I am hearing a sound which is similar to the sound of a jet engine upon start up. After about 15 seconds it winds down and goes away. I am not having any problems driving and the noise never comes back. Does any one have any ideas what this might be?

2004 Disco
57,000 miles
4.6 L
No engine mods

 

The sound of the flux capacitor charging up. Push the right combination of buttons on the radio and you'll get music from the 50's and 60's when the engine was designed..... Motown was hot!

Actually, this is a good sign. You want that noise. It indicates that your viscous fan clutch is fuly engaged because the fluid inside has pooled to one side. The rotational force and warming up smooths the fluid out, the front and rear of the clutch decouple to about 20%, and you save gas. When front of clutch gets above 170F it starts slowly turning the coupling back up, to provide extra cooling in hot stop and go traffic. When cold, you fan won't spin but just a fraction of a turn, will feel like peanut butter inside it. When warmed up, it should spin more, but not more than 1 revolution when released. If it freewheels, too much fluid has been lost, usually through the seal on the front, and it will have some grease on it (does not stand out on most Rovers). Should it go bad, the tech section has a $50 ish Chevy cross over, or junk yards can supply late 90's early 2000's Chevy / GMC clutch and fan for like $20. They screw right on our water pumps, six inch clutch, reverse rotation. A heavy duty clutch will couple back at like 90%, a standard duty is about 70%.

What is bad is people quit listening to the oldies, and for that fan noise on every cold start. And their fan clutch slowly dies, and overheating begins, slowly at first, but after many times of running warmer and warmer while the computerized temp gauge hides this from the driver, evil things begin to take place just below the valve covers. Heads warp, head gaskets let go, liners slip, all manner of problems. Brought to you in part by the wimpy fan clutch and inattentive owner. On that Saturday fluid check Spike talks about, a spin of the fan clutch is worth doing.

 

Thanks Savannah for the great information anda fun response as well! I will keep listening to, what is actually a rather cool sound and watching the Ultra-gauge. Oddly enough, I had just been reading about the switch to the other brand fans; I didn't notice anything about the noise though so this is great!

As for listening to the oldies, my wife used to be a DJ at any oldies station, so we listen to plenty!

 

Just saw a post about temps on D2 ultra gauge being in the high 180s to 190s, not haven gotten past 200 yet, 70F outside for that owner.

I have tried the stock D1 fan the chevy $50 clutch, a HD clutch, a black nylon fan from a Chevy ( more air) and a white nylon fan from a Blazer (more air due to HD clutch and blade pitch). If concerned about temps should also consider the in-line thermostat mod.

 

Have your wife cold start the truck while you are out listening with the hood up.

 

sounds like the secondary air injection pump to me. replacing the filter sometimes quiets it down. you have to make a new one. theres a writeup in the stickies somewhere.

 

Secondary Air Injection

 

Maybe, here's a pix, unplug and try. The SAI pump mostly comes on for a cold engine start after engine has set for several hours, so it might appear once a day. Many say it sounds like a hair dryer. Hell, it even looks like a capacitor...

 

Sorry, I should have mentioned that the noise only does appear on a cold start. Stopping to fill up with gas, the noise doesn't appear at all. However, the noise does occur after letting the truck sit overnight or while I am work.

I will check on the SAI and look at the sticky. For the test, do I just unplug the wiring harness and give it a start?

 

You could also pull the glow plug relay, and it will keep the SAI from coming on, but you'll get an SES light with a code for the SAI system.