Marinucci: Excessive RTV silicone sealer may crack castings

A hurried technician may damage a costly casting by applying excessive sealer or forcing a bolt into the wrong hole.

Contrary to what some bosses believe, these do happen.

A hurried technician may damage a costly casting by applying excessive sealer or forcing a bolt into the wrong hole.

Savvy owners and managers teach techs that taking a few minutes of extra care on a job is not a setback for them or the business. Instead, this additional caution dramatically increases the likelihood of fixing the vehicle correctly the first time.

Remember that fixing vehicles correctly the first time boosts a business' reputation.

Here are some points tire dealers and service shop operators should remember about applying RTV silicone sealers and neatly organizing hardware during a repair job.

Readers likely have seen threaded holes in automotive components of one kind or another. Sometimes, the manufacturer drilled these holes right through the part: Peer into the hole and you see daylight on the other side of the casting.

Other times, a threaded hole dead ends inside the component. In other words, the hole forms a small threaded cup in the part.

Depending upon component design and location, a blind hole may not be readily distinguishable from another hole.

What's more, a particular casting may contain a mix of "drilled-through" holes as well as blind holes.

For instance, the automatic transmission case shown in the accompanying photograph has both blind and conventional threaded holes.

At a glance, you may not distinguish one from the other in this case.

During a repair, some techs methodically remove all the bolts from a component, rinse them in the parts washer and visually inspect them. Then they carefully organize those bolts on a shop cart or workbench — in the exact order they were removed from the vehicle.

This simple step minimizes the risk, for instance, of mismatching a long bolt with a shallow, blind hole.

However, other techs pile the component's bolts onto a cart or workbench without noting if the bolts are all the same length.

Some techs habitually mark the locations of the longer bolts with a permanent marker or "paint stick."

Occasionally a tech zips a long, incorrect bolt into a blind hole, damaging its threads and possibly the casting itself.

The key takeaway here is that a little extra caution prevents this blunder from occurring.

RTV silicone sealer can create a versatile and durable gasket on many automotive applications.

The abbreviation "RTV" stands for room-temperature vulcanizing. This means that the applied RTV "sets up" into a pliable but durable gasket after it has been exposed to the air. This is why some suppliers state that RTV creates a gasket on the spot or "in place."

I began using RTV silicone sealers in the 1970s. It has advantages, but needs to be used it carefully and correctly.

For example, automotive sealing surfaces usually are designed for either a pre-formed, traditional gasket or RTV. Using RTV along with a conventional gasket is risky.

An RTV sealer remains somewhat wet and soft while it cures or sets up. For one thing, it may act like a lubricant, causing the traditional gasket to slip out of place. The resulting leak frustrates techs who do not realize that adding RTV sealer to a traditional gasket may be a mistake instead of added insurance against leaks.

For another, RTV sealer in this scenario often oozes into the engine or transmission. Blobs of sealer may restrict or totally block critical engine or transmission lubrication circuits. In particular, the sealer may restrict fine-mesh filter screens found inside may engines and automatic transmissions.

What's more, some techs overlook the risk excessive RTV sealer poses to blind holes in various components. Suppose a tech applies a heaping helping of this sealer to a gasket surface. Reassembling components often forces wet RTV sealer into an engine or transmission as well as blind holes.

Imagine what happens when a hurried, careless tech zips a bolt into a blind hole loaded with RTV sealer. A minuscule amount may escape around the bolt threads.

But most of this unwanted sealer remains trapped inside the blind hole. Forcing a bolt into this hole — against sealer that does not compress readily — may crack the component or casting.

Practice two practical precautions here. First, avoid doubling up RTV sealer onto traditional pre-cut or pre-formed gaskets.

Second, apply RTV sealer sparingly to sealing surfaces for which traditional gaskets are not available. Here, less is usually more — excessive sealer tends to ooze into places it should not go.

Steadily applying a proper bead of RTV sealer to a surface may seem tedious, but the extra care usually saves you from doing the job a second time or possibly cracking a part.