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.
Anti-seize compound made a wreck of this 2001 Dodge Caravan.
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 aluminum 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 aluminum 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.
"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."
Don't ALL spark plugs used in IC engines use the outer thread as the negative electrode? The high tension wire from the coil is one side of the circuit, the "load" is the gap between the electrodes, and the outer shell of the spark plug is the other side of the circuit.
Why is this "DIS" ignition system different?
Using NEVER-SEEZ or similar anti-sieze compound is not new. It was first employed decades ago when Chevrolet introduced the VEGA, which had an all aluminum engine, including the cylinder block. It was part of the procedure to apply a compound when changing spark plugs. Ask any "old-timer" who owned a VEGA, and serviced it himself. He'll tell you that IF you didn't apply the compound, after the recommended 10K or so miles, you COULD NOT remove the spark plugs. They became welded into the head.
And, there were kits available for those who stripped the threads. It consisted of a HELI-COIL insert, a special-sized drill bit, and the insertion tool. These kits were sold for more than just the VEGA. IF you went to an outboard motor shop, the mechanics there were very accustomed to performing that task also.
I was surprised to read that the use of anti-sieze on spark plug threads caused this type of issue. The installer must have used an excessive amount of anti-sieze on the plugs. It is common practice in the automobile repair business to place a little anti sieze on the spark plug threads to prevent galvanic corrosion of the steel spark plug threads and aluminum head joint, which are commonplace in todays engines. I have been doing this well over 25 years and never had an issue. I do however use a very light coat of anti-sieze as a little goes a long way.I am glad to see that spark plug manufacturers have finally addressed the issue, but I am not sure all have, especially with plugs that designed long ago for older non-aluminum head engines, but carried over after the switch to aluminum heads.
Carbon tracking down the side of a spark-plug is an indication that the plug itself was defective and had no center conductor or there was a conductive film on the outside of the plug (maybe Never Sieze??). There should be enough thread contact area that the 5-8KV firing voltage would break-down any minor contact resistance. Considering the number of spark plugs broken during removal, the use of an anti-sieze lubricant is the best insurance policy. Consider the number of copper and brass fittings applied using teflon tape, a much better insulator than metal filled paste such as Never Sieze, yet these applications exhibit excellent conductance.
The spark plug boot grease is more important than you would thing it would be. I understand the grease being a good way to not have the boot stick to the plug, but the containment of the 35000 volts seems like a much more important reason to use the grease
So.. the spark was interrupted with antiseize because it was not conductive and you just don't grease up spark plugs. After all... they make special sockets for spark plugs and always use a small wratchet so you don't apply too much torque. If you don't have a small torque wrench.
This is actually a fascinating diagnosis, in that it was the chemistry of the anti-seize compound which reacted and caused the backfire in the context of the aluminum engine block. I've personally encountered another issue which is the bane of alumnium blocks, and which is why the user in this case applied the anti-seize in the first place. Namely, it's very easy in aluminum blocks to cross-thread the spark-plug sockets, which will ultimately result in blowing out the cross-threaded plug (physically, as in shooting out of the engine block) because it's not being held in securely. Then you have to put a shield into the block to hold a new plug and it's a big mess.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
4 
