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Old 25-07-2021   #1
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Spark plugs and copper grease, should you?

I know we've had discussions about this before and there are those of us, mostly, I think of more advanced years? who were taught to use copper grease when we were learning our trade and have continued to do so but I've also become aware of the rising tide of advice that plugs should be installed "dry" because if you torque them to the recommended figures with lubricated threads you risk doing considerable damage to threads and plug body etc.

I've been researching this quite a lot lately and especially because this spring period is when I try to get to grips with the cars in the "family fleet" whilst the good weather is here. Consequently I've changed a fair number of plugs over the last few weeks.

I humbly submit that, for me, it seems to boil down to this:

1) Does the plug have a bright metal finish (ie, looks "chromed") If it does then the likelyhood is it's got a trivalent shell plating and should be installed dry IF IT'S A FIRST TIME INSTALLATION.

2) Dark metal finish, as all older plugs used to have, then some anti seize is probably a good idea. But be aware that copper based products are not perhaps the best choice because most heads are now aluminium and using a dissimilar metal is not ideal (possibility of electrolytic corrosion.) Products containing ground Aluminium or Nickel are preferred. I use Alumslip - made by the same people who make Copaslip.

That all seems straight forward enough so far doesn't it? However I still don't like the idea of leaving plugs installed literally for years as can be the case with long life modern plugs so I would like to remove the plugs every service or at least every second service just to disturb them and reduce the risk of them being "welded" in place when they finally need to be renewed. However I see a possible problem with doing this. The trivalent plating is designed to shear away from the threads so ensuring the plug doesn't get stuck in it's hole. Very good, if it works, because this should make plug removal after several years much less likely to end in tears. The problem is I've heard of instances where the plugs were still very difficult to remove after 4 or 5 years without being touched so I'm still inclined to take them out at least every second year. The trouble with doing this is that you're likely to, at least partially, shear away the trivalent plating so, by putting the same plug back in the hole dry, next time round corrosion may well have taken place.

At this moment in time I'm installing new, out of the box, bright shiny threaded plugs dry. Pretty much every plug I've bought lately has had bright shiny threads so the manufacturers seem to be all doing this plating "trick". Older "black metal" plugs I still lube with the Alumslip (although if you've got a head made of cast iron I'd be happy to use the copaslip if you want). I haven't yet removed the plugs from the Ibiza which is the only car in the fleet which has long life plugs and at 5+ years without being touched I'm sure they will leave their trivalent coating behind? So I've decided that in future they'll be coming out every two years but, whilst being fitted dry when new, they'll be getting a very light coating of Alumslip when they go back in the second time.

Of course there are problems in doing this - aren't there always - The "biggie" is that once a plug has been installed in a plug hole with lubricant on it then that hole will be contaminated with lube from then on so using a torque wrench becomes problematic. I know this is going to sound like I'm boasting but for me this isn't a problem because I've installed plugs for years simply by hand and I know how tight to do them - never had the slightest problem. Also be very sparing with the anti seize, you only need the thinnest coating and keep it away from the first couple of threads so you're not encouraging it to get into the combustion chamber.

Finally buy some dielectric grease and lightly lube the end of the HT plug cap - especially if you have the coil on plug type where each plug has it's own coil - Makes removal much easier next time.

Here's a pretty good article about it all which I found made interesting reading:https://www.driven2automotive.com/bl...g-spark-plugs/ The first comment at the bottom serves to support my suspicions that the trivalent plating is not the "miracle" it's claimed to be.
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Old 25-07-2021   #2
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Re: Spark plugs and copper grease, should you?

Thanks again Jock, for a well-researched post.

Like you, I've been fitting spark plugs for years, always used a very tiny amount of copper anti-seize, never used a torque wrench, never broken one, fitting or removing, including taper seat plugs. (I see the pic in the article shows a taper seat plug. Always a very silly idea.)

