Using Dielectric Grease on connectors. 

A lot of people use dielectric grease on connectors. Some people mistakenly believe that dielectric grease is a conductor. In fact, it is just the opposite. It is an insulator, and a good one. That is the basic definition of dielectric, an insulator. Dielectric grease is typically made of silicone grease.

As an insulator, dielectric grease is good for use on spark plug boots. This was one of the original applications on vehicles when the high energy ignition systems came out. It can help insulate the connector, and in particular on a motorcycle where it can get wet, it waterproofs the spark plug boot. And because it is silicone, it is fairly stable at high temperatures and won’t affect the rubber and plastics.

So why would you put an insulator on a connector? The idea is that you use a thin layer. When you push the connector together, the grease is pushed out of the way enough to get a connection, and the surrounding grease then keeps out water and oxygen. The connector will be protected from the environment, and less likely to corrode. Plus the silicone is safe for the plastics and PVC insulation.

That sounds good, so far. 

So why not smear it on everything? Well, there are a number of reasons.

1) Silicone grease outgases constantly. If the silicone gas gets near a connector or a contact such as a relay, and there is any arcing, the spark at the contact can create silicon dioxide. Some companies even suggest that the silicone gas from dielectric grease can travel many feet through the insulation on a wire and damage a contact on the other end. Omron states that even their sealed switches can be damaged by nearby silicone grease out gassing. Reference below for more info.

2) It is an insulator. It can prevent contacts from touching. If you must use it, use a very thin layer.

3) If you have a corroded connection, silicone grease will not help. In fact, it can only make a connection worse. It can never improve anything. Dielectric grease will never make a poor connection better.

4) It attracts dust and dirt and due to the out gassing, it hardens over time. This can only make a connection worse. 

This means that if you smear a lot of silicone grease on connectors, you may see nearby relays, switches or points fail later on. And since the silicone grease does nothing at all to improve the connection, and in fact may insulate the contacts in the connector increasing the resistance, the connector may still fail.

So what do you do? Look for a contact enhancer/lube. While most contact cleaners are simple solvents that just wash the connector off. There are contact enhancers that deoxidize the contact surface and actually work to lower the contact resistance (make a better connection). Most contact enhancers leave a lubricant behind that protects the metal and continue to deoxidize the metal and improve the connection. They can work to lower the resistance and actually make a BETTER contact as time goes by. The best you can hope for from dielectric grease is that it seals it enough to not get much worse. I have used Caig Deoxit on my bikes for a few years now. I first found out about this on my job when I had to correct an issue in a scale load cell connector system that could not tolerate even 5 thousandths of an ohm of resistance drift. We had a connector in the field that had been improperly plated and was starting to drift, mostly in warm humid areas like Florida. Our testing showed that the Caig Deoxit could be a good long term fix. We ended up using the Deoxit to stabilize the bad units until we could get corrected wiring harnesses built with the correct connectors.  We also put a layer of Deoxit on the new parts to protect and keep them clean over their lifetime. This totally solved the resistance drift issue that we had. Our information on this product showed that the contact would actually get better for a period of over 1 year. The resistance would then begin to deteriorate, but at a much slower rate that a connector without the Deoxit

I still use a small amount of silicone grease on my spark plug caps. It helps to waterproof them and makes it easier to pull the cap off. (have you pulled a plug cap on a Stelvio yet?) But I use it in very small amounts and never near a relay or switch. 

Useful links:

1)      http://www.ia.omron.com/product/cautions/30/precautions_for_correct_use.html

2)      http://machinedesign.com/article/lubricating-electrical-switches-1025

3)      http://www.echeloninc.com/contactlubrication.htm

 

Wayne Orwig