Putting a Diesel in your Motorhome.
In the 80's, there was an option box you could tick to add a Isuzu Diesel motor, in Normally Asperated, or Turbocharged, to your Classic Motorhome.
Those that didn't tick that box, are 350 or 454 gas powered.
There are numerous people here, that either have a wish to put a Diesel in to replace the gas motor, or have done it, or a previous owner has.
As someone who is planning to put a diesel in, I thought it was time to have a thread where we can get all the relevant info in one place.
The venerable Chevy 454 V8 gasoline engine
Let me start by discussing the commonly fitted Chevrolet Big Block 454/7.4L V8 fitted to our Motorhomes.
This motor is an Icon.
It is about as simple, powerful, torque laden, and as long lived as gas engines come. The Truck/MH block features the better/stronger and more stable, 4 bolt main bearing caps, cast iron heads, with small port(Peanut port) intake runner, that enhanced low RPM torque.
Earlier engines came with a Quadrajet carburetor, and later models had TBI injection.
As fitted to our Motorhomes, I believe the motor weighs in at about 600lb, and power output is specified by GM, and Airstream at 230hp/360ftlb Torque.
Remember those numbers... they are important!
Interestingly though, in a recent article, Car Craft Magazine(March 2018 edition), ripped an original, untouched/unmodified 454, from a 1986 Suncrest Motor-home. This engine had an indicated 35,000 miles from new.
After they removed it, they put it in a dyno cell pretty much untouched, with its original Quadrajet carb, but used headers, and ran it as was, to get the baseline scoop.
They were surprised(and me too!) that the motor put out 335hp and 485ftlb torque!
Quite different to the official figures!
Link to that article, and watch the video... its kinda fun
Given its task, of dragging up to 16,500lb (Airstream 345/350) around, it performs well enough, and most owners report about 6 to 8 mpg is general use for the early models with carb and 3 speed trans.
Later models had TBI and some had the 4L80E 4 speed Overdrive transmission. I have seen reports of 6 to 10 mpg from these.
Its fair to discuss modifications and tuning of the 454.
Having spent countless hours, mulling the 454, and possible improvements I reached the following basic conclusion...
On Carburetor, the venerable Quadrajet, when running right is tough to beat for power and economy. Some people hate 'em, and that is fine, but the experts say that the combo of the small bores for economy and larger bores for power is unbeatable. The correct "Motorhome" unit flows 800cfm, and I gather is special, rare, and right.
I'm also told that the stock, cast iron intake is better in the MH than any other.... an expert told me that the aluminum ones are not suitable, and even though they flow better, they hurt the torque and economy...
Same goes for heads.... The smal port heads are setup for torque. Im sure larger oval port heads(049, and 781 castings) make more power, but not where we need it! It may be that some valve work, and bowl blending on the stock head would help flow.
The stock cam is setup for torque, and there are numerous "RV/Towing" grinds out there that might add something.
The one area that is PROVEN to add power and economy is the exhaust manifolds and exhaust.
Banks Power quoted that their package which consists of Intake, long tube headers, and exhaust system adds about 100hp. It maybe that it did... compared to the official figures...
There maybe gains be had in putting on a modern, aftermarket Fuel Injection system, such as MSD, or Holley, or others. These kits cost $1000 up, and maybe very good for power, economy, and consistency, as well as consistancy.
TBI models can be improved slightly too, taking into account all the above comments!
One area that is worthy of comment is transmissions....
The standard transmission behind the Motorhome 454 is the TH475. This is a version of the famous and bulletproof TH400, with stronger, straight cut planetary sun gears, and normally a tailshaft mounted parking brake.
It is a 3 speed, and works well.
There is opinion that it does hurt economy, due to its lack of gears, lower gearing, no Overdrive, and slight slippage due to Non-lockup Torque Converter.
Many people have added a Gear-Vendors OD unit behind this transmission with good results.
There are some motor-homes fitted with Allison transmissions too, and I believe these are 4 or 5 speed OD units.
The modern solution would be a 4L80E or 4L85E, and indeed these were fitted to some later TBI Injected units. These are 4 speed, electronically controlled OD, Lock-up transmissions.
Later Allison units with 5 and 6 speeds are good too!
They will perform better and save gas.
So, lets talk costs, and do some simple math(Maths for Brits)... :)
Say you drive your 454 powered Motor-home 10,000 miles, in a year or whatever.
