Vinsil

I bought the truck in my sig back in November. First trip empty..netted me 19 mpg. VERY easy driving..and keeping it around 60 mph.


I've been driving back and forth to work, mostly town driving.


Consistantly getting around 16-16.5 mpg in town. Not horrible.


I have mods planned. Nothing done yet.


I put my trailer on Friday which weighes in at 1700 pounds. 16 foot tandem flat deck. I put my rock toy on (1986 4Runner...weighing about 4000k) and parts/tools and supplies for the weekend. I didn't stop at a scale to weigh the combo...but I will guess another 1000 pounds of stuff added in.


I traveled 300 miles round trip with the trailer. Did 60-65 mph for 80-100 miles on I-5...then hit a 2 lane road, lots of hills getting me down to 35-40 mph on some. I didn't push the truck hard..nothing full throttle. The load felt pretty heavy for the truck, but this being my first pulling with it and from what I've read the 1 gen truck are pretty weak bone stock.


I followed my friend with a similar load (he might have had 1000 more pounds) but he's also got a 2004 Cummins too.


Here are the results:

I hand calculated 12.5 mpg. Now...I'm pretty disappointed in this. I honestly figured I'd get closer to 14-15 mpg which I'd be plenty happy with! But at that rate...I'm really close to what my other friend gets with his 460 dually.


Was I pushing it too hard to get mileage like that? I pulled it out of O/D on the longer steep hills and was pushing close to half throttle to keep up speed. I don't have my gauges in but I could hear the turbo at full spool quite a bit and I gather that's not helping my cause.



I plan to check my mileage again this tank and see if something changes on it empty.

I haven't thrown on my overhead camper yet either...and now I'm half afraid it will get alot worse!


I won't even begin to complain about the lame brakes we have on our trucks. I have plans for that part..but can you guys help me on mileage? Is there something I can do mod wise to help out? Anything I'm doing wrong? Need more info on my setup? I know peoples driving style really affects mileage..but I'm also one of those who seems to drive pretty common sense wise and can usually get great mileage out of vehicles.



Here is a picture of my setup if it helps:





Thanks all. BTW...I do love towing with a diesel!!! I can't imagine going back to a gasser anytime soon! I'm just worried since I bought for fuel economy on top of being able to pull the loads I need to pull and have some very long distance trips planned and would like to get this sorted out before I take those. I have a 2000 mile trip planned for August and a 1000 mile trip in June coming up. Thanks for the help!!

wannadiesel

Several things I would help with both the mileage and the power. First, ditch the 21 cm turbine housing. Get a freer flowing exhaust on there, and advance the timing 1/8". If you can afford to do it, get a better torque converter in there. The stock one does a good job of converting torque to heat - not the best thing for a tow rig. The DTT 89% unit is very popular.

Once you get gauges, start turning the pump up. It will not hurt the fuel economy (except when you use the extra power). Also, don't be afraid to wind it up, dropping out of OD on a hill is not a bad thing, especially with the loose stock torque converter.

edit: The aerodynamics on that load look terrible. With it being such a small open trailer, I don't think there's much you can do, though.

Vinsil

Thanks for the tips.


I planned on doing the following:

12-16 cm housing/4" straight pipe
gauges
BHAF
and pump mods to follow suit.


I was also told the 3200 spring would help too. I'm just trying to stay away from things that hurt mileage unless I pour on the fuel.



As for the TC...this truck has a new trans in it. It was done to stock specs though as far as I can tell from the paper work. How much would the DTT 89% cost? This is something I'd prolly do if it made things better for the trans and towing.

As for pulling it out of OD on the hills...what sort of RPM do these motors like to sing at? My friend with the 04 trys to keep his under 2500 rpm...but if guys are doing the 3200 springs and loving it, do they like to sing up there and work? I noticed on a few of the hills my water temp gauge started to move up to about half way. Common? It never comes off the second line when empty.


Thanks for the advice. Will this help in mileage or just make it pulling the loads I do alot easier on everything? Is this pretty common mileage with loads like this?

Vinsil

Ah I just caught your edit. That is my concern...especially with my overhead camper.

G1625S

Hey Vinsil, you have the same 5th wheel as me! I thought mine was a hand made sort of deal...huh, pretty cool. On to the topic at hand...I think Wannadiesel hit all the bases for you. The auto is hurting you the most, from what I've read. I towed this:



and pulled down a hand-calc, if I'm lyin' I'm dyin' 18mpg. 15,200 gross, mostly 60mph. IMO, build the auto first. Everything you do under the hood is absorbed by that lame converter and it's only gonna get worse with more power and towing. I think the tranny will be the biggest bang for your bombing buck.

