7

I suspect that my 1999 Volvo V40 T4 has a leaky exhaust manifold gasket. In winter there used to be some odd faint whistling while the engine was cold and now I'm trying to find the reason of a ticking sound that is audible when revving the car (frequency follows revs).

It can be heard anywhere outside the car, even inside when the door is open (the middle muffler box is removed, might be the reason the sound is more apparent). It's more difficult to distinguish when listening under the hood because of the noise, but it's there.

I'm more inclined to think the ticking is caused by a hydraulic lifter failure, but I'd much rather go with the exhaust manifold gasket first hoping that it would fix it. However it's also a PITA job and I'd like to make sure that it needs replacing first.

So, how do I make sure my exhaust manifold gasket is leaking before doing a potentially pointless job?

Improve this question
2
  • Does the loudness increase when you press the accelerator or decrease when you release it?
    – Allman
    Jun 27, 2016 at 11:28
  • @Allman Loudness? No, not really. At idle it's inaudible, under throttle it maintains pretty much constant sound level until the engine noise overwhelms it.
    – I have no idea what I'm doing
    Jun 27, 2016 at 13:04

4 Answers 4

Reset to default
8

Seeing as how your car has a turbo, the only place it would be leaking and you'd hear a ticking noise is pre-turbo, so the exhaust manifold at the head (header) and the down pipe on the hot side to the turbo. The turbo, due to it's nature of homogenizing the exhaust flow, will pretty much eliminate any ticking noise which may be due to an exhaust leak. While you may have a leak downstream of the turbo, you'll not get a ticking noise from it. This eliminates a lot of "stuff" to look at.

The next place you need to look at is where the header meets the head. This is a usual suspect area on most cars with an exhaust leak. You are looking for black soot traces. This is your tell tale sign. On your car and most cars with turbos, this is going to be hard to see because of all the supporting "stuff" which is there. Plus, IIRC, the exhaust is on the back side of the engine next to the firewall, which makes it even harder to see. If you don't see any, it doesn't mean you don't have an exhaust leak though.

The next thing you need to do is check your trim levels. If you have an exhaust leak, you're vehicle will most likely be getting worse gas mileage. This is because if there is a leak, fresh air will be getting into the system fouling up the fuel trims. This seems counter-intuitive, but it is actual. Even though there is pressure where the leak is at, as the exhaust flows by, it will draw air in with it (there's a physics term for this, but I'm not remembering it right now - it works like a venturi in a carburetor). This messes with your O2 sensors, which makes the computer dump more fuel in to the system. You'll also be seeing more soot around the inside of the tail pipe due to richness of the burn. This isn't good for your cat, either.

If you aren't seeing any of these things, you can pretty much eliminate the exhaust as your problem. If you grab a piece of rubber hose about 3' long, you can use that as a diagnostic aid to help you pinpoint where the noise is coming from. Put one end of it up to your ear and wave the other end around in the engine compartment. This will help localize where the noise is coming from. There are also automotive stethoscopes which are very cheap at places like Harbor Freight. They can help as well, but I've found noise is usually transmitted throughout the metal of the engine, so it can help pinpoint sometimes, but other times it's not as apparent.

Improve this answer
4
  • That's where I'd expect the leak to be, either manifold or pre-turbo gasket. It really is on the back side and it's really tight in there, though I might try looking for soot with a little telescopic mirror, that's a good tip. My trim levels are roughly 5% positive. Never found the culprit as the vacuum lines are solid (smoke tested) and my exhaust doesn't seem to leak anywhere either, so it's very likely that some air is getting sucked in. I do have a mechanic's stethoscope, but I find it useless for finding exhaust leaks, the ticking leads to cams. A hose should do better.
    – I have no idea what I'm doing
    Jun 27, 2016 at 13:35
  • I cannot verify 100% for this year/model but many Volvo turbos housings are cast into the exhaust manifold. That should hopefully leave just one real point of failure barring any rust holes in the manifold or wastegate not in good shape.
    – RomaH
    Jun 27, 2016 at 18:16
  • @RomaH - Correct. I haven't dealt with them directly, but sounds feasible.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jun 27, 2016 at 18:27
  • @RomaH Not on this one. It's a Mitsubishi TD04L-14T turbo, has a 3 point connection to a short flex pipe and another 4 point connection to the exhaust.
    – I have no idea what I'm doing
    Jun 28, 2016 at 8:48
2

I'd say hyd lifter failure is pretty unlikely unless you ran your engine to extremely high RPM's right before this started. A leaking exhaust manifold can produce a sharp and short puff of exhaust that sounds like a tick. (Happened on my '92 Mustang often) If you can reach your manifold bolts, trying tightening them a little. They will definitely have actual torque specifications, but for testing purposes hand tightening them should have a noticeable affect on the "ticking". Also... Do this with the engine off and after it has cooled. If you needed me to say that last par consider take it to a mechanic lol.

JMR-(Auto Hobbyist/ Diesel Mech. 8 years)

Improve this answer
3
  • 1
    The reason why I'm leaning towards the lifters is that the ticking is pretty much inaudible when the car is cold and I only begin noticing it after it warms up. Which could mean that the oil viscosity reduces and the guilty hydraulic lifter quits doing it's job properly. Also, the previous owner sucked at oil change intervals.
    – I have no idea what I'm doing
    Jun 27, 2016 at 13:09
  • 1
    And as I understand a leaking exhaust manifold gasket tends to be louder when cold and the metal has not expanded yet instead of warm. I did try tightening the bolts before, a couple were a bit loose. The T4s are notorious for losing manifold bolts. Though I' not sure if the damage to the gasket wasn't done already.
    – I have no idea what I'm doing
    Jun 27, 2016 at 13:30
  • 1
    @IhavenoideawhatI'mdoing - Yes, you'd expect exhaust leaks to become quieter somewhat after warm up, at least as long as there isn't a tear (or damage) in the exhaust manifold gasket. The other way around would indicate valve train noise to me. Whether the valve train is having a big issue or if it's just noise ... who knows.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jun 27, 2016 at 14:43
2

Use a shop vac. Attach the hose to the side that blows with tape. Then tape the other end to the tail pipe. Now turn on the vac. its time to use the soap with water in spray bottle spray everything to find leek. This worked great for me. Hopefully This helps Someone.

Improve this answer
1

You could try the standard leak test: Mix some water with dishwashing soap in 1:1 mix and apply it to any surface that could harbor a leak. Bubbles appear at the site of the leak.

Improve this answer
2
  • I'd expect this to vaporize pretty quickly on an exhaust manifold. He might have a very short window while cold, but sounds like this is a bear to get to.
    – Shog9
    Jun 27, 2016 at 22:37
  • Yeah, this one would be tough. Noise is heard when the engine is hot, water sprayed on the boiling hot manifold would sizzle and vaporize instantly. And the manifold is at the back of the engine with access further hindered by the turbo heatshield.
    – I have no idea what I'm doing
    Jun 28, 2016 at 8:42

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .