I own an N343 which is equipped with an VP MD17D engine
with VP fresh water cooling
system. I had exchange the fresh water pump
3 years ago as the one before did leak.
Last winter the engine
got fitted with a new (used but tested) exhaust
manifold. The engine did never make any problems, starts immediately, never had heat problems, smokes a little (grayish, definition no stream).
We put the boat
in the water
end of May and had to motor
from ship yard into the marina, which is in total 2.5 hours. For the first 2h10min everything was OK, temperature around 75-78C (at the thermostat housing). We motored at around 1800-1900 rpm
. Then the temperature started slowly to increase. We still made it into the marina. When reducing rpm
in the marina the temperature started to increase towards the red an just touched the red when we finnished docking
What did we do since then:
- checked and changed impeller (the old one was not worn at all and just fitted during the winter, ... anyway)
- flip the seawater pump
lid around as it was a bit worn
- checked the seawater intake
- dismounted the heat exchanger
and checked it for blockage (i was newly fitted last year)
- checked the piping of the fresh water side
- drained the coolant
to see whether the is any dirt, mud ... - comes out fine and clean
- checked the thermostat
What we can see is, that the freshwater pumps (I do at least a good amount of coolant
being pushed into the expansion tank). What I cannot judge is whether the pump
develops sufficient pressure to pumps a sufficient flow through the heat exchange and the cylinders.
We can run the engine without load in different rpm with no issues. As soon as we put load on it it starts to overheat. The temperature of the heads and the cylinders is as well considerably higher then the temp at the thermostat housing (20 degrees more). The heat exchanger
gets warm, but I somehow feel that it used to be hotter in the past (but have no data to prove).
Anyone any idea what else to do/check?
Thanks for any idea.