Our Honda van’s engine makes a low intermittent hissing sound when it is cold. It is almost like a high pressure gas is escaping from a tiny hole, only when the pressure builds up to a certain point. We have not noticed that the hissing impacts on the performance of the engine or other aspects of the vehicle’s performance.
The sound comes from the lower passenger side of the engine compartment. It occurs during the first 5 to 15 minutes of being driven, and is more frequent when it is cold. It occurs predictably when the outside temperature is below 30 F and occurs sometimes if the temperature is below 55F. We park this vehicle outside.
We have taken it to our Honda dealership, and they have not had it hiss on them and they are unsure of what it might be.
Any guess as to what this might be?
this may be a utility (ribbed) belt slippage sound
when you’ve got the sound, try switching off all “big consumers” like headlights, rear window defroster, seat heaters, AC and blower
if hiss disappears, you have top replace your belt
alternatively, try switching on as many energy consumers as you can: AC, blower, all heaters, all lights, etc… - if it gets hiss to appear, diagnosis is the same
In addition, the air conditioner’s expansion valve is probably located between the glove compartment and the firewall. It can make such a sound. I’m not sure what it means but the AC system could be easily checked to be sure it has a full charge of refrigerant and its low and high side pressures are in the right range. If the heater and AC are working OK I would not lose too much sleep over the sound.