Let split the difference of 6 and 8 mpg, and call it 7mpg.
10,000 miles Divided by 7mpg is...... 1,429 gallons of gas.
Today, according to AAA, average USA price of gas was Nationally was:
Regular 87ron= $2.60/gallon.
Mid Grade 89ron was = $2.88/gallon.
Premium 91ron was =$3.13/gallon.
So, if you use regular, your fuel costs for 10,000 miles would be 1,429 gallons x $2.60 = $3,714.
Using that formula.
1 mpg improvement in economy saves you around $357...
2 mpg is about an $825 saving.
3 mpg is about an $1,114 saving.
Of course, if you use Midrange, or Premium gas, or you live somewhere like California, where gas is more expensive than the average, your numbers and savings may differ!
You can use the above formula, to figure out if that Fuel injection setup for
$1500 or that OD transmission will gain you mpg and how long it will take to pay off the investment!
Longevity of the 454 in our motor-homes, is a varied subject, with reports of engines expiring at about 50,000 to 70,000 miles, and some are still alive and kicking at 180,000 miles, so my guess is that its all about maintenance.
My info tells me that when a 454 wears out/expires, the cost of replacing it is very subjective.
People do what they want/afford, and the cost is all over the place.
I hear of people who spent $3k on a short block and reused everything else, and others who bought a GM crate 502, @ $8k and had it installed professionally with all the other bits, they are maybe $12k plus....
1/ Why put a diesel in?
There is a good reason why larger/heavier trucks are Diesel powered.
A/ Torque. Diesels have a higher compression ration, plus the compression added by a Turbo. A diesel always has more torque per CC/CI than a gasoline engine, and so they get the weight moving.
B/ Longevity. Diesels engines generally last longer. in use due to their beefier construction, and the natural lubrication in Diesel fuel.
C/ Efficiency. Pound for pound, Diesel fuel produces more power than gas, and so better fuel consumption.
My research tells me that the Isuzu Diesel installed in a 310, and driven in the same way as the 454 gives between 11 and 15 mpg.
Isuzu engine peeps please post your numbers, so I can confirm, update???
I gather, Cummins 6BT powered rigs are reporting similar.
So, lets apply the same math we did for the 454, but skewed for Diesel.
10,000 miles, split the difference at 13 mpg.
Diesel is more expensive Nationally @$3.00/gallon.
10,000 miles Divided by 13mpg is 769 gallons... x $3.00 = $2,308.
By my simple math, a Diesel will save you $1406 per 10,000 miles.
Same logic dictates that:
1 MPG increase saves $165
2 MPG increase saves $330
And so on.
Not enough to justify the investment in logical terms, of course.
But there is another factor.
Almost all Diesel vehicles command a premium because of the perceived increase in MPG and longevity.
I believe, based upon the sale prices recently, it might be $7,000 to $15,000 over a similar 454 powered MH.
2/ What Diesel engine should you choose?
There are many many options, and it is all about what fits, and what is proven to work.
Here is a basic overview of the Diesel engines that have been fitted, that we are aware of:
As already mentioned, this was the engine option from the factory, so maybe the easiest swap, either by buying the engine and drive train from a crashed Airstream, or replicating its configuration.
I will edit in the basic info when i get feedback from the experts here!
The Cummins 6BT, a straight 6, 12v Turbo Diesel, was fitted by Airstream, to just ONE known 345 in 1990. There is at least one other almost Identical engine conversion, and several others that use the same engine in different configurations.
The 4 cylinder version of this engine, known as the 4BT, might also work very well, in smaller lighter Motorhomes.
It seems to be the most common swap for many reasons.
GM Duramax V8
There is at least one guy who has put this motor in his Airstream 280 in Holland, and another in Florida.
I will be asking for his permission to post his pics and knowledge.
Isuzu swap info
Cummins Engine Descriptions
Lets start with breaking down the various Cummins engines that are out there that do fit, or should fit.
I am aware that Cummins built engines for road vehicles, commercial trucks and buses, marine, and industrial applications, such as generators and pumps. I will pretty much stick to the road engines, because I do not know much about the others.
I have gleaned this info from across the web, but to be fair, want to mainly credit:
Good info on Cummins engines, and swap parts here too...
