1997 Volvo 850 makes a hissing sound while accelerating

Hello, My 1997 Volovo 850 sedan at around 153K miles is suddenly making a light hissing sound (sort of like steam releasing from a vent) when I press the accelerator. Any ideas what could be wrong? I will take it to a dealer, but his openings are at least three weeks away. Besides, I was wondering about the reason. Many thanks for any pointers!

Does the hissing sound seem to pulsate? Does it get louder as you depress the accelerator and quieter as you release it? Or is it a steady hiss regardless of engine speed?

I am not sure about the pulsating part, but it is fairly steady when I press the accelerator. Yes, it gets noticeable when i depress the accelerator, and pretty much stops when I release it.

In that case, I’m willing to bet a vacuum hose or perhaps your PCV (positive crankcase ventilation) hose has come loose or is leaking. If this is the case it might lead to a performance loss but shouldn’t impact long term engine health if driven for a few days.

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Check if the air cleaner lid is loose.
If this 850 has the turbo charged engine, inspect the intercooler plumbing for leaks.

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No, it is not the turbo, the base sedan model. How do I check if the PCV is loose? Also, is there a way for me to tighten it if that is indeed the case?

Why would you need a dealer for this old Volvo ?


In my experience, the Volvo dealer (50 miles away) costs almost as much as the local guy (2 miles away) and gives me some sort of peace of mind. At least, I have not seen them push for unnecessary things, but I can not say the same of the local guy. Whenever I have taken it to the local guy, something or the other has gone off a couple of months later. Now, this is possible that it is circumstantial, but I don’t know. So, in the long run, the benefits of the local shop are unclear to me.

Wanted to add one more piece of information here. There is a very slow leak of a fluid, that is almost unnoticeable. Perhaps a very small drop since yesterday. It took me quite some time to confirm this. I can not tell what the fluid is, the smell and quantity are not enough (I put a cardboard piece under the car overnight and have now confirmed this suspicion). I don’t know how long this leak has been on. Could have been months.

To check your PCV valve, find and disconnect it from the valve cover (a quick Google search can show you where and how, I’m not familiar with Volvos) and shake it. Listen for a rattle. Rattle is good. Follow the hose and check both ends for tightness. Check for cracks or holes. As for the mystery liquid - give it a good look and feel. Is it watery? Oily? Thin/thick? What color is it? Where (approximately) is it leaking from? This is very exciting, I can see why the good brothers liked doing this over the radio.

Could it be some sort of exhaust leak?

Thanks, the mystery liquid is thin, somewhat blackish. Oily too. Any more leads?

Thin, blackish and oily can be engine oil, transmission oil, or MAYBE really old and burnt power steering fluid. If your PCV valve is bad your engine could be sleeping oil from the rear main seal (this specific answer is pretty reliant on the PCV valve being bad, but the rear main seal can sometimes leak on its own). Where approximately is it leaking from?

So, I am having difficulty figuring out where it is leaking from. It is somewhere in the middle of the front part of the car, but it is difficult for me to tell where because I can not look under the car. THe leak is so difficult to detect that I was able to detect it only by putting a huge piece of cardboard under the car. I will see if I can get a better sense. But the PCV valve sounds reasonable to me, without of course knowing much. Thank you!

I’ve heard this sound in an 850 turbo (not the 850 GLT that lacks the boost gauge) . The thought is that the boost gauge in the cluster has a leak in it. In theory it shouldn’t happen when the boost gauge is right in the middle. I’ll have to remember to experiment next time I can. And I’ll have to see if the method of reading the engine hours from the 850 OBD II port works!

The 850 has a crank case vent system that is known to clog and cause a main seal to blow out. The system must be inspected and cleaned to prevent this. There shouldn’t be pressure when the engine oil dipstick is pulled with the engine running. I’m not saying that this is related to the hissing sound.

I was wondering that as well.

While the car is parked and idling, if you have someone plug the exhaust with a rag and their hand at the end of the tailpipe. While they do that, crawl up and down alongside the length of the car to see if you can hear an exhaust leak.

I lived on the bad side of town while renting in college due to the cheap prices. The road we lived on was not the address you wanted in my town.

You did get to know certain cars driving by based on the sounds they made. Some would have a loud backfire that sounded like a shotgun or rifle every few seconds. Others were more of small pop pop pops like a string of firecrackers going off. We also had some that sounded like the exhaust was just dumping right out of the manifold.

Then there was the hisser. It was an older Caprice or something. All we could figure is that the converter was completely plugged and the only way it could remain running was because of an exhaust leak. The car was just always hissing at idle or when driving. It would lose all power and just crawl up any inclines, all while letting out an especially deafening hiss. You got to know the sound from quite a distance away and always knew when it was at the grocery, Wal-Mart, or wherever with you. It sounded like an extremely loud pressure washer nozzle and just kept hissing like a champ!

Of course our road was frequently traveled by police cars and ambulances with their sirens blaring as well.

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No experience w/your engine, but when I’m testing the carburetor on my truck, running engine sans air cleaner, there’s a definite hissing sound, even just at idle rpm, caused by airflow into carb. Louder at faster rpms. Hissing gets really loud if I partially obstruct air flow path. So the idea above to check the intake air flow path as a first step makes good sense. Exhaust leaks could conceivably cause this too, but I’ve never heard a hissing sound from an exhaust leak myself. Vacuum leaks at idle can make a hissing sound, but usually those diminish rather than increase the more your press on the gas pedal.

The car I mentioned would hiss louder like a pressure washer when going up hills. It would also just barely be moving and you couldn’t hear the engine running. You would think it ran on a source of power that hissed if you didn’t know better.

I have heard vacuum leaks hiss as well but nothing like the one I remember.