Why is one side of my motor hotter than the other?

[jdewaard]

I have a 2000 Pro Max 225. I have a a temperature sender installed in the top of each head right behind the thermostat. These senders are wired through a switch to the gauge so I can read the water temp on each head. At idle the port side runs about 150-155 degrees but the starboard head runs up to 170-180 degrees. Both sides have brand new Mercury brand 143 degree stats. I even replaced the starboard side with a third new Mercury brand stat. Any idea what is going on here? I don't like seeing that high of temp on the starboard side. Even at wide open throttle the starboard runs hotter. Do you guys think it is just variations in the sender?

[RIVERRUMMER 70]

I have a 2000 Pro Max 225. I have a a temperature sender installed in the top of each head right behind the thermostat. These senders are wired through a switch to the gauge so I can read the water temp on each head. At idle the port side runs about 150-155 degrees but the starboard head runs up to 170-180 degrees. Both sides have brand new Mercury brand 143 degree stats. I even replaced the starboard side with a third new Mercury brand stat. Any idea what is going on here? I don't like seeing that high of temp on the starboard side. Even at wide open throttle the starboard runs hotter. Do you guys think it is just variations in the sender?

SWITCH THE SENDERS AND SEE WHAT HAPPENS

[jdewaard]

That's a good idea. Why didn't I think of that. I will give that a try this weekend.

[Go Time]

Every engine I check with my lazer thermometer has one side hotter than the other (don't remember if its always the STBD hotter than the PORT. It may be because of the low water flow at idle and the STBD bank is higher than the port....meaning it will be less likely to be completely solid with water if there is any air in the system. ??

[jdewaard]

Thanks Go Time. That's the answer I got from Jay Smith also. Here is his reply:

"Starboard side will ALWAYS be a bit hotter dont sweat it is normal....

The starboard side is 1".750" taller than the port side and will always created a steam pocket at idle as water seeks its own level and leaves very top of the bore empty of water until the pump pressure and volume comes up...Senders are not that accurate........

Jay"

[1BadAction]

This is why the senders are normally on the stbd side, and 180 degrees at an idle isn't bad for a steel bore.

[Coupe427]

Every time Ive shot my motor with a temp gun the starboard side has been hotter than the port.

[jdewaard]

I am glad to here this info. I was worried that something was wrong. I heard that temps shouldn't exceed 145. This puts me at ease.

[1BadAction]

I am glad to here this info. I was worried that something was wrong. I heard that temps shouldn't exceed 145. This puts me at ease.

I'd start worrying if it stayed hot when on plane and running.

[jdewaard]

Nope, temps drop right down as soon as I get on the throttle. Water pressure never drops below 10 psi and runs at 15 psi most of the time. Temps at WOT are 130-140.

[perfmarine1]

You may swap wires on the gauges also. But I think you will find the stbd is hotter.