hot. Thermostats are working fine.
What could cause one head to run cool? I was thinking low compression but motor runs smooth. Will do a compression test today anyway.....

[99yam40]

maybe that cylinder is not firing, did you test stats in heated water to see what temp they open and closed?
Use a temp gun to look at all parts of heads and post the readings

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I put new stats in and no difference. When I tested with my hand I put it on the top of the head. Yeah, maybe that cylinder is not firing and thus no heat. Sure runs smooth to be running on 5 cylinders, though.....

Heat gun is good idea....should be able to isolate which cylinder.

Could poppet valve stuck make one bank run cool?

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Did compression test and all 12 were 115-120. Forgot my heatgun.....
I did notice that the cooler running motor's plugs were not the nice ****en brown (insulator) of the hotter runner. They were black and oily.

What would make it run too cool other than themostats?