What could make a humming noise from my engine? It only does it on long distances but not every time. I took it to the mechanic but he couldn't figure it out since it wasn't doing it then. It starts after driving for awhile & then keeps doing it when I slow down.

What type of noise is it in pitch ? Could it be your tires ? Sometimes noises come from tires based on road surface and speed.

Does it change pitch with engine speed? One thing that can be a cause is the alternator. If a bearing is going out or misalaigned. Try turning on your air when it happens and see if anything changes.

Most likely, it's a problem with a bearing, once it warms up. If it's a wheel bearing, the noise should get worse once the bearing is loaded. For example, if the left wheel bearing is suspect, turning the steering wheel to the left and then back again should make the noise more pronounced, when at highway speeds. If it's an air conditioner pulley, which is always rotating even when the A/C is off, the noise should be there but it may sound somewhat distant. Other bearings to check out are idler pulley, timing belt pulley, water pump, and alternator bearings. Use of a mechanic's stethoscope or large handle screwdriver may help. Isolating noises can be one of the hardest and most annoying problems to solve. Noises in the A/C pulley, for example, can transmitt through the engine block, making it difficult to isolate.

What year, make, and model car do you drive? What's the mileage?

If it's a wheel bearing, the noise can get much worse. It becomes a real safety issue if the wheel bearing disintegrates. Depending on the car, wheel bearings need replacing around 100,000 miles.

To Califdadof3 & TxGreaseMonkey: I tried to comment on your posts but it said to 'spread some Reputation around'? I don't have this site figured out yet. Anyhow to Califdadof3: the pitch doesn't really change it just gets louder & to TxGreaseMonkey: it's a 2007 dodge grandcaravan with about 45,000 miles on it. Do you think it's unreasonable to ask the mechanic to check everything that could possible be making the noise, that is, anything that could cause a potential problem while driving?

I'd like to know what year, make, model, etc also. We'll probably never know.
If we're placing bets here, I'd say a GM car and it's the electric fuel pump getting ready to give up.

Edit: oops, you just posted. Thanks. Ok, Dodge then. Same response.

With such a new low mileage car, it's hard to imagine a bearing or anything serious being bad. The problem may be something as simple as serpentine belt noise.

The weak link on your vehicle is the transmission. Every 30,000 miles, drop and clean the pan, change the filter, and refill with ATF+4. Furthermore, start using full-synthetic engine oil (e.g. Mobil 1), changing the oil and filter every 6,000 miles or 6 months, whichever comes first. If you take care of the transmission and engine, everything else that goes wrong is relatively minor.

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Originally Posted by suziq3

To Califdadof3 & TxGreaseMonkey: I tried to comment on your posts but it said to 'spread some Reputation around'? I don't have this site figured out yet. anyhow to Califdadof3: the pitch doesn't really change it just gets louder & to TxGreaseMonkey: it's a 2007 dodge grandcaravan with about 45,000 miles on it. Do you think it's unreasonable to ask the mechanic to check everything that could possible be making the noise, that is, anything that could cause a potential problem while driving?

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To respond directly to someone you would use the quote button. That way its easier to follow what's being said and to whom. If the noise is getting louder when the engine revs or the air is on or both then it could be the alternator or an idler pully ( the one on the end of the belt tensioner)

Does the noise go away at idle?

Quote:

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Originally Posted by califdadof3

To respond directly to someone you would use the quote button. That way its easier to follow whats being said and to whom. If the noise is getting louder when the engine revs or the air is on or both then it could be the alternator or an idler pully ( the one on the end of the belt tensioner)

Does the noise go away at idle?

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Yes, from what I remember it goes away at idle. It's been awhile since I took it for a long distance. Today I was trying to listen carefully & I can hear it very quietly when turning.

Bingo! Power steering fluid. Have the P/S system checked.

If the power steering pump is the culprit, consider using the product below:

AMSOIL - Synthetic Universal Power Steering Fluid (PSF)

Use a battery squeeze bulb ($2.99), which is like a turkey baster, and remove the old fluid from the power steering reservoir. Refill with Amsoil Universal Synthetic P/S Fluid to the same level. Do this when the system is cold. Repeat this process every 50,000 miles. Power steering units develop more heat than most people realize and are quite expensive to replace. This should really quiet the pump down and ensure the unit lasts a long time. I use this product in my own vehicles.