Loud bang, now lower gas mileage !!!

[captainquigg]

This one has me stumped:
I have a 2006 Explorer, V6 4.0, 5 speed auto trans, w/ 130,000 mi. I replaced the oil and filter at about 127,000 mi. Also changed plugs at that time w/ Iridium plugs (that was the first time and none broke off, lucky me), changed front disk pads and checked all fluids. Also added about a pint of "Marvel Mystery Oil" to my oil to clean internal engine components and block.

At around 128,500 miles, I was driving down the road and heard a loud bang/thump come from either under the vehicle or engine compartment. It felt like something hit the bottom of the vehicle, but I didn't see anything in the road. I don't know whether the bang scared me and I took my foot off the gas for a second, or the car lost power for a second. But it kept going and I have noticed no other problems other than my gas mileage has dropped about 3-4 mpg since the bang.

Car idles smoothly, runs smoothly, no noises or vibrations, seems to have same amount of power. Checked for loose wires, plugs, etc. but I can't figure out why the gas mileage has dropped so much after the bang. Since the MPG's were low, I changed the oil and filter again at 130,000. Thought maybe I had a blown head gasket, but oil didn't have water/antifreeze in it, and radiator didn't have any oil in it. Anyone have any ideas concerning "bang" and lower gas mileage?

 

[rhauf]

is it possible you just ran over something, and you noticed the mileage drop as a result of "looking for something wrong" so to speak?

 

[captainquigg]

Well, the vehicle's digitial readout used to say I was getting about 17 MPG, now it down to 14's-15.1.

 

[spalmer1214]

This has nothing to do with the bang but when was the last time you changed your fuel filter. They should be changed about every 30K

 

[01STrunner]

Not really on topic but the 4.0 doesnt really like "fancy" spark plugs.

 

[captainquigg]

It's on topic as far as I'm concerned, and it's something I didn't know. Also, I was gonna change the fuel filter, spark plug wires, coolant hoses and go to a 16 lb radiator cap. And repair a coolant leak somewhere around my thermostat housing. Can't tell where the leak is, but I understand these things have an ongoing problem with radiator/coolant leaks.

 

[edwx]

Maybe the "17" was a long term average. If you just reset the mpg, you might currently only be getting 14-15 due to the type of driving you are doing now. ie. city driving with a/c on, etc...

 

[rhauf]

I'd say its likely just time for a good tune up, as mentioned above.