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  1. #1

    Smile AQD40 / TMD40 fuel consumption

    Gents,

    May I ask for your advice

    background: I'm having an AQD40 / SP280 in my 26 foot boat

    The max RPM is 3550 / 23 knots

    I wonder if my fuel consumption is within specs?

    At 2800 / 13,5knots the fuel consumption is about 22ltrs / 5,8 US gallons
    At 3000 / 15 knots the fuel consumption is about 30 ltrs / 7,9 US gallons

    I feel in my case the consumption at 3000rpm is a bit high as I read from somewhere that the max consumption for this engine should be somewhere at 36 liters / 9,6 US gallons per hour at max power 3500-3600 RPM. As such I'm not far from that at 3000rpm?

    Now If I understand correctly many run this engine at 3200-3300 cruise rpm? Also, VOLVO states that 3300RPM cruise speed is fine.

    Based on your experiences I wonder what the cruise consumption at 3000-3300 range should be?

    I do think maybe I need to have a look on the turbo / injectors as I think they nave never been rebuilt. The engine has somewhat 800 hours on it and has good compression.

    thanks in advance,

    Artto

  2. #2
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    Default Re: AQD40 / TMD40 fuel consumption

    Is this the 130hp model? If it is I would say your fuel consumption is quite a bit too high. Even if it is the 165hp model your fuel burn is still high. I would be expecting to cruise at less than 20lph for the 130hp and around 20lph - 25lph for the 165hp. Does the boat sit properly up on the plane at less than 15knts? Some 26ft hulls might need to be doing 15knts+ to be properly out of the water and planing. If you are not properly up and planing that could partly explain the poor economy at those 13.5 and 15knt speeds.

  3. #3

    Default Re: AQD40 / TMD40 fuel consumption

    Quote Originally Posted by aliboy View Post
    Is this the 130hp model? If it is I would say your fuel consumption is quite a bit too high. Even if it is the 165hp model your fuel burn is still high. I would be expecting to cruise at less than 20lph for the 130hp and around 20lph - 25lph for the 165hp. Does the boat sit properly up on the plane at less than 15knts? Some 26ft hulls might need to be doing 15knts+ to be properly out of the water and planing. If you are not properly up and planing that could partly explain the poor economy at those 13.5 and 15knt speeds.
    Hi Aliboy

    Thanks for your reply

    Mine is the 130hp version

    What makes me puzzled is the engine does not feel loaded at all at either 2800 or 3000rpm. The boat feels to be better planing with less drag at 3000rpm / 15 knots yet the consumption is relatively much higher at 15 knots than at 13,5 knots as I wrote earlier?

    I used to have an AQAD31B engine years back and I do remember it consumed anything between 14-19 liters per hour at 2800-3200 rpm. However, the AQAD31B is a direct injection type of an engine which, according to VOLVO, should consume somewhat less than my current AQD40A engine which is a precombusition type of an engine.

    Anyways, I hope someone with a same engine chimes in to help me forward. At the moment I do think something is not as it should be..

    thanks again

    Artto

  4. #4
    Join Date
    May 2015
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    Oregon
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    72

    Default Re: AQD40 / TMD40 fuel consumption

    Fuel use goes up rapidly as you get near top end. On much bigger boats it's common to use twice the fuel used at hull speed for about 7-8 knots more. You're probably not fully planing. You're pushing water. My experience, with much bigger hulls, don't really plane until 18-19 knots and then the fuel can be cut back. Everybody with a faster boat wants to go faster yet and for free. You may need trim tabs, or better tabs or repositioned tabs. The hull shape may not be right. You may not have enough engine hp. That's a light duty/pleasure rating. And while Volvo says you can run at 3300, they only care that you make it thru warranty. Diesels run at near wide open throttle don't last as long. The killer is exhaust gas temperatures. Even though your engine cooling is not overheating, the exhaust gas is wearing away the rings, pistons, cylinders and valves. Turbos are engine killers in the wrong hands. Because the engine is light duty, the cylinders aren't sleeved, so overhaul is more expensive. And if you haven't bought Volvo parts, you haven't experienced expensive.

