temperture reading difference

[gmhardwick66]

I know there are a few threads already on this subject but I could not find the answer there that I need. I am talking about the placement of the water temp sending unit or thermal coupling. The different reading between the driver side head versus the passenger side head. I had mine in drivers side head and moved it to the passenger side head to allow for putting a second sending unit for my dual electric fans. When I placed temp gauge in passenger side head the temp reading was at least 30 degrees hotter compared to the reading when gauge was in drivers side head. Everything was exactly the same except temp reading. I am not positive but I am hoping the difference was due to the fact as the water circulates through engine and heads it heats up so when it gets to the gauge port on drivers side head it has soaked up a bunch of heat causing the difference in temp reading between the to ports. Can someone please tell me if this is correct or do I have another problem all together.