Cummins "B" or "BT" (1984 to 1998)
These are Direct injection, Overhead valve, Turbocharged Diesel "Inline" engines, with 2 valves per cylinder. The 4 and 6 cylinder versions are pretty much identical except the 2 cylinder difference.
Oil Pump, Cam, Injection pump, and Power steering/Vacuum combo pump are ALL driven off the crankshaft by gears. No timing chain or belts to stretch and break.
They are simple engines that are VERY common swaps into many vehicles for good reason.
They have no electronics, and it is said that they only need 2 x 12v wires to run. One to the starter(but in fact is is probably 2), and one to the fuel cutoff solenoid on the Injection pump to allow fuel to flow.
Of course, the reality is that you need at least the following for use: Coolant Temperature sensor, Oil Pressure, grid heater(Cold start), and maybe a water in fuel sensor. Many BT motors came with a 120v block heater for really cold weather use.
Inline 4 cylinder, with 8 valves, and normally displaces 3.9L.
Complete engine weighs about 750lb.
Standard output of the 4BT is 105hp/265ftlb Torque. VERY common engine in step vans.
This sounds weak, but do not be fooled... with modest mods, this engine can produce much more. Cumminshub state that it is suggested a maximum vehicle weight application as 16,000lb GVWR.
This engine might be suitable for smaller Airstreams, such as 20' to maybe 28', and also the B190 Van. It is generally accepted that this engine is a little "harsher" than its bigger brother due to the inline 6's natural balance.
I am not aware of any conversions using the 4BT yet.
Inline 6 cylinder with 12 valves, and is normally displaces 5.9L.
Complete engine weighs about 1100lb dry.
Quoted output varies dependent on year and specification, but the spread is 160hp/400ftb torque to 220hp/440ftlb torque. These are OEM numbers, and the factory tune is very conservative.
Well known, documented modifications that can double and triple these numbers. My research tells me that a tune with about 300hp and 700ftlb torque would be the sweet spot, without hurting MPG or engine life.
Injection Pump and Intercooling
I need to clarify and educate on these two items, because they impact the power, tuning, and fitment if you are looking at using a Cummins B series.
There were two very different Bosch Diesel Injection Pumps on the BT.
1/ Bosch VE44 series, rotary injection pump.
1989 to 1991.5 Non Inter-cooled Engines.
1991.5 to 1993 Inter-cooled Engines.
Plus Points: Simplicity, and compact size simple mods can give big power increases. Compact pump means ancillaries, like AC, and Alternator is easier to place
In an article in "Diesel Swap Magazine", they state that "These engines can make 250 to 300 rear wheel HP for almost no money"!
Minus points: Limited power due limited tune-ability, and limited aftermarket support. I read that 400hp is the accepted maximum output of pump. Non Inter-cooled version limited even more by heat and EGT, but inter-cooler can be retrofitted.
2/ Bosch P-7100 series inline injection pump:
1993 to 1998.
Plus Points: All Inter-cooled. Extensive aftermarket support. 500hp is easy and relatively cheap, and 1000hp plus available.
Minus points: Inter-cooler pipework more difficult to package. Large pump body impacts ancillary(Alternator or AC compressor positioning)
Known Engine reliability issues
Cummins state that the "Normal" service life of these engines is 350,000 miles.
This version is tried and tested, and has proven to be incredibly strong and long lived, but there are some well known issues to understand.
1/ Killed Dowel pin, or commonly called "KDP".
The front timing case, is doweled and bolted to the engine block. One of these dowels is not retained by any means, and sometimes works it way out of its hole, and falls into the engine. The results are ugly. It falls onto the Cam gear, and gets trapped between the gear and case, punching a hole in the case. Sometimes it can jam the gear, and damage it, or break the nose of the camshaft off, or seize the engine.
There are also some bolts that can work loose and cause similar damage.
The prevention fix is simple, a small tab from the nearby bolt, trapping the dowel in place, and while you are in there its suggested all the bolts are cleaned and "Locktite'd" in place. Simple when the engine is out, but an absolute must before installation.
2/ Injection pump failures:
Both pumps are fed by a "Lift Pump" on the Left side of the engine, normally off the camshaft. These fail, and work the main injection pump too hard causing wear and failure. Also, a good aftermarket fuel filtration is suggested to keep the fuel clean.
