Case Study #3

By Lyle Howard
Manager of Product Development
Metro - St. Louis, MO

In the 20-plus years I have been managing fleet equipment, I have seen technology significantly improve the operation and maintenance of many heavy-duty systems.

However, with cooling system maintenance, the basics still apply - systems must be cleaned, supplemental coolant additives must be maintained and samples must be tested.

For seven years, Bi-State Development Agency in St. Louis, where I am manager of product development, conducted an extensive study of the cooling systems of its transit buses.

The study covered more than 200 20-foot coaches, all of them either 1981 GMCs or 1988 Flxibles. The 150 GMCs were powered by either a Detroit Diesel 8V71 or 6V92 MUI, while the 57 Flxibles were equipped with 6V92 DDECs.

The test verifies the results Bi-State achieved by doing all of the conventional cooling system maintenance procedures in the traditional manner - except for cleaning. We accomplished this through the use of an aftermarket cleaner/filter that virtually eliminated internal clogging in the cooling systems of Bi-State buses.

This cleaning method had been instrumental in saving money, man hours and downtime in our fleet.

Overview

Bi-State Development Agency is the mass transit provider for metropolitan St. Louis, operating more than 650 diesel-powered vehicles in daily revenue service. These buses run in excess of 25 million miles each year.

In 1992, the agency began testing the Enviro-Cool^TM coolant cleaner filter to address several costly cooling system maintenance issues:

Solder bloom and silica gel dropout problems.
Labor-intensive cooling system cleaning procedures.
Excessive anti-freeze usage.
Downtime and progressive damage from various cooling-system failures.
For the purpose of the test, data was collected and reviewed beginning Jan. 1, 1990, to facilitate a more accurate analysis of trends before and after the introduction of the Enviro-Cool^TM coolant cleaner filter.

Fleet Analysis, Prior to Coolant Cleaner Filter Introduction

Cooling system maintenance and cleaning. In the late 1980's and early 1990's, Bi-State's cooling system maintenance consisted of maintaining the supplemental coolant additives (SCA's) through the use of inhibitor filters, precharging the supplemental coolant additives in liquid form, and monitoring the total dissolved solids (TDS) every 12,000 miles.

When the total dissolved solids reached 2000, the system was drained and refilled with water and a cleaning product. The engine was run in the shop to circulate the cleaning product, then drained again and refilled with new anti-freeze. The supplemental coolant additives were precharged in liquid form, and a new inhibitor filter was installed.

Because this process was labor intensive and relied heavily on accurate and consistent test procedures (nitrites were tested by chemical titration), it was not successful.

Coolant Additives

An audit of supplemental coolant additives and total dissolved solids performed in 1990 showed that only 40 percent of the buses tested were within acceptable limits, and most of that 40 percent were too high in total dissolved solids. This indicated the systems were not being cleaned properly, presumably because cleaning was labor intensive, expensive and messy. The Bi-State garages having the best results were cleaning the systems and changing anti-freeze annually.

Cooling system performance. The effectiveness of the Enviro-Cool^TM cleaner filter was most dramatic on our 1981 GMC buses, which had been in service nine years before testing began and had accumulated approximately 350,000 miles per bus.

Fleet maintenance statistics prior to test:

At engine overhaul, all radiators more than six months old were flow tested to determine if they were reusable. 95 percent of the radiators would not pass a flow test due to internal restriction from deposits.
Radiators were being replaced at a rate of 17-20 percent of the fleet each year for our 1981 GMC fleet.
Of the radiators replaced, 95 percent were internally clogged; would not pass flow test.
Defroster cores were also being replaced at a rate of 17 percent per year.
In hot weather, the engine fan thermostatic controls were bypassed so the fans would run at 100 percent of engine speed at all times to compensate for poor flow through the radiator.

Fleet Analysis of Primary Test Fleet, Coolant Cleaner Filters in Use

Start of test. In 1992, Bi-State tested Enviro-Cool^TM cleaner on a group of our 1981 GMC buses. On one bus, a radiator that would not pass a flow test was installed along with an Enviro-Cool^TM Cleaner filter and run for 6,000 miles. The radiator was then removed and re-tested, with no special procedure or rodding of radiator tubes. This previously clogged radiator now passed the test. Total dissolved solids in the anti-freeze did not increase appreciably, so the anti-freeze was reused. On the remaining test buses, vacuum readings were taken on the suction side of the radiators before application of the cleaner filters, and again after 6,000 miles of operation with the filters. The vacuum readings taken after the test showed an average 40-50 percent decrease in vacuum.

Cooling system maintenance and cleaning. Supplemental coolant additives (SCA's) are still maintained through the use of inhibitor filters, but in 1995 the agency began using precharged anti-freeze to eliminate the use of liquid SCA's.

SCA's now are tested with Detroit Diesel's Power Trac test strips rather than by chemical titration. Total dissolved solids (TDS) are still monitored at 12,000-mile intervals, but now when the reading reaches 2000, the system is simply drained and refilled.

Cleaning with Cleaner Filters

We have determined that cleaning with the Enviro-Cool^TM cleaner filters is only necessary on a semi-annual basis to maintain a deposit-free cooling system. No man-hours are expended on cooling system cleaning, as this is accomplished by replacing the inhibitor filter with a cleaner filter on a regular preventive maintenance inspection.

Cooling system performance:

Radiators are still being flow tested at engine overhauls. We have not encountered a clogged radiator in approximately four years - versus 95 percent clogging previously.
Radiators for the GMC buses are replaced at a rate of 8-10 percent per year. That's one-half the previous rate.
Defroster cores are replaced at a rate of 3-4 percent per year - one fifth the previous rate.
It is no longer necessary to bypass the thermostatic fan controls on the GMC's in hot weather. Since the use of the filter, we have not had a clog-related overheat.
Anti-freeze consumption fleet wide had been reduced 35 percent.
Engine failures due to prolonged overheating have been reduced by a minimum of 50 percent.

Flexible Fleet Analysis Coolant Cleaner Filter in Use

Bi-State's fleet of 1988 Flxibles also was monitored throughout the test period. These buses have been in service for 10 years and have accumulated more than 400,000 miles per bus. At the beginning of the test, this fleet had accumulated very few miles, and had established no record of cooling system failure.

Start of test. The test was started by simply applying the coolant cleaner filter on an annual basis.

Maintenance of SCA's and TDS was performed exactly the same as on Bi-State's fleet of 1981 GMCs.

Cooling system performance:

Radiator replacements have never exceeded 12 percent per year, even though these radiators are prone to clogging of the external fins.
Defroster core replacements have never exceeded 3 percent per year.
It is apparent that the implementation of regular cooling system cleaning had kept the failures at a much lower rate than we experienced on buses that had been in service nine years with sporadic cleaning.

Conclusions

The preventive cleaning of cooling systems with the Enviro-Cool^TM cleaner filter has benefited Bi-State in several ways:

Reduced anti-freeze usage.
Eliminated internal deposits in cooling systems.
Eliminated man-hours spent cleaning cooling systems.
Reduced heat-related engine failures.
Recent fleet audits show that over 85 percent of the fleet is within specifications for TDS in the cooling system.
Based on these results, the use of the Enviro-Cool^TM cleaner filter was instituted as an agency-wide policy for annual cooling system cleaning.

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