I've received different answers regarding the proper use of dialectric grease when cleaning and reseating connectors.

One school of thought is that it should only be used to seal the rubber boot on a weatherproof type connector or spark plug boot.

Another school (and the label) says that, additionally, it can be applied directly to the metal connectors (pins, blades, etc.) themselves to form a corrosion proof seal.

Thoughts?

 

Based on experience in the electronic industry and electrical problems on motorcycles over many years, my philosophy is to liberally apply the dielectric (silicone) products. Never had a problem with continuity and it sure kept the moisture and resulting corrosion under control.

 

I second Testpoint's thoughts on this - my experience is with helicopters operating offshore. Filling connectors with silicone grease (DC-4) can really help avoid corrosion-related problems. Check out Stabilant 22 for problems with environmentally sound connectors you suspect of causing problems with low power signal related systems.

Mike

 

LMAO! I'll keep my opinions to myself this time. I have a difference of opinion with another member, and he happens to be a moderator now.

 

I'll second Stratohammer, I've used DC4 in aviation connectors for just this purpose for years.

 

I can relate.

 

LMAO - laughing my a$$ off

Had to ask my grandson.

 

OK... I just can't let this go. I've heard people say stuff like "I've been using dielectric grease on the plug for my boat trailer for years and I've never had a problem!" Well there's a big difference between a boat trailer harness and the electrical connectors in a car (or an airplane). A boat trailer harness has 12 volts going through it at a couple of amps. The pins are big, fat, spring loaded things that put a lot of pressure on the connection points--enough pressure to squeeze out most of the dielectric grease.

Then there are the connectors that go to things in our Jags, such as the ECU or the BCM. Some of the wiring is shielded wiring. It carries digital electrical signals at 5 volts or less. The current is measured in milliamps. Minuscule changes in the electrical input can effect the way the module interprets the signal it is receiving. The pins only have a tiny amount of pressure on them, and in many cases it may not be enough pressure to squeeze the grease out from between the pins.

Our cars didn't come with dielectric grease smeared on the pins from the factory for a reason. The pins are typically chrome plated, and the chrome will not corrode. If the pins are corroding, it's most likely because they were plugged or unplugged while power was applied, and the arc burnt off the chrome on that pin. Dielectric grease isn't going to improve the conductivity of that burnt pin, it does the exact opposite.

So, cars and airplanes don't come with dielectric grease applied to the pins from the factory. The manufacturers of dielectric grease don't advocate its use on the pins of the electrical connectors. Avt007 explained that he uses it on his aviation connectors and frequently has to "re-rack" the equipment to get the pins to make good contact.

Putting dielectric grease on the pins of the electrical connectors is just a bad idea. Sure... on the boat trailer connector it won't be a problem. On the big connectors with lots of current going through them it won't be a problem. But when you get to the fine connectors with low voltage, low current, digital electrical signals, you're just asking for trouble if you put dielectric grease on them.

 

Of course you don't need me to say so, but that is exactly right.

The stuff is by definition an insulator. If it's applied to the conducting bits of a connector, and then things work when connected, it's in spite of any grease left on the conductors, not because of it.

 

I've had this discussion before, and someone pointed out that their tube of dielectric grease specifically said it was for use on "electrical connectors". But there's a difference between a "connector" and a "conductor". The connector is the plastic plug thing that connects all of the wires together. The conductor is the actual pin which makes the connection. I just changed out the light bulbs on my Expedition yesterday, and I applied dielectric grease to the rubber O-rings in the connector to the bulbs. But I did NOT put dielectric grease on the actual conductors. That would have been counter-productive.

I was looking for an actual paper from the IEEE or the SAE to settle this once and for all. Unfortunately I'm not a member of either, and to download the papers you have to be a member. Does anyone here have a membership? I have a degree in electrical engineering, and I used to be a member if IEEE, but I'm not a member anymore.

 

Yes, agree Dennis, Sam. Many of the connectors in these cars, and most associated with engine management are hermetically sealed at the point of connector contact. This offers sustained reliability over time in humid and dirty conditions.

In practice, when I have occasion to remove a connector, I use a contact cleaner used in digital electronics that dries completely and leaves no residue. I prefer these connections to be clean and dry.

 

Hey Rev--I am with you on this one as well. In fact the last time the subject came up I included a definition of "dielectric grease" in my reply as well as a link to a manufacturer who specifically states that the material, by definition, is NON-conductive. So it works well on sparkplug boots but is not intended for the sparkplug terminal. As a total aside, for my last car GM recommended the regular use of dielectric grease as a protectant for weatherstipping and to keep it from drying out. You should try this stuff on the strips of rubber/weatherstrip that the driver and passenger windows rub against when lowering or raising the window.

Doug

P.S. There has been an increasing tendency on the forum in terms of being overly polite to the extent that one feels like they are walking on eggshells if they disagree with another member and have the audacity to say so. IMHO, as long as the disagreement is kept rational and civil I do not see the problem.

 

Thank you, Reverend Sam!

I used dielectric grease on the fuel injector connectors of the XJ40 project car I'm trying to revive.

The whole time I was applying it, the thought was running through the back of my head that the whole concept just didn't make sense!
Then I just figured "what the hell do I know?"

Good to know that sometimes my gut instincts can be right!
I'll redo the job correctly this time.

