Managing Coolant Seepage and pH Balance in Cummins NTC Big Cam IV Engines

[MikePhua]

The Big Cam IV and Its Cooling System Vulnerabilities
The Cummins NTC Big Cam IV 400, introduced in the mid-1980s, was part of Cummins’ evolution in heavy-duty diesel powerplants. Designed for highway trucks and vocational applications, the Big Cam IV featured electronic fuel control refinements and improved emissions handling. Despite its robust performance and widespread adoption, one recurring issue in aging units is minor coolant seepage between the cylinder head and block—often visible as a faint puddle on the deck or a trail down the engine’s side.
This seepage is typically not catastrophic but can become a nuisance, especially when coolant contacts hot surfaces like the exhaust manifold, producing steam and odor. The root cause is often traced to wear at the liner counterbore or degradation of sealing O-rings embedded in the head gasket. Over time, thermal cycling and vibration can compromise the seal integrity, leading to external leaks without necessarily contaminating the oil system.
Terminology and Component Notes
- Counterbore: A machined recess in the engine block where the cylinder liner seats; critical for head gasket sealing.
- SCA (Supplemental Coolant Additive): Chemical additives used to prevent corrosion, cavitation, and scale buildup in wet-sleeve diesel engines.
- Coolant Filter: A device that may contain paper media or chemical pellets to regulate pH and deliver SCAs; not always a true filtration unit.
- DCA-4: A common SCA formulation used in green ethylene glycol-based coolants to maintain protective chemistry.
Stop Leak Products and Filter Bypass Strategy
To address minor external leaks without disassembling the engine, many operators turn to chemical sealants such as Dike or Conklin. These products are designed to seal micro-leaks in the cooling system but must be used with caution. Most manufacturers recommend bypassing the coolant filter during application, as the filter media can trap the sealant particles and prevent them from reaching the leak site.
In one case, a technician attempted to use Dike sealant but discovered that the bypass valve on the coolant filter housing was corroded and stuck open. The solution involved removing the filter housing entirely, cleaning the weep holes with a tap, and sealing them with short bolts and thread compound. This allowed the sealant to circulate freely and address the seepage.
Recommendations:

• Flush the cooling system thoroughly before adding sealant
  
• Use wet-sleeve compatible green coolant with fresh DCA-4 additive
  
• Remove or bypass the coolant filter during sealant application
  
• Monitor for pressure spikes or flow restriction after treatment
  

pH and SCA Management in Older Cooling Systems
Maintaining proper pH and SCA levels is essential in wet-sleeve engines like the NTC series. Imbalanced chemistry can lead to liner pitting, cavitation, and gasket degradation. While coolant filters were once the standard method of delivering SCAs, many modern practices favor manual dosing and test strip monitoring.
Operators can use heavy-duty coolant test kits (e.g., NAPA FIL 4107) to measure pH and nitrite levels. Matching the coolant color and chemistry to the additive ensures compatibility and prevents gelling or silicate dropout.
Best practices:

• Maintain pH between 8.5 and 10.5 for optimal corrosion protection
  
• Test SCA concentration every 250 hours or quarterly
  
• Avoid mixing coolant types unless fully flushed
  
• Replace coolant every 2 years or 6,000 hours, whichever comes first
  

Retorquing Cylinder Heads and Mechanical Inspection
Before resorting to chemical sealants, it’s advisable to inspect and retorque the cylinder heads. The Big Cam IV requires removal of the Jake brake and rocker housings to access head bolts. Torque specifications call for 300 ft-lbs, and uneven clamping force can exacerbate seepage at the counterbore.
In one field repair, a technician retorqued the heads and observed reduced seepage without further intervention. This mechanical step can often delay or eliminate the need for sealants, especially if the leak is minimal and not affecting performance.
Field Anecdotes and Long-Term Outlook
A public works operator in New Jersey reported success using Dike sealant combined with fresh coolant and DCA-4, noting that the leak was resolved for now. While acknowledging it as a temporary fix, the approach allowed continued operation until a full teardown could be scheduled. The truck was later sent for clutch replacement and assigned to haul a new excavator—proof that even aging iron can stay productive with careful maintenance.
Another veteran mechanic recalled that some Big Cam IV engines required oversized O-rings during head gasket replacement to compensate for block wear. These components were once available through Cummins but may now require sourcing from specialty rebuilders.
Conclusion
Coolant seepage in Cummins NTC Big Cam IV engines is a manageable issue when approached with a blend of mechanical inspection, chemical treatment, and coolant chemistry control. While stop leak products offer a temporary reprieve, long-term reliability depends on proper torque, clean cooling systems, and consistent pH and SCA monitoring. In legacy diesel engines, the battle against leaks is ongoing—but with the right tools and knowledge, it’s one that can be won without pulling the heads.