So why does my old, giant wagon, with a big motor get bad mileage?

Diesel oil has other additives, being a dirtier engine. We were taught in automotive tech that if you had those type deposits of which you would typically find in engines produced before the PCV valve was mandatory, you could simply do an oil change using Diesel oil. The innards would be clean, after the next oil change.
Over here, they still market S.A.E. 30 non-detergent of which was recommended by manufacturers of 2-stroke engines. Well, not so much recommended than a warning not to use oil containing detergent additives. This viscosity oil was no longer meant for such applications. Instead, it's recommended for old cars, for some reason
Speaking of 2-stroke applications, this same S.A.E. 30 is also advised for use in wet clutch motorcycles, irrelavent of stroke, for easier clutch engagement and shifting, since the heavier S.A.E. 85-90 gear oil would still produce friction with a disengaged clutch. For such applications, a detergent S.A.E. 30 oil isn't recommended, because no magnetic drain plug is used. The detergents serve to keep contaminants oilborn, so that they get carried to the filter. Where you don't have a magnetic drain plug, you'd want to keep the sediment at the bottom of the casing and not floating around to end up in the bearings

 

Thanks! Here are some oil analysis results to tell you the zinc content (or, for the 0w40, give you an idea; I didn't find an anlaysis of a virgin sample for T6 0w40 and the other two are virgin samples.)

Shell T6 0w40 Zinc (after 5,500 Miles in a 2015 RAM 1500 EcoDiesel: ) 1101 PPM;

https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/4740552/Rotella_T6_0w40,_5.5k_mi,_2015

Mobil 1 Turbo Diesel 5w40 Zinc: 1118 PPM;

https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/1939477/Mobil_1_5W-40_TDT

Shell T6 5w40 Zinc: 1262 PPM (may or may not be the highest since I have no data for Virgin T6 0w40.)

https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1939470&page=1

Honestly though, I just looked at virgin analyses of just a few Gas 10w40 oils and they didn't seem much lower in their Zinc content; one oil I saw that was ridiculously low was Dollar General brand (not surprisingly.) I don't suppose all Gas 10w40s have as much zinc in them as these two varieties but they're what I found just looking at BobIsTheOilGuy:

Mobil Delvac XHP 10w40: 1120 PPM

https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2717674

Castrol Syntec 10w40: 1133 PPM

https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/475924/1

Dollar General 10w40: 404 PPM

https://bobistheoilguy.com/forums/ubbthreads.php/topics/4280153/Dollar_General_10W-40

True. My post reflects a detail they didn't mention there, though; although 5w30 is thinner than 5w40, all numbers only refer to viscosity ranges which explains why the two 5w40s I posted in Page 2 aren't quite the same:

Mobil 1 Turbo Diesel Full Synthetic 5w40: 97.9 at 40° C, 14.5 at 100° C.

Shell T6 (Diesel) Synthetic 5w40: 90 at 40° C, 14.9 at 100° C.

Even the 0w40:

Shell T6 (Diesel) Synthetic 0w40: 75 at 40° C, 13.2 at 100° C (It's thicker than a 10w30 but not much.)

I guess manufacturers want to keep it simple on the bottle. I got all these numbers from the data sheets they publish online (and yes, they used the same testing method for both 5w40s: )

Mobil 1 5w40:

https://www.mobil.com/english-us/passenger-vehicle-lube/pds/glxxmobil-1-turbo-diesel-truck-5w40

Shell T6 5w40:

http://www.purseroil.com/wp-content/uploads/pdf/ShellRotellaT65W-40.pdf

Both of these Diesel 5w40s are good oils and I got higher fuel efficiency with them than I got with a slightly thicker 5w40. When you get all detailed in oils it gets a lot more complicated.

 

Why is nobody adressing direct drive, as a solution?

 

For that, he'd need an AOD transmission, for which exactly zero have the FE bellhousing pattern. I suppose Advance Adapters has an adapter plate, to sub as the separator plate, that would allow for it to be installed on a 390, as long as the face of the torque converter, and its four studs, will fit an FE flexplate.

