38 Open Fuel Tank Question

[HisDoghouse]

Hi all,

I’ve got a 2004 38 Open which I bought as the first owner in March 2006. I have the Yanmar 6CXM-GTE2 500 HP engines. Here is the background on my questions:

This past March, prior to going offshore, I top off all three of my tanks, the two ~80 gallon wing tanks and the single centerline ~ 400 gallon tank. I do not close the valves on the discharge of the wing tanks, and I do not operate the fuel transfer pump throughout the trip.

At the end of the day (about 80 miles each way plus a number of hours trolling), I return to the dock and top up my main tank to see how much fuel we used to share the costs with my friends. I was amazed at how little fuel we consumed! I pumped 188 gallons into my main tank, which results in an estimated and amazing .9 MPG! I based everyone’s share on the fuel I pumped, and everybody was happy.

The next day, I thought to myself that this was way too good to be true. So I lifted the hatch and looked at the fuel gauges on each wing tank. They both were down to almost the ½ mark! While the tanks are not rectangular, I estimate that each tank was down 30 – 40 gallons. So add 60 gallons (or more) to my 188 gallons for this trip and my estimated MPG is a more reasonable (and expected) .7 MPG.

My questions are these:

1. What are other 38 Opens getting for fuel economy?
2. Has anyone else experienced the same issue as me with fuel flowing without being deliberately moved from the wing tanks to the centerline tank?
3. Does anyone run with the fuel valves on the discharge of the wing tanks shut if you have the unintentional fuel transfer issue?

This is a great forum. I hope it is not turned into a Luhrs-bashing venue (and by what I have seen already, it won’t), but rather a more Luhrs-focused place to discuss issues and provide tips about our boats.

Joe
His Doghouse Too

[davku]

Hi Joe, I have a 2000 38 Open with 450 hp Cummins. I run the boat out of NJ. On a typical canyon trip which is about 80 miles out with an all day troll I will burn aprox. 225 gal. I thought that the fuel in the auxiliary tanks had to be manually transferred, I didn't think the fuel would transfer on its own but not sure. I only fuel up my main tank now when heading offshore.

[Reel-Deals-1st]

davku is correct about having to transfer it manually. You may want to check the vent on your aft tank to make sure it is not clogged and creating a vacume and pulling the fuel from the saddle tanks. Another thing that I have seen is the small screen that is in the vent will get clogged. If you take a small pick you can pull it out with out removing the vent. Without actually looking at it, its a little hard to trouble shoot. Something else I would suggest is filling your main tank with the fuel from the saddle tanks at the end of the day and refilling the saddles so you're always using fresh fuel. Ill keep digging and if I can come up with a resolution ill let you know. -Jeff

[HisDoghouse]

Jeff & davku,

Thanks for the suggestions. I will try to get at that vent this weekend. This was not the first time I had a similar thing happen with fuel unexpectedly disappearing from my saddle tanks. I just figured (wrongly) that I or someone else inadvertantly bumped the transfer switch. This is not something I even remotely thought of reporting as a discrepancy after I bought the boat.

Maybe the clogged screen is also the reason that when fueling I never get a burp from the vent, but rather out the fill. I would cover the vent with that suction cup collector thing to keep fuel from the water, but it would ALWAYS burp out the fill.

My vents are flush to the hull, do they still have the same screen somewhere inside?

And on always fueling from the saddle tanks, I'd prefer to carry less rather than more fuel unless needed. So I'd rather fix this problem right.

Thanks again,

Joe

[Reel-Deals-1st]

I just went out and looked at the vents we are using now and they did have the screens in them. If you look into the vent you should be able to see it. You may also want to check your vent hose routing and make sure it is not pinched anywhere. Hopefully, this will take care of your problem. Let me know.- Jeff

[HisDoghouse]

Before the weekend I did get a chance to pull the screens out of the vent fixture. They did not appear to be too terribly clogged, but who knows. WIth them gone, I will move the last of my fuel from the saddle tanks and plan on shutting the valves. Hopefully that will force the vent to do its job.

On the hose, from what I could see, it was not kinked. It did disappear behind the bulkhead (forward of the tank) and I can't see it, but I'd like to hope that the hose was laid out correctly and there are no kinks in the line.

I'll report how it goes. If you hear of a 38 Open going down because of a fire due to an imploded fuel tank - don't look for a response :001_cool:

I hope everyone had a great weekend (like we did).

Joe
His Doghouse Too

[Succession]

Joe,

The saddle tanks flow into the main tank if the valves are left open. I have noticed this when I made my run from Tampa to VA. If you shut the valves no fuel will make its way into the main.

It only happens when you are running the boat.

[HisDoghouse]

Kevin,

Thanks for the response. So yours does it too. Hmmmm. I have not had an opportunity to run the boat since I pulled out the screens on the vent other than take the boat to Bay Island over in Lynnhaven for them to finish the warranty stuff. I was hoping that the fuel didn't naturally gravity feed into the main tank, and that it was a vent issue. Interesting though that I have never burped fuel from the vent on the main tank, always out the fill. The saddle tanks however, is another story - they always have burped from the vent.

Do you run with the saddle tank valves closed? Have you experienced any problems whatsoever with running that way?

Glad you signed up. See you on the water,

[ALL SMILES]

Ive only owned my 38 Open for a little over a month, My fuel comsumption with 485 Detroits is 30 GPH. The ex owner and also the owners manual states not to run with the wing tank valves open as siphoning into the main tank may occur.

[HisDoghouse]

All Smiles,

I didn't know (hadn't read it) that the manual states to not run with the valves open. But that is now my method of operation. All I need now is to get the main tank fuel gauge to actually read correctly (or at least nearly so) and I'll be good to go.

