: Frozen Spark Plugs

01-25-04, 10:06 AM
Ugh...finally had the money and time to replace the plugs, hopefully to clear up some performance issues, and I can't budge any of them. Stuck as stuck can be. It's a 96 DeVILLE, which I have owned for a bit more than a year. 100k miles just rolled over.

Can anyone give me a clue as to how to get those plugs out. I was afraid to apply any more pressure for fear of breaking it in half.

01-25-04, 01:02 PM
I had the same problem with my Q45... They were the original ones from 1994 with 120k on them.... I had a 3ft pipe on the end of a long socket wrench... If your scared, just give spurts of pressure.... Eventually you will feel them get loose.... I dont know if you could spray some WD40 and make any difference, but it certainly couldnt hurt.....

I dont think you could break the plug, they are pretty tough... Not something that would concern me..... Just be certain the wrench is the right size and its on there really good..

01-25-04, 03:19 PM
The reason for being careful with taking out spark plugs, is because if you strip the thread on the hole... your done with! Be very careful; if you can, attempt taking the spark plugs out while the engine is moderatly warm (but i must danger you, exhaust manifold does burn you). Other than that, try as wes said - WD 40 or penetrating solvent... not too much though!

01-26-04, 12:40 PM
[QUOTE=JefferyG] (but i must danger you, exhaust manifold does burn you). QUOTE]

If you look at the spark plug location on a Northstar engine you will see that the plugs are no where near the exhaust manifolds. On pushrod engines the plugs are often in close proximity to the exhaust manifolds but on double overhead cam engines the plugs are always in the center of the combustion chamber and access is thru the cam covers....

01-26-04, 12:47 PM
Ugh...finally had the money and time to replace the plugs, hopefully to clear up some performance issues, and I can't budge any of them. Stuck as stuck can be. It's a 96 DeVILLE, which I have owned for a bit more than a year. 100k miles just rolled over.

Can anyone give me a clue as to how to get those plugs out. I was afraid to apply any more pressure for fear of breaking it in half.

Blow the spark plug wells out thoroughly with compressed air so that you know there is no dirt or grit in there to fall into the chamber...

Flood the spark plug well with some penetrating lube....generic things like "Liquid Wrench" and such may help. The best thing that I have ever used is a GM product marketed at the GM parts counter as "GM heat riser lubricant". It will penetrate and lubricate the plug threads to help break them loose.

Make sure you have a solid, well fitting spark plug wrench...and...are you ready for this...????.....get an air impact wrench and knock the plugs loose with it.

An impact will shock the plug threads and cause them to release. Sometimes, after lengthy installation and heat and time take their toll the plugs will start to seize in the aluminum threads of the head. Believe it or not, as much as I hate impacts around aluminum engines they are THE WAY to knock a stubborn plug out of the head without damaging the aluminum threads in the head.

Applying slow pressure will sometimes just bring the aluminum threads out with the plug...not a good thing. Shocking them loose with a quick burst from a strong impact will remove them handily. Seen it done many times.

Obviously, the plugs are going to be considered scrap once you have used an impact on them..but the idea is to get them out without damaging the cylinder head..not save the plugs.

01-26-04, 01:08 PM
do what he says lol ^^ it works

01-26-04, 02:01 PM
Actually, I think I've freaked myself out enough to just want to take the damn plugs I bought to my mechanic and let him deal with it. I don't have an air wrench, and I'm unlikely to buy one anytime soon. I thought about what the above poster said and was going to try using a pipe for extra leverage, but I'm terrified of breaking the plug, or stripping the threads. If that happens, I'm looking at a tow charge, on top of having it replaced.

If it happens at the mechanic, I can let him eat the charge.

I've had some hard to remove plugs to deal with in the past, but these are BAD!

01-26-04, 04:39 PM
They can get really frozen in the heads. That's one reason I suggest people change them a little early.
One old technique (if you want to try a little more) is to tap on the socket with a hammer while you are loosening it. It is better to use a breaker bar rather than a ratchet so you don't damage the ratchet. This is tapping straight down, it gives the shocking effect somewhat like an impact but weaker. It may be enough to break them loose.

01-26-04, 04:41 PM
One other thing, it doesn't matter if you break them taking them out...it matters if you break them putting them in !

01-26-04, 04:45 PM
I didn't reread the whole post so it may be in here...but just a reminder to use antisieze on the plug threads

01-26-04, 09:48 PM
I didn't reread the whole post so it may be in here...but just a reminder to use antisieze on the plug threads

It is not a good idea to use anti-seize on spark plug threads. For several reasons. The single most important is that the antiseize serves as a very effective high pressure lubricant in the threads. It reduces friction considerably causing, in effect, the plug to be overtightened and possibly broken or cracked by distortion of the shell. The torque on the plug goes into a redetermined amount of friction and tightening the plug by stretching it slightly. If the friction is greately reduced with the high pressure lube then more of the torque will go into turning the plug and stretching the shell....and the porcelean can get cracked internally this way and a misfire will result.

