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Big Thompson Diesel and Automotive

Loveland and Northern Colorado's Diesel and Automotive Repair Specialists

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This is a serious question I get asked over and over. Usually it is when a customer is faced with an expensive repair on their current vehicle. This is a very difficult question to answer. So from a very experienced diesel mechanics point of view I am going to try to educate everyone the best I can and help you answer: What is the best diesel truck for you? So while reading this please keep in mind your own personal needs and wants from your vehicle as well as how long you want to keep your truck.  Most of the time when I get asked this it is a hard question because I have to guess the customers financial status and judge what they are comfortable spending on their current vehicle and what is a comfortable price for them to pay on their next vehicle. Can they afford a brand new truck or are they on a tight budget? Do they just want a truck to do odd jobs or do they need to rely on it for work every day? I am going to try to break it down into common age groups of Diesel powered trucks. Usually GM, Ford and Dodge make major changes about the same time. So the breakdown is going to be full size trucks only which are half ton and heavier pickups from 1994 thru present.

Everything up to 1994

These vehicles are definitely getting older and most people will not be looking for a vehicle in this age group so I will keep it short.

These started out in the early 80′s with an international 6.9L V8 International Diesel engine. This engine was increased to 7.3 liters in 1987. The engines were reliable and had very few mechanical issues. They did have some glow plug system problems and some fuel system issues if it was poorly maintained. The fuel systems are fairly simple to diagnose and fix but the parts are starting to get hard to find and as they are getting very high in miles the cost of repairs can easily exceed the cost of the vehicle. These trucks, as a whole, were fairly solid trucks.

GM / Chevy

1978 to 1985

They had a modified Oldsmobile V8 gas engine that was fitted with slight modifications and a diesel fuel system. These engines made very little power and were smoky and smelly. This engine was in cars, trucks, and Blazers.

1982-1993 6.2L

This engine had a bit more power but lacked the power and reliability of the Ford but, overall, still had very few issues.


1988 ½ to 1994

Dodge entered the diesel market later than the others but almost immediately took over when they put a B series Cummins engine in their trucks. The 5.9 engine is still basically the same block, crank, cam, and rods used in the Ram trucks today. There have been changes to the heads, fuel system and even displacement but is it the same base design. The Cummins started life in the trucks with 160hp and 400ft/lb. torque and had an optional 190hp and 425ft/lb. engine available. This was over 100 ft. /lb. of torque more than the competitor’s engines. The engine and fuel system were extremely reliable but the Dodge truck was fairly clunky and had a lot of body rattles and rode like a lumber wagon. It had brake issues as well but overall, was an extremely durable truck.

These trucks brought many changes to the diesel truck world. This was the beginning of a horsepower war that is still going on today. These trucks are still a bit old for most people but are the last of the “old school reliable diesels”. All of the trucks were changing year to year.  Technology was changing fast and electronics and computer controls started making a big impact in this era of trucks.

Ford 1994 ½ – 2002

Ford introduced the Powerstroke engine. It was the same International block as the previous 7.3L engine with massive changes to the cylinder heads and fuel system. It now had a HEUI fuel injection system which is a Caterpillar fuel system that they bolted into an International engine. The HEUI (Hydraulically driven Electronic controlled Unit Injector) means the injector is driven by hydraulic pressure that is created from the engine oil and controlled by a computer. This was a very complex system for its day but when maintained properly was extremely durable as well. There are few issues with the injectors but they do start to get weak internally and around 200000 miles usually need to be replaced. The rest of the engine had some fuel and oil leaks and the complex valve cover gaskets could burn out and cause a dead cylinder or more. However, the mechanical side of the engine is extremely reliable. It is not unheard of to have an engine with over 500000 miles on it with no issues as long as it was properly maintained. In 1999 Ford changed the truck body to the newer body style and with the change, they upgraded the 7.3L with a larger turbo, different valve cover gaskets, and an intercooler to cool the air after the turbo going into the engine. The trucks were very solid. The brakes are exceptional, the transmission is very strong, the cab and chassis are good, and they have good suspension. The weak spot of the truck was the ball joints, engine oil leaks, and valve cover gaskets.

