"Howling" noise

My '89 328 has made a howling noise when started from cold in cool/cold weather since I have owned it. I had assumed that it was oil cooler resonance, as has been discussed in other threads. But in replacing all the belts, I decided to actually pay more attention and found that it is not coming from the oil cooler. It is coming from the front (belt side) of the engine.

The noise occurs most frequently when the car is started from cold in cool/cold weather. When it starts/goes to fast idle - around 1800-2000 RPM, it howls. The noise does not change pitch with RPM it basically turns on and off like a switch within a narrow RPM range. If I rev engine above the fast idle speed, the howl disappears, returning when the engine drops back to fast idle speed.

As the engine warms up and the RPM drops, the noise disappears. From that point on, it does not make the howling noise, even if I hold the RPM at the same point where it was howling. It never howls when started from warm.

It does not sound anything like belt squeal and, since the pitch does not vary with RPM, it seems unlikely to be related to a bearing. But I welcome any thoughts...

 

"So in that way it IS RPM related, even though the volume and pitch don't change."

Yes,you are right. In that sense it is RPM- related. When I said it wasn't I was thinking in terms of the usual sort of bearing or other noise that rises/falls in frequency/volume with the engine RPM. I'm now wondering if it could be some sort of vacuum - related component, something that is activated when the engine is cold. I'm not familiar with the operation of the components of the Ferrari system - cold start valve/related components as far as how they operate or their internal "structure" that might cause noise.

 

Yes - my stethoscope is in Mexico so I just ordered one for here...

The cheap stethoscope - piece of hose - found the sound to be loudest near the crankshaft pulley - I didn't move the hose over toward the Oil pressure relief valve...

I'll try that...

 

Of course, when I tried that, there was no howling at all!

 

Found several videos of US v8s with the noise that sounds identical and with the same symptoms - noise on cold start, disappears as engine warms up. The two "fixes" seem to be, 1 - replace the oil pump, and 2 - ignore the noise. Unlike the 3x8, the US v8s do not have an externally accessible oil pump relief valve/springs; the relief valve is contained within the oil pump itself. If it was the oil pump gears, the frequency and volume of the noise would vary with RPM and would not disappear after a couple of minutes, so SMGs suggestion makes sense that it is spring/valve related.

 

Thanks - have to admit I'm not sure why an oil pump relief valve could make that noise but it's clear from the videos I've seen that it can! Now curious if different weight oil would make any difference - 0W40 which I've used for years VS 10W40. It would be easy enough to try...except for the part where I just bought 11 qts of 0W40 so I don't really want to buy 11 more of 10W40!

 

No, I don't need 0W40 but the local parts store never has Mobil 1 10W40. I could go to a different brand but I've been using Mobil 1 since it came out and I hate change! Good point re the mech gauge; I have a mech gauge and used it to check operating pressure on the car a couple of years ago. I didn't write anything down but my point at the time was to "calibrate" the car's OP gauge and I remember that my thought at the time was that it was "close enough."

"I would check the cam drive bearings too."

Actually that was one of my first concerns though it strikes me that the symptoms are wrong for a bad bearing - I would expect bearing-generated noise to change frequency and volume as the RPM changes. I wouldn't expect it to turn on/off in a very narrow RPM range, and to totally disappear a couple of minutes after cold start. Also, I've never heard the kind of sound I'm hearing come from a bearing. But hey, I've been wrong before.

I think this is how I'm going to approach it: I'll see if I can return the unopened oil and exchange it for 10W40 synthetic of some other brand. If that does nothing I'll seriously look at the check valve - maybe buy a new ($65 !!) spring! If that doesn't address the problem...

Interestingly, and sort of unrelated - at O'Reillys auto parts, their website list shows ALL Mobil 1, regardless of weight, as "not suitable for an '89 Ferrari 328." However, OReilly's own labeled oil IS shown as suitable.

 

It doesn't appear to be the oil pump relief valve. Stethoscope picks up no 'howl' from that assembly. I just checked and although the engine howled very briefly, it was loudest with the stethoscope held an inch or so from the crankshaft bolt in the center of the crankshaft belt pulley. However, moving the stethoscope as close as possible to the back side of the pulley/harmonic balancer, there is no howl. IOW, no unusual noise from the crankshaft/bearing. I'm mystified! I guess I'll just do as I have been doing for the 12+ years I have owned the car...ignore the noise since it goes away in a minute or two!

 

I may pull the belts as a final check. But it's annoying because I have to unbolt the AC compressor to get the belts off. The AC belt can't be fitted or removed by loosening the tensioner.

Re oil pump gears - again, as a gear or bearing thing, I can't associate the noise with that. The on/off nature, the fact that it only occurs at one narrow RPM range and because it disappears after a minute or two doesn't sound like any sort of gear or bearing issue I have ever seen. Agree re Baldwin filters - they are the only filters I ever used on marine diesels...and my Ferrari 328!

 

Oil pressure is good per mech gauge from the instant the car starts cold and at full operating temp. It is definitely not gear noise or bearing noise. It seems to be some sort of resonance but from what, I have no idea. As Johnk pointed out with his example, my 328 has always done it and at the PPI for the car in 08 the mech said..."Some of them do that!" I'm not sure why I suddenly decided to look into it...

 

I'm going to pull the belts today and run the engine. All pulleys/bearings are smooth-turning with no roughness whatsoever so I do not believe the WP, AC compressor, or Alternator or their associated tensioners are causing it. It's absolutely not the AC compressor because the same noise was present with the York compressor as with the new Sanden compressor. Heck, maybe the belts themselves are resonating.

Hmmm... Maybe I'll first reduce the belt tension a bit and see if there is any change. If it's a belt, a tension change should change the pitch. It really does sound like the crankshaft belt pulley is acting as an amplifier but what it could be amplifying, I don't know. Unless, as Gino suggested, it's that darned synthetic oil!