Technical Noise

[Marco92spv]

Dear friends,

A while ago after inspecting the timing belt on my fiat 500, while I was screwing the last bolt on the top plastic cover, the one that faces the rear of the car, near the dipstick, I have accidentally dropped it. As you can imagine I have never been able to recover it, I've also tried with a telescopic magnet stic bought for the purpose, no luck. I have recently started noticing a strange noise, it's very subtle. I can only hear if I'm driving on a quiet road, close to a wall so that the sound can bounce back. Some times it sounds like a grinding noise. It's very short, it usually happens if I'm driving uphill. This makes me think it must be rolling down, hitting a component of maybe the alternator, then bouncing away. Then rolling down again where it will produce the noise again.

Do you guys think this is a plausible explanation?

I found a picture of the fiat engine. I dropped the bolt in that circled area where it "magically" disappeared.

If that's not what it's causing the noise. What else could possibly be?

Many thanks to all

Marco

 

[Marco92spv]

I found a better picture. The bolt in the circle at the top, fell in the gap in front of the AC compressor. It never hit the ground. Magnet stick can't catch it. How dangerous is that?

 

[bugsymike]

Is it possible to have dropped into the alternator, I see it has large ventilation holes?
When you know it is making the noise, could you remove the alternator drive belt to see if noise goes away?
I hate when a nut or bolt drops and will do everything to locate it, knowing if falls wrong it can be cause expensive damage.

 

[Marco92spv]

Hi bugsy, thanks for your reply. Unfortunately it's an intermittent noise. Only last for like a second. So removing auxiliary belt won't help I think.

 

[John202020]

If the alternator is working then it's highly likely its on the road somewhere lost forever the noise is probably unrelated?

 

[Marco92spv]

If the alternator is working then it's highly likely its on the road somewhere lost forever the noise is probably unrelated?

Hi John I think you are right. After work I lifted the car and tried again checking from top and from bottom, squeezing my hand in the gaps and trying the magnet stick. It doesn't seem to be anywhere. Then I drove the car again, I noticed the noise occurs when either I'm driving uphill or if I have the AC on, or sometimes while accelerating, so under load. I really don't like the noise it's making, it seems to be from engine. If I just rev the engine, it spins smoothly, no dodgy noises.
I just read that engine knock sound can be caused by improper fuel ignition, due to worn spark plugs. Thinking about that, I have never replaced them since I got this car, and don't know if they were ever replaced before. What do you guys think? Shall I give it a try?

 

[John202020]

Always worth replacing the plugs, if keeping till scrap use Iridium or try standard and a tank full of E5 fuel whilst on change the oil and filter, I noticed in the Haynes manual you can use 10w40 which is much cheaper than 5w40 ?
The engine is generally the most reliable part of the car as its ancient tech late 80's, I think, don't turn off the ac leave it always on. When was the ac recharged and the cabin filter replaced?

 

[Marco92spv]

Hi John, I do oil changes and all the filters every year by myself. Last one was done in winter. Only thing I never done is the spark plugs. It's the first thing I'm going to try in the weekend

 

[Ralf S.]

The sound is likely to be the driveshaft / inner CV joint if it only does it when driving up hill (or over a crest in the road). It's not serious.. probably just normal wear and the car will drive even if all the internals of the CV fall apart. My Stilo proved it..

You will find the lost bolt in 2 weeks time, even though you moved the car and inspected the whole area on your hands an knees. That's how lost bolts work.


Ralf S.