Screeching From Under The Hood

I agree, but nothing has self destructed, yet. I drove it yesterday and nothing. AC is cold, alternator is charging, steers OK.

It's not a daily driver any more, but the wife loves it because it has 4 captains chairs and they are more like couches than seats.

If it were a conventional vehicle, I'd have already gotten in there and spun everything.

Not the diodes in the alternator, they fail one time and stay that way. And will not cause audible noise under any conditions except possible at moment of failure, sound of 1/2" metal cylinder case rupturing.

Perhaps it hasn't been trained to sing properly...

Yeah I had that happen it was a tensioner pulley...not a big job....

If only it would make some noise.

It might be the bearing seizing and the belt slipping that's making the noise...just get a crowbar, and with the engine off, pull back on the tensioner and release the belt, then spin the bearing pulley, that should tell the tale....

The belt isn't slipping. I can watch it turning when the noise is loud.

I'm beginning to think it's cold weather that hardens the grease till things get warm.

The idler is the #1 suspect.

Where would I insert a crowbar? Not that I'm going to do it.

You just gotta get one of those Greg Morris "Mission Impossible" tool kits!

I concur. Had a bad idler bearing that eventually seized and spun off its shaft. It then put a hole in the radiator. I was a long way from home = expensive fix. Jim

I think you are correct about the grease heating and working into the lube surfaces. Grease is just oil/wax that hardens below a carefully designed temperature/pressure. It has to be liquid to lubricate properly

The belt only slips incrementally, probably at the frequency you hear. You'd probably need a strobe light set up for some harmonic of engine speed to see it. it has to be a low frequency to see it with your eyes, and then bad burn spots appear just before separation.

A crowbar allows you to pivot the spring loaded tensioner arm from a distance, sometimes easier to do this that to position the 1/2" drive breaker bar in the square hole in the tensioner arm. Tight quarters in there, but there has to be access to the tensioner, while engine stopped. Pretty unsafe to modify tension while running, these flat belts run off easy, much easier than old V belts.

Old mechanics trick to apply wax to the belt surface, often while running. This eliminates the belt itself as the source of the noise, older vehicles used the alternator as the tensioner, but fixed bolted position. As the belt wears, you need to get under the hood and loosen the top alternator bolt, use a crowbar to tension the belt by pivoting the alternator, tighten the top bolt, tighten the pivot bolt, possible to exceed the radial rating of the alternator front bearings....

The belt isn't slipping so that it slows down or stops. It may just be "slipping" past the stationary/sticking pulley but maintaining full drive on/over the others. Do you own a mechanics stethoscope?

It's a quantum physics phenomenon, the problem disappears when you are looking for it...

I'd start with belt dressing. Cheap and even if it doesn't solve the squeal, your belt will squeal with delight.

You might too!

I'll suggest that to my mechanic.

Mystery solved....a near cat astophy

My vote is either an idler pulley bearing or water pump bearing. In my experience they've always seemed to be the ones where the seals break down first.

Good luck.

Usually the front seal on the water pump fails before the bearing catastrophically fails, but I think you are still bringing in residual grease to the bearing surfaces as the bearing gets hot, still able to quiet it down.

I had a water pump bearing go before the seal. In wet weather, when the belt got wet, it would slip and squeal, but as soon as it dried out it was ok. Only when the bearing really got bad did it finally take out the seal. Never any sign of coolant leakage until the end. When I replaced the pump, I was amazed that it had worked at all.

So what your saying, is that you had a problem with your car and it fixed itself and you want us to tell you how to unmuck it, so you can figure out what went wrong in the first place ?,

No. I'm asking if someone has any ideas or may have experienced this themselves.

These problems rarely cure themselves.

Apparently you don't have any ideas, but thanks anyway.

If even one diode in the rectifier bridge has gone, there is no screech, you just suddenly don't have electrical power and the vehicle becomes extremely heavy and stops. Half an hour later it will start and run just fine.

Obvious choices will be V belts, tensioner roller on the timing belt, water pump pulley or the radiator fan. If the van has a turbo, check that too.

Last choice is to banish the banshee.

Have you thought of the fan clutch? https://itstillruns.com/test-fan-clutch-chevrolet-5865385.html

Just a quicky fix suggestion.

Sometimes the belt/pully surface gets polished and any other negative traction influence will cause a belt to slip a little, slipping heats up the belt and makes it a little stickier, completed feedback loop.

Belt dressing will fix this temporarily.

A bit of dry dusty dirt tossed onto an appropriate belt/pully surface will also fix this temporarily.

Dirt is usually readily available and already exists in the environment of the motor.

Pick up a mechanics stethoscope very inexpensive and listen to all the rotating components, most have extensions to keep fingers safe. You will hear things that are not audible. The good money is on the idler/tensioner.

Maybe, "not otherwise audible' would have been better.

I've got some old garden hose around here, somewhere. Maybe I'll cut a length off and use it to listen. Sometime.

But remember, if it ain't broke, don't fix it comes into play here.Never mind.