Secondly, antiseize is conductive. Having antiseize smeared thru the threads makes it very difficult to get another plug in there without contaminating the tip or the porcelean with stray antiseize as you move the plug around to get it in the hole. Before long everytimet there is a plug change several new plugs are destroyed by getting the antiseize from the holes on the tips.

The OEM plugs are nickel plate to prevent corrosion and minimize the sticking in the aluminum heads. Additional antiseize is NOT recommended.

01-27-04, 07:17 PM
Plugs were tight in mine too, here's how I got em out.

Very long winded answer to a question no one asked:

Heating up the engine does sometimes help removing the plugs. Its usually not recommmended especially in aluminum blocks like a Northstar because aluminum has a high CTE (coefficient of thermal expansion) thus changes dimension more than a steel block.(gets big when hot, contracts when cool) So if you pulll the plugs, and the engine cool and shrinks while the plugs are out, then there's a chance the spark plug hole on the block may shrink into a warped, or out-of-round shape, not good.

BUT here's the catch, even if the engine is hot (OR cold) as long as the temperature is pretty constant around the plug and block, then it shouldn't really make any difference on the removability of the plug should it?

The CTE of the plug is (and I assume most other parts on a complex machine like a car) matched to the CTE of the block so that the plugs and the engine block shrink and contract toghether when the temperature is raise or lowered. Otherwise all the parts won't work together, they need to all expand or contract the same amount or there are sure to be interference and clearance problems.

In our spark plug example, the plug and block would have expanded together resulting in no change on the amount of torque required to remove the plug. So the only benefit I can 'theoritically' justify would be that the grease or scum on the thread gets warm and helps slide.....or maybe the threads get so weak they 'give' or something....

Although designed to expand/contract together, parts really don't match EXACTLY. Also, the temperature is never quite uniform everywhere. (the exposed top of the spark plug is cooler than where the threads touch the head etc etc) In effect, you have parts at slightly different temperatures, with slightly different thermally induced dimensional changes. So the heating method works quite readily in reality! Especially if the temperature difference are big.

The best compromise I figure is to set up the biggest temperature difference accross these parts WITHOUT heating the block up too much to avoid damage:
So (finally), I street parked overnite in the winter, drove the car for about 1 or 2 minutes in the cold weather (snowing here) the next day. Immediatley removed ONE plug, replaced, then moved onto the next.
Effectively this causes a large temperaure difference accross the parts in question, causing the most change in dimension of these parts you can get, causing it to loosen just a bit. The whole time the block temp never really got too high in the minute you drove it, thereby avoiding the whole 'don't change plugs when hot' issue. Just change them one at a time and do it quick (ie. put the new plug back in right away)

Anyways, this couldn't have been more long winded.....but it worked for me like a charm.
All 8 plugs came out pretty easily using a 10 inch long (cheap and tiny) ratchet.

01-28-04, 03:11 PM
Powerglide....I don't disagree with the idea of the thermal expansion and such...but...applying the idea to the spark plug ports the way you did may have led to some confusion.

It is commonly stated to never pull the plugs on an aluminum head engine when the engine is hot. This is possibly good advice , but the problem or concern is not that the plug hole will shrink too small or shrink out of round. The plug holes are machined when the part is at room temperature, not when it is at 220 degrees F coolant temperature. So the plug will fit when the head is cold or at room temperature. The aluminum head won't shrink out of round.

The reason the "old wives tale" to not pull plugs on a hot aluminum head exists is because of the thermal expansion of aluminum being greater than the steel of the spark plug shell...but as it applies to the threads in the head expanding more when hot than the threads in the plug...actually it would be more accurate to say the pitch of the threads. It isn't the diameter of the hole or the plug would get looser when the cylinder head expands as the aluminum would expand more and make the hole larger than the plug. When hot, there is a near interference fit with the spark plug thread pitch due to the greater expansion of the aluminum....thus...if you start to force the plugs out the aluminum threads are more likely to be damaged since they are being held very tightly to the spark plug threads due to that uneven thermal expansion. In other words, the plug holes and the thread pitch were machined to fit perfectly at room temperature (it is hard to machine the heads while they are at 220F) so they will interfere to some extent when hot and common sense says to leave them alone when the threads are so tightly bound together.

Having said that, I have seen a LOT of spark plugs removed when the aluminum heads were hot without every having a problem.. Of course, they were not MY cylinder heads.....LOL

I think your partial warmup approach was very a very good idea and I suspect that it worked by bringing the coolant up near normal room temp (60-80 F) so that the head was probably near the temp that it was at when the spark plug holes were machined originally.

BTW...there really is a differential in the thermal expansion of the plugs (steel shell) and the aluminum head. That is real. The facts above also mean that the plug gets progressively tighter as the engine gets colder (below room temp) as the aluminum threads are shrinking still further and they are shrinking more than the steel. So the threads interfere as well as the hole gets "too small." May be a good reason that they are hard to get out when the engine is very cold outside.