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Thread: Dielectric Thermal Paste

  1. #1
    Senior Member jiott's Avatar
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    Default Dielectric Thermal Paste

    I'm going nuts over the proper use of dielectric or thermal paste. I have a tube of thermal heat sink paste, the label says it is dielectric, thermal heat transfer paste; most commonly used to get good heat transfer between a microchip and a heat sink. Now I have heard several people, on this forum, say this stuff is also good to use on wiring terminals and contacts to get a good electrical bond and prevent corrosion at the joint. But when I read the definition of a "dielectric" it says that means it is an insulator. Won't this stuff actually prevent electrical contact and be very bad to put on a ground terminal, etc.

    Some of you professional "Sparkys" out there please help me with this.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

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    Senior Member rv9ralph's Avatar
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    Default Re: Dielectric Thermal Paste

    I am as confused as you. I too looked up dielectric and read the same definition. Then I looked up a photo I have of the product I use for my plugs, and on the bulleted list of what it is it states both:
    "High Dielectric Strength" and "Superior Conductive Quality"
    Although in this usage it could mean heat conductive, but on the front it states
    "Excellent for automotive electrical applications, i.e. Alternator, regulators and rectifiers."

    Go Figure!

    Ralph

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    Senior Member Av8r_Sed's Avatar
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    Default Re: Dielectric Thermal Paste

    Straight dielectric grease is a silicone based product. Thermal heat sink compound or thermal paste has a similar base but have fillers(often zinc oxide) to give it superior heat transfer properties.

    Dielectric grease is clear, while heat transfer compound is usually white or silver due to the fillers.

    I use dielectric grease to protect wiring connections from oxidation, such as battery terminals - as a topical treatment after I tighten the connection. I also use it to protect and rejuvenate rubber products such as carburetor and spark plug boots.

    I use the thermal compound between my voltage regulator and it's heat sink as well as on spark plug threads. The trick with this stuff is to use it sparingly. More is not better. It also makes a big mess if you get it on other stuff.
    -- Paul S
    Model III SN910
    582 IVO Med

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    Senior Member jmodguy's Avatar
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    Default Re: Dielectric Thermal Paste

    I would not use thermal paste unless you need to transfer heat. The automotive use mentioned is for high heat parts, i.e. regulator and rectifier to pull heat away from the electronic part and shed it to a metal heat sink more efficiently. And Av8r is correct in that it is very messy, no matter how neat you think you are!
    If you want to seal an electrical connection with something like RTV, make sure you use an electronics grade RTV. Standard RTVs contain acids that can cause corrosion in some metals of electrical connections.
    Make sure all connections are made BEFORE applying the sealant!
    Jeff
    KF 5
    340KF

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    Default Re: Dielectric Thermal Paste

    According to my A&P, also use thermal paste on spark plug threads. In my 2 stroke days I always used the silver anti-seize. It always worked just fine as far as I knew. My old plugs always came out easy enough. I never knew that "heat transfer" was an issue. I always replace my spark plugs when we do my annual and do the compression check. It's pretty cheap insurance. My A&P is super anal about doing everything by the book and I'm glad he is. My 912 runs like a fine Swiss watch. He uses the same thermal paste that he uses on the GA stuff. I'm sure Spruce and the other parts suppliers carry it. I'll look it up. James Thomas

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    Senior Member jmodguy's Avatar
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    Default Re: Dielectric Thermal Paste

    OK I was curious so I looked up "spark plug thermal paste". Many of the returns were Rotax specific. Unless I read it wrong it looks like the main reason for using thermal paste on spark plugs is for plugs that have a picky heat range. The paste should be from the top of the threads to about midway down.
    I have never heard of using thermal paste on plugs before... huh.... Learned something today!
    Jeff
    KF 5
    340KF

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    Senior Member jiott's Avatar
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    Default Re: Dielectric Thermal Paste

    I think we all agree that thermal paste is good for heat transfer on spark plugs and heat sinks, but what I am looking for is a definitive answer on whether it is OK to use on an electrical terminal, say between the ring terminal and the post or tab it is screwed on to, or between a spade terminal and its socket, etc. If the label says it is dielectric, I think the answer is no, but yet I hear of folks who do it. I'm hoping for someone to chime in who really, really knows.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

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    Senior Member jmodguy's Avatar
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    Default Re: Dielectric Thermal Paste

    Thermal paste is not made to seal or waterproof electrical connections. It is made to transfer heat. Some thermal pastes are electrically conductive but this is not their intended purpose. The purpose of thermal paste is to fill the small air gaps between a part and the heat sink. The heat is transferred primarily through aluminum or silicon particles suspended in the material.
    Dielectric grease is primarily used for preserving and waterproofing rubber parts, i.e. spark plug boots.
    If you want to seal an electrical connection use an electronic safe RTV or potting compound.
    Do not seal the contacts of a multi pin connector. The low contact pressure can be contaminated or overcome by any substance on the contacts.
    I have been wiring military and civilian aircraft since 1980 and have never heard of using thermal paste on a terminal connection of any kind. I have used thermal paste only on voltage regulators, bridge rectifiers, and other high heat producers.
    That doesn't mean folks will not use it for such and will debate the merits of using it.
    My recommendation - do not use thermal paste to seal terminals. It is not made for this application.
    Jeff
    KF 5
    340KF

  9. #9
    Senior Member jiott's Avatar
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    Default Re: Dielectric Thermal Paste

    Thanks Jeff, I am thinking the same way.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

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