Today I read an article in Design News that discusses this - and the problems that it can cause.
Case of the Anti-Seize Backfires
We had a 2001 Dodge Caravan with a 3.8 engine and a little over 118,000 miles come into our automotive shop. Intermittently it was hard to start. When it did start, it ran rough, misfired, and sometimes under a load, it would even backfire through the throttle body.
We tested fuel pressure, crank and cam sensor signals and scoped both these sensors, at the same time confirming they were in sync and the timing chain was sound. After some experimentation, we found we could get it to act up by power-braking the engine and running the RPM between 1,500 and 2,000.
The most challenging of these symptoms was the backfiring through the throttle body. For this to occur, combustion has to take place in a cylinder while the intake valve is open. This led us to take a close look at the spark plugs. On plug number three, we found a carbon track where the spark was jumping down the side of the plug. For this reason, we decided to pull the plugs for close inspection.
We found excessive amounts of anti-seize compound on the threads. This vehicle has a DIS ignition system, which uses the threads of the spark plugs as an electrical conductor. We later found out the owner of the vehicle installed the plugs six months earlier and used anti-seize compound. We installed new plugs and cleaned the threads in the heads, and the problem was solved.
We were still curious and confused. How could using excessive anti-seize compound cause the engine to backfire through the throttle body? We checked with three different spark plug companies to see what their ideas were on this subject. All three of them recommended against the use of anti-seize compounds.
They told us they already put a tri-valent zinc dichromate plating on the shells of their plugs to prevent the steel threads of the spark plug from seizing in the aluminium of the cylinder head. They also told us the problem with using oil or anti-seize on the plug threads is that it affects the torque setting. With aluminium heads, it is an important aspect of spark plug service these days to use your torque wrench to accurately tighten the plugs. NGK said that the concern is the threaded outer shell of the plug. If you overtighten the plug, there is a danger of stretching or even breaking the threaded portion of the plug.
They also told us that their recommended torque setting can be misread by as much as 40 percent if the threads have been greased or lubed prior to installation. The danger is not so much that the plug will break, but rather that it will be very difficult to remove the next time around.
They pointed out another problem. Many anti-seize materials come in a jar with a brush built into the top. With such an applicator, it is very easy to put too much goop on the threads. When this happens, installing the plug will effectively pump the excess material either toward the spark gap end or the spark plug wire end of the spark plug. The likely story is that it will do some of both.
Anti-seize compound is basically a mixture of grease and metal particles. Aluminium, copper, and zinc powders are commonly used. The way this works is that whenever you have two different metals, in this case the aluminium of the head and the steel of the spark plug shell, you can set up a battery action if there is an electrolyte between them. This is called a galvanic cell. What happens is that you get a transfer of metal that could cause the plug to effectively weld itself to the cylinder head. Putting the metal particles between the threads of the plug and the threads of the head gives the galvanic cell something to work on rather than the materials of either the head or the plug shell.
Anti-seize works in the same way as putting zinc on a garbage can, which is called galvanizing. It prevents rusting. The zinc sacrifices itself to the rust reaction, leaving the steel protected. The downside to anti-seize is what happens when too much of it is used. The grease and the metal particles can wind up in places where it not only doesn’t help, but it can actually interfere with the operation of the plug and the engine.
Several things could result from such contamination. The central electrode of the spark plug has a ceramic base that insulates it from the steel shell of the spark plug. To the extent that this is covered in metal particles and grease, it gives an unintended path for the spark. Instead of the spark being in the right place across the electrodes, it could wander off down the side of the plug. This can result in a misfire or even a late firing event.
To the extent that it is the grease that covers the firing end of the plug, this can cause a no-fire condition. Excess fuel fouling of the plug can cause much the same situation. When we look at these plugs, what we see is that we have deposits on the ceramic insulator that do not belong there. We can also see anti-seize residue on the threads and at both ends of the threaded area
In modern ignition systems, the coil is typically capable of producing more than 35,000 volts. That is almost double the capability of the old, round cylindrical oil-filled coils used years ago. When this voltage cannot jump the spark gap, it will find the next best path to ground.
With this car, we also saw another installation problem. Plug number three had a cracked ceramic insulator. This too can be caused by excessive installation torque. The high voltage arced along the ceramic of the plug and hit the ground shell. Under a microscope, you can see a burn mark on the steel shell.
We also found the spark left carbon tracks on only the tops of the insulator ribs. This means the material of the boot didn’t settle down into the bottom of those ribs. Boot grease serves at least three purposes. It prevents the boot from sticking to the plug, but it also allows the boot to settle in and form to the shape of those ribs. The ribs are here to make the path the spark would have to travel longer. The grease also fills the gap between the boot and the plug to prevent that from becoming a gap that the spark can travel along.
When we examined this wire set, we found that the grease had not been installed. We see this quite a bit. Oftentimes service techs, and especially do it yourselfers, do not really appreciate why we put those grease packets in the box with our wire sets and ignition coils. That grease really does need to be there.
In looking at these wires, we also noticed a lot of grease and other contamination. It is probably worthwhile to remind you that we are trying to hang on to 35,000 volts here. That is not easy to do. It is important to use the boot grease, put the wires into their plastic holders and separators, and keep the outsides clean and dry.
One last comment -- if you really do want to use the anti-seize material, go ahead. Just keep the advice from the spark plug makers in mind. You need to limit the amount of anti-seize you put on the plug. This is one of those deals where a little dab will do ya, and more won’t help you. Don’t let the anti-seize material get in the wrong places.
Take the time to grease the boots, and make sure the plug wires are properly installed. Finally, be carefull when you tighten the plugs. The spark plug companies want you to reduce the amount of tightening torque by about 40 percent. If you don’t, you run the risk of cracking the ceramic and/or stretching or even breaking the threads on the plug shell.
This entry was submitted by Mark Hicks and edited by Rob Spiegel.
What Bobbi said!
