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Discussion Starter #1
Hello fellow T4 owners,​
We have 1998 T4 2.5TDi ACV panel on 223,000miles, partly converted.​
There’s no difference in the brake performance when driving. But when I get to a destination and turn off the engine, I can hear a subtle whining/buzzing noise coming from around the coolant reservoir (the black N75? boost control valve solenoid??). I then pump the brake pedal a couple of times, the whining pitch goes higher and then stops.​
For couple of occasions I sat in the van after turning off the engine and the noise eventually goes off, perhaps after a couple of minutes. I also tried to turn on the engine and off again, and the whining noise sometimes stays on after the engine is off.​
It’s not impacting on the braking performance but I don’t think it ever did this so I’m’ wondering what is causing this whining noise post-engine off and whether I need to repair something.​
What do you think? Many thanks for any suggestions or advice.​
 

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Sounds like a vacuum leak. Check all the tubes in the engine bay. I would replace all of them with silicon tubes.
 

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Discussion Starter #3
Thanks Indian,


I replaced all the braided vacuum hoses with silicone ones when we got the van (3years ago, 23,000miles done since). I'll double check if any of the hoses got damaged for some reasons.



I replaced the brake servo over a year ago (about 8,000 miles done since). I'll also check the thick plastic hose from the servo.
 

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Discussion Starter #5
No, I'm not 100% sure that it's brake system.​
But the fact that the noise pitch goes up and then disappears when I pump the brake pedal gives me the impression that it's somehow related to the braking system.​
Though I'm not sure why I'm hearing the noise around the coolant reservoir. It’s not actually from the reservoir but around there, or it could be the valve solenoid.

Hence the question on here as everyone's been very helpful to troubleshoot any issues.
 

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Full of Cr*p....
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Well, the "after-run" pump is down at the front of the engine, but as it's circulating fluid, a noise "could" be coming from the reservoir.
Just an idea.
Not sure why pumping the brakes would make a difference though!

As my sig says..."Full of Cr*p" !
 
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