[C320-list] Another Perkins M30 Overheating Help Thread

[Paul Hetherington]

Yes our M30 is running hot.  2500 rpm = 190, much over that and it pushes
over 200.  Haven't had the guts to push it right into triggering the
overheating alarm (203? - not totally sure it's functioning).  But we used
to be able to run at 2700 with no overheating (185-190) and now it heats up
very quickly.

I am pretty sure I have read all the previous threads and tried many of the
suggestions but we are still stuck, so posting our detailed approach is
only to clarify it to myself, but hoping to get some insight/ideas from
your experience.

Here is what we have tried:

   - Checked the raw water intake and all was clear.
   - Removed hose between seacock and water filter and confirmed good water
   intake flow through seacock
   - Diver conformed no obstruction from below at the entrance of the
   seakcock
   - Topped up the coolant
   - Replaced the impeller
   - Replaced the thermostat (Even though the old thermostat was working
   fine when I tested both of them in boiling water)
   - Took out the heat changer and cleaned in a bath of muriatic acid. It
   was then very clear.  It was not that clogged up to begin with though
   - Replaced the exhaust elbow (after ordering one with current downstream
   tube diameter)
   - Replaced the raw water hoses between the intake seacock, between the
   raw water filter and the water pump with new reinforced hoses to make sure
   that they are not collapsing
   - Kept testing the engine in forward gear, tied to the dock, and
   measured temperature with heat gun all over engine block, to confirm it
   wasn't a gauge issue.
   - When engine was ran at 2500 rpm or higher, measuring temperatures
   between 195 and 200 around the coolant pump
   - Always seemed to have good water flow coming out of the boat

Right around the time we started to have overheating issues two other
events happened that may or may not be related.  We switch from a tired and
chipped 2 blade prop to a 3 blade Campbell Sailer prop AND the water pump
was leaking so we replaced it with this one from parts4engines:
https://www.parts4engines.com/perkins-perama-m30-raw-water-pump/

Any help is appreciated.

Cheers.

----------------------------------------------------------------
Paul Hetherington
Hull 155, 1994 C320