2005 GC- Mileage, Plugs

You should read off the underhood sticker what was in there originally, and put them in there. I've never used a Bosch Plug that I was happy with. I run Champions in my '87 Jeep because that's the way the engineer designed them, although I like Autolites better, but it runs better and gets better mileage on the OE style plug.

Spdloader

Well you don't really have a traditional Jeep engine, but you should be aware that most of the older Jeep 4.2's and 4.0's basically refuse to run on Bosch platinum plugs. They work for a couple weeks, then foul and fail. Not all of the engines. but a 'lot'.

I have fixed more bad idle problems (or as many) in 4.2 engines by simply tossing their new 'fancy' platinum plugs in the trash and going back to stock plugs, than I have by fixing that dreaded Carter BBD carb.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > Just checking in, the missus has the 3.7L and the specs say plugs every 30k.

Thanks all! I think I'll stay OEM...

Wrong plug in that vehicle. The OEM NGK's are a good choice as are dual plat plugs from Champion. The current Bosch plugs are a gimmick.

There is no 3.7 in the GC. It's a 3.8. The spark plugs on the 3.8 are replaced at 100K. The plugs on the 2.4 (4cyl) are replaced at 30k.

Glenn Beasley Chrysler Tech

As far as I'm concerned, there are NO "pros" to Bosch platinum plugs. The tiny center electrode is a perfect design... IF your goal is to completely negate the longer wear life of Platinum by forcing the arc to strike in exactly the same place every single time. And if you want to make sure that the metal electrode erodes down so that its below the face of the surrounding hard insulator, and therefore one little fleck of deposit can cause it to misfire.

If you want platinum plugs, buy a set of Autolites. They're 100 times better than the Bosch crap.

Uh, no... The Grand Cherokee comes with the 3.7, 4.7 or 5.7 liter engines. No 3.8 liter available.

The spark plugs on the 3.7 are replaced at 30K miles.

No 4 cylinder offered in the Grand Cherokee -ever-

Alrighty, read lots of posts and I thank you all for the input. My buddy (Manager) at the local 'zone is a Mopar nut and sees it all...

He stated that he read an article or TSB somewhere that stated Chrysler did not recommend anything other than the OE plugs, citing their belief was that the Bosch platinum (and variants) caused pre-ignition. So, I went OE, although no NGKs were available, so in went Autolites. Funny thing is, 'zone's system states gap at .044, underhood sticker says .040. Set them all at 40 and took her for a spin to Laughlin and back. 75 miles, 20 mile 6% grade down into the valley and back up- 23.2!!!!! We have never gotten that result before.

In brief, I'm stuck on the OE plugs, and just put Autolites in my 97 Ford

460 motorhome chassis. Have yet to run a full tank through her...

Thanks all for your valuable insight!!!!

My bad, thinking this was not a truck forum I thought GC was a Gran Caravan. I dont normally read what is written under the op's name at th bottom

Glen

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Well technically its not a car, truck OR minivan forum really. Just all Chrysler products.

That's funny. Whenever I see "GC" the ONLY thing I think is "Grand Cherokee." Whenever people use "GC" to actually mean "Grand Caravan," I get it wrong.

Anyone have spark plug recommendation for a 99 GC 8 cyl? How about the gap setting?

When did they get away from the 100K plugs with the V-6 engines? When I bought my older Grand Caravan they had a $100 item on the sheet for

100K miles on the plugs. I thought you had to actually tip the engine to get at some of the back plugs!

Mike

Jeeps have 'straight' six or V8 engines and rear wheel main drive with

4x4 tossed in most for good measure.

I have a fiberglass flip front on mine so I just sit on a tire to change my plugs...

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > When did they get away from the 100K plugs with the V-6 engines? When

As was mentioned so far in this thread, OEM is best. If you look under your hood, there will be an emissions sticker that will give the spark plug type and gap recommended.

Same for spark plug wires for those that still have them. The longest lasting and cleanest burn always seems to come from the OEM wires. I am even running OEM distributor cap and wires in my old 86 CJ7.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > Anyone have spark plug recommendation for a 99 GC 8 cyl? How about the > gap setting?

Although "a spark is a spark", the spark plug brand and configuration CAN and do make a difference in how well things work.

Back in the middle '70s, I tried a set of Bosch plugs in my '70 Monaco

383 4bbl rather than another set of Champions. NO compelling reason to use the Bosch plugs as they didn't last or perform as well as the OEM-style Champions . . . BACK THEN.

Bosch has a great old name and reputation, but their products don't seem to justify it, from what I've seen. I didn't mind charging a customer fullpop retail for a set of AC plugs after he said he'd put some Bosch Platinums in his Chevy pickup and it didn't run right, so he wanted stock brand plugs back in it.

In a modern emissions controlled engine, it takes a very consistently-delivered spark to fire off the fuel/air mixture. Having a spark that CAN skip around to a number of different ground electrodes is not a good thing to have, it would appear. It'll always jump to the one with the least resistance anyway.

I know the "fine wire" center electrode plug works really good in my lawn mower and in my weed eater, but how well they work in an automotive engine can be variable.

Sometimes, I think that if Bosch didn't have the many sales promotions at the auto supply chains, they wouldn't have any sales at all.

Enjoy!

C-BODY