What’s made of ground-up ginger root, almond shells and binder? And causes confusion in auto service departments?
Some people call them coolant pellets, but the proper name is Cooling System Seal Tabs. And we hope to clear up some misunderstandings about them.
How They Work
Seal tabs are dissolved in the engine coolant and the resulting fibres circulate through the cooling system. At a microscopic level, the tabs break down into irregular, long, thin fibres. When a small leak or seepage occurs, the coolant carries the fibres into the opening, where they cluster up and jam together. (Think of logs and branches in a beaver dam.) This mechanism is very effective at stopping leaks. Any fibres that make it to the surface will crust over and enhance the seal.
This sealing method is useful only for small-scale leaks and seepage, and tends to work best in conditions where the surrounding parts aren’t moving. The seals tend to break down in areas between metals that are expanding and contracting with temperature changes, for instance.
A Secondary Benefit
The traditional green-colored coolant, used until DEXCOOL® was introduced in 1996, contained silicates, which deposit on cooling system surfaces. The tiny fibres from the seal tabs acted as scouring pads, removing silicate deposits from the water pump seal faces, which contributed to longer water pump seal life.
Side Effects of Seal Tabs
In addition to the benefits of sealing small leaks and scrubbing silicates from water pump seals, seal tabs also have some side effects.
After awhile, a brown, dirty-looking stain may form on translucent coolant bottles. Residue may form on the backside of the radiator cap. And deposits that resemble rust may be found in the cooling system.
These are not problems, in the sense that they cause no physical harm. But their appearance can be alarming, especially on a new vehicle. Both customers and well-intentioned technicians can be misled by these deposits.
Another side effect comes from overuse. When seal tabs are used in the prescribed amounts, they will not cause restrictions or plugging in an otherwise properly operating cooling system.
But, if a little is good, a lot must be better. Wrong!! Overuse can lead to plugging, especially in the relatively small tubes used in heater cores.
Some History
There was a time when seal tabs were installed in every new vehicle, at the factory, to account for the inevitable small leaks that occur in castings, joints, and so on. By the mid ‘90s, manufacturing and machining techniques had improved to the point where the seal tabs were no longer needed on a universal basis.
With the introduction of long-life coolant, silicate deposits were no longer a concern, so the scrubbing action from the seal tab fibres was no longer needed.
TIP: GM plants, as well as other manufacturers, still occasionally use seal tabs to address specific concerns.
Today’s Recommendations
In short, GM no longer endorses universal use of seal tabs. Procedures in SI have been specifically written to discourage their use in most cases.
When a condition appears in which seal tabs may be beneficial, a specific bulletin is released, describing their proper use. One such bulletin is Customer Satisfaction Program 03034, dated 7/7/03. This applies to specific 3.8L engines only, and is in effect until July 31, 2005.
TIP: After performing the procedure in the bulletin, be sure to install a recall identification label to the vehicle to indicate that the seal tabs have been installed.
TIP: If seal tabs were installed in a vehicle at the factory, it’s OK that the proper amount of tabs be installed if the coolant must be drained and replaced.
What’s a Recommended Dose?
TIP: Use this information only when instructed to do so by bulletin or SI procedure.
The proper number of Cooling System Seal Tabs depends on the capacity of the vehicle’s cooling system. Use between 1 and 1 1/2 grams of tabs per liter of cooling system capacity.
TIP: Cooling System Seal Tabs are packaged in two sizes.
12378254 Small tabs (4 grams each) 5 tabs per package
3634621 Large tabs (10 grams each) 6 tabs per package
