I have a 2001 PQ 290 with 2 454's. The water temp guages read between 10 to 60 degrees off. I had a computer plugged in all weekend while I was driving it and that is how I came up with those numbers. And I also checked it with a Reytek point and shoot temp gun.
This is what has been replaced this year
(2) 160 therm.
(2) gaffrig senders
(2) waterpumps
(1) aftermarket temp guage (same reading as gaffrig)
So any ideas on what the next step should be??????
Calvin

I'm assuming both gauges are off?? As well as I'm assuming their really not running hot or cool just a bad reading?

Both guages read the same.
Engine temps are fine.
Calvin

So both gauges are reading low at the same reading? Say for example 130deg each? Yet when you check them with the gun they are reading 160 which would be the correct running temp??
If thats the case I would assume that you have the wrong temp sending units. Maybe try putting a stock one back on one engine to see if that corrects the problem.

Calvin
I have that same problem since day1. after changing thermostats/sending units/and checking engine connections I found the engines running with in specs but the gaffric gages read high.also on my boat if I turn on the nav lights all my gages go up about 1/4.
one day when I have nothing to do I will check the ground for the gages,I think you will find your problem been electrical.
Tom

Calvin
I finally fixed my gages,
simple repair.I ran a new ground wire to the dash.
got a #10 gage wire and ran it from the battery to the the ground bus bar thats located behind the dash panel.
now all the gauges work good and they dont jump up every time theres a voltage spike.
PowerQuest wires them in series and uses a thin wire and with all that voltage going thrue the gages the thin ground wire cant handle it.

Tom,
Had the same thing done, fixed my problem also. Sorry I forgot to tell what he did to fix it.
Calvin