Chevy/GM 1994-2002

GM tried upgrading the 6.5 to keep up with Ford and Dodge. They added a turbo to it and added an electronic controlled mechanical fuel injection pump. The system was plagued with issues. The injection pump control module as well as the control wires were buried under the intake manifold where lots of heat baked the wires and the module. This was a source of repeated failures and many peoples anguish with no starts and stalling. As far as the injection pump went, they had several internal issues as well. If you pulled a trailer and pushed the engine hard it would crack the cylinder heads. If this was caught early enough it could be fixed without complete engine replacement but it usually hurt the engine before the driver even knew anything was wrong. Overall this was a poor diesel engine. They were loud at idle, smoked a lot, had low power while pulling, and if pushed hard like a diesel, they would get hot.  The rest of the truck was ok but the engine kind of ruined the whole package.


Dodge 1994-2002

The Dodge truck engine went through some major changes but the rest of the truck was virtually unchanged other than minor cosmetic and interior changes. Cummins added a more robust P7100 injection pump in 94. This allowed them to boost the horsepower, add more adjustability, and offer higher injection pressures. This made it quieter and had more power while holding a tighter emission standard. This engine design had very few issues and would usually outlast the rest of the truck several times. The worst issue with this engine was the killer dowel pin. This was an alignment dowel inside the timing cover that could work its way out and fall onto the cam gear and break out the cam gear housing and that was all if the customer was lucky. Sometimes it could break the teeth on the cam gear and the crank teeth but this was rare. In 1998 1/2 Cummins came out with the 24 valve engine. This was still the same base engine but had an upgraded cylinder head and 4 valves per cylinder. It had a new computer controlled rotary injection pump. The engine design made a combination that was very durable and powerful. They fixed the killer dowel pin issue and had very few oil leaks or mechanical issues of any kind.  The downfall of this engine was the injection pump. It was a good pump unless you starved it for proper fuel.  It became delicate very fast. The primary cause of fuel starvation was the poor quality fuel lift pump. When the fuel pump was starved for fuel it could overheat and hurt the rpm sensor, bake the injection control module which was a non-replaceable part of the pump, and could score the timing piston. All of which would result in injection pump replacement. This issue was easily remedied by installing a good quality aftermarket fuel lift pump and usually installing a fuel pressure gauge or a dummy light to come on when the fuel pressure dipped too low.  The rest of the truck is decent. It has a good transfer case, good brakes, and a sound, but still a bit rough, suspension and frame. The one weak link of the truck was the automatic transmission. The engine now made enough horsepower and torque that the transmission was now at the extent of its abilities. It could be modified to hold the power but it was a little costly to fix. The other weak link was the trac bar. Replacement trac bars usually did not stay good for long but there are aftermarket solutions that all but permanently fix the issue. All in all this is one of the most powerful and reliable diesel powered trucks on the market!!

Of all of the 94-02 diesels you can’t go wrong with the Dodge or the Ford. The one downfall of all of the trucks is they are now over a decade old and are probably nearing or over the 200000 mile mark and have had several owners. If you are lucky you can still find one with low miles on it. These trucks are probably in need of some maintenance to get them back to a reliable state but parts are still readily available and they are fairly inexpensive to fix compared to their predecessors.

03 – Present Diesels

The 03 to present trucks are probably where most people looking for a diesel truck are going to be looking.  Major engine designs across the board happened in 03 and have been continually changing since then.  The problem with this generation of diesels is most of the changes are to clean up the exhaust and the result has been a decrease in reliability and increase in the cost of repairs.  Most of these trucks can be repaired and even upgraded to not fail as easily.



