New Engine Problem

[stacer]

I had a new engine installed last June (Beta 20) and up until a couple of weeks ago it ran perfectly. One day after about 3 hours running, the engine suddenly ran unevenly at about 1400 rpm but opening or closing the throttle restored normal running. Each time the throttle was set to about 1400 rpm, the problem returned. Suspecting a fuel problem, the engine was serviced with all filters replaced, the only thing of note was some blackening of the air filter. The exhaust lagging was removed, no evidence of a leak was seen but all joints were externally sealed with high temperature silicone and the lagging replaced. After 3 hours running, the problem returned and any attempt at 1400 rpm resulted in uneven running. After a further 6 hours running, it was noted that the water level in the expansion tank had increased and the new air filter was once again becoming blackened on its outer surface. The next days cruise was about 6 hours during which the problem returned as before and when the engine was cooled, the water level in the expansion tank was overflowing when the cap was removed. 

RCR engineer attended and said the blackening on the air filter element was normal, bled the skin tank which let out a fairly large amount of and  returned  the water level to normal. His opinion was that the problem was caused by air in the system despite 200 trouble free hours since installation. 

Any ideas would be most welcome.

 

 

 

 

[rusty69]

Welcome to the forum.

Could it be dodgy fuel, or water in the diesel? Did the symptoms occur after filling up.

If its less than a year old, any warranty on it?

[stacer]

Fairly sure it's not fuel, no water or debris in the primary filter, all fuel filters changed. Also problem only occurs after 2-3 hours running, so more likely to be temperature related. Also there is the question of the air lock and raised water level in the expansion tank.

[Dalslandia]

valve problem, or head gasket, injectors?

just at 1400 make it tricky...

[Neil Smith]

It should still be in warranty so speak to beta, also was it a like for like swap if not the skin tank could be on the small side.

Neil

[Sir Nibble]

Is the air filter being blackened by belt dust? is the water pump ok?

[stacer]

I have spoken to BETA and agreed for an engineer to visit if the problem persists, BETA to pay if it's an engine problem, me to pay if not. Belt dust should not be a problem with the poly fee belt and it was a like for like swap so the skin tank should be fine. Thanks everyone for your ideas, it all helps.

[system 4-50]

Do you have a calorifier? Are you running an inverter? Do you have an immersion heater? How old is your boat? What is your great-aunt's maiden name? (no that's not right)

[Neil Smith]

If it runs smoothly above 1400rpm say 1600rmp then you can rule out fuel starvation, the water overflowing when you open the filler cap when hot is normal as it's under pressure, I wonder if it could be vibration that sets up at those revs by an alignment problem or an engine mount come loose.

Neil

[mross]

You could get a compression test done, or even do yourself, to give confidence that the pistons rings have not seized slightly.  Unless you know the engine has overheated or run short of oil this is very unlikely.  I've seen engines overheat to the extent that plastic components melt but still the engine internals were not damaged.  If an engine has overheated you will normally see blistered paint.  I suspect a tiny air leak on the fuel system so check all connections, washers, seals and 'O' rings on the low-pressure side.  (My theory is that at higher revs the pump is able to draw the air through OK; at low revs the suction pressure is not high enough to pull air in through my 'tiny leak'.

[Bee]

Hmmm, So long as the pistons are going up and down and the fuel is being squirted in at the right times then diesels are pretty much bound to work unless there is an electrical problem with the stop solenoid or some other fuel issue. Unlikely to be major mechanical, gasket problem or anything. Temp gauge OK? or if no gauge does it smell really hot? I would imagine it will turn out to be a fuel problem but where and what might take a bit of finding. I have diagnosed problems like this by getting a container of fresh fuel and connecting it straight to the engine and therefore bypassing all the pipework from lift pumps, tanks etc. If the problem still persists then its within the engine somewhere. Keep us informed and good luck.

[mross]

11 minutes ago, Bee said:

I have diagnosed problems like this by getting a container of fresh fuel and connecting it straight to the engine and therefore bypassing all the pipework from lift pumps, tanks etc. If the problem still persists then its within the engine somewhere. Keep us informed and good luck.

Good suggestion.  Or, temporarily connect a small container of diesel near the fuel tank, but raised.  This will put the whole system under a slight positive pressure when any leaks should become evident.  Or you could see if you could pressurise the tank with a bicycle pump (only 1 or 2 psi) but this involves blanking off the air vent and making some connection to the filler.

[Flyboy]

I've seen similar symptoms caused by a blocked fuel tank vent. Try running the engine with the fuel cap off .

[stacer]

Many thanks everyone for your ideas, I remain fairly confident that it is not a fuel problem given the bleeding and changes of filters etc. The engine may be overheating but not enough to set off the alarm which may of course be linked to the airlock found in the skin tank adjacent to the cooling input pipe. I will be taking the boat out again in about 2 weeks time so I will see if this is correct or not. The blackened air filter element might be explained by the location of the exhaust outlet, immediately adjacent to the port side air intake. The new style beta air filter seals tightly against the filter housing and perhaps in locks might pull in exhaust gases?

I'll keep everyone posted as this develops.