Head temp difference

[FredM]

I have a 2 cylinder '81 18hp merc. While doing maintenance I noticed that the top cylinder head (integral type) runs significantly hotter to the touch than the lower one. I can hold my finger on the top one for a couple of seconds but the lower one I could hold all day. The tell tale only ever gets warm at full throttle. Is this normal?

 

[corm]

Re: Head temp difference

Hi Fred,<br />The teltale is cold water from the pump. The top<br />cyl does run hotter than the bottom on these motors. However it should not boil water off the head or spark plug metal after running motor hard. It doesn't sound like it is too hot because your not burning skin. Too hot to hold my finger on is about 150-160 degrees.

 

[FredM]

Re: Head temp difference

Thanks corm,<br /><br />The tell tale on the 18 runs from an elbow fitting above the top cylinder on the block cover - so I assumed the tell tale water was from the water jacket around the top cylinder. Is this the case or is there another passage from where the water pump tube connects to the block? <br /><br />Cheers - Fred M

 

[corm]

Re: Head temp difference

Hi,<br />The water tube goes into the powerhead through the exhaust manifold and fills to the top of the top cyl. The very end of the combustion chamber will be hot, but the water jacket should be cooler.