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

--
"Se viriamo, viriamo viriamo viriamo;
Se andiamo dritti, viriamo"
(Cit. "il tattico")

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

In article ,
"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.

My first thought was something like the fuel tank strainer, which Howard
covered well. A second thought is an intermittent air leak that
(wonderfully) self-clears. That it only seems to happen at 2400 points
to a restriction in the line (try another Racor filter & replace the
on-engine primary) or possibly a marginal lift pump. Try boosting to
above 2400 and see if it happens faster.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

Dopo dura riflessione, Jere Lull ha scritto :
My first thought was something like the fuel tank strainer, which Howard
covered well.


Well done, guys.

That one was the problem.

At the present, we just cleaned the fuel line BEFORE the filter and
replaced the filter itself (it was factory new, anyway we replaced it),
but as soon as the boat will stop for few days, we'll dismount the tank
and we'll wash it (Croatia fuel is really dirt...).

Thanks you all.

Alberto

--
"Se viriamo, viriamo viriamo viriamo;
Se andiamo dritti, viriamo"
(Cit. "il tattico")

"Albe V°" wrote in
:

Any idea/suggestion/confirmation?


Look for fuel starvation.....

Disconnect the fuel line from the engine and connect an outboard motor
primer bulb or some kind of hand pump to it. Pump out fuel into a
container and see if it pumps easy for several minutes. If it first it
pumps out easy but becomes increasingly hard, take off the fuel filler cap
and try again (clogged vent on tank). If that doesn't make it pump easy
we're now looking for a clog in the fuel lines, other than that brand new
filter you just installed. If anything that looks like black gook comes
out, the algae has contaminated the system and probably clogged the
injection pump/injectors. Polish the fuel:
http://www.trawlerworld.com/features_06.htm

Tear apart the old filter, if you can. If it looks black, algae infection
is in the tank. If you kill the algae with a biocide, it will just keep
clogging the filters for years. The tank needs fuel polishing and
agitation to clean it out. Polish the fuel on Saturday AWAY from the no-
wake zone. Let the wakes agitate the fuel in the tank.

If none of this happens and the pumping is easy....bad injection or primary
pump on the engine...not pretty.

--
Larry