Dodge RAM: 3.7 V6 to 6.7 Cummins Every Generation, Every Fault

The 3.7 litre Powertech V6 is the oldest and most modest engine in the RAM lineup that we regularly see in New Zealand. It puts out 215 hp and 319 Nm of torque from 3701cc, with a 9.7:1 compression ratio and a bore and stroke of 93.0 x 91.0 mm. The ECU is a Motorola NGC4, and it predates the more sophisticated Siemens/Continental setups that came with later engines. On paper it looks like a stopgap, but plenty of these trucks are still working hard in New Zealand and they deserve proper attention rather than being dismissed as the cheap option.

The Powertech V6's age is where its problems live. Timing chain tensioners and guides wear on higher mileage examples, and a rattle on cold start is the first sign they're letting go. Don't ignore it, because once the chain jumps, the repair bill climbs steeply. These engines are also prone to oil sludge if the service history is patchy, which is common on trucks this age. The cylinder head casting on early 3.7 units has a history of cracking if the engine has been run hot, so any truck with a questionable cooling history needs a careful look. Ignition coils, spark plugs and the crank and cam position sensors are the usual culprits behind misfires and rough running.

The 3.6 Pentastar replaced the 3.7 Powertech and immediately made the entry level RAM a more capable proposition. Capacity is 3604cc, compression rises to 10.2:1, bore and stroke are 96.0 x 83.0 mm, and the factory output jumps to 305 hp and 365 Nm. The ECU is a Siemens/Continental GPEC2A, the same platform used in the 6.4 Hemi, which means proper factory level diagnostics are non negotiable. A generic scan tool simply doesn't communicate with this system properly.

The Pentastar V6 has a solid reputation overall, but it has its own set of known issues. Early versions had left bank cylinder head problems that showed up as a ticking noise and rough running. Listen carefully during any inspection of an earlier example. Rocker arm and lifter wear can cause a tick or misfire on higher mileage units, and the oil filter housing and cooler are known to weep oil, so check around that area during any service. The Pentastar uses a timing chain rather than a belt, which is good news for long term maintenance costs, but the chain and tensioner still need inspection on older trucks.

This is the engine that defines what a Dodge RAM is supposed to feel like. The 5.7 Hemi V8 in the RAM 1500 displaces 5654cc, runs a 10.5:1 compression ratio with a 99.5 x 90.9 mm bore and stroke, and in its earlier RAM 1500 tune produces 345 hp and 540 Nm. ECUs vary across the production run, covering the Chrysler NCG3, NGC4, NGC5 and the Siemens/Continental GPEC2A on later examples. That ECU variation matters for diagnostics because each requires the correct configuration within wiTECH to communicate properly. A generic scan tool won't read them all accurately.

The 5.7 Hemi has a trait that every owner eventually encounters: the Multi Displacement System, or MDS. It's Chrysler's cylinder deactivation setup, designed to save fuel by dropping to four cylinders under light load. In theory it's clever. In practice, the MDS lifters and cam are a well documented weak point, and a ticking noise is often the first sign that a lifter or roller is failing. Exhaust manifold bolts shearing is another classic, causing a tapping or blowing noise that's most noticeable on a cold start. Oil consumption and spark plug wear show up on higher mileage trucks, and this engine uses sixteen plugs, two per cylinder, so a full plug change is a proper job that needs time allocated correctly.

The correct oil grade matters more on this engine than owners often realise. The MDS system is sensitive to oil viscosity, and running the wrong spec accelerates lifter wear. Always use the factory specified grade. Stage 1 tuning on the early 5.7 RAM 1500 takes outputs to 365 hp and 560 Nm, gains of 20 hp and 20 Nm.

The heavier duty variant of the 5.7 Hemi steps output up to 396 hp and 552 Nm from the same 5654cc displacement and 10.5:1 compression ratio. The ECU options here are the Siemens/Continental CM2100 or GPEC2A. That extra output comes from factory calibration differences, and it's a meaningful step up in real world driving, particularly for towing. The Stage 1 tune we offer on this variant takes it to 424 hp and 586 Nm, a gain of 28 hp and 34 Nm, which is the strongest gain available across either 5.7 Hemi variant.

The fault profile is almost identical to the RAM 1500 version. MDS lifter and camshaft wear remains the headline concern, and the classic Hemi tick is just as likely to appear here. Exhaust manifold bolt failures are consistent across both 5.7 variants, shearing under the thermal cycling of a heavily loaded truck. Oil consumption, spark plug fouling and the sixteen plug service requirement carry over exactly. The difference is that the HD variant is often used harder, doing more towing and more kilometres under load, which tends to accelerate MDS wear and put more stress on cooling system components.

The 6.4 Hemi is the RAM at its most committed. Six thousand four hundred and ten cc, a 10.9:1 compression ratio, bore and stroke of 103.9 x 94.6 mm, and a factory output of 410 hp and 582 Nm. The ECU is a Siemens/Continental GPEC2A. This is a proper big block petrol engine in a world that's largely moved on from them, and it carries that character with everything it does. It also carries the same MDS cylinder deactivation system as the 5.7 Hemi, and on a larger displacement engine running higher compression, the stakes for maintaining it correctly are even higher.

MDS lifter and camshaft wear is the primary fault to watch on the 6.4, and the ticking noise it produces is unmistakable once you've heard it. Beyond the MDS, exhaust manifold bolts and manifold cracking are a consistent issue on these engines the thermal mass of a 6.4 litre V8 is significant and the manifolds feel it. The oil cooler and cooler housing gaskets can seep, and coolant leaks around the water pump show up with age. Fuel and ignition condition matter on any engine this size because fouled plugs on a big block translate directly to wasted fuel and rough running.

The 6.7 Cummins ISB is a completely different animal from every other engine in this lineup. It's a diesel, an inline six displacing 6685cc with a 17.3:1 compression ratio and a bore and stroke of 106.9 x 124.0 mm. Factory output is 350 hp and 890 Nm of torque from low in the rev range. That torque figure puts every petrol RAM engine in the shade for towing work. ECU options are the Siemens/Continental CM2100 or CM2350B. Stage 1 tuning takes it to 380 hp and 950 Nm, gains of 30 hp and 60 Nm, and on an engine optimised for towing, 60 extra Nm at low rpm makes a real difference.

The 6.7 Cummins is a tough engine, but it carries its own specific set of problems, and most of them live in the emissions system. DPF clogging is the headline fault, particularly on trucks that do a lot of short urban runs, because the DPF never gets hot enough to self regenerate properly. EGR cooler faults and NOx sensor failures follow closely behind. The variable geometry turbo can stick or gum up with soot, which affects boost delivery and fuel economy before it throws a code. Exhaust manifold bolts and injection pump behaviour are also worth inspecting on any example that's done hard kilometres. Front end suspension components wear with age and heavy towing loads.