The only known OEM Cummins powered Airstream 345, used a 6BT, probably in 160hp/400tq tune, an an owner reported 15 or so MPG when cruising.
There are 3 other known Cummins 6BT conversions, in various configurations.
Cummins 5.9 24V
From 1998.5 to 2002.
No known swaps yet.
Cummins Swap Info
The 6BT fits.
Its been done by Airstream, and its been done by owners.
Here are links to the threads by the owners and/or conversion owners, that contain a great amount of information...
OEM Airstream Cummins, by the then owner Wxbouy. Now owned by member DsPaw.
Cummins motor appears to be a 1990/1991 6BT with Non Intercooled, with VE44 Inection pump. LH high AC Compressor above it. RV style exhaust Manifold with Turbo top, or high mounted. Also of note, is it has a Jacket Water After Cooler(JWAC) style intake neck that is plumbed into the cooling system, thus theoretically heating the charge air in cold weather, and cooling in hard use. These were common in the early days, but now not considered inefficient compared with the later grid heater/Inter-cooler combo.
Cummins Conversion done to a 1985 345, by a previous owner, but documented by Wayne Olsen in 2006. This conversion looks IDENTICAL the the OEM Cummins above.
Cummins Conversion done by GWBaker to a 1979 Excella 280.
Here are some important notes, with the known problems and solutions.
1/ It has been reported, that the engine cannot be fitted with the head and/or Oil pan in place. It is too tall to fit between the upper framework, and engine cross-member stated GW Baker, however, his earlier motorhome maybe the issue, as it has a different layout/dash to the later models.
Solution is to fit the head after the motor is in place, or the oil pan.
2/ The stock low right AC compressor mounting cannot be used. The Right hand, or passenger side Airstream chassis leg clash with that area.
Solution: run without engine AC compressor, or mount the AC compressor elsewhere. Factory Cummins mounted AC compressor high on the left side of the engine, above the VE injection pump, but I do not believe that will work with P pump. GW Baker Conversion did not appear to have AC compressor. Choctawmel found a mid right mount.
3/ The stock "Pickup type" exhaust manifold cannot be used. The turbo flange is angled at 45 deg and pushes the turbo too far outboard and the turbo will hit the Motorhome floor supports. The solution is using the "RV Style" manifold, which mounts the Turbo closer to the engine. There is an option to mount the manifold 2 ways, with the Turbo on top, or below.
If using an Inter-cooler, it looks like mounting the Turbo under-slung, next to the block will benefit routing of the pipework.
I am not seeing active links in your posts...
Its coming Bruce... waiting for editing rights so I can add them.
I have long had links to conversions in the "Classic Motorhome Sticky" thread first post if you want to look now.
My basic idea is to cover the known conversions and collate info gleaned from looking at the Factory Diesels, and the conversions that were done later.
People who have gone before, like GWBaker, and of course our recent HERO Choctawmel have blazed the path, learned by trial and error, and skinned knuckles what works and what doesn't.
My hope is that we can begin to bring together the info on the pros and cons of each engine, and its fitment, in the MH chassis, and so help with conversions going forward.
I have already grabbed pictures of conversions, which I plan to post, with peoples permission, as well as links, part numbers, and as much info as I can glean.
Just going to add my two cents.....
Isuzu 6BD1 A or T
A model pros: The A is a great motor with impecable credentials. Tough, endlessly rebuildable with removable sleeves, a true commercial diesel with lots of street cred. Smooth and quiet compared to NA diesels of the comparable era like the Cummins 6BT.
Cons: Pricey and scare parts, low hp unless it has BAE aftermarket turbo kit. However turbo is limited to max of 10 PSI or things get too hot and bad things happen.
T model pros:better than A model, as it was made for turbocharging with stiffer internals and oil spraying on pistons to reduce heat. Still endlessly rebuildable as long as no holes in the block. Can turn up the wick on the fuel pump and install a slightly bigger turbo for better power but you will loose MPG if you do so.
Cons: Same cons as A model with pricey and scarce parts.
If I was to go Isuzu I would look at a pre 2007 6HK1 with as few computers as possible; up to 300 hp and 800+ lbs of torque from a 7.8l motor, that is only marginally bigger than the 6BD1's. However packaging an intercooler and ancillary drives could prove a challenge, BUT not insurmountable, with enough money thrown at it. The 6HK1's come with 6 speed Allisons and a max rpm of 2,400 rpm, so max power is down low in the rpm range.
