My 2016 V6 is at 22K miles (yes I’m not trying hard enough!). According to the maintenance schedule I should be at 96K so time to change the plugs. But I’ve always been told they’re a miles based wear item. True or false ? They are a pain to get to so I admit to complacency with no indication of rough running or misfires.

Thanks!

Stu

 

I have a 2016 with 17k and I changed mine this year- wasn’t very expensive and figured it’s worth being diligent on service items. It’s unlikely that they are in bad shape but I would not leave a set in for 100k. I have another car with stupid HP that I change every couple thousand due to the rich fuel mixture, but that’s more of an extreme case.

 

Generally you replace spark plugs based on miles not age as they don't wear just sitting there.
Especially the modern Iridium plugs which are designed to last 100,000 miles plus before they need changing.
BUT some say that with age and despite low mileage the plugs can be become stuck in their holes due to carbon build-up, heat cycles etc and become a real PITA to remove, so they should be replaced based on age and not just mileage.
On a car where the plugs are easy to remove I would at least remove and inspect them every couple of years but as you say they are complete pigs to remove on the F-Type which pretty much rules that out.
The scheduled 96,000 miles or six years replacement is based on the same idea as the scheduled oil change intervals of 16,000 miles or 12 months whichever comes first, ie 16,000 miles per year.
My car is now over seven years old and is just about to hit 70,000 km or 43,500 miles and I have no intention of replacing the spark plugs just yet as there are zero signs they need replacing.

 

Change based on miles for me as well. I will replace the same spark plug the vehicle came with no matter how good the competitors are.

 

Since I am at the 6 year mark, but only 30K miles, I will likely wait until 50k. However, there is some good wisdom on this thread, as far as inspecting the plugs, ensuring they aren't seized, etc. I learned the hard way recently.

Over this past holiday season i took some time off to spend time with the family as well as get things done on both the F-Type (fluid changes, lowering springs) and to diagnose a misfire on my E46. Turns out the #2 spark plug came loose over the years (unknown change history, I acquired the car in 2018) which was causing a ticking noise, and eventually the misfire. I had misdiagnosed the ticking noise as a lifter tick which is very common on the BWM M52/M54 engines and thus had let it go.

What made it so much worse was when I went to inspect the plug, it was spinning freely in the block. Turns out the threads were basically destroyed. The plug had blown out and the heat of combustion actually cracked and frayed the rubber end of the ignition coil. So.. was my engine worthless since it couldn't hold 6 plugs?

I figured I would throw a helicoil at it, and if it didn't work, a machine shop would be needed anyways. Tapping the block to rethread was nerve wracking for sure. I probably could have re-used the plugs since they looked decent, but the coils were OEM and 20 years old. Glad to say one helicoil repair, 6 coils, and 6 plugs later, the straight 6 is running smoother and quieter than I have ever heard it. Here's to hoping it holds up.

 

The whole service schedule does seem crazy. Brake fluid is time based but you’d think other items would be based on mileage.
My V6S has just had its 5th service at 35k miles. I think it was a 65k miles service. They replaced the plugs and serviced the AC as well as usual oil change.

 

Most items wear based on usage (mileage), but as they may be exposed to various chemicals, combustion, heat cycles, etc., you need to consider other things like carbon build up and bi-metal corrosion etc..Things can get coated or stuck.

With fluids, time is important due to their characteristics. Brake fluid is hygroscopic (absorbs water) so it is recommended to change every 2 years as it becomes less effective when it heats up and the water becomes vapor in the lines (think bubbles!). Similarly, when motor oil heats and cools it becomes acidic, so even if it has low miles, you want to replace it with fresh. The wear packages also breakdown over time.

Just FYI.

For the OP....You do not want to leave plugs in for long periods as they tend to seize. (Or loosen)

DC

 

OR
They will loosen on you. (I hear more and more instances of that across several makes.)



I replaced the plugs on my daughter's Honda and six months later, 2 of 4 were less than hand-tight. (YES I tightened to spec)

 

Good point...I edited my post to include that scenario as well.

DC

 

Seems to me some of these engine designers should spend some time on the shop floor doing routine maintenance on them and maybe they would rethink their designs can’t wait to change the air filters ;-)

 

Better yet, they should PAY for the maintenance one or two times!

 

FWIW, I just did my plugs at 32k miles on a MY14. I didn't feel any urgency, and I'm generally mileage minded on plugs, but time plays in at some point. I also did brake fluid for the 2nd time and the supercharger belt, based on age. From discussion on the forum, I also did the differential fluid, even though it's not on the maintenance schedule.

The one fluid item I haven't done yet is replace the coolant. So many engines are using plastics in the jackets that can break down with older coolant, I'm surprised that the schedule only calls for it after 10 yrs/100k mi. Since I'm well below both, I've held off for now, but I'm sure I'll get twitchy one of these days and do it anyway. It ain't hard or expense, and the potential issues are.

 

basically the same for me, did the SC belt with the plugs even though mileage was low - mine sits in a climate controlled garage too but at some point I may sell and I would rather show more maintenance than less and I like the peace of mind. I’ll be doing coolant and brake fluid services with my annual oil change next spring as well.

 

At my recent service I told them not to upgrade the software. “Are you worried about the exhaust noise?” they said. I replied that I was too old to care about that and that anyway the actuators had both sheared so I couldn’t change it anyway.
My concern was that the car was behaving just fine and that in any event I’d fitted CarPlay and didn’t need the JLR stuff.

 

If you do end up deciding to change the plugs...Here is a LINK to a DIY with pictures etc.. Should help you out. Funny (but not joking)..One of the biggest PIA is getting those stupid insulating shields in and out

Seems like the going thought these days (from VAP and others) is to stick with the factory/OWM plug and heat range. If tuned, you just want to gap them down to about .028 = .032

Good luck.
DC