Joe

[HisDoghouse]

A few months ago (while still in warranty), my dealer replaced the defective fuel tank sender on my main tank. The symptom then was that the fuel would burn down in the tank, and the gauge would follow it until it got to about 3/4 full. Then the gauge would drop to empty.

The dealer replaced the sender with a new one, and I thought all was great. It read full with a full tank. I didn't notice that the needle was NOT creeping down. Bottom line - the sender they installed was CONSTANTLY reading full and they got a new sender. I took out the sender they installed, and noted that it felt like it was hanging on something near the top of the tank.

I installed the new sender using the same orientation that they used - wth the float unit pointing straight aft. My concern is that if the float hung up once, it may hang up again. With a five bolt pattern, I can rotate the sender one hole either way (actually, maybe two but I'm not positive on that). My question is this: does anyone from Luhrs know how the sender should be oriented in the tank? Should I keep it pointing straight aft and risk it hanging again, or is it designed to be angled towards the port or starboard quarter?

I have asked (via voice mail) my dealer if they remember how the original sender was oriented, but my guess is that they don't remember. Heck, if they knew which way it was supposed to face, I'm hoping that they would have installed the (first) replacement correctly. By the way, the sender I took out does work fine outside the tank - I now have a spare when the one I put in dies.

Any help or information would be GREATLY appreciated.

Joe

[davebanks]

can you tell me at 30 gal per hour is at what speed, im looking at buying 38 convetible and I am trying to get some idea of feul cosumption
this guy is saying he's getting 20 knots cruise and 24-26 max
Is this the best I can expect from 900 plus hp in this boat

[CrazyIslandMoFo]

Davebanks, These boats don't seem to be speed demons. My 29' with 600+ hp only realy wants to go 15-18 kts, My bertram 28 with only 520 hp does plane a lot nicer and sooner... soooo, always a trade off, I like the layout and design of my luhrs more, I like the way she drifts, I like hanging out with my buds on deck, I miss the way my bertie runs on the water. My luhrs is more siuted more me...

[HisDoghouse]

I'm going to be testing the FloScan NMEA 2000 capability on my boat soon, and I'll be able to post what my fuel numbers are in the near future. I'll throw it in a new thread.

Joe

p.s. Has anyone else had trouble posting the past few days (up until just recently)?

[HisDoghouse]

Looks like the problems from the past few days has been resolved.

[Rusty]

I have a 1999- 32 ft. Open.

A couple of weeks ago in route to the fuel dock my fuel gauge drop to zero. When this happens it puts the 'worries" on you quick. Needed 211 gallons in a 360 gallon tank.

Last week returning from an 80 mile overnighter, the fuel gauge started jumping and then the volt meter likewise started jumping. I have already replaced the VDO gauge system. Installed 216 gallonsof fuel in the 360 gallon tank and all guages are well.

Bottom line is that these guages appear to work "half-ass". I always log in engine time and compare run time with conditions.

The only way to assure consumption is with the flow guages. My next expenditure will be the flow scans. Keep us posted on your results!!

Rusty

[HisDoghouse]

I will keep you informed on the NMEA 2000 FloScan progress. I am getting gal/hour data on my Raymarine E120. That's the only data that the Raymarine unit CAN display. I'm working with Raymarine to get additional data elements (i.e. MPG, total fuel, etc) to be incorporated into the next software release.

I'm also testing a new capacitance-type of tank sender. The developer's site is www.tidewatersensors.com/ (http://www.tidewatersensors.com/), and he will be going into production soon (if he's not already selling). I'm doing the beta testing as a diesel boat.

My initial impressions are that the water sensing is very sensitive, and I may be getting him to shorten up the sender to keep it out of the (minimal) water that's in the bottom of my tank. We also need to recalibrate as right now I'm off quite a bit. Also, it appears that system voltage has a direct coorelation to indicated tank level. We're also working on that one.

More to follow,

joe

[davebanks]

at 30 gals / hr what is your speed and do you know what size props your running also whats your max speed

[HisDoghouse]

Yesterday I was able to give an (uncalibrated) test run of my boat with the FloScan installed on my port engine. At 2,400 RPM, I was making 25 knots, and was burning 18 - 19 gallons per hour on one engine.

That means I was buring 36 - 38 gallons per hour (assuming both engines were consuming fuel at the same rate) at 25 knots. That works out to between .69 and .66 Nautical Miles per Gallon economy.

I have 24 x 31 props, my max RPM is 2,900, and I have a 2:1 transmission. My top speed is approximately 31 knots.

[Esquire]

Hey Dog..
Always wanted to say that..
How is the new sender and flo scan project working out?

Scott

[HisDoghouse]

Scott,

The FloScan device is installed and working fine. I have not gotten a Fuel-Tron display yet, but the NMEA 2000 device is providing data to the E120 via the NMEA 2000 bus. The only data element is still just the gallons per hour.

I'm hoping that once Raymarine kicks the SPX autopilots out the door, they'll be able to focus efforts on the E series software. I've strongly requested that they add additional fuel data elements to the next release (i.e. MPG, total fuel consumed - resettable, etc). If they do, these FloScan devices will be invaluable to us.

I haven't taken on fuel since I topped up after adding the device. I'm planning on filling up in the next couple of weeks, and will see if the total fuel consumed that's on the NMEA 2000 box is close to what I take.

The fuel tank sender is reading accurately. At idle speeds in a rolling sea, it is detecting water in the tank (the device beeps and the needle swings). There is a trace of water in the tank when we do a water paste test on a dip stick, but nothing significant. We may want to go shorter on the sender to stop the water notification from taking place. I need to discuss it further with the inventor.

Joe