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MG
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771 Posts
Discussion Starter · #1 ·
I just had another fun exchange with the folk at AutoZone (I'm visiting my folks in Wisconsin):

Yesterday I bought 8 spark plugs from them and went with their computer specs - they gave me the RN11YC4. After a look at the workshop manual, I found to my dismay that the OEM specification is RN11YCC, or, for my vehicle, which is the Australian version, it calls for the RN11YC (no 4, which is a "wider gap" required by California). The RN11YC is not available.

Curiously, the "tune-up kit" (distributor cap, rotor arm and plugs) from Atlantic British comes with the RN12YC, which got me thinking about the wisdom of AutoZone.

The 11 and 12 numbers refer to plug operating heat ranges, while the last letters of the designation refer to gaps and insulator tip. Comparing the two together, it is quite apparent that the insulator tip on the 12YC would portrude further into the combustion chamber than the 11YC4 (I don't have access to any 11YC for comparison). Hmmmm.

I'm guessing that AB knows better than AutoZone, so today I went and exchanged the 11YC4s for 12YCs, not before I got into an argument with the guy behind the counter - I ended up just insisting that he give me the 12YCs despite his advice.

During our friendly conversation (really, it never got unpleasant), they mentioned to me that the plugs needed to get properly "gapped" anyway and that their system showed that a 0.032" is the correct gap size. Then they showed me how the 11YC4s had the proper gap, while the 12YCs had a 0.035" gap.

So ran home and looked up the gap requirements in the workshop manual and found that the OEM specs call for a 0.033" to 0.038" gap range. Ha! Score one for MG...

Now I only worry about the specified heat range, the specs call for 11s (not 12s), but I don't know that it's going to make much of a difference. Anyone know something about this?

Any comments from the more experienced and knowledgeable DIYers?

Those of you who run Champions (I know a bunch run NGKs and Bosch P-4s), which product number do you buy?

While I'm at it, Happy New Year everyone!

Cheers,
 

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My $.02 worth so late in the year.
The heat range will show up as a difference in power and a ping that should be corrected by the engine management system. If it drives the same, and is not too long, hiting the piston, then don't loose any sleep over it.
I am running Bosh Platiumn Plus 4's, don't remember what number, and it is raining like hell or I would go out and look, but they are now nealy 55,000 miles old and have really worked well.
By the way, don't know what your mileage is, but have you changed your plug wires, they are probably warn out if you are over 50,000 miles.
Good luck,
Mike J.
 

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I have been using single electrode Bosch platinums for years with no problems.


The plug i use is Resistor # 4220 that # will be on the box, On the plug itself it will
read WR9DP. Atlantic british have sold these plugs for years.

Autozone sell's them, pepboys as well.

The dickhead's in autozone & pepboys will only recognise the 4220 # on the box
 

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the part # for the bosh p-4 are 4478 I just picked some up also.


Happy New Year All!!! :drink1:
 

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MG
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771 Posts
Discussion Starter · #5 ·
Thanks guys!

Once I have some data, I'll post some results.

Cheers,
 

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Rudy R said:
the part # for the bosh p-4 are 4478 I just picked some up also.


Happy New Year All!!! :drink1:
Rudy,
have you up dated your plug wires yet? You really need some 8mm. wires rated at 55,000 volts or higher so you get the full Bosh punch, lots of low end torque will show up with the combination.
Mike J.
 

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me.guevara said:
I just had another fun exchange with the folk at AutoZone (I'm visiting my folks in Wisconsin):

Yesterday I bought 8 spark plugs from them and went with their computer specs - they gave me the RN11YC4. After a look at the workshop manual, I found to my dismay that the OEM specification is RN11YCC, or, for my vehicle, which is the Australian version, it calls for the RN11YC (no 4, which is a "wider gap" required by California). The RN11YC is not available.

Curiously, the "tune-up kit" (distributor cap, rotor arm and plugs) from Atlantic British comes with the RN12YC, which got me thinking about the wisdom of AutoZone.

The 11 and 12 numbers refer to plug operating heat ranges, while the last letters of the designation refer to gaps and insulator tip. Comparing the two together, it is quite apparent that the insulator tip on the 12YC would portrude further into the combustion chamber than the 11YC4 (I don't have access to any 11YC for comparison). Hmmmm.

I'm guessing that AB knows better than AutoZone, so today I went and exchanged the 11YC4s for 12YCs, not before I got into an argument with the guy behind the counter - I ended up just insisting that he give me the 12YCs despite his advice.

During our friendly conversation (really, it never got unpleasant), they mentioned to me that the plugs needed to get properly "gapped" anyway and that their system showed that a 0.032" is the correct gap size. Then they showed me how the 11YC4s had the proper gap, while the 12YCs had a 0.035" gap.

