Winterizing Apparatus Cooling Systems

Winterizing Apparatus Cooling Systems


As the winter season approaches, many departments will be servicing their apparatus cooling systems. However, keep in mind that maintaining a cooling system is an ongoing process that should be carried out more than once a year. Unfortunately, many departments service their apparatus cooling systems on an annual basis only.


First, let’s discuss antifreeze. There are several common mistakes that are made when installing antifreeze. One of the biggest misconceptions is that all you have to do is add some new antifreeze to last year’s supply, and that will be sufficient until next year.

In most areas of the United States, a mixture of 50% antifreeze and 50% water will be adequate. If this balance is off, it can cause big problems. Antifreeze is in a progressive state of breakdown. Simpfy adding to last year’s supply will tip the scales and result in hundreds, if not thousands, of dollars worth of damage.

It is more cost effective for you to drain and flush the entire system and install new solution that is properly balanced. Also remember that if you add solution during the year, make sure it is mixed in the same proportions.

Another common mistake involves the type of formula used in the system. Not all brands are the same, so don’t let brand name or price determine which product you purchase. There are even differences in the formulas sold under the same brand name. So before you buy, make sure you read the engine manufacturer’s recommended antifreeze solution chemical content and the label on the antifreeze container.

This picture shows the radiator cores clogged up due to silicate dropout.

Photo by Robert J. Stark


Now that we have established the correct antifreeze solution, let’s take a good look at the mechanical items in your cooling system. Inspect your belts for cuts and frays, and for cracking from dry rot and improper adjustment. Maintain proper belt tension at all times. If the belt has stretched, replace it. If you are even in the least bit of doubt about the condition of a belt, replace it. And remember, if belts are a matched set, you must replace both of them, not just the defective one.

Hoses are the next item on our list. If your apparatus still has rubber hose, replace defective hoses with the new silicone type. Silicone hoses cost more but they are worth it because they last longer. If you have a cooling system pressure tester, run a test for at least 10 minutes and look closely for leaks and bulges in the hose system and its connections. If you are in doubt about any condition, replace it and the clamps that hold it.

Thermostats should be replaced every two years. Both gas and diesel engines are most efficient when they run at their proper operating temperature. Depending on the engine manufacturer, you could have one or two thermostats in the housing. If you have two, replace both of them and make sure they both have the same temperature rating.

Look at the number in degrees that is stamped on the thermostat. If you are in doubt about what temperature rating to use, refer to the engine manufacturer’s manual. If you are in a highresponse department, your thermostats should be replaced annually.

Radiator caps should be replaced annually. These are low-cost items and are extremely easy to exchange. You will not be able to detect a defect just by looking at the cap, so make sure you change it every year even if it appears to be in good shape. Remember that thermostats and pressure caps are both affected by water temperature, and heat does have an effect on spring tension, which regulates their operation.

If you have a diesel engine, make sure you change the water filter. The spin-on is the easiest type to deal with—just spin off the old and spin on the new. The older type bag filter is very effective, but it can be messy. You must also contend with the sacrificial anode plate. Examine the plate carefully and replace it every 12 months or with each filter change if necessary.


Because the use of aluminum is becoming more and more prevalent in cooling systems and engines, antifreeze manufacturers had to devise a method to protect the metal from deterioration. The answer was to increase the supply of silicate to the antifreeze solution by as much as 300 times the amount of a few years ago.

A result of this additional silicate is in the form of silicate dropout. Silicate dropout is the formation of silica-gel on heat transfer surfaces when temperatures fall. Some heat transfer surfaces on your apparatus are oil coolers, heater cores, radiators, and heat exchangers.

Silicate dropout can occur in any design of cooling system. The main cause of dropout is the amount of temperature drop in the system. The more the temperature plunges, the more possibility there is that the system will be plugged with gel. When you apply this concept to your fire apparatus, make sure you consider the use of the heat exchanger and just what type of cooling system you have.

Today’s apparatus could have one of two types of cooling systems: low-flow cooling or air-to-air. Some low-flow systems have an 80 °F drop, so they tend to form the most gel. These systems require special maintenance and filling techniques. You must also maintain check valves, flow rate orifices, and filtering screens.

Low-flow systems cannot be repaired using conventional methods. The radiator tubes are too small, and a number of components are sealed units that cannot be disassembled for repair.

Take note: If your apparatus has an automatic transmission, it will not have a low-flow system because the low-flow system does not allow sufficient cooling of the transmission cooler. If you have, or are thinking of purchasing, an apparatus with a standard shift transmission, it is to your benefit to determine the type of cooling system that goes along with it.

Make sure you use the heat exchanger on your pumper only when needed. Remember: The greater the temperature drop, the greater the possibility of dropout. And, as mentioned earlier, remember that the proper antifreeze/ water mixture is essential.


The process of maintaining your apparatus cooling system should be an ongoing program. I recently discussed engine replacement with a fire apparatus engine manufacturer representative. He told me that the replacement cost for a diesel engine with a rebuildable exchange, including installation, was estimated at $10,000. A faulty $10 radiator cap could cause overheating and engine failure. Which item would your budget best absorb: a $10 radiator cap or a $10,000 engine?

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