Vinsil

That is funny! I thought mine was hand made too!!!!


Anyway, I'd kill for 18 mpg!!! Maybe I should do the TC first then. I should have held out for a 5 speed like I wanted I guess.

wannadiesel

Sounds like a good plan except for the straight pipe. They are fun in town, but for a long distance tow rig you will hate it. Put a muffler on it, BC847 did a nice writeup on his BHM a few weeks ago.

I would go with the 16 cm housing on your truck. It's an automatic, so you only gotta spool it once.

The 3200 RPM spring will not hurt the mileage. The stock spring starts to defuel around 2300 RPM if the high idle has not been "tampered" with. If you are running over 2300 RPM all the time it will hurt the mileage. The motors really seem to like to run between 1900 and 2100 RPM for good mileage when towing. The point of a 3200 RPM spring on a tow rig is to allow you to keep up with traffic on hills while keeping EGT and trans temp in control.

None of the mods we do will hurt the mileage by themselves, a diesel only uses as much fuel as is needed to make the power requested by the driver. That said, you'll get better mileage blasting up a hill in direct at 70 than you will crawling up it in 2nd at 35 with a stock engine - you're spending less time on the hill working the engine.

The water temp was mainly due to the torque converter, although the increased HP needed had a little to do with it..

I think the mileage was a little low, 14 mpg towing is not unreasonable. Better airflow and some more timing should get you in the ballpark, and the TC will help, too.

I'm a stick guy myself, I have not priced TC's.

G1625S

''I should have held out for a 5 speed like I wanted I guess.''

I waited many, many moons for that white money pit to come along, that's for sure.

Your temp gauge is normal--it even says it in the manual For daily driving, I've seen the best economy at about 1800 rpms. While towing, my egt's run coolest around 2100, but anything over 2k is good. Below that, my lack of intercooler allows things to get hot quickly. Pulling the hills coming up I81N I wound her up in 4th a couple times...now I know why guys (and girls) who pull for a living usually don't have a 5'' stack 2 feet from their slider window! To answer your question, these beasts sing at any rpm. With the auto, you simply cant lug it, so just mash the loud pedal and have fun.

Vinsil

Thank you very much for the advice. I've heard it both ways on the straight pipe thing...but I honestly think I'll take yours since the wife and kid might be a little cranky with a long trip!


I'm seeing your point with the mods also. The motor would basically be working less hard to pull that hill than a stocker. Makes sense.


I guess I'll give DTT a call and figure it out. I just explained to the wife about our poor mileage and my needing to spend money on the truck. I didn't get a noway..just a "That trip to Moab is gonna cost alot at 12 mpg!" so maybe I can offset that thought with spending some on the transmission.


Thanks again, looks like I have a baseline to work off of.

JD730

Now that your mention it, I have the same 5th wheel hitch laying out in the fence row.

Everyone else hit the nail pretty square. The torque converter does do an excellent job making heat. If you put in a converter I would suggest some sort of valve body work at the same time, a shift kit like transgo at the very least.

I'll admit I got lucky and bought a 47RH(lockup torque converter) with everything I needed to mount in my 93 out of a little free paper.
My best empty is 19.5mpg with the current setup(first truck in the sig) My last big trip to get a truck I got 13mpg empty(with trailer of course) and loaded at 70mph+. Gross weight was around 19,000lbs. Pulling hills and going fast kill mileage, doing both at the same time doesn't help it.


Is it just me or are there more auto trucks out there than 5 speeds? I have 4 1st gens here and they are all auto's.

wannadiesel

I had a heck of a time trying to find a stick - ended up going to Texas to get it.

Vinsil

I hate this 5th wheel hitch..I can't seem to give it away either!




I guess the trans is gonna be my best bet for now. Telling me about 1st gen auto's!! I looked a long time and my price range put me in the 1st gen or a torn up 2nd pricing. I couldn't for the life of me find a extra cab 5 speed 1st! ALL autos.


Valve body too? I'll ask DTT what they think when I call I guess. Or are they super expensive?

wannadiesel

You can get a valve body, but you can get pretty much the same results from a shift kit.

JD730

I'm tripping over 1st gens with autos around here, literally. There's a D250 auto up the road from me that is cheap and would make a great donor. Wanna even told me about a D350 crew cab in his area, but unfortunatly they want too much for it and I have my plate full with projects right now.

kcprecision

Last summer I pulled a 7000# boat and tandum axel trailer with my 93CTD. It is stock as far as I know but does have the getrag 5 speed and I was getting some where around 15 MPG. I was in hog heaven.