Albe V° wrote:
My Volvo MD2030 diesel engine experiences a problem since last month.

Normally running at about 2400rpm (that's my cruise rpm), it suddendly
goes down of rpm, approximately at the minimum rotation speed, for few
seconds. Then, with no apparent explication, it returns to previous rpm
rotation.
This happens periodically. Turning at lower rpm (around 2000rpm), it
happens once per hour. Turning at higher rpm (around 2600rpm), it
happens every 10'.

Even if I lower the throttle, it doesn't shut down. It simply reduces
rotation exactly if I had lowered the throttle, but with no irregularity
nor noises nor smoke.
That's why I don't think it is some kind of overloading.

Water flows perfectly at a very normal temperature (I can keep my hand
in the hot water huge flow).
Smoke: just a very light white smoke, disappearing after few minutes of
operation.
Leds in the cockpit are off (they light on at the led test).

I changed oil, oil filter, and mainly Fuel filter, with no result.

My opinion, but I'm not able to find any confirmation, is that some kind
of 'overheating thermostat' is going crazy, and it reads a wrong
temperature, lowering down the engine to protect it. Then, after few
seconds of low rpm, it cools and the engine becomes ok again.

Any idea/suggestion/confirmation?

Alberto

Alberto,

This may not fit your symptoms but.............

I recently had a fuel contamination problem that would cause my Volvo
MD7 to periodically slow down. The fuel line had a "strainer" on the
fuel pick-up IN THE FUEL TANK. That "strainer" had gotten clogged but
some fuel was able to get through. The engine would run fine for a
while and then throttle down and go back to full RPM. Eventually it
just shut off, but would start again after a few minutes when the vacume
in the line would cause sufficient fuel into the filter. Then the
process would repeat. The fuel filter was clear because the debris was
being caught in the tank.

Another symptoms was very high vacume on the Racor filter. Also, I
could not blow back into the tank using my breath. Once the obstruction
was clear I could (with difficluty) blow back into the tank with my
breath and hear the fuel bubbling.

Nigel Calder says of in tank strainers "cut it off." So I did. Problem
solved. Of course I had to open the tank, remove the pick up, cut off
the strainer, clean off old gasket material, put on new gasket material,
and reinstall pick-up while laying in coffin size cocpit locker, in the
rain, while becalmed, near an rocky island. But, hey, what are boats
for? (I exaggerate, but only slightly, for dramatic effect. It all
reeally happend, just not at once.)

Hope you don't have this problem.

Howard