Why 50/50% which I think puts it arounf -35* or so. I'm no diesel expert
but I wouldn't set it any lower than the temps is your climate. 60/40% mix
removes more heat from the engine than 50/50 or 100% antifreeze.

"Tom "HappyFunBoater" Treadway" wrote in message
m...
I've got two Cummins 420hp diesel engines. They're both about 5 years old
and I've never changed the coolant, but I have made sure it was topped off
through the years. So two weeks ago I decided to replace the coolant.
When I drained the old coolant, everything looked fine, i.e., no rust or
particles. Then I refilled, slowly, with a 50/50 mix with Prestone
coolant that met the engine specs. I didn't start the engines until this
weekend - two weeks later.

Before I changed the coolant both engines very consistently ran around
170F. The engines are rated for 160-180F. Now both engines run around
190F - 20F hotter! I ran for about a hour thinking that maybe the coolant
needed to mix, or air bubbles needed get out of the system, but it made no
difference. The temperature is dead on 190F.

What the heck did I do wrong?

Thanks for your help.
TT