Kamd42a one engine using more fuel than other engine

[Momac]

Your right!! the only bit of an oil leak is off the intetcoolers they both look like they weep a bit , I read. Something on this forum a while ago but I came to the concision that they all do it a bit and it was nothing to worry about ? It doest actually drip much oil on floor as such more of just a weep, this is on both sides ,the intetcoolers are very hard to get to on this boat

If the oil escape is very small - a few spots on the floor its not an issue. The intercooler has a small condensate drain hole. It is oil passing by the turbo when the engines are slow running and not up to temperature. Any oil from the intercooler should stop after the engines have had a good blast up to temperature. I had one engine where the oil would not clear up and the amount of oil leaking though not huge and not enough to make a change on the dipstick level, became a more significant patch on the floor rather than a few spots. I had the turbo removed and repaired which has cured the fault. I caught it early and the cost was not cheap but a lot less than a new turbo.

Wipe up the oil and keep an eye on it. Also check the air filter boxes for any oil and if the air filters are dirty fit replacements. By the way the air filters are relatively cheap if you but from a car spares shop.
https://www.gsfcarparts.com/122vo0010
Use discount code GSF30

Oil in the intercooler may inhibit engine power slightly in that the intercooler is not cooling the charge air quite as efficiently as it should. I am not sure if that could explain could explain or contribute your revs and fuel issue.
Initially just clear up the oil and monitor. It may be come to nothing.
A friend has a F36 and I understand the issue with engine access. I don't think its much different on any other similar mid engined shaft drive boat of about the same size. I have a F33 which is on outdrives so the engine access is far easier.

 

[boatmike]

Lots of good sense talked so far but I think you could turn the argument around the other way. For both engines to use identical fuel everything has to be in top condition. Fuel filters have to be clean (not just operational but same DP) Same for air filters, turbo condition, injectors, props, bearings and alignment, in fact just about everything that affects efficiency. You are a lucky guy if everything is in such good condition on both engines. Very rarely are they! I have twin TAMD41a Volvos. I have flow meters fitted that tell me the real time consumption of both engines. One engine used to use more fuel than the other and I found the filters were getting fouled up fairly quickly. Clean the filters and things got better of course but I am currently cleaning out both tanks and am sure this will help but I have also just fitted boost gauges and it is obvious that one turbo is less efficient than the other. So they are now off being reconditioned. The injectors have been serviced and valve clearances adjusted. Again one engine was better generally than the other. Compression is now good on both and I have high hopes of more power when everything is back together. It will be interesting to see if the burn rate is then similar..... I think the point is that there are so many things that can affect fuel efficiency that it's unlikely to be a single identifiable fault. If you only had one engine you would have nothing to compare with and would never know!

 

[BruceK]

35 l is not much. My port engine was consuming 20 - 30% more than starboard consistently. That really started the paranoia going. It was all down to revs and one engine working much harder. Then I noticed how much harder one engine was working while at cruise by noticing how much revs dipped or climbed on the port engine my small changes to the throttle on starboard. Quite out of sync when repeated in reverse. First issue was the alternator pulley wheels were slightly mismatched. You know the story. Replace an alternator dont think to change the pulley because it looks identical etc. Better but no cigar. Then I noticed one alternator belt was slightly worn because I could see teeth patterns on the pulley wheel base. Once that was sorted I used the tooth counter on the blowers to set an accurate baseline on both the rev counters. (blowers cut in at 1700 rpm) You can adjust the tachos on the back. I synchronised both counters. Problem sorted.

Now the thing is before I was listening to harmonics to balance the engines suspecting the tacho's may be slightly out. I have a good enough ear and can tune and play a couple of stringed instruments. However once I had sorted out the tacho's and knew them to be balanced at least if not accurate the engine harmonics took on another note altogether. What I noticed when calibrating the tachos is a tiny offset at 1700 rpm becomes quite significant at 32 - 3400 rpm. 100 rpm can become as much as 600rpm and you can get a nice synced harmonic in between this 600rpm and still be say 200 rpm out.
Whether this is your issue or not is of course an entirely different matter. But I had exhausted everything including counting reduction teeth in the lower outdrives to double check they were matched. Silly little thing in the end and caused me no end of sleepless nights worrying over potential expense bills.

 

[No Regrets]

Am I right is suggesting that with twin engines, both rotating in the same direction, that there may be a gearbox which has a built in contra rotating gear!?

Mine have (TAMD40b with MS3 gearboxes) and one is slightly different to the other in every way....

 

[tico]

possibly a daft idea , but does one engine run a power steering pump?

 

[scottie]

possibly a daft idea , but does one engine run a power steering pump?

Not daft at all
Very good question
You could look at calorifier and charging systems and even do you always start one engine first
Add them all together?