As one who used to have a Dodge Ram diesel, I would love to have a Tundra diesel. With the last Ram I had (2002 2500 QC 4x4 long bed with fiberglass cap and 54 gallon replacement tank), I averaged 17mpg highway, the same as I get on my Tundra, not bad for a 7200 pound truck. I would still have a Ram diesel if my wife could step that high, but two knee replacements prevent that even with a step. As for numbers, here are some factors to consider:
- engine cost difference
- per gallon fuel cost difference
- mileage difference
- maintenance cost difference
Let's address these one at a time
engine cost difference:
It is almost a guarantee that the 4.5L diesel will cost more than the 5.7 gas. However, as other have mentioned, it is very unlikely the engine for a 1/2 ton truck will have the same premium as that for a 1 ton truck. A $3000-4000 price difference seems reasonable to me. Though this is an added up front cost, it is not all a lost expense, as compared with a fuel cost difference. The diesel engine has an increased residual value. The difference between this residual value and the initial cost is the actual non-recouped expense. This is the expense amount that needs to be spread over the life of the vehicle (until sold or replaced). The initial engine cost would only be spread over the life of the vehicle if the vehicle is kept for its entire life. Also, diesel engines are likely to last longer than gas engines. At a 100,000 miles, the Cummins is barely broken in. This increases the 'life' of the truck to spread the cost over if keeping it for its entire life.
per gallon fuel cost:
The cost of my last fill-up was $4.06 for regular. Diesel at the same station was $4.80. This has diesel at an 18% higher cost than regular. In this comparison, the important number (for comparison purposes) is the percentage difference. For example, if regular was $4.26 instead, the difference would be about 13%, though the diesel cost was the same. If you can fill up at a truck stop, this percentage difference could be reduced.
mileage difference:
If I baby my Tundra, I can get 19.2 mpg highway. I normally don't baby it. My highway mileage is closer to 17 mpg. If the mileage of the diesel was 22 mpg, this would result in me getting 29% better mileage with the diesel engine than with a gas engine.
maintenance cost difference:
It will like cost more for oil changes on the diesel. The actual amount can vary greatly. Depending on where it was changed in the Ram I had, it varied from a low of $65 (in Alabama) to a high of $120 (near Chicago). Of course, you can control the cost somewhat by doing it yourself.
conclusion:
Looking at just the difference in per gallon cost or figuring in the entire engine cost as an extra cost is insufficient. Doing this would be looking at only the negatives and ignoring the positives. There are two sides to the equation. Look at both.
Compare the per gallon fuel cost percentage difference with the mileage percentage difference. The overall fuel cost is a combination of both of these percentages. For the example numbers above, the 29% mileage increase more than offsets the 18% per gallon fuel cost increase. As long as the mileage difference for the diesel is greater than the per gallon fuel cost difference for diesel, it will be less expensive to fuel a diesel engine than to fuel a gas engine. As fuel costs rise even further, these percentages are a key factor in evaluating the benefits of diesel versus gas.
But, to see how this fits an individual's circumstances, this difference needs to be compared with your other factors, like the engine cost (initial - residual) over the useful life (or until sold), and your cost of maintenance. These other costs vary from region to region and from dealer to dealer. The more important numbers are still the mileage increase percentage versus the higher fuel cost percentage.
As for me, unless the percentages flip, I will continue to prefer diesel to gas. It may cost more to fill the tank, especially with the 54 gallon replacement tank the Ram had, but the extra range more than made up the difference. I expect a diesel Tundra to have a similar upside.