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2008 Civic EX 4 door, 1.8L....

How often should I replace the spark plugs?

When I ask the dealers, they seem wishy-washy about answering such a simple question. I did not find the recommended mileage intervals for replacing the spark plugs in any of the owners manual booklets.

It's getting lousy MPGs even though it runs smoothly. All other aspects of proper upkeep are met accordingly.

Help.

 
Rep Power: 517

Plugs are on the 100,000 mile schedule in that car.
See the maintenance minder description (about the numbers and related services) in your owners manual, the number for plugs will pop on with the oil change reminder around 100k IF you let the oil change reminder go until the wrench light comes on (15%).

Precious metal plugs may be a bit expensive, but they normally last a damn long time. The wear is so slow they might even outlast the engine if you dared to try it --- as long as the engine doesn't cause them to foul out. LOL.

What do you consider lousy, and what sort of crazy traffic congestion are you trying to drive in there?

Any time the engine is running and you aren't moving, MPG is dropping. Stop and go traffic kills gas mileage. So do hills..

Best gas mileage bet is driving steady 50 MPH non-stop for an entire tank of gas. I know, it can't be done LOL

 
Rep Power: 149

Most people would never need to change them. I'm old school from way back and I started getting ansi at 90K and changed them out of concern of being stuck. They came right out and probably would have gone another 90K. If you gas milage was plugs, it would throw a code. It knows if it was missing. Make sure your brakes are not dragging. (jack car and spin wheel by hand) Drive like you have an egg under your gas pedal. Lift for red lights. I know, hard thing to do now without getting run over.? HA I can get 10 mpg better then my wife but I do see many people beating the steering wheel as we come up to a red light including her if she happens to be behind me.

 
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Its got about 65K on it. My wife does drive it hard. She basically races to the next traffic light then slams on the brakes. We do live in the foothills so I expect lower MPGs but it was getting almost 25 average per tank (mixed driving) and lately it's only getting just over 21. To me that is considerable.

When it was new, I got 43.5 MPGs driving conservatively from Los Angeles to Phoenix. To and from our local desert it would get around 36. I doubt it will get that now. Air filter is new and tire pressure is good. We just had new brakes installed front and rear so I will check again after the next fill up.

 
Rep Power: 517

It'll never get good gas mileage with her driving like that.
I bet if you drive it for a while on the highway, you can get mileage up.

Next time you have to get tires, look at LRR.
I bet it can.

 
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on my 2008 Civic I changed mine at 125,000kms they were the
original Denso"s from Honda. plugs came out pretty easy that's after spraying them down with a squirt of PB blaster and letting them sit over
night then loosening them up in the morning. after changing them out using
the same oem kind.

i did notice the engine ran & started
a little stronger afterword good idea to change them. don't know why
anyone would want to leave s/plugs in forever especially when you consider the risk of them seizing in the engine from being in there for so long...?
and if there seized in there good luck getting them out with-out breaking
one or more..

 
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Just replaced the spark plugs in my newly purchased '06 EX with 146,000 miles. I think they were original. Nowhere on the Car Fax does the maintenance show a spark plug replacement. Lots of oil changes, no mention of plugs. They were pretty worn, and it was idling about 550 rpm. Now she's idling at 800 rpm and lacks the dead spot on acceleration. Easiest plug change ever. Took about 10 minutes.

 
Rep Power: 142

I have an 06 EX also. The owner's manual says maintenance minder #4, no idea what that translates to in miles. If you have never seen this come up on the instrument panel yet maybe it's 150K miles. In the past I used 100K as a guide based on when these owner's manually actually told you the mile intervals.

 
Rep Power: 517

It comes up with the oil service reminder nearest the 100k-105k mark (if I recall correctly).....but you would only see it if you let the minder run down to 15% warning (that's a maybe), and you would see the "number" as the minder is being reset (during the oil change).

If nobody caught it in that short time, then it was missed.


The reminder number for coolant service usually comes up around the same time as the spark plug reminder (but not necessarily always at the same interval though)