Strange Noise at Start up

Yesterday morning when I started my XJ, I heard a strange noise while doing my daily check on the vehicle (signal light, brake lights, and tire inspection), so I opened the hood and kind of narrowed it down to possible the AC compressor. The sound is similar to a quiet "siren" of sorts. I drove it for about 5 miles to the store, got out and didn't hear the sound anymore. Then I drove it to play tennis for a few hours, again no sound when I started it up again.

I started it up this afternoon for the first time today, and the sound that I heard the previous morning is not there. Maybe it's temperature related? The other morning was 50 degrees F and this afternoon is high 70's.

I'm just trying to catch the problem while it's still a small one, we have a trip (+1,000 miles) coming up, so I want to make sure that the Jeep is running correctly so there a no surprises.

Has this happened to anyone else before?

Ooops, I forgot to add the spec: 1996 XJ, 4.0

Was the compressor clutch engaged when you heard the sound? If you had the HVAC set to "defrost" it would have been engaged.

joe_peters said:

Was the compressor clutch engaged when you heard the sound? If you had the HVAC set to "defrost" it would have been engaged.

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I am pretty sure that everything was off. I usually make sure to turn everything off (HVAC) when I park the Jeep. It almost seems like something temperature related, only because of the sound early in the am @ 50 degrees, no sound later in the afternoon, and then no sound this afternoon(24 hours later) when I started it. I just want to make sure that nothing is on it's way out. I guess the best bet is to do a load test on the alternator? Maybe I should expand that and take off the serpentine belt and spin the pulleys, but then that leads to more $$$, because why not replace the fan clutch when all of that stuff is off?
My wife said she wanted to type "dummy" to me on my OP, maybe she was right.
I just want this thing in tip top shape before we go on our trip 1k+ away from home, AAA or not.

Could be a bearing going out in any of the belt driven accessories or an idler.

I would first try and use a vinyl hose, about 3' long, about 1/2" I.D., stick one end in your ear and carefully move the other end around the front of the engine to try and locate the source. STANDARD warning about moving engine components and clothing/human flesh being a poor mix.

If you can't isolate it that way then pull the belt and try spinning/wobbling things by hand.

Good luck.

joe_peters said:

Could be a bearing going out in any of the belt driven accessories or an idler.

I would first try and use a vinyl hose, about 3' long, about 1/2" I.D., stick one end in your ear and carefully move the other end around the front of the engine to try and locate the source. STANDARD warning about moving engine components and clothing/human flesh being a poor mix.

If you can't isolate it that way then pull the belt and try spinning/wobbling things by hand.

Good luck.

Click to expand...

Thank you very much. I'm going to try that tomorrow. As I noted before, the afternoon start up had no noise, but when I started up this am, the noise was there. I took it to my friend's house (7 miles away), and the sound was gone. He seems to think that it's my A/C clutch.

Now I am going to try your methodical and intelligent methods. If the A/C clutch is bad, will I be able to tell by spinning it with the serp belt off? Is the clutch replaceable?

I still find it strange, that it only makes the sound in the cool morning, and then goes away when it warms up.

Thank you for your help!

Update, it was the fan clutch.........................

Yeah, with the fan clutch the silicone fluid drains out of the reservoir overnight so the fan clutch will engage first start of the day for a short period until the fluid has been spun back into the reservoir.