98 V70 Hissing PTC

Post by **erikv11** » 08 Mar 2014, 15:13

There has been a pretty loud hiss in the engine bay, today I tracked it down and it is coming from inside the PTC. If I kink the line from the intake manifold nipple to the PTC, the hiss stops. No leaks in that line itself. The hiss also diminishes (goes away?) if I rev the engine. I know the PTC is wide open if you are looking in from the top (through the larger opening). And pulling that big line off doesn't change the hiss.

Is this normal or do I need to fix something? I thought it was a vacuum leak by the sound of it, and I feel like there is a small one somewhere but I can't find one. My R doesn't make this sound.

tdlund · Post by **tdlund** » 08 Mar 2014, 16:36

I was just working in that area of my 98 V70 today and didn't hear any hissing from the ptc nipple. I wouldn't think that the pcv system could give enough pressure to make that kind of sound. Just my thoughts.

Post by **MoVolvos** » 08 Mar 2014, 17:37

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So that's what it is! Mine hissed for a over a year but I did not attributed to the PTC. I discovered that it was not pressed fully into the Intake Tube when I was working on the Heater Core. Now that you mentioned it I've never heard the hiss after the Heater Core work. Always thought it was a huge Vaccum leak but the car ran ok.

Blessings,

BKM

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Post by **erikv11** » 09 Mar 2014, 23:34

Well I removed the PTC and inspected it, it was installed correctly and totally clean.

So I grabbed a spare PTC and fresh air hose, again totally clean and properly assembled, and installed that. It has the same hiss, it is due to vacuum from that line from the intake manifold.

Maybe the hiss has to do with the diameter of the hose I used or something? I will leave it as is for now, at least I know what is going on now. At some point I will compare it with the vacuum pull that hose has on my R.

Post by **jblackburn** » 10 Mar 2014, 08:08

I take it you don't have the normal Volvo oil trap to PTC hose in place there?

Post by **erikv11** » 10 Mar 2014, 10:08

Correct, I have DIY vacuum line in there.

BatStig · Post by **BatStig** » 17 Jun 2021, 22:09

erikv11 wrote: ↑10 Mar 2014, 10:08 Correct, I have DIY vacuum line in there.

Sorry to bring this thread back from the grave, but this is the only post I have found on the internet about this. My 850 is doing the exact same thing immediately after installing my own larger DIY vacuum line.

What was the outcome? Is it simply the larger vacuum hose causing this? I have smoke-tested the system and can't find any leaks.

Post by **erikv11** » 17 Jun 2021, 23:17

I've still got the car, it has 65,000 more miles on it now, it still has the hiss and it still runs great. I just never messed with it any further.

Post by **Clemens** » 20 Jun 2021, 14:57

After upgrading to a bigger hose I got that hissing sound as well. 4 years later it still hisses, runs great and passes the glove test.

Post by **abscate** » 21 Jun 2021, 10:03

Good luck vs UKR today , Clemens. A victory will be celebrated with Kangaroo steaks on the Barbie