Cooling System Cleaning Through the Use of a Chelating Cleaner Filter

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Lyle Howard
Bi-State Development Agency

A new method of cleaning cooling systems has been developed that uses a filter with a chelating alkaline cleaner that is released into the cooling system. The cleaner filter is installed in place of the inhibitor filter on heavy-duty engines and left in place for one service cycle. After the service cycle, the cleaner filter is reinstalled. This represents a major change in the method traditionally used for cooling system cleaning.

A large Midwestern transit authority tested the cleaner filters and documented the results on two of its subfleets over a seven-year period. Data was collected and analyzed from a computerized maintenance management system, and all cooling system related entries were analyzed and separated into categories. The test was undertaken to address several costly cooling system maintenance issues:

• Solder bloom and silica gel dropout problems
• Labor intensive cooling system cleaning procedures
• Excessive antifreeze usage
• Downtime and progressive damage from various cooling system failures.

The goal of the testing was to determine if the cleaner filter cleaner the cooling systems adequately, if it performed the cleaning task using fewer man-hours of labor, and if there were operational improvements to the equipment attributable to regular cooling system cleaning.

Fleet Analysis, Prior to coolant Cleaner Filter Introduction

In the late 1980's and early 1990's cooling system maintenance consisted of maintaining the supplemental coolant additives (SCA's) through the use of inhibitor filters, precharging the SCA's 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 SCA's 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) it was not successful. An audit of SCA's and TDS performed in 1990 showed that only 40% of buses tested were within acceptable limits for nitrites and most of that 40% were too high in TDS. This indicated that the systems were not being cleaned as required, presumably because cleaning was labor intensive, expensive, and messy. The locations that had the best results were cleaning the cooling systems and changing the anti-freeze on an annual basis.

The effectiveness of the cleaner filter was most pronounced on a fleet of 1981 GMC buses with 8V71 Detroit Diesel engines. These buses had been in service for nine years and had accumulated average mileages of approximately 350,000 miles each. The following condition existed prior to the introduction of the cleaner filter.

• At engine overhaul, all radiators over six months old were flow tested to determine if they were reusable. 95% of the radiators tested would not pass a flow test due to internal restriction from deposits. Per Detroit Diesel, the radiator should be capable of a flow of 100 GPM at 2100 R.P.M. The tester was used independently of the engine to measure total flow capacity, which on a new radiator was 110 G.P.M. range
• Radiators in the subfleet were being replaced at a rate of 17% to 20% each year.
• Of the radiators replaced, 95% were internally clogged and would not pass a flow test.
• Defroster cores were being replaced at a rate of 17% per year. These also were clogging due to being in a low flow area of the cooling system.
• In hot weather, the engine fan thermostatic controls were bypassed so that the fans would run at 10 0% of engine speed at all times to compensate for poor flow through the radiator.

In 1992, the Agency tested cleaner filters on a group of 1981 GMC buses. On one bus, a radiator that would not pass a flow test was installed along with a cleaner filter and run for 6000 miles. The radiator was then removed and retested, 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 6000 miles of operation with the filters. Vacuum readings should be close to a steady 1.5 in. Hg across the entire operating range in a clean, properly sized cooling system with a Detroit Diesel 8V71 engine. Vacuum readings taken before application of the cleaner filter were in the 2.0 to 2.1 in. Hg range. The vacuum readings taken after the test showed an average 40% decrease in vacuum.

Supplemental coolant additives (SCA's) are still maintained through the use of inhibitor filters, but in 1995 the Transit Authority began using precharged anti-freeze to eliminate the use of liquid SCA's. Data was analyzed on radiator replacement in the GMC subfleet from 1990 forward to determine if the reduction in replacements was attributable solely to application of the cleaner filter, or if the use of precharged antifreeze also had an effect. (fig. 1) The greatest reduction in radiator replacements occurred in 1992 when the cleaner filters were first applied. The introduction of precharged antifreeze in 1995 had no notable effect on radiator replacement rates. SCA's are now tested with 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. It has been determined that cleaning with the cleaner filters is necessary on an 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.

Fig. 1 - GMC Radiator Replacements

The following improvements were achieved with the use of the cleaner filter:

1. Radiators are still being flow tested at engine overhauls. This Transit Authority has not encountered a clogged radiator in approximately four years. (vs. 95% clogging)
2. Radiators for the GMC subfleet are replaced at a rate of 8-10% per year. (1/2 the previous rate)
3. Defroster cores are replaced at a rate of 3-4% per year. (1/5 the previous rate)
4. It is no longer necessary to bypass the thermostatic fan controls on the GMC's in hot weather. (Since the use of the filter, there has not been a clog related overheat)
5. Anti-Freeze consumption fleet wide has been reduced 35%.
6. Engine failures due to prolonged overheating have been reduced by a minimum of 50%

Another subfleet that was monitored throughout the test period was a fleet of 1988 Flxible buses. These buses have now been in service for eleven years and have accumulated over 400,000 miles per bus. At the beginning of this 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. Maintenance of SCA's and TDS was performed exactly the same as on the 1981 GMC subfleet.

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

The preventive cleaning of cooling systems with the cleaner filter has benefited the transit fleet in several ways:

• Reduced anti-freeze usage
• Elimination of internal deposits in cooling systems
• Elimination of man-hours spent cleaning cooling systems
• Reduced heat-related engine failures
• Recent fleet audits show that over 85% of the fleet is within specifications for TDS in the cooling system.
• Over the term of the test period, soft metal and elastomer components exposed to the coolant were inspected for any signs of degradation attributable to annual cleaning with an alkaline product. Particular attention was paid to injector tubes and 'o' rings, and tube to header soldered joints in radiator, heater, and defroster cores. The usage of these items over the test period remained almost constant, with radiator cores and injector tubes being replaced as required at the time of engine overhaul.
• Since coolant service life was being extended beyond the yearly replacement, samples were analyzed for by products of ethylene glycol degradation, as the coolant would exceed the TDS limit and be changed out prior to degradation of the ethylene glycol. Coolant changes after the introduction of the cleaner filter in 1992 were extended by as little as 60 days and as much as one year.

Based on these results, the use of the cleaner filter was instituted as a standard policy for annual cooling system cleaning.