Spark Plug Replacement
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Northstar Engines and System Technical Discussion Discussion, Spark Plug Replacement in Cadillac Engine Technical Discussion; Hello Eveyone! I've had my 99' caddy STS for about a month now and am treating it like my baby. ...
  1. #1
    PWCadSTS is offline Cadillac Owners Member
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    Question Spark Plug Replacement

    Hello Eveyone!

    I've had my 99' caddy STS for about a month now and am treating it like my baby. I LOVE these cars. I got it from a dealer and it currently has 105K miles on it. But about 75% of those miles are highway miles which isn't bad at all. Here is my question though. I want to change the spark plugs in it. The main reason is because the dealer nore the previous owner knew of when the last time it had been done so I want to do it just to keep it in good shape, plus re-gain any lost power. The ones in there now are the recommended ACDelco spark plugs and of the front 4 of 8 I pulled out, they look REALLY worn and burnt. I want to put the Bosch Platinum +2 spark plugs in it, but any of the spark plug sockets that fit those plugs won't fit down into the engine. The sockets are to fat. So there is absolutley no way of putting them in let alone tighting them as I can see. The socket fits the plug, but then the socket doesn't fit into the spark plug hole. Does ANYONE know how to get these in there? Is there a special tool or something? Can someone please let me know ASAP about this if possible.

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    EcSTSatic's Avatar
    EcSTSatic is offline Cadillac Owners Connoisseur
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    Re: Spark Plug Replacement

    Your Caddy is trying to tell you it wants the right plugs. The AC Delcos are recommended, why do you want to use another brand?

    Don't take my word for it. Search on it. Try "Delco plug", Try "Bosch"

  4. #3
    JimD is offline Cadillac Owners Connoisseur
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    Re: Spark Plug Replacement

    Quote Originally Posted by EcSTSatic
    Your Caddy is trying to tell you it wants the right plugs. The AC Delcos are recommended, why do you want to use another brand?

    Don't take my word for it. Search on it. Try "Delco plug", Try "Bosch"
    I will second that motion....

  5. #4
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Spark Plug Replacement

    Ditto here. Stick with OEM, Delco 41-950.

  6. #5
    mcowden is offline Cadillac Owners Connoisseur
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    Re: Spark Plug Replacement

    Quote Originally Posted by Ranger
    Ditto here. Stick with OEM, Delco 41-950.
    I'll join in the fun. Do yourself and your car a favor and return the Bosch plugs to wherever you got them. Whether they have 1, 2, 4, or 93 electrodes, they're all junk. Stick with the manufacturer-recommended plugs, which are the AC-Delco 41-950 plugs everybody is talking about. Your car will be much happier. You should probably change the wires while you're at it. At 105k miles, they're due just like the plugs are. Your car needs AC-Delco model 748N wires. Again, the general concensus is that the AC-Delcos are superior wires to anything else out there, probably because the engine was designed with Delcos in mind. I changed my plugs and wires with AC-Delco all around and I'm very glad I did. It had Bosch platinum single-tip plugs in it previously, and as soon as I changed them it started faster and ran stronger without any doubt at all. It will cost you a few more bucks, but I think most people here will tell you that it's worth the difference. If you love the car, treat it right with the parts it was designed to use.

    OK, now for the second favor you should do for your car: Change the coolant. You will need probably 2 gallons of a Dex-Cool coolant (orange stuff), 6 pellets of Bar's Leaks or 2 tubes of Bar's Leaks Golden Seal powder, and 2 gallons of distilled water. Take the surge tank cap off while it's cold and open the radiator drain over a container that will hold 2+ gallons of fluid. While it's empty, pop off the top hose and drop in the 6 pellets or 2 tubes of sealant, then put it back on. Close the radiator drain. Mix up a 50/50 mix of Dex-Cool and distilled water and fill up the system with it. Drive it for a day, then check it cool and make sure it's still full. If not, top it off and you're done. The level should be 1-2" below the neck of the surge tank. You can fill it higher than that and it will just drain off the excess as it expands, but don't worry if you keep filling it up and it drops to that level next time you drive it. Maintaining the cooling system is very important on these cars.
    Mike

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    EcSTSatic's Avatar
    EcSTSatic is offline Cadillac Owners Connoisseur
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    Re: Spark Plug Replacement