 

I don't know what AOD stands for. But, it's not uncommon to use a THD 400 on a Ford. There'll be a prefabricated adapter, to fit between the Ford flexplate and the GM converter, if they haven't yet gone over to fabricating a specialized flexplate for this particular application

 

Ford automatic overdrive (AOD). And yes, some use a Turbo 400, but they also use a 9" rear. It just takes the correct adapter, and if the engine and trans both are from the same manufacturer, it makes adaptation much easier if parts are available.

 

I noticed a difference when I switched to the Shell T6 5 W 40 in my 300 TD the old diesel rolls over and seems to rev easier with it verses the old 15 W 40 dino, the only thing I was concerned about with the T6 was the zinc content but judging by the numbers you posted I needn't have been which will save me a few dollars for zinc additives.
As for the OP's issue have you done a compression test to check for possible intake/ exhaust valve leaks or tried different tune setups ie: different base timing positions and/ or changing the timing curve, also do you know what the gear ratio in the rear end is. There are to many things that will affect the efficiency of any engine.

 

How old is the information on bobstheoilguy website? All the diesel oils were reformulated a few years back to meet the new standard requirements. If I remember correctly a lot of zinc has been removed from the shell diesel oils. I used to use them but stopped as a result of the reformulation. If an oil is labeled "high mileage" the standards dont apply and they usually contain a higher zinc level. It's with a wink and a nod that allows the companies to produce a higher zinc and phosphorus level oil to sell. Its because higher mileage engines are usually past there emissions life span that they can sell this stuff. I used royal purple high milage for a short period, because of the high zinc content. Waiting for sales was a pain so I am now using amsoil in everything. I use the Z-rod oil in my 05 ram, 64 Cadillac and 77 colony park. It also has a high concentration of anti rust additives, formulated for long term storage (acids) and some of the highest zinc and phosphorus amounts out there. Remember, oil opinions are like bellybuttons everyone has one.

 

They reformulated the oils? Oh. Here are the dates the posts linked were posted on:

1: Shell T6 0w40 Zinc (after 5,500 Miles in a 2015 RAM 1500 EcoDiesel: ) 1101 PPM - April 27, 2018:

https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/4740552/Rotella_T6_0w40,_5.5k_mi,_2015

2: Mobil 1 Turbo Diesel 5w40 Zinc: 1118 PPM - July 1, 2010:

https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/1939477/Mobil_1_5W-40_TDT

3: Shell T6 5w40 Zinc: 1262 PPM - July 1, 2010:

https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1939470&page=1

4: Mobil Delvac XHP 10w40: 1120 PPM - August 17, 2012:

https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2717674

5: Castrol Syntec 10w40: 1133 PPM - February 4, 2004 (Most likely has been reformulated)

https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/475924/1

6: Dollar General 10w40: 404 PPM - December 20, 2016

https://bobistheoilguy.com/forums/ubbthreads.php/topics/4280153/Dollar_General_10W-40

I'd think #5, Castrol Syntec 10w40, would have long since been reformulated. Shell T6 0w40 may still be the same, T6 5w40 might also still be the same but I'd have to look it up.

- Austin

 

Yes that is the reformulated T6. It was around 1400 to 1600 with the original formula if I'm remembering correctly. Amsoil Z-rod is a bit over 1300 and 1400 for phosphorus and zinc content. I like it because its shipped to my door almost overnight for free if I spend $100 and I became a member. I use enough oil with three cars and two boats its worth it.

 

I try to drive on non windy days just for a few more mpgs.

 

Driving close behind semi-trucks also helps. Maybe, a sail wouldn't be a bad idea, while driving with the wind blowing from behind the vehicle

 

I'm only going to drive down hill in the future

I had a compression test done on it and they said it was 'good'. These guys specialize in old classics (they weren't happy I was putting EFI on it) so I'll take their word for it.
They redid the timing too, and it's 'to spec', which again I'll have to take their word for.
I don't know what the gear ratio is for that rear-end, presumably it's stock, whatever that is.

 

I have Amsoil (though not Z rod) too, I use it in both Chevrolets but not the Mercury Wagon (which gets Castrol Magnatec 5w30; 112x Zinc PPM.)

Amsoil Z Rod only comes in 10w30 and 20w50 though. Neither are what Eric's after.

 

Amsoil Z Rod only comes in 10w30 and 20w50 though. Neither are what Eric's after.

Me to, that's why I use 3 10w30 and 2.5 10w50.