  5. #5

    Default Re: AQD40 / TMD40 fuel consumption

    Quote Originally Posted by Lepke View Post
    Fuel use goes up rapidly as you get near top end. On much bigger boats it's common to use twice the fuel used at hull speed for about 7-8 knots more. You're probably not fully planing. You're pushing water. My experience, with much bigger hulls, don't really plane until 18-19 knots and then the fuel can be cut back. Everybody with a faster boat wants to go faster yet and for free. You may need trim tabs, or better tabs or repositioned tabs. The hull shape may not be right. You may not have enough engine hp. That's a light duty/pleasure rating. And while Volvo says you can run at 3300, they only care that you make it thru warranty. Diesels run at near wide open throttle don't last as long. The killer is exhaust gas temperatures. Even though your engine cooling is not overheating, the exhaust gas is wearing away the rings, pistons, cylinders and valves. Turbos are engine killers in the wrong hands. Because the engine is light duty, the cylinders aren't sleeved, so overhaul is more expensive. And if you haven't bought Volvo parts, you haven't experienced expensive.
    Hi Lepke,

    Good remarks, you are referring to phenomenon which happens when you try to exceed hull speed. In that situation load increases substantially while speed doesn't.

    However, in my case as the hull is planing better (less load or drag) at 15knots / 3000rpm yet the fuel consumption goes up by about 35% compared to 13,5 knots / 2800. That's the reason why I feel puzzled.

    The max rpm of the engine is 3550 so 2800 is about 79% and 3000 is about 85% of the max rpm. Maybe the 3000 is just a peak where the fuel use goes up rapidly?

    In order to find out wether the 3000 is a "magic peak" I hope someone with a similar setup or at least same engine chimes in to share his / her practical experience to know

    thanks again for all good comments so far please keep your thoughts coming!

    -Artto

  6. #6
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    Default Re: AQD40 / TMD40 fuel consumption

    We had a pair of KAD32's (165hp I think they are) and they burned around 20 - 25lph at cruise (around 3200 - 3400) depending on load. My more modern 5.9l 330hp engines burn 40lph at 85% load. Your fuel numbers look pretty bad even for a slightly older technology. I would first up put a boost gauge on the engine to check what boost numbers you are getting. Volvo turbos are pretty notorious for rusting in the exhaust housing and making low boost as the clearances between the housing and vane tips opens up. After that I would be getting the injectors checked. Does the engine start quickly and does it smoke much at idle? If it does is the smoke white, grey, or black? Does it black smoke much when you are running at cruise?

  7. #7

    Default Re: AQD40 / TMD40 fuel consumption

    Quote Originally Posted by aliboy View Post
    We had a pair of KAD32's (165hp I think they are) and they burned around 20 - 25lph at cruise (around 3200 - 3400) depending on load. My more modern 5.9l 330hp engines burn 40lph at 85% load. Your fuel numbers look pretty bad even for a slightly older technology. I would first up put a boost gauge on the engine to check what boost numbers you are getting. Volvo turbos are pretty notorious for rusting in the exhaust housing and making low boost as the clearances between the housing and vane tips opens up. After that I would be getting the injectors checked. Does the engine start quickly and does it smoke much at idle? If it does is the smoke white, grey, or black? Does it black smoke much when you are running at cruise?
    I think the boost gauge is a good idea. I will do that. I think I can check the boost value specs at a Volvo maintenance book?

    The engine starts good and does not smoke at idle or cruise speed. Of course there is a tad grey smoke when I crank the engine. Other than that I can't see balck or whit smoke. While the engine does not seem to smoke at least 2 injectors feature a different pulse than the rest 4. Also, one of the injectors with different pulse produce a special sound that i think comes from combustion.

    thanks for hints!

    However, when I used to have a pair of AQAD41B engines they smoked a lot more and there was always soot to be cleaned form the transom. But they were direct injection engines and as such had tendency to smoke more.

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