2005 Sea Ray 420 - 480CE fuel burn difference

NJMatt50

Member
Apr 28, 2009
225
Jersey Shore
Boat Info
2005 Sundancer 420. Sea lift platform, Axiom Pro, FLIR.
Engines
Cummins 480ce
Took a trip 3 hours each way with my 05-420. The smart craft showed the port motor burning more fuel per hr. I was full when I left, filled up upon return so the real numbers of used fuel were 84 gallons for the port, 76 gallons for the stbd + genny running on that tank as well. Genny was on the entire time so figure knock 6 gallons off for that so that leaves a difference of 14 gallons burned between port/stbd. That to me seems like a big difference for the 6 hours running. What would cause this difference? Am I not burning enough on one side or too much on the other? I have 24x27 which is known to be over propped. Thanks.
 
Took a trip 3 hours each way with my 05-420. The smart craft showed the port motor burning more fuel per hr. I was full when I left, filled up upon return so the real numbers of used fuel were 84 gallons for the port, 76 gallons for the stbd + genny running on that tank as well. Genny was on the entire time so figure knock 6 gallons off for that so that leaves a difference of 14 gallons burned between port/stbd. That to me seems like a big difference for the 6 hours running. What would cause this difference? Am I not burning enough on one side or too much on the other? I have 24x27 which is known to be over propped. Thanks.

do you have other parameters on smartcraft? I think those engines show burn rate, exhaust temp, boost, and more importantly engine load percentage?

if one is showing higher load it could be a dinged prop, misaligned driveline, or some other loading issue.

my understanding from reading Info on those engines while we were in the market was they should burn about 13.5 gph at 2200 and 24Gph at 2600 or they’re likely to drop a valve from overloading
 
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These motors only show fuel burn on the smart craft, no load readings. The port is showing higher burn rate as it does correspond with the amount I had to add to fill. I did add EGT's and that motor also runs a little higher, low 700's. That motor also has a higher coolant temp. I have to do more testing but the difference in fuel burn seems to differ at around 1800 RPM. I don't have any vibrations, I know there was a little play in the cutless bearings but I don't know that can account for the great difference. 4 years ago the 1000 hour service was done and I saw on the receipt that some injectors were replaced. I just got this boat 2 months ago. I plan on getting boost readings next.
 
Yeah, I read up on that. I am at 14.5+ on the port. 13.5+ on the stbd. In the ocean under wave load these numbers climb.
 
Yeah, I read up on that. I am at 14.5+ on the port. 13.5+ on the stbd. In the ocean under wave load these numbers climb.

any record of the props being done? I’d get some good rpm/speed data along with targeted burn rate and feed that to a good prop shop to scan and adjust them. Also worth checking alignment and other basics like air filters, fuel filters, etc since it’s a new to you boat.

our starboard side had a higher burn and while we also needed the props cut back on both sides, the higher burn rate was from a pretty severely vent strut causing shaft drag
 
Yeah, I plan on doing all the maintenance in Sept. I am going to do all the cooling system. I did notice there was a little play in the cutlass bearings, visually the props looked ok but until they are scanned there is no way to tell. I know the previous owner did do the props about 4 years ago.
 
You might consider having oil analysis done on both motors and see if there is fuel detected in the oil on the hotter running motor.
If they changed injectors it could be a bit more fuel, also need to know turbo boost numbers
 
Update on this. So I found the stock 22x27 props were bent flat a bit on some fins, stbd worse than the port. I picked up a set of 22x25 props that are Tienbridge and have way more surface area. The fuel burn went down but now the opposite motor burns like a gallon more fuel per hour. Not sure what’s up with that. Any ideas? I think I am now under propped.
 

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Update on this. So I found the stock 22x27 props were bent flat a bit on some fins, stbd worse than the port. I picked up a set of 22x25 props that are Tienbridge and have way more surface area. The fuel burn went down but now the opposite motor burns like a gallon more fuel per hour. Not sure what’s up with that. Any ideas? I think I am now under propped.

looks more in line with where you’d want to be but that starboard side is more loaded so it makes sense it’s burning a little more. We’re these new props scanned to make sure they’re in spec? Even brand new from the factory they can be off
 
The new props were definitely reconditioned but I did not have them scanned. They were sitting in a basement for a bunch of years.
 
Try pushing the throttle up on the port side and see how much it takes to climb to 46% or whatever the stbd is at. I bet it doesn’t take much ans then the other numbers, boost and burn, will match. If that’s the case it’s almost certainly a loading or prop discrepancy and the engine is doing what’s being asked of it
 
Try pushing the throttle up on the port side and see how much it takes to climb to 46% or whatever the stbd is at. I bet it doesn’t take much ans then the other numbers, boost and burn, will match. If that’s the case it’s almost certainly a loading or prop discrepancy and the engine is doing what’s being asked of it

so I kinda did that. It’s like a 40 rpm difference. Check this pic
 

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so I kinda did that. It’s like a 40 rpm difference. Check this pic

So, roughly .25” pitch could equal that 40-50 rpm, or a small variation in the cup. Not that props should deform just sitting inside basement but it wouldn’t take much to knock it out by 1/4”

I’d get them scanned and balanced before chasing anything on the engine side or you might be after a ghost.