Until the introduction of taper seat plugs, I doubt any garage ever used a torque wrench on plugs. Then the Ford Pinto engine caught so many out, and ham-fisted 'mechanics' everywhere were breaking them off. Like any taper seat fitting, only a light tweak is required once contact is made. (Plumbing fittings come to mind. The harder you tighten them, the more they'll leak, as teh olive distorts.) Always needs care to keep any anti-seize away from the seat of the plug, whether crush washer or taper seat, as this is the heat path. Recommended torque settings are mainly to ensure proper crushing of the washer on new plugs, or to avoid over-tightening of taper seats. (The plug body is quite thin, and higher torques can twist them apart, so there's that too.) There has always been a recommendation to replace the washer if the plug is to be refitted, but I've not seen washers available since the late eighties. Reusing a crush washer should need a lower torque figure.

My plugholes will be nicely coated with copper anti-seize by now. Should I be poking a cotton bud into them until clean? And how many can I drop into each cylinder without worrying?

If the trivalent coating is sacrificial, does the new plug shove it into the cylinder? I wonder how the metal interacts with those in the catalyst? Some lubricant that prevents it shedding seems a good idea.
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Old 26-07-2021   #3
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Re: Spark plugs and copper grease, should you?

So many questions PB aren't there? I don't have definitive answers to most of them either so I'm just ploughing my own furrow and doing it my way, which has worked Ok for me for many many years.

Never worked for a Ford dealer but remember the Pinto engine well because it was a 1600cc example of that engine which I mounted up on a test stand and used for live engine running procedures when I ran my evening classes for our local education authority. I was also amazed to find the spark plug in the old Ransoms lawn mower - which is my next restoration project (Villiers Midget engine) - is a Pinto spark plug. Of course it's not the right plug, which should have a crush washer, but it must be the only one the previous owner could find to fit the large diameter thread form. I see the original plug type is available on line from specialist dealers, but at quite a price premium.

I don't remember having any particular problems with Pinto plugs snapping off although it was common to often find them overtightened. The ones I do remember as being an absolute sod were the wee taper seat plugs in the Vauxhall slant four cylinder which they fitted to the Victor and CF van which would regularly snap off leaving the threaded portion on the head. This was an awkward problem to resolve on the Victor with the engine being canted over to the N/S but an absolute b****r to deal with on the CF where the engine was half tucked up under the bulkhead.

Edit PS Crush washers? yes, of course should only be used once. But, like you, I don't see them readily available at my local factor. I find them a very useful indication of when you've tightened a new plug correctly. Having spun the new plug down by hand until you feel it go finger tight - thus indicating the "slack" has been taken up - when you start tightening with your wrench you usually find the plug goes about a quarter to half a turn with very little resistance at all. This is just the rest of the "slack" being taken up. Then the plug becomes moderately hard to turn and maintains this same resistance to turning for around half to three quarters of a turn. This is the washer crushing up. Finally, once the washer is crushed, the plug strongly resists any further turning and it's at this point that you should stop applying any more turning effort. The effort required at this point in the procedure is what you need to mentally retain because that's what you are trying to achieve when reinstalling a used plug where the washer has already been crushed. Once you've mentally stored away this "feel" dealing with plug installation becomes quite routine.
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Last edited by Pugglt Auld Jock; 26-07-2021 at 08:42.
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Old 26-07-2021   #4
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Re: Spark plugs and copper grease, should you?

I gave up using copper grease many moons ago. I use Black Moly high temperature grease for all nut/bolt/brakes/wheels/plugs/external self tappers/etc. Even use it on exhausts.

Over the years I found copper grease just dries out and is a poor performer when it comes to damp/water.

Have never had any issues with black moly grease even on brake components. On the brakes I use use it on the piston (small smears inside, pressure face and lip edge to dust shield), sliders, pad backs and slide surfaces, bolts. Initially I was concerned using on brakes instead of copper grease but after 6000 miles of motor sport (track days, sprinting) with some very long days/sessions (e.g. Castle Combe 215 laps/281 miles, Goodwood 120 laps/288 miles, Mallory 143 laps/193 miles) that really worked the brakes hard all day I can say all my concerns were unfounded.

That takes care of the heat side. Regarding water resistance then it is far superior compared to copper grease.

Well this is what I have found, what I use and have never looked back. No more stuck, rusted, etc. nuts or bolts. Easy disassembly every time!

The last time I used copper grease (not that longer ago) was in a non automotive application where I wanted it as a temporary heat sink/transfer application.

I am cautious of using moly or any grease on Nyloc nuts/fittings. It can be done but care has to be taken to use minimal amounts. A thin amount at the base threads of a bolt (no than 60% to 70% of the threads that make up 60% to 70% of the Nyloc nut depth) as that ensures that when the nut is put on the thread and done up then no moly/grease contacts the Nyloc locking ring.
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Last edited by s130; 26-07-2021 at 09:04.
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Old 26-07-2021   #5
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Re: Spark plugs and copper grease, should you?

Quote Originally Posted by Pugglt Auld Jock View Post
Edit PS Crush washers? ... I find them a very useful indication of when you've tightened a new plug correctly.
Quite a few years ago, had to deal with a warranty claim against some plugs. One piston had a hole in it. Daihatsu 3cyl.
Requested all three plugs to be returned. Arrived next day in a jiffy bag.
I tipped them out onto the desk, and could see the problem immediately. The one with the melted tip had a perfect, uncrushed, washer. Not tightened properly. Had been nipped up, as there was little evidence of gas blow-by, but of course, that changed the heat path, so it ran hotter than it should. Oops! Not warranty.
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Old 26-07-2021   #6
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Re: Spark plugs and copper grease, should you?

Quote Originally Posted by s130 View Post
I gave up using copper grease many moons ago. I use Black Moly high temperature grease for all nut/bolt/brakes/wheels/plugs/external self tappers/etc. Even use it on exhausts.

Have never had any issues with black moly grease even on brake components. On the brakes I use use it on the piston (small smears inside, pressure face and lip edge to dust shield), sliders, pad backs and slide surfaces, bolts. Initially I was concerned using on brakes instead of copper grease but after 6000 miles of motor sport (track days, sprinting) with some very long days/sessions (e.g. Castle Combe 215 laps/281 miles, Goodwood 120 laps/288 miles, Mallory 143 laps/193 miles) that really worked the brakes hard all day I can say all my concerns were unfounded.

That takes care of the heat side. Regarding water resistance then it is far superior compared to copper grease.
I had to read that a couple of times, but am happy with it now. Was worried about moly grease getting onto the hydraulic seals, but you seem to have that covered, with care taken.

Moly grease (molybdenum disulphide) is the black stuff used in CV joints, and resists leaving your skin once applied. With heat it does become more fluid, and I'd expect its melting point to be lower than the copper based stuff, so there may be a risk of it melting and runing down onto brake linings, depending on quantity and location, so it should be used carefully. I fear some may read this and slather it on, with issues shortly later.

I hadn't thought to use it as an anti-seize. Might try that sometime.
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Old 26-07-2021   #7
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Re: Spark plugs and copper grease, should you?

Appreciate the angle/view you (portland_bill) are coming from.

As with all things one has to be careful and understand what good/not good/ etc.

I specifically mentioned brakes and hard track use to point out a) my initial concern and b) all was OK. Very thin smear is all that is required on the pad metal contact areas and piston. Yes if you dollop it on you are going to have real problems.

Using moly (other than for packing CV joints) is like using a glue. As little as possible is all that is required.
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Old 26-07-2021   #8
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Re: Spark plugs and copper grease, should you?

Quote Originally Posted by portland_bill View Post
I had to read that a couple of times, but am happy with it now. Was worried about moly grease getting onto the hydraulic seals, but you seem to have that covered, with care taken.

Moly grease (molybdenum disulphide) is the black stuff used in CV joints, and resists leaving your skin once applied. With heat it does become more fluid, and I'd expect its melting point to be lower than the copper based stuff, so there may be a risk of it melting and runing down onto brake linings, depending on quantity and location, so it should be used carefully. I fear some may read this and slather it on, with issues shortly later.

I hadn't thought to use it as an anti-seize. Might try that sometime.
Very much my reaction PB but if it's been used on a track car and subject to the heat and "abuse" that implies without any problems then I'm really quite interested. Mention of using it on the inside of caliper pistons caused a quick suck of breath through the teeth, just, I would imagine, like you, however it then became obvious he's not talking about a caliper rebuild (where red rubber grease would be best) but rather I think he's applying a thin smear to the hollow inside of the piston and around where it bears on the back of the pad which would tend to stop the corrosion which often builds up here - certainly not under the dust seals? Like you I'm anxious a not too well informed person might use it incorrectly and in too large a quantity (I'm thinking about the great gobs of copaslip I found on the Jazz pads) but then any product like this used inappropriately will lead to tears.

Edit PS - Sorry I wrote this as you must have been posting your above post.
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Last edited by Pugglt Auld Jock; 26-07-2021 at 12:34.
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Old 26-07-2021   #9
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Re: Spark plugs and copper grease, should you?

Quote Originally Posted by Pugglt Auld Jock View Post
Very much my reaction PB but if it's been used on a track car and subject to the heat and "abuse" that implies without any problems then I'm really quite interested. Mention of using it on the inside of caliper pistons caused a quick suck of breath through the teeth, just, I would imagine, like you, however it then became obvious he's not talking about a caliper rebuild (where red rubber grease would be best) but rather I think he's applying a thin smear to the hollow inside of the piston and around where it bears on the back of the pad which would tend to stop the corrosion which often builds up here - certainly not under the dust seals? Like you I'm anxious a not too well informed person might use it incorrectly and in too large a quantity (I'm thinking about the great gobs of copaslip I found on the Jazz pads) but then any product like this used inappropriately will lead to tears.

Edit PS - Sorry I wrote this as you must have been posting your above post.
Yes in the hollow and around the lip/dust seal where corrosion can build letting water etc. behind the seal.

I think, based on comments on my post it could have been better written. That said I have other stuff on my plate so I've just typed as I thought which is never a good idea!

All I would say is that try a little moly where you did not before. Spark plugs is a great place to start. All those trim/wheel arch/undertray/ etc fittings.

Also the inside of the alloy wheel hub contact surfaces.

I personally think that the use of black moly grease has been underestimated and confined to bearing/cv applications.

I had Email discussions with Guy Croft (RIP) on the use of moly on head and camshaft carrier applications and he thoroughly agreed.

So I can only leave it to you guys and gals to carefully try black moly grease in both general usage and places where you would not have considered it.

Not sure what else I can add other then a little smear is all that is required unless packing a bearing/CV joint etc.
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Old 28-07-2021   #10
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Re: Spark plugs and copper grease, should you?

Here's an other option for plug anti-size, Milk of Magnesia. Yes, the indigestion medicine, preferably the unflavored version. This is often used as high temperature anti-size on aircrft gas turbine (jet) engines. it leaves a thin layer of magnesium hydroxide.


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Old 29-07-2021   #11
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Re: Spark plugs and copper grease, should you?

Quote Originally Posted by g8rpi View Post
Here's an other option for plug anti-size, Milk of Magnesia. Yes, the indigestion medicine, preferably the unflavored version. This is often used as high temperature anti-size on aircrft gas turbine (jet) engines. it leaves a thin layer of magnesium hydroxide.


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I inherited a bottle a couple of years ago from my mother. Expiry date was early 70's. Now if only I had kept it I could have used it all up!
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Old 29-07-2021   #12
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Re: Spark plugs and copper grease, should you?

Similar find at my mum's only this time it's syrup of figs. Best disposed of I think!
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