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Are New Diesels Reliable & Running Biodiesel fuel - Top Diesel Tech Questions

You've Got Questions? We've Got Answers!

Jason Sands
Jun 28, 2015
Photographers: Jason Sands
Are New Diesels Reliable?
I have an ’06 Duramax with 155,000 miles on the odometer. It runs great, but I'll probably have to sell it due to a long military deployment. I'm thinking about getting a new diesel truck when I return, either the new Chevrolet Colorado or Nissan Titan XD with the Cummins engine, but I'm curious as to how reliable the newer diesels with an EGR, DPF, and SCR are in the long run. I know data is still limited to some degree, but I wanted to get an experienced opinion. Are you seeing lots of newer Cummins, Duramax, and Power Stroke motors hitting 250,000 miles or more with emissions equipment intact? Have they tuned the fuel mileage back up? Do DPF filters need to be removed/replaced after a few years? How much does that cost? Is the EGR killing cylinders and injectors prematurely? I guess I just want to know if the investment in a nicer, newer truck will net me the same long-term durability as my old Duramax LBZ, or even be somewhat close. If I can look at 10 or more worry-free years out of a new diesel—even with the trifecta of EPA foolishness—I may go that route.
Josiah Swim
Photo 2/4   |   Ford Super Duty On Dyno
Great question! We'd love to be able to answer you with absolute certainty, but since we don't have a crystal ball, we'll have to take our best guess based on what we've seen so far. There are certain systems, like EGR, that we can give a pretty definite answer on, as they've been used on diesel-powered trucks for years. Other technologies, such as selective catalytic reduction, are newer, so those particular systems may require some intuition. Finally, every manufacturer is different, so something that may be a problem on one brand of engine (such as an EGR cooler or DPF), may not be an issue on another application.
First of all, there are plenty of newer trucks in the 250,000-mile range, but many of them are driven by hot-shot truckers, who usually take care of their vehicles very well. Many of these emissions systems have small issues (like a DPF that's starting to get plugged up) that can get a whole lot worse if the problem is ignored. The first thing to remember is that if something does go wrong with a DPF/EGR/SCR system, try and get it fixed as quickly as possible.
With regard to mileage, the surprising answer is: “yes.” With the widespread use of urea injection, tuning of most newer diesels has been altered to the point that the engines can burn clean and achieve good fuel economy numbers. Driving like a maniac will, of course, net poor mileage. But we've seen all the Big Three (Ram, GM, and Ford) ¾-ton trucks get close to 20 mpg while driving down the freeway at a constant speed. If you're looking at buying a smaller diesel pickup (like the ½-ton Ram or Colorado), then you can expect 30 mpg—or even more!
While the mileage might be good news, we actually have to give you a bit of bad news on the DPF front, especially if your vehicle is driven sporadically. New trucks used for shorter trips are more than likely going to have issues with the diesel particulate filter clogging at some point in the vehicle's life. Having a DPF cleaned involves removing the unit and putting the filter in a special oven that uses very high temperatures and pressures to burn off excess buildup. This procedure usually costs around $400 to $700, depending on who is doing the work. If the DPF does need to be replaced, expect to pay around $2,000 for an OEM-style substitute.
While we've seen major failures in newer engines (cracked pistons, blown head gaskets, or scarred cylinder walls) that have EGR systems intact, engines with more than 200,000 miles are typically still in pretty good shape. If something does take them out, it's usually a lack of maintenance combined with the owner driving with an existing problem (like a blown head gasket or bad injector) for some time.
Though we handled many of the questions individually, we still haven't tackled the big one: With new emissions regulations, will diesels still be reliable? It's our view that modern emissions controls are part of the new and complex diesel world we live in, and while problems may arise within individual systems, these devices don't compromise a diesel vehicle's integrity as a whole. You can’t go wrong either way, really. Your ’06 is powered by an LBZ Duramax—GM’s last pre-DPF diesel. And, unofficially, your rig is the favorite model year among people shopping for Duramax-equipped trucks. However, the thought of a new diesel lasting for decades and hundreds of thousands of miles certainly makes the idea of “buying new” sound pretty good.
Anyone Got the Time?
I have a ’94 Dodge with the 12-valve engine and was wondering if I should get my timing adjusted. It's been lightly modified with a fuel plate and governor springs for more rpm, but I heard advancing the timing will get me better mileage and more power. Is this true? Can you run too much timing?
Ray Messer
-via email
Photo 3/4   |   Keating Machine 12 Valve Cummins Timing Cover
Adjusting the timing on a ’94 to ’98 Dodge with the 5.9L Cummins isn't the easiest thing in the world to do if you're a new mechanic, so let's start off by saying you should probably have a shop perform the timing adjustment. From the factory, your engine’s timing was most likely set at about 12.5 degrees before top dead center (BTDC), but if you want to make sure, check out the engine's ID tag, which is located on the front driver side of the gear case.
Now, why was your engine set at only 12.5 degrees? Well, engineers had to take cold starting, turbo spooling, and engine noise into account. Adding more timing (or adjusting the injection event further before top dead center) means the engine will be a little harder to start, the turbocharger a little slower to spool, and the total combination a little louder.
There is an upside, though. By adding more timing, power and mileage will both increase. While you're not going to get another 100 hp, adding another 20 to 30 hp isn't out of the question, as well as another 1 to 2 mpg. We would start with bumping the timing up to the high teens or maybe as far as 20 degrees, then assess the engine’s performance. If the advanced timing isn’t to your liking, you can always return it to the stock setting.
Finally, is there a thing as too much timing? Well, sort of. We've seen power gains all the way up to and beyond 30 degrees of timing on really hot street diesels, but at some point there will be a level of diminishing returns. Also, turbo spooling will be painfully slow, and starting up a diesel with very high timing can be quite a chore in cold weather.
Bio-Stroke Mileage
I’m looking at buying a’95 Ford with a 7.3L Power Stroke engine, and I’m wondering how they do on mileage. Also, can I run biodiesel?
-User JJBurch29
Photo 4/4   |   Usa Gasoline Fuel Prices
We get a lot of questions concerning biodiesel, especially from concerned newer truck owners who don't want to ruin their engines or injection systems. However, a ’95 7.3L Power Stroke has a fairly archaic injection system on it, and we've seen them run on biodiesel, straight vegetable oil, and even transmission fluid.
As long as the fuel is filtered properly, we've seen very few problems come from running various combustible fuels in early 7.3Ls. Since most biofuels you find at regular filling stations have to pass the same testing as regular diesel fuel, we wouldn't hesitate to run any percentage blend of biodiesel in your old Power Stroke.
As far as fuel economy is concerned, it largely depends on the type of driving performed, the modifications (if any) to the vehicle, as well as other factors, such as tire size, transmission type, and gear ratio. As a general rule, most owners of older 7.3L-powered Fords see around 15 to 20 mpg on the highway, and about 8 to 12 mpg towing a large trailer. While it's possible to bump up mileage a bit with a programmer, achieving anything beyond 20 mpg takes a pretty concentrated effort.



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