Engine Sound Question:

[Captain D]

Hello,

I was curious to see what the ideal distance should be between a fan-shroud collar and the pulleys (69' Charger, 383 4 brrl BB).

Reason being, we've been hearing this new sound that is a cross between a vibration and a buzzing sound intermittently towards the front of the engine bay. To make a long story short, here is a list of things that we've already ruled out:

-  the belts (all new + belt conditioner used),
- alternator in perfect working condition (bearings, bushings, etc.),
- power steering pump passed after a slew of tests,
- fuel pump working perfect,
- no leaks from the water pump,
- all the belts are neither too tight or too loose,
- everything is all tight and secure under the hood overall with no leaks anywhere.
- and, the car drives and handles flawlessly.

The only thing changed recently was having a new aluminum fan-shroud installed onto an existing 22'' aluminum Champion Cooling radiator. The shroud is a universal shroud custom-made to fit your vehicle:

http://www.ebay.com/itm/Summit-Racing-Adjustable-Aluminum-Fan-Shroud-Kit-380459-SH/390930556285?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140602152332%26meid%3D4db07f014446432e991831b6cd406884%26pid%3D100011%26prg%3D20140602152332%26rk%3D1%26rkt%3D10%26sd%3D390909869594

While I have better airflow, I'm curious to learn if anyone else here has experienced a similar sound after having one of these units installed? Also, the reason why I ask what the ideal distance should be between a fan-shroud collar and the pulleys is because...when looking directly down into the front engine bay, the collar is only about 1'' inch (perhaps even slightly less than a 1'') away from both; the power steering pump pulley and the lower-bottom most cam pulley. Is this too close? If so, perhaps I'm simply hearing the sound of both pulleys echoing inside of the aluminum shroud/collar and its magnifying the sound. One test that we did was to remove the power steering pump belt and listen. We heard, faintly, the sound continue and then gradually ease up altogether...even after we hooked the belt back up. Went for as test run, came back, and thankfully all was still quiet. But then, again today - the sound came back. The odd thing is that, on most occasions, the sound is not obvious at the initial cold start, but most prevalent the closer the engine gets to warmer operating conditions (around the 170 degree mark).

As a side note, a friend suggested, "That is a nice custom piece, I like that and it looks great. Now just my opinion, the fan is sitting fully inside the curved part of the shroud, but it should rest about 1/3 outside of the shroud; not fully inside of the shroud altogether. The air on the exit side of the fan is turbulent compared to the air in front of the fan. A shallower shroud like mine would help limit sitting air and increase flow but I think you noise is the curved section. It get louder as the metal expands due to heat and the space gets bigger. Consensus of opinion is that its air vibration off the fan. That shroud is tight and the fan is pulling all air thru the hole - the vibration of air is causing the hum. You can still tighten it and place some rubber washers to isolated vibrations where the curved section meets the shroud, but it seems to all point to air movement."

If there is anything else that anyone could add, I'd be interested in hearing what you have to say as something like this simply drives me crazy - especially when going out on the road when safety is an issue. The only things that were done recently consisted of: simple wiring connector upgrades, the band adjuster adjusted, got a new bottle of lead additive, and this shroud. I realize that I can always just run it and wait for something to become more evident if its going up, but I'd like to take some preemptive action if possible,  .

Thank you for your time in reading my collar-to-pulley distance question and for any input,
Aaron  

[JB400]

From the picture posted on Summit, the shroud looks flimsy.  My guess is it's the shroud making noise.

[fy469rtse]

One way to know for sure that its to do with fan and shroud , take off belts , motor will run for a short time without water pump to cool it,
No noise put belts on without fan , no noise. Install fan , noise check , ? Maybe some thin insulation tape between shroud and radiator , check that
Clutching at straws now , because I'm not there , but I know how frustrating this type of thing can be ?

[c00nhunterjoe]

To elaborate a little more, as i have looked at the car and briefly heard the noise in person;
     It is a middle piched noise, if that makes sense. Not a grinding noise like a bearing thats shot nor a whining noise either. It is VERY hard to describe. It is not very loud but you can hear it when it makes its presence known. It can be isloated to the front of the engine compartment. It is definatly not the alternator or ps pump. I did not run the engine without the water pump spinning since the noise is so intermittent i did t want to have to run the engine that long without coolant flow. I did listen to the pump via a stethescope while the noise was present and heard nothing in the pump. The bearings are smooth and no water from the weep hole.
  The fan shroud is pretty sturdy. It is a 2 peice design so i had suspected a possible vibration BUT the noise doesnt really sound lime that. I did wiggle and push on the shroud and it had no effect on the noise. Engine rpm didnt seem to effect it either, which also led me to beleive it was not a water pump or the physical fan/airflow either, but it wasnt present for a very long time either.
  I feel that the noise at this point, is not a danger to the car breaking down. It is frustrating that you dont know the source of it and i understand the uncertaintly of a new noise in your car. (Happens to me alot....lol) the fact that the noise has a low volume compared to the rest of the normal engine sounds makes me think a video will not work as the speaker probably wont pick it up.

[jlatessa]

Are you using a clutch unit with your fan?
I've run into noisy ones on occasion.

Joe

[c00nhunterjoe]

He has no clutch, direct drive fan

[Captain D]

Thank you gents for the many replies,  .

Since I was still hearing the sound/noise again today (just odd that I hear it when warms up @ the 170 degree range), I decided to measure the distance between the pulleys and the shroud collar. Both the power steering pump pulley and the bottom-most drive pulley are exactly 1/4'' apart from the new fan-shroud collar...its that tight. You'd be lucky if you could put your finger through either of the two gaps. So, perhaps I'm hearing the sounds of the pulleys magnified throughout the shroud. But, odd again that sometimes I hear the vibration and a buzzing sound intermittently. Also, I shut the hood and while the car was outside of the garage, I listened to where I thought that the sound seemed to come from (top, middle, or bottom sections) and it was practically dead-center of the grille of where the fan sets.

So, that's pretty much all that can be added & thank you again for any and all insight,
Best regards,
Aaron     

[fy469rtse]

What mods are done to engine,
Now that you mentioned this , I thought it was my imagination , I didn't here it on the dyno , but now engine in car with all accessory added , including fan shroud , I can here my gear drive more through grill , it's almost like it funnels the sound out through grill ?
All the alloy added to this engine amplifying the normal noises ? Maybe