Volvo D13 Problems and Mack MP8 Issues: What to Check

Volvo and Mack trucks are a common sight around Charleston, from port drayage and regional haulers to dump trucks and construction fleets. Many of them run a Volvo D13 or a Mack MP8, and the most common Volvo D13 problems tend to show up on the MP8 too, because the two engines have more in common than the badges suggest. This post covers the issues that come up most on both, what to check first, and where the two engines differ.

Is the Mack MP8 the Same Engine as the Volvo D13?

Not exactly, but they are close relatives. Mack has been part of the Volvo Group since 2001, when Volvo acquired Renault's truck business, which included Mack. The MP8 and the D13 are both 13-liter engines built on a shared Volvo Group platform, and major hardware such as the block and crankshaft is common to both. Many parts are listed to fit either engine.

They are not identical, though. Mack sets its own ratings and calibrations for the MP8, and some components and configurations differ. The core mechanical knowledge carries over, but diagnostics, software, and parts lookup still need to be done for the specific engine, chassis, and model year in front of you.

What Are the Most Common Volvo D13 and Mack MP8 Problems?

Most of the complaints on these engines fall into a few groups:

• EGR cooler problems: soot plugging and internal coolant leaks.
• EGR flow faults: often caused by the differential pressure sensor, its wiring, or plugged sensing ports rather than the valve.
• NOx sensor failures and SCR efficiency codes.
• DEF dosing and DPF regen faults in the aftertreatment system.
• Heat-related derates when a marginal cooling or exhaust system gets pushed too far.

None of these automatically mean the engine is wearing out. Most are components doing a hard job in a hot, dirty environment, and the key is sorting out which fault is the cause and which ones are reactions.

Why Is My D13 or MP8 Losing Coolant?

Like every modern diesel that uses exhaust gas recirculation, these engines route exhaust through an EGR cooler before it goes back into the intake. Over time the cooler can plug with soot and carbon, which cuts flow and sets EGR codes. EGR coolers can also crack or leak internally. When that happens, coolant gets into the exhaust side and is burned off or pushed out. Signs include:

• Coolant loss with no puddle under the truck.
• White smoke or a sweet smell from the stack.
• Bubbles in the surge tank or coolant pushing out of the overflow.
• EGR and emissions codes, sometimes with a derate.

An EGR cooler is not the only possible cause, so it pays to confirm it before replacing one. A cooling system pressure test, a look for coolant in the exhaust and charge air side, and a check of external hoses and fittings are the first steps. Our post on finding the source of a coolant leak walks through that process. Topping the tank off and moving on only hides the problem.

EGR Sensor and Wiring Problems

A lot of what gets called an "EGR problem" on these engines is really a sensor or wiring problem. The system measures EGR flow using a venturi and a differential pressure (delta P) sensor. If the engine does not see the flow it expects, it can lose boost, run poorly, and derate. Common culprits include:

• Connector fretting: vibration wears the sensor terminals until the connection gets loose or intermittent.
• Chafed wiring: the harness can rub through its insulation and send a bad signal.
• Plugged sensing ports: soot and debris in the venturi ports or sensor lines skew the reading.

Volvo has released updated kits for the venturi and sensor on some earlier D13 engines, so it is worth asking a dealer what applies to a given serial number. Either way, before replacing an EGR valve or cooler on a flow code, check the sensor, its connector, its wiring, and its ports, and compare the reading to what the engine is actually doing.

NOx Sensors and Aftertreatment Faults

The aftertreatment side brings the usual set of complaints: NOx sensor failures, DPF regen problems, DOC efficiency codes, DEF dosing faults, and SCR efficiency codes. Faults on this side often chain together:

• A DOC that is not lighting off properly can make regens fail.
• An exhaust leak near a NOx sensor can skew its reading and make the SCR look like it is failing.
• A sticking or restricted DEF doser can set SCR efficiency codes on a catalyst that is fine.
• EGR flow that is off target can raise engine-out NOx or soot, which puts more load on the SCR or DPF.

If the filter itself turns out to be loaded with ash, it can often be cleaned rather than replaced. We offer on-site DPF cleaning, and our guide to DPF cleaning versus replacement covers how to make that call.

Heat Makes Marginal Systems Fail

Lowcountry summers are hard on these trucks in the same ways they are hard on every diesel. Loaded trucks idling in port lines, stop-and-go traffic on I-26 and I-526, and hot jobsites all push coolant and exhaust temperatures up. A cooling system that is slightly weak, an EGR cooler that is partly plugged, or a DPF that is loading up can get by in the spring and then tip into a derate in July. Catching those problems in the cooler months is the easiest version of the repair.

What to Check First on a D13 or MP8

When a D13 or MP8 has a complaint, a sensible order looks like this:

• Pull every code, active and inactive, and note which ones set first.
• Read live data for EGR flow and differential pressure, boost, exhaust temperatures, soot load, NOx readings, and DEF dosing.
• Check connectors and wiring at the sensors named in the codes, especially anything mounted where vibration is heavy.
• Find any leaks on the exhaust, boost, and coolant sides before condemning a sensor or cooler.
• Pressure-test the cooling system if the truck is using coolant.
• Confirm the repair by rechecking live data after the fix, not just clearing codes.

That approach avoids the most common and costly mistake on these engines: replacing emissions parts because a code named them, when the real problem was a wire, a connector, or a leak.

A Note on Software and Updates

Volvo and Mack both release engine and aftertreatment software updates, and some fault patterns are addressed with a calibration change rather than a part. If a truck has a repeat problem that parts have not fixed, check with the dealer whether the engine is on current software and whether any service bulletins or campaigns apply to that VIN.

When to Call a Volvo or Mack Diesel Mechanic

If your Volvo or Mack is derating, losing coolant, or throwing EGR and aftertreatment codes that keep coming back, it deserves a real diagnosis instead of another guess. Lowcountry Diagnostics provides Volvo truck repair in Charleston and Mack truck repair in Charleston, with all work done on-site. Joseph Cufaude, who founded the company and leads the technical work, has spent 13 years in the diesel trade. Through our mobile diesel repair service, we handle these jobs wherever the truck is parked, at any hour. Call (843) 310-0995 to get your truck diagnosed and back to work.