both engines overheat at idle speed only. Run a little warmer at speed then normal, about 180 F.
I'm thinking impellers as they are a couple years old. could it be anything else i.e. thermostats ?
Oil temp, water pressure OK.
These are stock 454's.
Thanks,
ed

I change my impellers once a year reguardless of the water I run in. I would say to start there.

BOTH ? problem started at the same time ? the odds of a dual simultaneous failure are about a billion to 1. are you certain you didn't lose an instrument ground and are just seeing a data "offset" ? there is something else going on here...

Both is weird, seems like some other problem. I change the impellers EVERY year regardless. There just rubber flaps spinning on plastic. Of all the parts in your motor don't let one (or both) come apart because of these "disposable parts".

Did you get into any mud/sand, or seaweed? Check the transom hoses for kinks or collapses.

One engine reads about 220 - 230 F water temp after start up and about a 15-20 miute idle out from the marina. The other gets up in the 180-190 F in about the same time.

Both go to 180 F when I'm at cruise. Prior to this they we're more in the 150-160 F rqnge at cruise. The temp pick ups are at the thermostat housing and the connections are in place. Doubt the gages are in error , the thermostat housing seems hotter on the engine that reads high temp.
I'll pull the pumps and check the impellers and housings, UGH what a ***** to remove.
Thanks,
ed

Probably easier (and cheaper) than pulling the engines,huh? BOB

sounds like a low or restricted flow issue.... low revs low flow. i had a client here whose raw water inlet to the pump was a "no wire" type and had gotton soft and collapsed and would do this... im trying to justify the higher speeds/higher thermal loads making things cooler and the only logic i can come up with is that the pump is driven faster making more flow... so intuitively means better cooling.... but just musing outloud ...