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Discussion Starter · #1 ·
Hi, I have a 05 Honda pilot 4wd with 180k miles. I've owned the car for only about 4 months so far. Two months ago had to replace thermostat and radiator due to a stuck closed thermostat disaste, also changed egr valve, plugs and ignition coils since they needed it anyways. I replaced it with a fail safe thermostats and that ended up not working out either. The other week that thermostat stuck open and was causing the engine and temp gauge to run cold, no heat, poor gas mileage. I changed out the failed thermostat with a OEM one and haven't had issues since in that regard. However since the current thermostat replacement my gas mileage has gotten even worse. I filled up yesterday and have only drove 63miles and I'm already on the half tank mark!! The decrease in gas mileage was also almost instantaneous after I started driving it after I replaced the thermostat. Some days it's like a cartoon how fast the gas tank gauge goes down in such a small distance. Everything was replaced correctly. all electronic harnesses are secure and look in good condition, no gas smells from anywhere, no leaks so am at a lose of ideas. Anyone else have a similar experience or any insight? Thanks and would be greatly appreciated
 

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Check to make sure your intake hose has not been cracked and hose clamps are on air tight.
Check for loose/dry/old vacuum lines that may be leaking air.
What brand/kind of spark plugs were used?
Do you have a check engine light on?
 

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Just presuming a 20 gal tank, 63 miles would be something like 6.3 mpg. Do you see black smoke coming out the tailpipe?
 
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also changed egr valve, plugs and ignition coils since they needed it anyways. I replaced it with a fail safe thermostats and that ended up not working out either.
If it NEEDED spark plugs, and ignition coils- it would misfire/run poorly. Was it?
What's a fail safe T-stat? That didn't work?

Are you having to apply more throttle to go the same relative speeds?
I'm sorry, not really sure what the problem is.
 

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Hi, I have a 05 Honda pilot 4wd with 180k miles. I've owned the car for only about 4 months so far. Two months ago had to replace thermostat and radiator due to a stuck closed thermostat disaste, also changed egr valve, plugs and ignition coils since they needed it anyways. I replaced it with a fail safe thermostats and that ended up not working out either. The other week that thermostat stuck open and was causing the engine and temp gauge to run cold, no heat, poor gas mileage. I changed out the failed thermostat with a OEM one and haven't had issues since in that regard. However since the current thermostat replacement my gas mileage has gotten even worse. I filled up yesterday and have only drove 63miles and I'm already on the half tank mark!! The decrease in gas mileage was also almost instantaneous after I started driving it after I replaced the thermostat. Some days it's like a cartoon how fast the gas tank gauge goes down in such a small distance. Everything was replaced correctly. all electronic harnesses are secure and look in good condition, no gas smells from anywhere, no leaks so am at a lose of ideas. Anyone else have a similar experience or any insight? Thanks and would be greatly appreciated
6 mpg isn't too good that's for sure. What clue did you have the thermostat stuck closed? If the engine overheated how hot did it get and for how long? Head gasket ok? (comp check)

Did the thermostat take down the radiator too? Were you getting good mileage before you changed the EGR valve? Still have it by any chance?
 

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Any diagnostic trouble codes reported?
If you fill up the gas tank when the needle says half full, how much gas do you need to fill up the tank? Perhaps the needle no longer reads the correct value.
 
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Discussion Starter · #7 ·
Back in late summer it overheated melted rad cap and cracked it thankfully I pulled over within a few seconds but did have some light smoke from under hood. It's been running fine since initial repairs. Pilot came with misfire codes when bought but after all repairs they went away. No current codes, no abnormal exhaust of any kind and runs fine. Used Bosch double platinum plugs. Gas gauge has always seemed like a lil bit of a floater since I got it so that thought crossed my mind. If it is a bad gauge issue what kind of labor is in involved in that?
 