    Quote Originally Posted by mcowden
    ....Change the coolant. You will need probably 2 gallons of a Dex-Cool coolant (orange stuff), 6 pellets of Bar's Leaks or 2 tubes of Bar's Leaks Golden Seal powder, and 2 gallons of distilled water. Take the surge tank cap off while it's cold and open the radiator drain over a container that will hold 2+ gallons of fluid. While it's empty, pop off the top hose and drop in the 6 pellets or 2 tubes of sealant, then put it back on. Close the radiator drain. Mix up a 50/50 mix of Dex-Cool and distilled water and fill up the system with it. Drive it for a day, then check it cool and make sure it's still full. If not, top it off and you're done. The level should be 1-2" below the neck of the surge tank. You can fill it higher than that and it will just drain off the excess as it expands, but don't worry if you keep filling it up and it drops to that level next time you drive it. Maintaining the cooling system is very important on these cars.
    This is the first time I've read anyone do this procedure like me. Why anyone would want to mess with a lower rad hose instead of using the drain plug and upper hose is beyond me.
    Good job Michael

  8. #7
    lry99eldo is offline Cadillac Owners Fanatic
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    Re: Spark Plug Replacement

    Hmmmmm, I would agree that using the factory recomended is best and same goes with the ignition wires.
    This is what I have learned over the years. I don't know squat! By this I mean I know what a sparkplug is as well as an ignition wire (i.e. sparkplug wire). What I don't know is what they are made OF and most importantly, by what engineering standard they were made. Sheesh, ever see how many designs there are for both of these items? Case in-point: Ever think you're going to improve the performance of your ignition system and get that special "heat range" plug along with those hot hot hot new wires that perform better than stock? All to find out that it won't idle, it backfires, won't fire at all, piston hits the plug electrode breaking it or closing the gap, radio gets static, points or modules burn out, and so on and so on. All these better or other than stock parts are most likely OK on their own, BUT, the original teams of engineers chose a specific unit for a specific reason and never had or wanted the oportunity to use these other products. Sparkplug, wire, simple, right? If you had a chance to ask any of the engineers on the project what determined their decision you'd be asking for aspirin real soon, LOL! Moral to the story; replace it with it! " probably because the engine was designed with Delcos in mind", (from above).
    Also agree with the coolant change, yet here is another sticky area acording to all the posts on the subject. Supplement? Yes, you bet, it's a natural base derivative in this case, won't hurt a thing, and is recomended in the manual. But I would place it in the LOWER hose as opposed to "pop off the top hose", (from above). I think the top hose is the RETURN path to the radiator, the lower hose is the INTAKE path to the engine. It's of more value in the engine than the radiator. As I said, this is all good, but there is one thing I would do before changing anything that is not causing problems or leaking. That would be to test the coolant with a special meter that determines the mixture ratio. It's a funny looking tool that you smear a little current fluid on a glass pallett surface, close down on that another clear thingy and then look into the sight of the tool. It will indicate the ratio of almost any additive compared to water. Your local radiator shop or, gasp, dealer will have at the ready. As strange as it may seem, the coolant may not need be changed........................yet.
    lry99eldo

  9. #8
    mcowden is offline Cadillac Owners Connoisseur
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    Re: Spark Plug Replacement

    I agree with you lry99eldo. Good point on the various systems that can be affected by untested parts (i.e. coils, radio, etc.)

    If it was me, I think I would go ahead and change the coolant. I want to know that it's good beyond any shadow of a doubt because the coolant change is such a critical piece of maintenance on these cars. That's just my preference. I don't know what test will really tell you how old the coolant is or whether its protection additives are depleted. To stay on the safe side, I would just change it. I think the testing tool you're talking about is called a refractometer, and it can determine the concentration of the mix but not the state of the corrosion inhibitors. Shell recommends a concentration no greater than 67/33 and no less than 40/60 with their particular version of Dex-Cool. I suspect the other manufacturers are probably right in line with those numbers as well. 50/50 is what I aim for.

    I think the upper/lower hose debate over supplement has come and gone once before and the concensus was that it didn't really matter as long as you put the supplement in there somewhere other than the surge tank. My own personal preference is to use the powder stuff, but if the pellets are all you can find, go for it. In either hose, it's going to circulate throughout the entire system sooner or later. What doesn't get used to plug porosity or minor gaps may eventually settle into low-flow areas, but I think as long as it's in there, especially at twice the dosage specified in the manual such as bbob recommends, the purpose will be served just fine.

