Temperature drop

[dudaduma]

I have dual fresh water cooled 2001 VP 5.7s with duoprops. While idling, the temperature seems constant on both of them (~170 degrees, according to temp gauge). However, when I run the boat at 3000 RPMs for a couple of minutes, the starboard engine's temperature drops drastically, to around 100 degrees while the port drops to around 140. I'm worried and need some help / advice.

I recall reading something similar here last year, but can't seem to find that discussion.

Thanks in advance for any and all insight.

 

[Gregory S]

I had a similar problem last year. One of my thermostats was stuck open. I doubt you have two stuck thermostats. Did both engines always drop to 140 at cruise? What thermostats are in there now?

 

[dudaduma]

Yes, both engines would drop to ~140 last season, is that abnormal?

I don't know what type of thermostats are in there now, but will get to the boat sometime this week to replace them both.

Thanks!!

 

[Gregory S]

I bet you have one thermostat stuck open and have two 140 degree thermostats. Most FWC systems call for 160 degree stats.

 

[jtybt15]

My guess, too.