Welcome to Top Tech Questions. Oftentimes, readers contact us with questions about articles, or to praise us on what a good job we are doing. But our favorite form of reader communication is tech questions. Our Top Tech section is a place where you ask what’s on your mind, and we answer it. Got a trouble code? Wondering how to get your engine to make more power? Send us an email at jason.sands@sorc.com and we’ll do our best to answer it.
6.0L Power Stroke MPG
Question: I was looking over the results of some of the Diesel Power Challenges from the past years, and I noticed the 6.0L Ford trucks got a lot worse fuel economy on the Ride and Drive, even though all the other diesels were modified, too. I am in the market for a Ford, and I was curious as to why the 6.0L Power Strokes are so bad on fuel economy even though they have a smaller engine than the previous 7.3L generation. I don’t want to buy a 6.0L if it will only get 15 mpg on the highway. What can I do to make sure it gets closer to 20 mpg?
Scott Moore
Oceanside, California
| Although it has a 4-inch lift and 35-inch tires, we’ve been able to greatly improve the fuel economy our 6.0L (Project Outcast) has achieved. Before any modifications (other than a tuner), it averaged about 11.5 mpg. With a Stage 1 FICM, Elite Diesel Insanity tuning, and 155cc nozzles, it’s now averaging a little less than 16 mpg.
Answer: That’s a good observation. And it’s something we’ve also noticed over the years. While we have no 100 percent clear answer for this poor mileage mystery, we can tell you what our theories are. We think it’s a combination of things.
First, while the HEUI fuel system was efficient enough to meet emissions standards in its day, it isn’t as efficient as high-pressure common-rail systems from a fuel economy standpoint.
Second, the ’05 (and newer) Super Dutys more than likely took a hit in the mileage department when Ford introduced the coil spring, radius-arm front suspension, and a thicker, stronger frame with a fully boxed front section, which entailed the thickest gauge steel used on a pickup frame at the time. These things added considerable weight to a truck that was already pretty hefty to begin with. It’s typical for a crew cab, four-wheel-drive version to weigh 8,000 pounds or more. By contrast, the Dodge and GM trucks of the same era with the same configuration would weigh at least 400 to 500 pounds less.
Third, the difference between the 7.3L generation you mentioned and the 6.0L is that the 7.3L had more bottom-end grunt, thanks to its cubic-inch advantage. The 6.0L Power Stroke makes its power much higher in the powerband and, frankly, it’s happier at higher engine speeds. The drawback here is that higher rpm means more fuel consumed. Now, add in a larger (possibly even fixed geometry) turbocharger like you see in the Diesel Power Challenge, and the 6.0L loses even more torque and requires more rpm for it to come to life.
To be fair, we have seen some 6.0Ls achieving near 20-mpg numbers, but all of them had factory height, stock-size tire combinations working in their favor. They were all religiously maintained and 100 percent healthy, too.
It’s more about what you shouldn’t do than what you should do to see 20 mpg. Don’t lift the truck or add larger tires and wheels. That’s the easiest way to eat into your fuel economy.
What’s It Worth?
Question: I see many highly modified and well-built trucks in your magazine, and I have a question. How do they insure these vehicles for proper appraised or replacement value?
Victor Bowser
Titusville, Pennsylvania
| If you’re going to be trying to get the real value of your modified vehicle out of an insurance company, make sure to keep all your receipts from the entire build and take some killer photos of the completed vehicle. Even if you don’t get the full cost of the vehicle, you at least have some ammo to up the dollar amount of your reimbursement.
Answer: This is a good question, and one we’re actually in the middle of answering with our own ’89 Dodge that has been an ongoing magazine project. The going rate for a first-generation Dodge, even with nice paint, in no way reflects the $15,000 that was sunk into transmission and engine parts. Sadly, many people don’t even look into it, and they end up getting paid far less than their vehicle is worth if it is stripped or stolen.
There are a few ways around this, although it isn’t easy. Most insurance companies view things like aftermarket stereos or paintjobs as legitimate and easy-to-price upgrades, but a fabricated intake and dual fueler on a diesel, not so much. We called around and couldn’t find a single insurance company that had a box they could fit a modified diesel truck into.
If the vehicle is used mainly as a play toy and kept in a locked garage, insurance companies such as Haggerty or American Collectors Insurance might be willing to insure the vehicle, but if the truck is a daily driver or tow rig, then a mainstream insurance company might be your only choice. Many companies such as USAA, State Farm, and Allstate will offer a clause in their comprehensive vehicle coverage that allows for modifications, but usually there is a dollar limit, like $3,000 or $5,000, that would be paid out in modifications.
More than anything else during our insurance company search, we found that being patient and calling around were very beneficial. After all, insurance companies want your money, and if a little more is paid out to guarantee the true value of the vehicle, then everybody wins.
To Rebuild or No? Question: I have a ’95 Dodge Ram 2500 with a 12-valve Cummins engine and an NV4500 transmission. I have owned the truck since the age of 14. I am now 24, and it’s time to do some drivetrain and engine work. With the motor approaching 300,000 miles, I don’t think it’s wise to start adding power without rebuilding the entire motor. I want to make about 400 rwhp, and I use the truck for towing 10,000 to 20,000 pounds, but mostly daily driving empty. Do I need to do a full rebuild?
Tanner Smith Fremont, Missouri
| On Project Triple Threat, our 300,000-mile ’95 Dodge, we’ve blown a head gasket (twice—once at 215 rwhp and again with head studs at 564 rwhp), but other than that, there are no signs that it has any type of ring, bearing, or bottom-end issues.
Answer: We get a lot of questions concerning rebuilds, and most of them (surprisingly) are regarding 5.9L Cummins engines. First off, the good news—your engine may not need a rebuild! Cummins lists the 300,000-mile mark as about the 50/50 point, as in, there is about a 50 percent chance that your engine will need a rebuild. So with that type of mileage, there’s still a chance your engine is good enough for added power.
The shortcut test for the type of shape your engine is in is to remove the oil fill cap when it’s running and see how much smoke comes out. A little is OK, but if a big cloud of white or blue is puffed out, then the engine has some blow-by, probably because of worn-out piston rings. Unfortunately, worn piston rings usually mean a full rebuild, as honing a cylinder out and putting new rings in is potentially just a temporary fix.
Another reason your Cummins may need a rebuild is because its gaskets are just plain worn out. We’ve seen engines that still look good after 500,000 miles but will leak a ton of oil—and everything else. In this case, a lot of new gaskets may be all that is needed.
If it were us (and we are kind of in the same boat), we’d just look for a low-mileage take-out engine from another truck, rather than go for a full rebuild. A used Cummins engine in good shape can be found for a couple grand, and swapping an engine in and out is a lot easier than a full rebuild.
If you do decide that you need a full rebuild, it will usually run around $7,000 to $10,000. If you can do some of the work yourself (say, like pulling the head, intake, turbo, etc.) and then send the short-block out, that can easily take a couple grand off the cost—although not all shops are willing to do this because of liability reasons. Any way you look at it, we wouldn’t be afraid of adding more power to a 300,000-mile Cummins until we knew for sure it was worn out.
