Colder plugs...worse mileage?

[MellonRover]

Got around to doing plugs on the new to me lr4. It looks like new spec is one colder. At 137k Likely the ngks in there were original as they were "6's", now they spec "7's".
I have run a tank through it and it looks like mpg dropped. Anyone else seen this?

 

[ktm525]

What year LR4? My originals in the 2010 were NGK 6C10 and the replacements were 7C10. At some point in 2011 LR started using 7C10s. I thought 6C10s were NLA?

Poking around I can see NGK discontinued the 6C10s and replaced with 7C10s. You either bought old stock (possible) OR you may have counterfeits? You didn't buy off amazon or ebay did you? Lots of fake plugs out there.

 

[djkaosone]

I know back in the tuner racing days, people put colder plugs on boosted cars to stop it from detonating. Not sure if the LR4 uses the same plug for the V8 and SCV6. There's a possibility that the SCV6 uses a colder plug.

 

[MellonRover]

OMW... looks like LYSDEXIA strikes again.
6 came out, I put 7's in. I'll fix the original post.
But they looked good. Viewed as they would be in relation to driver seat (lhd.) lower left is closest to driver.

 

[ktm525]

those do look good.

 

[powershift]

Gas mileage could drop if the system needs to pull back timing advance from using the wrong plugs.

 

[ktm525]

You bring up a good point although it is quite hard to use the wrong plug with NGKs since there is only one spec'd. To the OP: Did you check the gaps before installing? Generally they are fine but...

 

[MellonRover]

I did not check gap. Ive always left thin electrode plugs as is so as not to damage them. I only gap copper plugs. Ill see what a few more tanks of gas have to say. Of that first tank I did a few hours on highway at 80+ so i think efficiency fell off the cliff at those speeds

 

[16FujiDisco]

How much of a change in mpg are we talking about between the two sets of plugs?

 

[ktm525]

FWIW all the NGKs I have installed in the last 10 years were gapped appropriately out of the package so I think ou are fine. The 80 MPH cruising? Yeah that's the culprit. It's a box...