By Colin Dilley, Ph.D.

For the modern day fleet manager, buses on the road equate to revenue growth, while those in the shop minimize margins and put additional, unnecessary stress on the remaining vehicles. Optimizing change intervals for cooling system maintenance is one way to positively impact the bottom line, but if done incorrectly the long-term cost can significantly outweigh the short-term savings.

Before optimizing a heavy duty vehicle’s antifreeze/coolant (AF/C) change interval, it’s important to understand the critical role coolant plays in protecting an engine and the engine manufacturers’ recommended coolant-maintenance intervals.

OEs recommend specific change intervals for AF/C to ensure the system operates properly. AF/C producers work with heavy-duty engine manufacturers and standards organizations to refine their formulations, with the goal of developing a product that optimizes heavy-duty engine performance within the OE guidelines.

Further, in order for modern gasoline, diesel and/or Liquid Petroleum Gas (LPG) engines to meet the lofty federal efficiency, exhaust and environmental parameters, engine manufacturers have introduced new engines that are running hotter – especially those that rely on LPG and have Exhaust Gas Recirculation (EGR) system to reduce nitrogen oxide (NOx) emissions.

The problems these higher temperatures may cause include possible “hot spots” that can cause pre-ignition, oil degradation and thermal distortion. These conditions can have an adverse effect on engine performance and lead to premature breakdown or failure.

The ‘musts’ of cooling system maintenance

Remember these things when it comes to bus cooling system maintenance:

  • Understand the engine manufacturer’s coolant requirements and industry standard for coolant performance and change intervals.
  • Always use the recommended coolant at the correct concentration.
  • Test the coolant regularly for proper additive levels and freeze/boilover protection.
  • Maintain proper additive levels and regularly top off coolants at regular service intervals.

If the cooling system is not operating effectively, the vehicle’s horsepower, fuel efficiency, emissions and overall durability may be compromised.

Change interval optimization

The goal in optimizing a vehicle’s AF/C change interval is to keep the vehicle on the road longer, generating revenues and avoiding costly downtime. The risk of extending the change interval beyond the recommendation is that it can impact the engine’s efficiency, health and possibly void warranties. So how do you safely optimize change intervals within guidelines?  It starts by ensuring coolant quality with regular testing.

Testing the coolant concentration (mixture of glycol, water and inhibitors) is an important part of engine management. If the coolant concentration is too rich or too low, not only can freezing and boilover protection become a problem, but the correct level of inhibitors necessary to protect the essential engine components can become a concern. The correct mixture of coolant concentrate and water will deliver the proper amount and type of inhibitors, which will guard against corrosion. Corrosion, and rust in particular, can degrade the effectiveness of a cooling system, negatively affecting performance and putting the long-term health of the engine at risk.

The complete solution

As an inventor and innovator of modern-day antifreeze/coolant technology, Prestone remains dedicated to providing the best cooling system fluids to the heavy duty engine markets. The company’s U.S.-based technology center works closely with major engine manufacturers and standardization organizations to create technologically advanced, patented formulations and related products that are best-in-class both today and into the future.

The Prestone and Prestone Command® line of antifreeze, additives and testing products deliver the technology and innovation fleets can trust to protect engines from extreme on-road conditions and corrosion while increasing uptime.


To safely optimize change intervals, a thorough maintenance plan needs to be put in place to ensure that all of the vehicle’s components are operating at their utmost efficiency
and effectiveness.

Colin Dilley, Ph.D, is the Vice President of Technology for Prestone Products Corporation. Prestone Products Corporation manufactures and markets Prestone® antifreeze/coolant and related products. For more than 85 years, the Prestone name has provided customers with high-quality products, including one of the leading brands of antifreeze/coolant. Visit