Ed Murlatt & Associates, Inc.
RF Services for the Broadcast Industry
IOT Transmitter Cooling System Maintenance
Liquid cooled IOT transmitters typically use either Dowtherm SR-1 or UCARTHERM as an antifreeze.  Both are glycol solutions with dyes and inhibitors, and both are now a product of Dow Chemical.  It is important to know the two fluids are NOT compatible, and considerable system cleaning is recommended when changing from one to the other.  Assistance with cleaning is always recommended, especially if you are considering changing between the two transfer fluids (more on cleaning).

With the exception of ESCIOT and CEA devices, the glycol mixture comes in direct contact with the collector where it is exposed to extreme heating.  Regardless of which glycol is used, maintenance of the coolant is required.  In most cases, the optimum coolant solution is a 50/50 mixture of Glycol and distilled water, and the percentage is best measured using a refractometer.  Beyond maintaining the proper mixture, it is important to monitor the overall health of the solution to assure the inhibitors are still in good condition and the pH is in range.  The latter can be measured at the station, but the former must be verified by a qualified lab.  One such lab is located in Pennsylvania:

GLA Water Consultants
201 Burch Dr.
Moon Township, PA  15108
Phone: (412) 262-4827
GLA Website

We recommend having your coolant tested annually.  Heat is the enemy, so we feel it best to have it analyzed well before or shortly after the hottest part of the summer in your region.  With conventional collector IOTs where the coolant comes in direct contact with the collector, we recommend changing the coolant after a maximum of two years for stations in hotter regions, and a maximum of three years in all cases regardless of the test results.  This gives sufficient time to replace the fluids in a non-winter period and still avoid sweeps periods.  If the fluid is maintained properly, one need only drain the existing fluid into acceptable containers for recycling, refill the system with distilled water and rinse for at least 30 minutes (heating to 130º is recommended), drain (check for local codes and/or recycle the rinse water) then refill with a 50/50 mixture of distilled water and glycol.  Since one never gets 100% of the water out of the system, filling with premixed fluid is NOT recommended.  You will still need to add pure glycol to the system to achieve a 50/50 mixture.  Also, since there is no agitation in the container the glycol and water tend separate with time.  For ESCIOT and CEA amplifiers, it may be safe to base coolant exchange on the testing. 

If testing indicates the coolant is breaking down replace it!  We do not recommend use of additives or other corrective measures regardless of the application

Severe damage to the IOT can occur when the coolant breaks down.  We have successfully restored the collectors of some IOTD2100s and IOTD2130s, but IOTD3100s and IOTD2130s cannot be restored in the field (have a look at some before and after pictures).  While we have successfully restored the external surface of the collector, some damage remains.  It should also be noted that in addition to spending hours disassembling and cleaning the IOT collectors, we had to spend another 12 - 14 hours cleaning and refilling the cooling system.  The cost to correct this situation far exceeded that of the recommended periodic system maintenance.