I did also consider a 6BG1T at 6.4L, out of a street sweeper and have recently seen an ad on Classic motorhomes for sale where someone supposedly stated they had a 6.4l Isuzu but no pictures. It would fit though.
I'll let John fill you in on Cummins or cole3444 who just bought a 310 with a Cummins conversion.
I knew you were gonna pipe up Tony, and thanks.
As soon as I have permissions I will add this info to the Isuzu section.
hey key air
Doing a motor swap is a can of worms. I've thought about it, our325 has 5400 miles on it. So high miles isn't an issue. The only thing I can think of why you'd do it, is for better milage. These things get about 7 mpg. If you put an overdrive, or an Allison 6 speed in it ,I'm going to guess you'll get, maybe 11-12 mpg. Putting a diesal in would give you a gain off of that of about 3-4 mpg? That's a lot of work for not to much gain. Plus diesal isn't half the price of gas anymore. I'm paying 2.89a gallon now. Gas is at 2.40 ish. I just can't see the gain, except bragging rights. I can buy a cummins w an automatic cheap. I could do it, but I just don't want to if I can hold my speed down around 62 mph, I may be able to pull ten, out of it. So, I don't know, it would be cool to dump a turbo end cummins in it. Keep me posted . I'll live vicariously through you.
For me, itís not about the difficulty, mpg, or simple math, itís about the whole package.
Those that follow my craziness know despite the fact my 454 is fresh, I recently picked up a 6bt in need of a rebuild.
The reason for the thread is simple. People want more... more power/torque, better mpg, and a longer lived motor. The 454 is a great engine but itís pretty much maxed out, and whilst adding all the normal tuning aides like free flowing exhaust, fuel injection, and OD lockup transmission, the core motor cannot be improved that much. A big block needs X amount of gas to run efficiently and adding power is pretty much at the detriment of mpg.
A diesel motor is the best solution to all of the above.
We all know engine swaps are not simple, but I hope to gather enough info and present it in a logical fashion so people know whatís involved, and the costs, and can make up their own minds.
In many cases the 454 is tired or broken, and people are faced with removing and rebuilding it. When this happens, the decision is whether to repeat the same, and maybe spend $4/8k on the rebuild and replacement, or go diesel.
This thread is about info and decisions for those willing to try another route.
Yup, Steve's right. It seems the average lifespan of the 454 in a 325 or larger AS motorhome seems to be 60,000 miles at the low end; yes, there are people that state they get more out of their motor than that, but these are the people that take very good care of their rigs. I would be surprised to see a 454 last over 100,000 miles in most applications.
The diesels on the other hand are true lifer motors, (with good care and maintenance of course). My 6BD1a is used as generators motors on trawlers and heavy equipment like excavators; running at 2500-3000 rpm's all day long for weeks and months on end. Do they break? Yes; often? No. A 454 certainly would not be able to handle the abuse my Isuzu can.
Add to that the cost or re&re a 454 engine into our beasts, say three times to my none at 8-10g's a pop, and it can make a diesel swap look inviting. FYI, I looked at 345 in Leemington Ontario that was on his third motor at 180,000 miles. The second time our dollar was so bad in comparison to the US dollar, he had the 345 floated up from Tennessee to Windsor Ontario to do the engine work.
Well you got my interest, woe is me.
The original engine in my 345 now has over 180k miles and is pretty healthy. Using little oil, tho some does get past the rear main seal. It may be down a little in power from original, But I've driven nearly 30k miles on it since I've owned the coach, lots of that in mountains of Colo and the PNW. Nearly 7 k of that towing a car. Can easily cruise in the high Sixty mph with the over drive. Have found myself in the mid seventy mph when not paying attention, while in favorable conditions. I usually cruise around 63 for fuel economy. And Generally get 7 or 8 mpg.
That to me is very satisfactory performance from the high mileage 454 gasser.
The engine noise is probably less than the diesels, and the lighter weight is a plus in weight distribution and front end longevity.
It's been interesting hearing from diesel owners thinking of joining the coming motorhome traveling rally, saying that anything over 58 or so is pushing their rigs.
So yes the commercial diesel are probably longer lived that the BBC, but they don't seem much better at powering these coaches, at least as installed by airstream.
