Filter Cleaner System Passes Test In St. Louis Bus Fleet.

Bi-State Development Agency, St. Louis, Mo., is the mass transit provider for the St. Louis metropolitan area. The agency operates more than 650 diesel-powered vehicles in daily revenue service, running in excess of 25 million miles each year.

Among the many operational issues the fleet

has had to deal with are those concerning the cooling systems in its vehicles. Typical problems encountered have included solder bloom and silica gel dropout and the effects of excessive usage of antifreeze. These led to labor-intensive cooling system cleaning procedures and downtime and progressive damage from various cooling system failures.

In 1992, Bi-State began testing the Enviro-Cool coolant cleaner filter to address several of those problems, according to Lyle Howard, manager of product development at the agency. The Enviro-Cool system, developed by Enviro-Cool Inc., St. Charles, Mo., is designed to clean engine cooling systems and allow significantly extended intervals between coolant system drain and changeout.

In operation, first use test strips are used to determine if the inhibitor and coolant level is correct. Then the Enviro-Cool spin-on cleaning filter is installed in place of the conventional filter. The vehicle is then returned to service for a period of two to four weeks, during which time, the filter cleans the system. The cleaning filter is then removed and after the cooling system is checked for the proper level of dissolved solids, the conventional inhibitor filter is re-installed.

By using the cleaner filter once a year, Enviro-Cool said that vehicle operators can go as long as five years between cooling system drains.

Prior to the test, data was collected and reviewed on the buses selected for the test to ensure a more accurate analysis of conditions before and after the introduction of the Enviro-Cool coolant cleaner filter.

According to Howard, at that time, the cooling system maintenance and cleaning consisted of maintaining the supplemental coolant additives (SCA) through the use of inhibitor filters, pre-charging the SCAs in liquid form and monitoring the total dissolved solids (TDS) every 12,000 miles. When the TDS reached 2000, the system was drained, refilled with water and a cleaning product, run in the shop to circulate the cleaning product, then drained again and refilled with new anti-freeze. The SCAs were precharged in liquid form, and a new inhibitor filter was installed.

Since this process was labor intensive and relied heavily on accurate and consistent test procedures (nitrates were tested by chemical titration), Bi-State was interested in finding another method.

The test was undertaken on 1981 GMC buses, which had been in service nine years before testing began and had accumulated mileage of approximately 350,000 miles per bus. Conditions prior to the test also included:

* At engine overhaul, all radiators over six months old were flow tested to determine if they were reusable. Approximately 95 percent of the radiators would not pass a flow test due to internal restriction from deposits and were replaced.

* Radiators were being replaced in the GMC bus fleet at a rate of 18 to 20 percent each year.

* Defroster cores were being replaced at a rate of 17 percent per year.

* In hot weather, the engine fan thermostatic controls were bypassed so that the fans would run at 100 percent of engine speed at all times to compensate for poor flow through the radiator.

To test the effectiveness of the Enviro-Cool cleaner filter, the buses were first run on a chassis dynamometer to operating temperature. Temperature drop across the radiator and fan speed were recorded. The coolant level was also checked, along with the freeze point, total dissolved solids and nitrate levels. The inhibitor filter was then replaced with the Enviro-Cool cleaner filter.

After running in daily service for 12,000 miles, the buses were brought in for inspection. The more significant results included:

* Temperature drop across the radiators was reduced an average of 3[degrees].

* In most cases, total dissolved solids were not impacted to the point that a coolant replacement was required.

* There was no significant impact on nitrate levels.

Several radiators were removed, disassembled and inspected and were found to be free of scale, corrosion and silicate deposits.

On one test bus, a radiator that failed a flow test was installed along with an Enviro-Cool cleaner filter and run for 6000 miles. The radiator was then removed and retested, at which point it now passed the flow test.

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 6000 miles of operation with the filters. The vacuum readings taken after the test showed an average 40 to 50 percent decrease in vacuum.

SCAs are still maintained through the use of inhibitor filters, but in 1995 the agency began using precharged antifreeze to eliminate the use of liquid SCAs. SCAs are now tested with Detroit Diesel's power track test strips rather than by chemical titration. TDS are still monitored at 12,000-mile intervals, but now when the reading reaches 2000 the system is simply drained and refilled.

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

With the continued use of the EnviroCool filter cleaners, Howard reporteda dramatic drop in the incidence of clogged radiators -- not one in four years of operation -- and the replacement rate for radiators in the GMC buses has falled to 8 to 10 percent a year. Defroster core replacements are also down to 3 to 4 percent a year and it is no longer necessary to bypass the thermostatic fan controls on the GMC buses in hot weather.

Another subfleet that was monitored throughout the test period was a fleet of 1988 Flxible buses. These buses have now been in service for nine years and have accumulated over 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.

This test was started by simply applying the coolant cleaner filter on an annual basis. The maintenance of the SCAs and TDS was performed exactly the same as on the GMC vehicles.

On the second test group, radiator replacements have never exceeded 12 percent per year and defroster core replacements have never exceeded 3 percent per year, Howard reported.

Based on the test results, the use of the Enviro-Cool cleaner filter was instituted as an agency wide policy for annual cooling system cleaning.