2018 F150 5.0 liter.

We have an intermittent whistle when the engine is off after a drive.
Sounds like vacuum leak somewhere, but it can last a half hour.
Has anyone found an answer for this?
Maybe a diagram of the vacuum system? I find it very hard to pinpoint because it sounds the same everywhere. Really gets people looking at the truck.

 

Rather than a vacuum leak, I would think it may be a pressure leak. As the engine heats up, things expand. If there's a small hole or gap somewhere, it may cause a whistling noise if there's any internal pressure as that gap is expanded when the engine is hot. As it cools down, that gap or hole would constrict down eliminating the whistle. I guess it could go both ways whether it's pressure out or vacuum in. Either way it's super annoying.

 

I have a similar whistle in my 17 3.5L ecoboost. It's coming from the engine compartment. I finally gave up trying to figure it out

 

Try a mechanic's stethoscope like this with the funnel amplifier. I swear it will make a gnat fart sound like a trumpet right in your ear.

 

There was a similar thread recently. The whistling is the A/C equalizing when the low side pressure exceeds the high side pressure.
https://www.f150forum.com/f118/whist...unning-412016/

 

Next time, I will put my gauges on the AC. If it is too high on the low side I will find out what is building the pressure. I will let all know. That was my trade.

 

SSM 50445 - 2017-2021 F-150 - High Pitched Squeal/Whistle Noise From The Engine CompartmentAfter Engine Shut Off - Built On Or Before 01-Feb-2021

Some 2021 F-150 vehicles built on or before 01-Feb-2021, 2017-2020 F-150 vehicles equipped with a 3.5L EcoBoost engine, 2018-2020 F-150 vehicles equipped with a 2.7L EcoBoost or 5.0L engine, 2019-2020 F-150 vehicles equipped with a 3.0L diesel engine may exhibit a high pitched squeal or whistle type noise from the engine compartment after the engine is shut off. This condition may be due to the air conditioning (A/C) low side system pressure exceeding the high side pressure resulting in equalization of A/C system pressures through the A/C compressor. An updated A/C compressor has been released to resolve this concern.

 

Thanks for the help, Is it heat from the heater coil warming the evaporator? We are now out of warranty, So maybe a low side to high solenoid would be cheaper than a compressor?
Thanks

 

Do you know if they’re gonna issue a recall for the whistling compressors? Or just call with a warranty claim?

 

I seriously doubt it. This issue only affects a very small quantity of vehicles.