2003 – 2007

Ford dropped the 7.3 engine because it could not make more power and pass the stricter emissions standards.  The introduction of the 6.0L still stayed with the HEUI injection system although the caterpillar injectors are now out and Siemens injectors are in.  This engine also had a variable geometry turbocharger, EGR valve and cooler, catalytic converter and was a very clean running engine that runs good “when it is running good”.  The problem is, early on in the engines run, it got a bad reputation for being in the shop over and over and over again.  Usually it would have numerous EGR coolers, injectors and head gaskets replaced, as well as variable geometry turbo failures.  As the engines fell out of warranty and the trucks started going to shops other than the dealer, mechanics and aftermarket parts suppliers were forced to figure out why the repeated failures.  Once the root cause of all of these failures were figured out, this engine could actually be made to be very reliable and, because of its reputation, can usually be purchased for a good price compared to the GM and Dodge in these years.  However, if you plan on buying one, plan on just upgrading the whole thing.  Spend the money and have a reliable diesel.

2008 – 2009 6.4 Powerstroke

Off all the diesel trucks this one had one of the nicest cabs, great chassis, good tranny but the engine is completely horrible.  Though it makes good power, it gets horrible fuel mileage.  It has weak head gaskets; the new common rail fuel system was suspect to multiple failures including hydro locking the engine when the injectors fail.  This could cause catastrophic engine failure.  They also have been known for turbo failure; the front cover corrodes and slowly weeps coolant into the crankcase oil.  This can cause the oil to loose lubricity and quickly destroy the crank and rod bearings, wipe out turbo bearings and in general quickly destroy the engine.  Most repairs on this engine are extremely expensive and because it only ran for 2 years, there really are no real aftermarket upgrades so repairs on this are so fare just patch jobs until the next catastrophic failure.  It is all repairable but home much is too much?

2010 – Present 6.7L Powerstroke

Thus far, the engine has proven to be more reliable compared to the previous 6.4L but they have not come out of warranty on a large scale yet so, as an independent repair shop, we have yet to see the failures this engine will have once warranty is up.  Some of the oddities of this engine is the 2 radiator system is very complex and the thermostats are an integral part of the radiators.  This system also takes 2 water pumps so this doubles the amount of wearable parts.  Plus, if you need thermostats you must replace the radiator.  Another oddity is the amount of plastic on the engine and the plastic intake manifold holding 40x PSI of pressure, plastic oil pan (it’s reliable as long as you don’t hit anything).

Chevy – GMC

2003 – 2004 ½

Chevy finally caught up in the diesel world in 03 with the Duramax diesel engine.  The truck is one of the smoothest trucks to drive and has lots of creature comforts.  GM has a lot of state of the art electronics and are fairly durable.  One of the major issues GM has is the instrument clusters tend to lock up but it is easily repaired.  The Allison transmission is a very durable and sought after transmission.  This same basic transmission is used in medium duty trucks so imagine how durable it can be in your 3/4 or 1 ton truck.  They have had very few problems.  As for the engine, the 03-04 ½ engine had a sever injector problem.  So bad that GM went ahead and warrantied the fuel system to 10 years or 200,000 miles.  This was above and beyond what they had to do but it was respectable.  As they went through years of injector warranty issues, the manufacturer of the injectors found some issues and updated the injectors.  So once they are out of warranty (which these all are now), most people can expect to replace the injectors.  The good news is the injectors usually do not ruin the engine by melting pistons or hydro locking cylinders, but they could leak fuel in to the oil and wash out engine bearings, turbos, and cam bearings.  This was usually few and far between so if you want a very durable truck, this is a decent truck if you can get over the sticker shock of 13 hours of work and the price of injectors.  Once you fix the injectors and do some small fuel system upgrades, the injectors can last 100,000 miles with no issues.

