elvenrider

Hi everyone,

It has been 7 years since I bought my trusty ES used. I added 50k km since then — now at 270k km. The car’s fuel economy has never been stellar, but it never showed any symptoms that suggests replacing the spark plugs. No rough idling or trouble starting. I also used the OBD device and did not see engine misfiring.

Now after 7 years, I wonder if I should proactively replace them or if to keep them running until troubles show?

Would proactively replacing them yield in better fuel economy? Or is that unlikely to happen if no misfiring? For informational purposes the current economy sits at (15-16 L/100 km) mixed driving

I don’t know if the previous owner(s) every changed them.

LeX2K

When were they done last? These spark plugs wear slowly the spark gap gets bigger and bigger, it will take almost forever before you have misfires. It would not surprise me if your plugs have never been replaced.

You fuel economy is quite poor.

elvenrider

Yes, I would not be surprised either. I don’t know if they ever changed it.

So you think the fuel economy should improve even if the car is not showing any other signs of worn plugs?

LeX2K

You should get a mild bump, over time the job will pay for itself.

Arsenii

Hello,

15-16L/100km is in the city or on the highway? Either way it is lots even for those engines, my 2000 ES300 was able to make it to Chicago and back on one tank, calculating about 7-8L/100km on the highway, so there is definitely something to look into.

Some not so fair mechanics would only replace the front row of plugs, leaving the rear hard to access ones intact while charging the full price, and as LeX2K pointed out, it may take month to find out. In any case, if you are not sure, it will never hurt to take them out and replace them, here you can find those for a reasonable price. With the mileage, you may as well get new Valve Cover Gaskets along with the plugs as they will be in direct access once the Manifold is off.

Other thing to do is look at the Fuel Trims, as well as MAF and A/F sensor data to make sure that the engine is running normally. Fuel Trims should be as close to 0 as possible, anything above 10 is in need of diagnostics. MAF sensor should show about 3.5 - 4.5g/sec, if it is noticeably lower, there may be a vacuum leak in the system. A/F sensor should be close to, but not stuck on 3.2V, abruptly floor the pedal and you should see an instant dip in the readings to the Rich side, if it is slow to react, or doesn't react at all, the sensor is on the way out.

Hope this helps and best of luck!

elvenrider

That definitely helps. I trust my mechanic — Aussie Auto Mississauga, Ontario. I am sure he will change all the spark plugs if asked to do the job.

That is what baffles me, the highway mileage is of no concern averaging 8 L/100 km but when you start adding city driving to the mix, it goes unreasonably high to 17-18 L/100 km taking my avg of mixed driving to 15 L/100 km.

I don’t drive like a drag racer in the city, very gentle on acceleration and breaking.

Will be intriguing to see if replacing them will provide an improvement, even a mild one like how @LEX2K2 suggested