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Vacuum leak in a turbo, damaging to drive?

I have a 2008 volvo S80 T6 (inline 6 with a turbo).

This week I noticed a rhythmic squeaking like a bad belt. I had also noticed a decrease in power and one instance of what sounded like a backfire during a quick acceleration. The vehicle computer has not thrown any warnings.

I brought it to the mechanic and he initially thought it was a belt too, but then wanted to “try something” and pulled out the dipstick. There was an audible hiss of air being sucked in and the squeaking immediately went away. When he replaced the dipstick, the squeak came back quickly. He could reproduce the same effect by loosening the oil cap, which also made a sucking sound and was very difficult to pull away from the top of the engine. He said there shouldn’t be that much vacuum in the dipstick/oil cap and that I should take it back to the dealer to have the vacuum system checked out (bought it used a few weeks back and still covered under the Massachusetts lemon law, so they’d have to fix it for free, otherwise I would have had it repaired right there and then). I went out and listened to the car running later and I could swear I heard a hiss but the mechanic didn’t mention it earlier and we were both standing there listening.

The mechanic suggested leaving the oil cap loose until I could get the vacuum problem fixed as that would make the squeak go away. He said something about the oil pan and vacuum but I didn’t quite catch it (or I just can’t remember it now). I left the oil cap loose like he said and there was an immediate and dramatic increase in power when driving and I can’t figure out whether the vehicle was that powerful before the problem.

Because of my job I both need to drive the car (at most 20 miles in a day and probably more like 4 miles) and cannot get the car to the dealer for a week.

Am I going to damage the car by driving it with a vacuum leak or whatever the heck is going on?

Thanks in advance!


I would strongly suggest not driving the car to much. Are you sure about the lemon law? All of the ones I know about only cover new vehicles and it takes a lot of effort to make happen. A 2008 would most likely be sold “as is” or sold with an purchased warranty.

Yeah MA has a really good used car law, it’s 60 days for cars with 60-80k and the form you fill out specifies what is covered. The place I bought it from already replaced wiper fluid reservoir with no resistance and said they thought whatever this was would be an easy fix.

I basically just drive 2 miles surface street to the train station every morning then back. Farthest I’d have to go if I got a call would be 10 miles highway.


Here’s the exact thing I saw at the repair shop on the exact same engine. Oil trap eh?

I don’t have any experience w/Volvos or Turbos, but it sounds like you have a problem with the crankcase venting function. On all my vehicles I’ve had, that’s done with the PCV system. Suggest to ask your shop to test those components. When the PCV system fails it can damage engine seals, so don’t wait too long to address this.

I’d get it back quicker as your warranty period will run out and you’ll have less leverage once a fix is in place. I find it very odd the check engine light is not on. Does it illuminate in on position of key but engine not started?

My concern is that the crankcase is exposed to vacuum created by running the engine. Vacuum is only available when the turbo is not building any boost. If something in the crankcase evap system failed, will it allow boost pressure to build in the crankcase? Not a good situation.

Had an evap problem on a turbo Saab. It blew oil ALL over the front of the engine causing the serpentine belt to jump off (and be ruined by oil) plus it left me stranded.

Ok so there are no warning lights when engine is running. With ignition in position 2 (it’s a push button start so really just holding down button for a few seconds without foot on brakes) the check engine light is steady for a few seconds, then blinks 5 or so times, and repeats.

Inside the engine compartment there is a fine deposit of some kind of oil on the starter motor (it is odorless and clear), but not anywhere else.

Ever since ran it with the oil cap loose for a few miles, the chirp has not come back, but the strong vacuum in the dipstick tube is still there.

On the collective wisdom of the forum, I am going take it in to the shop this weekend and borrow my mom’s extra vehicle for the week.

I’ll let everybody know how it turns out.


Hmm…not sure what would do that…unless they plumbed the turbo intake into the PCV system in some way…and even then the turbo would need to be spooled to an un natural speed to produce so much vacuum…

In fact you should feel the opposite when you take off the oil cap …you should feel pressure coming OUT…not sucking in.

If you want to relieve this vacume for the time being I would suggest simply unseating the dipstick tube and NOT the oil fill cap. Then get her checked out.

I would have to do some research on why you would have vacume at those locations…it should be the opposite actually…you sure that it is vacume and not excess crankcase pressure behaving in the same manner? Something is awry…and it may begin at the Turbo…or the PCV system.

I would like to see this actually…


How many miles on the odometer?


Definitely vacuum, can hardly pull the oil cap off when the engine is running.

Wow… Let me call my Volvo head and ask him…

Here is the deal…there is a device called an “Oil Trap” on this application… It receives intake manifold vacuum on one side of a diaphragm to do its job…

This diaphragm ruptures and thus applies intake manifold vacuum…excess vacuum to the engine block

Replace the Oil Trap and this will go away… The diaphragm has ruptured.

Picture of the part here…aparrently its stuffed behind the engine and might require axle removal…fun fun


Wow, thanks for the super thorough response Blackbird!

Definitely can’t do that myself!

I’ll relay this info to my mechanic.

No prob… being the type o guy I am…I would be inclined to pinch off the vacuum feed line to this oil trap to see if the condition stops…thus further proving the theory… Then replace or leave it pinched.

Id have to see just what this oil trap actually does and if it would hurt to eliminate it alltogether… You can play around when you are a mechanic…not so much if you cannot do the work yourself.


That diaphragm rupturing wouldn’t by any chance make a loud pop would it?

I kind of floored it to merge into traffic, heard a muffled pop I thought might be a backfire and the problem started right after that.

This oil trap gadget came up during a Car Talk episode, I think I heard it during the past year. Only certain makes of cars use it I guess. As I recall it performs a similar function to the PCV valve used in most cars. If I recall that call correctly, it may have a flame suppressor function too. So definitely get it checked. Best of luck.

Found talk of PCV’s still looking for the oil trap episode :

That diaphragm rupturing wouldn’t by any chance make a loud pop would it?

Indeedy it WOULD…and is likely what you heard…the condition you described would or could definitely contribute to a not so flexible diaphragm rupturing…

Swap it out…and you’ll be good to go.


@qroberts … I found this reference by typing “flame suppressor” into this website’s search box.

Two calls from 3.21.2015 show: Volvo Flame suppressor

Take a listen to the 3.21.2015 show maybe.