2004 ½ – 2011

The Duramax engine got a major upgrade in 2004 ½ model year.  The very difficult to get to injectors of the previous Duramax got remodeled and re positioned outside of the valve covers.  Now injectors failures could not ruin the engine by dumping fuel in to the lube oil and when they moved the injectors they also become a lot more durable.  It is not uncommon for these injectors to go 200k before having issues.  So what issues does it have?  The previously very durable fuel injection pump and fuel filter housings now tend to wear out causing continuous fuel filter lights to be set and sends the engine in to limp mode and limits power.  The filter housing is easy to fix but when the injection pump dies it can be expensive to fix.  Other changes were the introduction of the variable geometry turbo, EGR systems and, in the later models, DPF and VREA exhaust systems.  Compared to Ford and Dodge, Chevy did not have a lot of issues with the exhaust after treatment systems.  It has been a fairly robust system for GM, but could be the cause of some failure down the road.  These engines in whole have proven to be extremely durable and have good power.  The trucks suspension is a bit softer than the Ford and Dodge which is nice on a long drive.

The next major engine change came in 2012 when the whole V8 design got flipped around.  For the Duramax engine’s run up until now the typical V8 layout where the intake manifold is between the cylinder heads in the engines valley and the exhaust manifolds are outside the cylinder heads.  Then, hot pipes are looped around the engine up the back and into the turbo which then sits in the valley.  This created a lot of heat.  The 2012 Duramax basically flipped the cylinder heads over so now the hot exhaust exits the top of the head and straight into the turbo, than cool intake manifolds and piping run around the bottom and outside the engine.  This design drastically reduced under hood temperatures which helps keep all of the delicate electronics alive.  So far these are all still under warranty but we have heard nothing bad of this engine yet.


2003 – 2007

The Cummins engine had a fuel system make over which made it quieter and more powerful.  Unfortunately the fuel system was less durable than previous models.  The injectors had a lot of issues which caused everything from misfires to no start issues.  The injectors were eventually updated so now all of the replacement injectors from Bosh are updated with stainless steel inner parts that do not fail as quickly as the old ones did.  The injectors in the 2004 ½ to 2007 models, if they fail, could quickly melt the pistons, so as soon as you saw the first sign of injector issues you better shut it down and get it to the shop because $3000 worth of injectors can quickly turn in to a $15,000 engine.  The rest of the Dodge truck in these years is very durable with very few transmission problems.  They have weak factory ball joints but can easily be upgraded to a very durable ball joint and eliminate most front end issues.  The differentials and transfer case are strong.  The engines make a ton of horsepower and torque and are still more durable these years than the Ford and Chevy engines.

2007 – Present

The Cummins B series got a face lift in 2007.  It went from 5.9 liters to 6.7 liters.  It got a newer, very durable injector design and a variable geometry turbo which doubles as an exhaust brake.  It also got an EGR valve and a DPF exhaust filtration system.  Dodge had a lot of software issues with how they controlled the DPF system but software upgrades made the delicate system a lot more durable.  The variable geometry turbo has had a few issues but the most of the issues come from the heavily modified vehicles.  Stock trucks have very few variable geometry issues.  The engine is back to the most durable diesel truck engine on the market.  The transmission was also drastically updated in 2007.  The cab was modernized and they put in lots of creature comforts.  If there is a weak spot in this truck it is the weak ball joints still and the DPF system but both are easily upgraded and fixed.

So when you are looking to buy a used truck, there is a lot to consider.  First is your budget to buy the truck.  How much do you want to pay for the truck and how much do you want to spend to fix the truck after you purchase it?  What are your needs?  Do you want a comfortable quiet ride or can you sacrifice comfort for outright durability?  Everybody’s needs are different so when you are in the market for a used truck, hopefully this helps but if you have more questions or would like us to look at your truck before you purchase it, please call of email us.  We would be happy to answer any other question.  We always recommend you do a prebuy before purchasing any type of vehicle.  It might cost you some money up from but it could potentially safes you thousands of dollars down the road.


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