It is impossible for me to see inside the engine compartment well enough to stick anything in there.

Left photo: there's an alternator down there, somewhere.

Right: The top of the idler pulley tensioner housing, with yellow tag.

Started it up and no noise.

You can get a fibre scope but it will be a waste of time and money. Quick possible fix. Spray the entire engine and bay with WD40 and leave it for half an hour before driving. Dint dry it off just run the engine, it will evaporate and leave a film that will waterproof the electrics and clean up the engine block and parts. No, it will not damage rubber pipes.

To get into the engine bay, the front end needs to be removed, i.e grill, radiator, cross member that the rad is attached to. Only then will you get near the pulleys and tensioner's. Possibly a weekends work. The WD40 will work just fine.

If you think the noise is inside the engine block, ass some Wynns, or Bardahl or Forte oil additive and that will lubricate very well, all bearings and journals, cams, valves and rods and the engine will be very quite.

https://www.google.com/search?q=wynns&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjx4qjUh-zhAhUsmIsKHTMJBlQQ_AUIDigB&biw=1280&bih=648

https://www.amazon.in/Bardahl-Oil-Supplement-250-ml/dp/B00S0ORVD2

https://www.google.com/search?biw=1280&bih=648&tbm=isch&sa=1&ei=nRXCXIWoL6iymwXj-pHICQ&q=forte+engine+oil+additive&oq=forte+engine+oil&gs_l=img.1.4.0j0i24l4.46577.48275..53552...0.0..0.104.545.6j1......1....1..gws-wiz-img.......0i7i30j0i67j0i7i5i30j0i5i30.QLG0urwVL4M#imgrc=C0Oy2GSnJ2L7XM:

I am in the process of repairing a Honda Prelude, 4WS 2.0i 16 valve and the entire engine is cleaned up and WD40'd. Now I await the new rad. In all cold countries the first thing I do is WD40 the entire engine to keep the road salt from wrecking the engine and parts. And I always add Wynns to the oil and Redex to the fuel. Try the above if you like, you may find it works quite well for you and I assure you the engine will last a lot longer with less hassles.

This has stood for 5 yrs and is a 1987 model. Now runs, cleaned up and a nightmare to work on. Just awaiting a new radiator. And all WD40'd to clean it up.

I no longer work on cars. I think I said that somewhere.

It is not an engine noise, it comes from the accessories that are belt driven.

I'll pass on the WD-40 spray, for now.

At this point, I suspect the idler or the alternator. Not diodes, but the noise seems to be coming from the alternator side of the engine.

Thanks for the tips.

Remove the neighbours cat from the exhaust manifold. Had that a few times.

I have heard water pumps make a squealing noise that was very hard to find.A water pump can also have a slight leak and leave no sign of leakage because it is leaking at the bottom and the water is being blown back on the block and evaporating.Do you smell antifreeze? Also, a slipping alternator belt will squeal when the motor first starts,and is putting out a lot of juice to charge the battery.It will stop after a brief period,and will not slip again until the alternator is under load. At the factory,they lower the body onto the chassis with almost everything already mounted.The engineers do not consider maintenance difficulties.Not their problem. If you have never changed the serpentine,it is probably a good idea to do so or have it done.

I got my first car when I was 16. I did all my own repairs and maintenance until I was about 60, 12 years ago.

No antifreeze smell.

I've experienced slipping V-belts but this is different. That makes me lean toward the idler since I've never had/heard one fail.

The belt seems tight but I can't get my click-it on a suitable section of belt to check.

• 
Gates 91107 Belt Tension Tester

Great little tool, by the way,

Umm, an idler pulley does not create belt tension.

An idler pulley serves as a device to guide the belt.

A tensioner removes the belt slack.

You can put your fancy tool on the belt all day and it won't tell you that the idler is bad.

The only way to tell if it is bad is to remove any tension from it.

Fortunately none of those engineers are members of this forum,,,,

My truck had extra loud motor sounds when taking off from a start. It would quiet down when it shifted up (20-30 mph). I never identified the cause until pools of water were found under the engine. It was the water pump.

No clues.

Now that it's hot, I'm thinking the grease is soft enough to lube whatever it is.

I'd rather have something fail and fix it, but............................

Lyn, If that engine does not have a rocker shaft but rockers that pivot on a halve round "ball" it sometimes fit so well in the rocker that oil does not reach the sliding surface. I fixed this by sanding it a bit and I put some grafite-ghrease on the sliding surface. With the tappet cover removed and the engine running, loosen each adjusting nut two full turns at a time; If the noise does not stop, re tighten it and try another one. The agents could not find this on a friends car.....I must have just been lucky!

Best of luck

This is not valve train noise. It's a screech, when it happens.

It comes from one of the belt driven items on the front of the engine, that much I know.

Being a conversion van, the engine is not accessible from under the hood.

After the weather warmed up, it is silent, so the mechanic doesn't know what's bad.

Thanks for your thoughts.