Run a WOT test too, the prop shop would want that info
 
Yeah. I think I am just going to roll with it for now as is. Do you know what percentage load at cruise should be? See attached pic of how I am running. I have to see how that fuel burn is calculated because a weird thing is at idle in the slip the motor in question stbd is at .03 and the port is reading 0.0. I almost need to get the port to 800 to start to see a reading. Not sure how accurate the readings are.
 

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I'm watching the thread. I too have a port engine that burns more than the other. I have the old 450 mechanicals. I can't monitor anything other than fuel gauges and how much I actually add when refueling. Engines otherwise run well.
 
Yeah. I think I am just going to roll with it for now as is. Do you know what percentage load at cruise should be? See attached pic of how I am running. I have to see how that fuel burn is calculated because a weird thing is at idle in the slip the motor in question stbd is at .03 and the port is reading 0.0. I almost need to get the port to 800 to start to see a reading. Not sure how accurate the readings are.

I’m not sure, that’s where my knowledge ends on these. According to that sbmar article 13.6gph at 2200 is the target so you’re nearly spot on to the recommendations. I’d roll with it as well, maybe get the props tuned up down the road
 
These motors only show fuel burn on the smart craft, no load readings. The port is showing higher burn rate as it does correspond with the amount I had to add to fill. I did add EGT's and that motor also runs a little higher, low 700's. That motor also has a higher coolant temp. I have to do more testing but the difference in fuel burn seems to differ at around 1800 RPM. I don't have any vibrations, I know there was a little play in the cutless bearings but I don't know that can account for the great difference. 4 years ago the 1000 hour service was done and I saw on the receipt that some injectors were replaced. I just got this boat 2 months ago. I plan on getting boost readings next.
I think you will find there are no actual flow meters for fuel burn rates; the values are calculated by the engine's ECM using a host of engine operating parameters. Throttle positions, manifold pressure, air temperature, RPM, coolant temperature and injector duty cycle are used to calculate the burn rate. If one of those parameters are skewed for one reason or another the calculated burn rate can get falsely skewed. It can be a mixed bag of things also that are nominally operating but all stack up in one direction to differing flow rates. Even one engine could be low and the other high - you simply just don't know if mechanically everything is right without dedicated flow meters.
If your oil analysis is showing good and equivalent for both engines and when engine sync is on the data is all on par you are probably pretty close on burn.
 
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I'm watching the thread. I too have a port engine that burns more than the other. I have the old 450 mechanicals. I can't monitor anything other than fuel gauges and how much I actually add when refueling. Engines otherwise run well.
If it’s not more than 5 or 10 gallons per tank fill and somewhere close to the prop curve, I would just go with it and do some checks on the next haul out. Without flowmeters, it’s impossible to tell with these motors on short every weekend bopping around trips to restaurants and beaches. On longer trips you can get pretty close on estimated burn by running regimented segments at constant rpm. My wife is our flowmeter and a genius at this and can get it within a few gallons most days. We run a lot of slow cruising at 1100 and she uses 5 gph, we like to cruise at 2280 and she uses 32 gph as a base and sometimes tweaks it to account for seas, wind against the bridge glass if it’s not open, then throws in a little Kentucky windage based on how the egt is running that day. She uses .6 gph for the gen. She adds it up as we go along and then checks the fill up against her numbers to get a feeling for how happy the engines are or if I need to figure out why we’re burning too much.
My starboard fuel gage is wacky, it never reads correctly and drops faster than the port gauge. Most of my gauges don’t read correctly but they are consistent in their inaccuracy and I can deal with that. So long as the needle is pointing to the same place all the time, that’s all that matters.
Last long trip we were on was when we were up in your neck of the woods. Here’s a shot of the last two full pages of her scrap book on our way home.
5D282D00-23A2-416C-9910-B2FE767842C4.jpeg
 
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If you read that article, it has really good advice, and you would preferably like to see the engine propped for a target of no more than 23 Gal/Hr at 2600 RPM. Basically your under propping the engine to reduce fuel consumption/load and reducing EGT as well (and the heat is the killer).

All this needs to be done with a good clean bottom and running gear in good shape. Additionally, you need to make sure your RPM #'s are accurate, so either use a digital photo tach or get a set of Aetna tach's. Depending on where the data is coming from, there may be some rounding/calculating that throws your display off (My N2K tach's are +/- about 15 rpm, Aetnas +/- 1). But since getting the props worked is expensive, good data saves money.

Pick a set of props you think are the best, but swapping back and forth will likely change your numbers (maybe dramatically).

Sounds like your going to add EGT gauges and these are very worthwhile. Once you get the props dialed in and some baseline Speed@RPM/Boost/EGT's any change in the load (change in weight, bottom fouling, dinged props) will show up immediately as a change in speed/boost and EGT. Once you get this info, you'll have a little warm fuzzy that you've done all you can to make your engines last.
 
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