So ran home and looked up the gap requirements in the workshop manual and found that the OEM specs call for a 0.033" to 0.038" gap range. Ha! Score one for MG...

Now I only worry about the specified heat range, the specs call for 11s (not 12s), but I don't know that it's going to make much of a difference. Anyone know something about this?

Any comments from the more experienced and knowledgeable DIYers?

Those of you who run Champions (I know a bunch run NGKs and Bosch P-4s), which product number do you buy?

While I'm at it, Happy New Year everyone!

Cheers,
If you look at Robison Motors website, they recommend RN12YC over the factory recommended RN11YC, they prefer that heat range , for some reason. I don't know why, but they are an authority on LR. I think their advice can be trusted.
 

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MG
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771 Posts
Discussion Starter · #8 ·
Thanks!


I did in fact decide to stick with the 12YCs - AB (and now Robison) have more credibility than AutoZone...
 

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Rudy,
have you up dated your plug wires yet? You really need some 8mm. wires rated at 55,000 volts or higher so you get the full Bosh punch, lots of low end torque will show up with the combination.
Mike J.
I just got off boschautoparts.com, this is my search result:
"Platinum+4 Spark PlugsPart number not compatible with 2003 Land Rover Discovery" that is copy and paste.

Now I have searched these +4s myself on other sites and have been given results on initial search but then when I hit one, open it up isolated, it then confirms it is not a match for 03 Disco 2. Every one....4449 ..4469 ..4417 ...4418 ...

Just tried Amazon again, thoroughly. Identical results. Initial lists many plugmodels of all brands under vehicle, but it not a refined and accurate search. It is programmed to market and suggest and ..unreliable. How often do searches yield specific and strict adherence? I can't get one to stay even within perameters when I use filters. Now, I just ran this: again copy and paste//--search was in quotes "Bosch Platinum 4 spark plugs" for 03 Land Rover Discovery II.
Result: [No results for "Bosch Platinum 4 spark plugs" for 03 Land Rover Discovery II.]
Same for full quote: [No results for "Bosch Platinum 4 spark plugs for 03 Land Rover Discovery II"]
Autozone site now: plugged in Google: "Bosch Platinum 4 spark plugs for 03 Land Rover Discovery II" no +4 listings verify for Discovery. I just just did eBay, No +4 match. Again, on all they show when asked for on initial results. Amazon never shows them unless asked for in regard to LR Disco 2...no matter how you keyword it. If you plug in Bosch products, the Platinum+4 never match. Now, it was my logical conclusion that a mainstream plug, marketed and pushed for it's performance and cutting edge latest greatest technology when it hit the marketplace...yada yada..I figured it fit all. ALL. I figured 'mostly' if I pick a HOT plug, it'll have a match. But I am learning a lot these days again. I could swear I had verified a +4. As I went back, I am convinced it is an initial hit, EVEN WHEN IT IS PREFACED ON EVERY SITE BY "This fits your..." Most of the time if you open up each item singularly, they all do NOT in fact match. So, the "check and recheck and triple check after a double check rule" is in effect. Several of you guys posts share about descrepancy issues even in stores. Of course! In a perfect world... Lol. We wouldn't need parts nor forum. NOW---Disclaimer! Mike, you other guys: I am not verified perfect in any category but the less desired. Check this out, I publically qualified once, get this, by a prom date as "a waste of skin!". There is an opinion-hated list on all of us. But I am doing my diligence with this Disco dancing. I have time, I decided to make it. I don't have unlimited funds, and I I've learned how to learn since I got out of school. Please do not be offended. I am only relaying my sound and factual as I can come up with findings. I am no computer techy and no guru of nada. These searches are not accurate. Many products car oi as over in many areas. Spark plugs are at most not much different (in regard to so many are in fact quite similar, others as re obviously not.) Minute gap difs and who knew they even have play/irid infused? While I was on eBay I found was match and confirmed, and at this point I am well done:
Just one of many confirmed--a match: not big and bold on purpose. I copied and pasted
Set of 8 OEM Land Rover NLP100320 Double Platinum Spark Plugs
for Discovery 2 and Range Rover P38
$44.82


If a plug fits and I gap it close, won't most function close? I don't know but I figure so. And next thing you know, It makes the re ounds and gets accepted. It works! We've all had it hapoen. Great when i does. It really is. I suggest if it works and well...Bosch may not know.

My summary: I think that $40+ is too much right now. I keep going back to the Denso Plat TT 4503 $28 total and Bosch platinum 6702--$27 total. Wires from British Atl. God bless yall.
 

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For the past 2 years I've used NGK Iridium IX #3764 on my 4.0L V8 gapped at .038" with no engine issues.
If had to get another set of plugs, I'd go for the Bosch Platinum Plus 4's #4418. I personally know other Disco 2 owners who swear by these specific Bosch plugs for their 4.0L V8.
 
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