Another Head Scratcher

[floridaguy]

2004 Sport Trac with 88,000 miles. Problem started a few months ago. After I go through a car wash that has an undercarriage wash, when I leave the car wash as I'm accelerating and approaching 60 mph, I start hearing a deep sound like open exhaust, I back off the gas and the sound disappears. The next day the truck runs fine.

The problem after the car wash has gotten progressively worse. Starting at a lower speed and lasting longer.... like a day or two. Now the sound has changed. When it starts, it now sounds like a fan blade edge rubbing on something. It sounds like it's coming from the engine compartment near the passenger side firewall. It almost sounds like it's coming from under the black plastic cowling/grill by the wipers. It still stops if I back off the gas. On the 3rd day after the car wash now and it has not gone away this time. Turning off the AC and vent fan have no effect on the noise

I'm an old guy and can still do simple things but this has me beat so far. Took it to a local garage, no symptoms at the time and they said everything was OK except for a leaking valve cover and thermostat gasket. I had it fixed but it did nothing for the reason I took it in. Any help would be appreciated.

 

[J_C]

I don't know about the exhaust sound except to smoke test the exhaust. The other sound seems likely to be your HVAC blower fan motor failing, unless you mean that turning off the AC eliminates BOTH sounds? Just sayin', a fan blade edge rubbing sound, isn't at all like a loud exhaust sound. I wouldn't expect same problem to cause both sounds.

 

[floridaguy]

I don't know about the exhaust sound except to smoke test the exhaust. The other sound seems likely to be your HVAC blower fan motor failing, unless you mean that turning off the AC eliminates BOTH sounds? Just sayin', a fan blade edge rubbing sound, isn't at all like a loud exhaust sound. I wouldn't expect same problem to cause both sounds.

Thanks JC. What originally sounded like exhaust now sounds like a fan blade. And yes, turning off the HVAC fan motor and AC has no effect on the sound.

 

[429CJ-3X2]

I'm going to suggest something that you'll think is crazy, and expose myself as an idiot. Check your oil level. My wife drove my '01 Sport Trac several days last summer when the a/c wasn't working in her car. I noticed it was getting loud - really loud. From up top and underneath, it sounded for all the world like an exhaust leak - 2 leaks actually, at the converters. From the inside, it sounded a lot like what you described - the tip of a steel fan blade hitting something. I didn't drive it much over the next several months. One day I checked the oil and found it was 2 qts low. (Valve covers leak bad.) Changed the oil, and now it's quiet except for the slight exhaust leak it's had for several years. My theory is the valvetrain/timing chain noise caused by the low oil level was somehow amplified by the exhaust.

 

[floridaguy]

I'm going to suggest something that you'll think is crazy, and expose myself as an idiot. Check your oil level. My wife drove my '01 Sport Trac several days last summer when the a/c wasn't working in her car. I noticed it was getting loud - really loud. From up top and underneath, it sounded for all the world like an exhaust leak - 2 leaks actually, at the converters. From the inside, it sounded a lot like what you described - the tip of a steel fan blade hitting something. I didn't drive it much over the next several months. One day I checked the oil and found it was 2 qts low. (Valve covers leak bad.) Changed the oil, and now it's quiet except for the slight exhaust leak it's had for several years. My theory is the valvetrain/timing chain noise caused by the low oil level was somehow amplified by the exhaust.

The problem has persisted through the last two oil changes but I'll check it to be sure. Thanks for the help.

 

[Josh P]

I'd remove the serpentine belt to see if it is an accessory making that noise.

 

[floridaguy]

I'd remove the serpentine belt to see if it is an accessory making that noise.

I'll try it.

 

[410Fortune]

The passenger side timing cassette is exactly in the area you describe

 

[floridaguy]

Problem solved and I'm embarrassed it took me this long to solve. The wind deflector on the roof was loose and in the above described circumstances was flapping/fluttering on the roof and creating the noise that lots of people, including one shop couldn't diagnose. Thanks for your help.

 

[410Fortune]

Best case scenario!

 

[Josh P]

Thanks for the update