Loud hum from engine compartment at 3,200 revs/80 mph

V40onepointeight · Sep 19th, 2020, 13:45

I've been a lurker on here for many years and so firstly apologies for not signing up before, and thanks for the many great tips I've used to fix my various Volvos.

I currently have a tidy standard 2001 V40 1.8 petrol with 118,000 miles on the clock. It's been well maintained and flew through the MOT last week with no issues. Runs a little cool (about 87/88) but a fresh thermostat should fix that.

Invariably there's a loud hum from the engine compartment at around 3,200 rpm and a touch over 80 mph. At 84 it's gone, but deceleration down below that and the hum is back, and then it's gone below 82 or so.

There's nothing obviously wrong so I'm just curious to know if anyone else has it or knows what it is. I'd guess airflow or some kind of resonance issue, but it would be nice to know.

flyingtech55 · Sep 20th, 2020, 09:04

Is the noise present at 3200rpm or is it present at 80mph?

TimR

V40onepointeight · Sep 21st, 2020, 14:55

Quote:

Originally Posted by flyingtech55

Is the noise present at 3200rpm or is it present at 80mph?

TimR

I took the car for a run this morning and observed it more closely. Revving the engine through 3,200 at lower speeds doesn't produce the same kind of hum. I had a passenger keep an eye on the data from an OBD reader, and the loud hum starts at about 79mph with the revs at 3,200 or so and persists through gradual acceleration to about 83 rpm at around 3,400 revs, then above that speed it immediately disappears. Subsequent deceleration back down the revs and speed range have the hum re-appear until the car is back below the range when it immediately disappears. The run was on a straight, fairly flat road, no inclines or descents. There is no obvious vibration. The hum is loud enough not to want to stay in that range for too long - in fact it acts as a reliable if unintended warning of my speed. I'm more curious than concerned, so any ideas would be appreciated.

flyingtech55 · Sep 21st, 2020, 18:45

If you do 3200rpm in say 3rd gear or 4th gear, do you get the noise?

TimR

V40onepointeight · Sep 22nd, 2020, 15:49

Quote:

Originally Posted by flyingtech55

If you do 3200rpm in say 3rd gear or 4th gear, do you get the noise?

TimR

No, it seems to be just in that narrow range of revs at that speed in 5th.

Sep 19th, 2020, 13:45	#1
V40onepointeight New Member Last Online: Jan 19th, 2024 17:39 Join Date: Sep 2020 Location: Aylesbury	Loud hum from engine compartment at 3,200 revs/80 mph I've been a lurker on here for many years and so firstly apologies for not signing up before, and thanks for the many great tips I've used to fix my various Volvos. I currently have a tidy standard 2001 V40 1.8 petrol with 118,000 miles on the clock. It's been well maintained and flew through the MOT last week with no issues. Runs a little cool (about 87/88) but a fresh thermostat should fix that. Invariably there's a loud hum from the engine compartment at around 3,200 rpm and a touch over 80 mph. At 84 it's gone, but deceleration down below that and the hum is back, and then it's gone below 82 or so. There's nothing obviously wrong so I'm just curious to know if anyone else has it or knows what it is. I'd guess airflow or some kind of resonance issue, but it would be nice to know.

Sep 20th, 2020, 09:04	#2
flyingtech55 Senior Member Last Online: Feb 18th, 2024 12:18 Join Date: May 2013 Location: Ayrshire	Is the noise present at 3200rpm or is it present at 80mph? TimR

Sep 21st, 2020, 18:45	#4
flyingtech55 Senior Member Last Online: Feb 18th, 2024 12:18 Join Date: May 2013 Location: Ayrshire	If you do 3200rpm in say 3rd gear or 4th gear, do you get the noise? TimR

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