I am having the same problems with low operating temps on my 454's. Just changed thermastats to 160. Engine's run around 100 degrees and I know thats way too cool. The therm. housing has this spring and plastic 3 fin diverter inside. Don,t know much about this type of setup. How can I get the temps up without buying new recirulating pumps and all the harware? I do not have a bypass and do not seem to have pressure problems.

Is there any water flow thru that engine when the thermostat is closed?

Been out on the river all weekend and boat running good. It seems to be putting water through engine . You can feel water going through the small hoses at therm housing. Ran boat at 4000 rpm for 30 min. crossing lake and the highest temp got was 105.

What cross over and motor do you have???

Are your exhaust manifolds even getting warm?

Maybe something stuck in the thermostat keeping it open? I had the small cork gasket that goes on top of the thermostat slip out of place on reassembly and cause a similar problem, but to a lesser degree. It just took longer to warm up than my other motor.

Maybe a defective temp sending unit?

Don't know what kind of x-over. The exhaust manifolds are getting warm but certainly not too hot you cannot leave your hand resting on it. I have changed both temp sending units. When at house on the muffs, running 1000 rpm I checked exhaust water temp and it was around 105 degrees.

forgot, the engines are 1989 mark 4 454's built with larger cam, crane roller rockers, gil headers, weiand single plane, 850 double pumpers. Boat is a 1991 30' Baja Sport.

Thermostat stuck open?

Both brand new from C P performance.