    Just my opinions here. Not trying to prove anything. I'm not an automotive engineer, just a computer guy who wants to maintain things properly.
    Mike

  10. #9
    dkozloski's Avatar
    dkozloski is offline Cadillac Owners 10000+ Posts
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    Re: Spark Plug Replacement

    In case anybody is interested. GM has had the reputation of producing the best ignition wire for at least 50 years. Back when I was a kid, Smoky Yunich was endorsing Delco Packard 440 wire which was a GM product. They still lead here.

  11. #10
    EcSTSatic's Avatar
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    Re: Spark Plug Replacement

    You said it right mcowden!

    I may get flamed for this but here goes: First off I need to say that if someone tells that this brand or that brand works and they speak from experience, I'll listen. And if several people say the same thing, I won't even hesitate. Hence, I'll go with the AC Delco plugs that the board recommends.

    When it comes to the wires, I'm going to commit heresy. I owned a Ford Thunderbird TurboCoupe for 18 years and let me assure you, they were real touchy about which type of wires to use. Put the wrong ones and the car would buck like crazy! They required suppression-type wires and everyone on the TurboCoupe and Turbo 2.3L forums swore that only MotorCraft would work properly.
    Well some guys, including me, thought they could do better with some other performance wires. Almost every other brand failed to improve, and most made the cars run worse. The only performance wires that perfomed consistently were Magnecors.
    Magnecor is a fantastic aftermarket company. Go to their website and learn more than you ever needed to know about ignition systems. I've used them on my cars and they perform flawlessly. And if that's not enough, they have a lifetime warranty!
    You can order them directly from Magnecor or get them significantly cheaper from a distributor like UltraRev. Google on "magnecor distributor" and you can find other distributors. For the '99 STS the 7mm set is p/n 87261 and the 8mm set is p/n 80261.
    I don't make a penny on this. It's my contribution to the enhancement of this forum.

  12. #11
    PWCadSTS is offline Cadillac Owners Member
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    Re: Spark Plug Replacement

    Ok guys, here is whats up. 2 of the 8 Bosch plugs I got originally were in the wrong box, so thats why those wouldn't fit. I got the right ones and put them right in. I know I have heard of other Caddy's having problems with the Bosch Platinum +2 plugs, but Mine isn't having the slightest problem. They are actually performing a little better. I am going to replace the wires also, just didn't have time to do it today. Also, I have already flushed and cleaned the cooling sytem on it. So I am way ahead on that issue. So as of right now, the car starts better, runs better, and has better re-action time so I guess the plugs worked fine me. I know it's still early with the new ones, but I would think SOMETHING, even if it was mi-nute, would have shown up by now if the plugs didn't function properly for the car.

  13. #12
    dkozloski's Avatar
    dkozloski is offline Cadillac Owners 10000+ Posts
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    Re: Spark Plug Replacement

    The big problem with brands other than AC is that they don't last. If trouble shows up don't mislead yourself by saying "It can't be the plugs. I just changed them.".

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    zonie77 is offline Cadillac Owners Connoisseur
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    Re: Spark Plug Replacement

    Back to the coolant suggestion.

    The reason to change it is to refresh the anticorrosion additives, not the antifreeze level. Change it early, change it often, just change it. The headgaskets you save may be your own.

  15. #14
    mcowden is offline Cadillac Owners Connoisseur
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    Re: Spark Plug Replacement

    Quote Originally Posted by dkozloski
    The big problem with brands other than AC is that they don't last. If trouble shows up don't mislead yourself by saying "It can't be the plugs. I just changed them.".
    Good point, dkozloski. When my car first had the Bosch plugs put in, everything was just fine. It wasn't until a year or two later that it started taking longer to start, then it developed a misfire. Everything else checked out fine, so replacing the plugs and wires was the last thing I did. Once those were replaced, everything was great again and so far everything is still working perfectly. When I took out those Bosch plugs, the platinum tips were gone from two of them. Because of that, I'll never put Bosch plugs in any car of mine again. Yeah, they're cheap, but they're cheap for a good reason. They'll work just fine for a while, but don't be surprised if you have problems down the road that point back to the plugs. When you have to change them again, stick to the 41-950s for better longevity. Plugs don't affect a car's performance much anyway, except when they go bad.
    Mike

  16. #15
    calponte is offline Cadillac Owners Member
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    Re: Spark Plug Replacement

    you guys didn't even touch on the most important point as why not to use a bosch +2 plug. IT'S A GIMMICK... simple as that.
    Electricity flows to the path with least resistance. Keyword here: the. Singular...
    It will not fire 2 electrodes at once.. .can't happen.
    Congrats on wasting your money

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