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Nobili spiritus embiggens pequeño sparus tyre.
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Used Bosch double platinum plugs.
The Bosch Plug Curse strikes again.
143771


Replace those with Denso or NGK Laser Iridium or Ruthenium spark plugs from a reliable source (caveat Amazon fakes) like Rockauto.com:

2005 HONDA PILOT 3.5L V6 Spark Plug | RockAuto

Since you say you've also changed coil packs, make sure those are legit, too.

Do also carefully verify for cracks on your air intake tube, as suggested above, e.g...

143767


143768


It may be more subtle than these illustrations, like on the underside near the hose clamps. It can crack when it gets bent to change the engine air filter or when other service is performed.

 

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I'd replace the Bosch Double Platinum plugs with NGK 4363.
 
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IMO, the NGK IX is a lesser, and will probably work, but not as long. I personally would not want them, especially with the problems the OP is having.
NGK Ruthenium plugs are an adequate substitute.
I agree. I just suggested those, depending on budget or how long OP intends to keep the vehicle, because the NGK Laser Iridium I usually favor doesn't appear to be available for a 2005 or earlier, only starting in 2006.

2006 HONDA PILOT 3.5L V6 Spark Plug | RockAuto

And if budget is a concern (or even if you're just frugal like me :)), don't forget the 5% Piloteers discount. If Ben Franklin were on this forum, he'd say,"5% saved is 5% earned."

5% Discount Code: 31517DFA058403
Expires: February 12, 2021


Please enter this code in the ‘How Did You Hear about Us’ box to receive the discount. Please enter ONLY the discount code, no other words or numbers. All orders are placed online and the discount code must be entered before an order is submitted to receive the discount.
 

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Discussion Starter · #13 ·
Thanks for the replies. I will be sure to triple check all my hoses and vaccum lines again today. If it was a problem with plugs then why would the severe decrease in gas mileage only have started after I replaced the second failed thermostat just the other week? I replaced the plugs back in late October and havent had gas mileage issues until now. At this point its Monday morning, I filled up friday morning and have drove 136 miles and already down to little less then quarter of a tank left.
 

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Thanks for the replies. I will be sure to triple check all my hoses and vaccum lines again today. If it was a problem with plugs then why would the severe decrease in gas mileage only have started after I replaced the second failed thermostat just the other week? I replaced the plugs back in late October and havent had gas mileage issues until now. At this point its Monday morning, I filled up friday morning and have drove 136 miles and already down to little less then quarter of a tank left.
Just from my personal experiences and confirmation from others on this forum and other Honda forums, it's well documented that Honda engines do not do well on other brands/kinds of spark plugs, even though the maker claims they fit. There are those of us who have learned this the hard way. The hard way meaning that, we've replaced a whole lot of other parts, searching for a fix, only to find out that we shouldn't have gone to a different cheaper spark plug. In fact, I won't help someone (family/friends) any further with an engine problem until they replace them with the correct ones. It's that important.
 

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Discussion Starter · #15 ·
I will replace the plugs this weekend with the recommended ones you all have suggested and see if that helps. In the event that doesn't correct it then where would u go from there?
 

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I will replace the plugs this weekend with the recommended ones you all have suggested and see if that helps. In the event that doesn't correct it then where would u go from there?
Since fuel air mixture may still be an issue when everything was fine before, I'm still concerned with anything that could be causing a vacuum leak, air intake hose cracked drawing in excess air causing extra fuel to be delivered. Evap system possibly (new fuel cap). Have you ran diagnostics? Any check engine light?
 

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Discussion Starter · #17 ·
I had the CEL light kick on last night on the way home from work. When I hooked my scanner up I got a P2279 - "intake air system leak bank 1." Is bank 1 the of engine that had pcv valve? I googled the code and the three main issues it says it could be related to is vaccum leak, a faulty maf sensor or faulty pcv valve. Guess I'll check the pcv valve since it seems fairly easy to check it from the fee articles I read. Thanks again, I've only been getting into working on my own cars over the last year so still got alot to learn.
 

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