So some where down the line when this engine gives up on me, I'll probably replace it with a new gasser that will fit right in with little extra work in getting it fitted, and probably better power and mpg.
Hearing the trials involved in changing over to a diesel in a former gasser also confirms my inclination to stick with a gasser.
Sorry if this is contrary to the focus of this thread, but may be a sensible counterpoint to consider.
I just hope I don't jinks this engine in saying all of this.
I'm hoping to many more miles on this one.
No problems Richard, and your input is a valid counterpoint.
My MHís original engine looks like it expired at about 70k miles after at least one documented overheating episode. I know of some that have lasted more than 100k but they are almost exceptions, and yours is amazing!!!!
I think itís fair to have a balanced discussion of pros and cons and I welcome it. Who knows, my Jasper remanufactured engine may prove to be a gem and the Cummins might never make it under the doghouse!
The GM crate 8.1L/502ci is attractive, and strong, but I am unsure if itís cam and setup is ideal for a Motorhome. Also last time I looked it was about $8,000, bare.
Maybe an LS would work!
There is one other angle that I have not thrown in yet, but itís another interesting point... Smog, or Emissions compliance.
You may live in a state or area that does not require it, but many do, and I predict it will be coming for most of us. Here in CA, itís here now. Even a 16,500lb Motorhome has to pass its emissions test to be registered every 2 years. That means the old Carb has to be within spec and all the emissions gear be visually there and functional. This is a pretty tall order, for us, and the 1980ís technology.
I know someone is gonna tell me to register elsewhere, and point out that CA sucks, etc, but please keep your opinions to yourself, as itís just a distraction. I believe smog and testing will catch up with us all.
There are options... convert to a later GM TBI or Approved MSD Atomic Injection, at about $1000/1500 min plus the cost of having the system verified by the smog referee, and then you still have to have it smogged every 2 years...
Or, put a Diesel in.
Now, in CA, currently, the Diesel engine has to have come from a road vehicle, newer than the vehicle itís transplanted into,
and be a proven Fed or CA smog approved engine, and be in its original smog approved configuration. [emoji6]
If the Diesel engine is from a 1998 or earlier vehicle, after the Smog referee has verified it, there is no further smog test required(currently). If the motor is post 1998, after Referee approval you still have to smog every 2 years to the spec of the donor vehicle.
Now, you begin to see why I personally selected a 1990 Cummins from a D250 Pickup. It has the motor plate on it still, that verifies this.
There is also the ďvalueĒ discussion.
It is already becoming clear that Diesel powered Motorhomes are fetching more money.
Hopefully I will get admin approval soon so I can begin to post the info I have amassed.
This is a very interesting thread. I will be curious at the overall cost of the conversion. It doesn't appear to be very cost effective. I have heard that pre-smog diesel engines are going for a premium, plus there is a finite number of them. Most gas engine rebuilders will match your cam to the application for maximum power, so having the wrong cam may be the owners fault when they ordered the rebuild. While a diesel engine may take more abuse, but why would you abuse your equipment? I wish you good luck with this project!!
I have owned several Airstream motorhomes and have yet to replace a 455
Heat and hi rpms are the killers
The 454 has a high torque
If you let the engine do the work properly by letting the revs drop. To about 2200
Before downshifting you may not be the first over the top but you will get a lot of miles out if the 454
A crate drop in is a pittance in cost versus switching to a diesel
The extra weight of a diesel on your front end is also a problem as is the noise and smell
And since when will the body and undercarriage last for a half a million miles
KISS stick with a 454 and enjoy your life
I get the impression the thread has deviated somewhat from I think was it's intended scope of documenting which diesel to pick and how to swap if you are doing a conversion.
Justifying the conversion vs dropping in a replacement 454 seems a totally different subject to me.
I agree with Martin here. I don't think that "payback" or justifying the swap in dollars and cents is Steves purpose of the discussion he opened up. If that was the case, none of us would own and "use" one of these antique beasts to start with. Steve has the skills, knowledge, and tools to pull off a diesel swap doing most, if not all, the work himself. So he is in a different situation than most of us here on the Motorhome forums. In his case, the only justification needed is "because he wants to". Which is awesome to me. Looking forward to following the thought process here and I'm sure I'll learn a great deal. If you take a look at the first post, there is no reference to the cost or payback in better fuel economy or reduced maintenance $$$.
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