Speed & revs problem

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Lemanix

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Dear All,

I have a twin Volvo Penta KAD42. One of the engines at full throttle revs 3200 rpm while the other is only putting up 2500 rpm and after a while the engine with low revs tempreture alarm goes on.
I had changed all diesel filters, air cleaner filters and also the water pump impeller of the engine with low revs but nothing changes.
Any suggestions?

Best Regards

Lemanix
 
Hi,

to get the best advice here I would recommend you give as many details as possible.

ie what did they used to rev to?
is it a sudden change or gradual?
What are the gauges reading when the alarm goes off?
How clean is the hull?
Have you made any recent changes? props etc
How long is 'a while'?

The more info you give the better the answers will be!

good luck.
 
I agree with all that targa31 has said.

Is there any abnormal smoke?

When next out, once up to operating temperature, try each engine on its own to see what speed and revs are achieved.

If you are on drives, it might be worth lifting them and swapping props from side to side or at least looking for damage. As targa31 implied, if the change was a step one, it could point to hitting a prop off something.

Best of luck.
 
Normally they rev 3200 now one is doing so but the other not.
It is a sudden change.
The props are stainless steel and very well clean. There does not seems to be any damage on them.
The hull is not that bad but I believe if its a hull issue both engines will not reach the revs.
after 5 min in full trottle the tempreture gauge shows 185 and the alarm goes on of the engine that is only reaching 2500 revs.
There is no smoke at all.
I am thinkig that it could be the nozzles or the diesel pump.
What do you think?
 
These engines are meant to rev up to 3850 I believe. Are the props the correct size? I use b6 on a targa31 if that helps.

Is the compressor still on when trying to get up to speed at 2500? It should be.

I am not an expert but I would start with the easy stuff! Are the fuel filters clean? Are there any air leaks with the compressor/turbo running? ( this can be tested in neutral)
 
If you have an overheat at lower rev's you have an issue with cooling water.

Not much info to go on here, but to start :

If you have good fresh water/coolant, then that side is probably OK as it seldom gets clogged up and as the overheat happens "after a while", then your circulation pump is probably OK as well ... so that leaves raw water side.. such as exchangers and exhaust elbow (assuming raw water pump is OK). KIS, so four bolts and two clamps on exhaust elbow to remove and check for blockages ... (assuming this is above water level of course). I also think that blocked exhaust could reduce engine's ability to expel gas, so could affect performance. There after I'd look at exchangers etc.

Is the engine smoking black when not reaching WOT ?? or are there any other info on engine ... if so, you have not enough air, or too much fuel .... which opens up loads of nice discussions around compressor, turbocharger, etc...
 
Lemanix said:
Dear All,

I have a twin Volvo Penta KAD42. One of the engines at full throttle revs 3200 rpm while the other is only putting up 2500 rpm and after a while the engine with low revs tempreture alarm goes on.
I had changed all diesel filters, air cleaner filters and also the water pump impeller of the engine with low revs but nothing changes.
Any suggestions?

Best Regards

Lemanix
Click to expand...
Could it be a faulty/ blocked inter cooler ?
The air is not getting cooled / dense enough for full power from the turbo to take it much over 2500 rpm -and the raw water impediment eventually leads to a overheat ?
 
This happened, recently, to a friend of mine. He has twin TAMD63's and it transpired that one of the hoses from turbo to inlet had split, not obvious as very limited space, replaced pipe, all good. Good luck.
 
If the speed is down and you have outdrives, I'd suspect the rubber bearing twixt the prop and the outdrive. If this has failed, it will allow the engine to rev normally but would not be doing the work, leaving the other engine to do most of the work and therefore pulling less revs. Happened to me when I owned a Cougar 35. Exactly the symptoms you mentioned. So, the clue is if the speed is down.
 
This isn't just he good old KAD42 overheat problems that afflicted the early engines resulting in Volvo releasing the KAD43 to fixed all the issues.
Have the engines had all the updates? Personaly have always avoided KAD42 engined boats just in case.
 
+1 Piers and Viscount.

Test each engine in gear on its own. Note engine revs AND hull speed.

Engine with failed propeller will have higher engine revs for lower hull speed. (as it has only got 1 propeller instead of 2 effectively)

Easier to eliminate this first before stripping things down
 
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