 

OK, to clarify, I was following aircraft manufacturers directions to entirely fill an electrical connector with DC4, to keep moisture out. This manufacturer had mounted pressure switches with the plug at the top, making it easy for moisture to flow down the wires into the connector. This caused corrosion and failure of the system. This is a standard aviation industry practice, and it's exactly what DC4 is made for.

From Dow Cornings website, aviation section;

APPLICATIONS
A moisture proof seal for aircraft, automotive and marine ignition systems and spark
plug connections, disconnection junctions in electrical wiring systems also in
electrical assemblies and terminals.
 Used as a seal and lubricant for cable connectors, battery terminals, rubber door seals,
switches and rubber and plastic O-rings and as a assembly lubricant for various metal-
on-plastic and metal-on-rubber combinations.
 Moisture resistant
 Good thermal oxidation and chemical
stability
 Meets MIL-S-8660C
 Retains its grease like consistency
from -55ºC(-67ºF) to +200ºC(392ºF)
• Electrically insulating
• Excellent rubber lubrication
• Excellent release and sealing
properties
• Resistant to oxidation
• Essentially nontoxic and non-
melting
• Show little tendency to dry out in
service

From the automotive section;

Uses of Dow Corning® 4 Electrical Insulating Compound include:
• Moisture-proof seal for aircraft, automotive and marine ignition systems
and spark plug connections
• Waterproof electrical connections
• Electrical assemblies and terminals
• Seal and lubricant for cable connectors, battery terminals, rubber door
seals and rubber and plastic O-rings
• Assembly lubricant for various metal-on-plastic and metal-on-rubber
combinations
• Lubrication for control and pressure plug valves

It is not used in dry locations, there's no need. But it will not cause any problems by using it.
For a dry location I recommend a contact cleaner product, allowed to dry, then assembled.

I've worked on aircraft for over 23 years, in a very rainy part of the world, and have never seen a problem attributed to the use of DC4.

Now, having said all that, have I ever felt it necessary to use it in a car? Not so much, other than trailer connections, since pretty much everything else is usually well protected in a car anyway. Research it on the net, and make your decision.

 

I'm not an engineer but I've been working on cars and motorcycles since 1964. I do use dielectric grease but only to add wateresistance or prevent seizing on outer boots of connector assemblies, I never put it on terminals in contact. I use electronics cleaner on these only. It's worked fine for me so far. Greasing up the terminals just makes me nervous and it looks messy which I don't like either. Deep down I know that the actual contact is where the metals touch but somehow the consistency of the grease worries me that it might hold the terminals apart more than if it wasn't there, degrading the contact, especially in tigth terminal areas with multiple connectors that might get a buildup of grease and pressure the terminals apart..

 

Note that it doesn't say "waterproof electrical conductors". A connector is not the same as a conductor. I concur that dielectric grease can be used to waterproof a connector. Heck, it can even waterproof a conductor in connectors with lots of friction at the conductor pins where precise voltages and currents aren't critical.
I have put dielectric grease on battery terminals before... after the cable has been bolted down. Several companies make a spray-on silicone compound that you can spray on circuit boards and then dunk the entire circuit board underwater. But it is sprayed on after all of the electrical connections have already been made.

I have no doubt that people who own boats and jet-skis and stuff smear dielectric grease all over ever electrical connectors and it never causes a problem. But a starter motor circuit on a jet-ski, or a lighting circuit on a boat is completely different than a 5v digital signal operating at a few microamps on 18 or 20 gauge wire in your Jag. Do you really want to smear grease in the serial data connector between the ECM and the BPM? Or on the connector to the Key Transponder Module where the module is picking up a signal from the key chip in the microvolt range?

Dielectric grease got this reputation for being great for electrical connectors because good ol' boys figured out that they could put it on their spark plug boots and drive their tractors underwater. Twenty years ago cars didn't have data busses and computers in them. The most complicated piece of equipment in the car was usually the radio. But our Jags have numerous electronic modules all communicating with each other through data travelling on the shielded cables between the modules. The engineers designed them to work without dielectric grease in the connectors, and I'm not going to try to out-think the engineers.

 

It's possible we have a violent agreement here.

I bet we all know intuitively that in an assembled connector, we want good, direct metal-to-metal contact between conductors. And that if grease has been applied to these prior to assembly, we're counting on the assembly process to sort of wipe it off.

It's probably true that for some connector designs and working environments, best practice is to slather on the grease for protection knowing that assembly will do the wipe-it-off thing.

More generally, we need to keep the grease away from the conductors because if any gets in the way of metal-to-metal contact after assembly, that's not so good.

Just thinking out loud ...

 

I completely agree with you BUT have always filled a connector with the silicone grease, especially on a motorcycle.

A violent agreement?

 

I agree. Someone pointed out in another discussion about this topic that the building code requires that aluminum building wiring, when connected with wire nuts, be sealed with silicone grease. I looked that up and it was correct. But, we're talking about a completely different situation. The wires are twisted together and then a wire nut, which contains a spring with a cone-shaped spring with a sharp edge, is twisted onto the cluster of wires. The wire nut compresses all of the wires so that they are all forced together under great pressure. I don't know the numbers, but the pressure of the wire nut is enough to force the grease out from between the wires. Plus, the wires are carrying 120 volts or more, which can easily overcome the resistance of a microscopic layer of grease.

I'm not saying that there's never a situation where it's correct to put dielectric grease on the joint where two conductors connect. If I had a boat I'd be packing the trailer light connector full of it. But on sensitive electronic equipment where digital data is travelling at low voltage and low current, I'll keep the grease away.