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Intermittent low knocking from engine bay, heard when hot and at idle - s70 NA Manual

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

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smacknab
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Intermittent low knocking from engine bay, heard when hot and at idle - s70 NA Manual

Post by smacknab » Thu Sep 26, 2019 11:51 am

Hi everyone,

As you might be able to tell this is my first post in the forums, but i've been following whats been going on here for a few weeks and it seems like an amazing resource. I'm a first time Volvo owner of about 5 days and very excited to learn how to DIY any maintenance/repair issue and get the car back into shape! I've been reading up alot on the forums and talking with alot of friends, however I haven't been able to pinpoint exactly whats going on with my 1999 s70 NA Manual. I am an amateur but pretty mechanically inclined and hoping to learn to DIY pretty much everything on my car. ANY help is greatly appreciated.

My car is a 1999 s70 NA Manual with about 205,000 miles on it. I did not hear this sound during the test drive or immediately after.

Here is a video of the sound:

(the sound described can be heard from 0-4 seconds and 25-30 seconds in the video)

The Issue:
I seem to be getting an intermittent low knocking from the engine bay (say 20 seconds off, then 3-6 seconds on), which I can only hear when the car is hot and at idle and under 1500 rpm. I haven't heard the sound yet neither when the car is cold nor warming up before being driven. I only really hear it after about 30 minutes of driving, and again only at idle/when the car is stopped. Depressing the clutch pedal doesn't really seem to affect the sound. If I rev in neutral (say between 1000-1500) when the sound is 'on' it will also pick up frequency with the engine. To me, the sound seems to have some 'self exciting oscillation' where it increases its own speed until cutting out (heard in seconds 24-30 of the video). Location-wise, I think the sound is lower in the engine and up near the timing belt side of the motor. I have not used a tube yet to try to exactly pinpoint it's location.

I am an amateur but I've been scouring the forums and found little that matches what i think i'm hearing except this thread (viewtopic.php?t=74369) which was solved by reconnected vacuum line, which I'm planning on checking tonight.

My friends have suggested and helped quite a bit! They've suggested possibly the thrust or a journal bearing, rod knock, a spun rod bearing, or piston slap. Online I seem to find some stuff relating to ignition/misfire issues. My tow-truck driving brother in law said it could be a water pump. A mechanic who heard it quickly, almost in passing, said maybe throwout bearing, but also that i should just drive it more.

So my plan for this weekend is to do as many diagnostics for these issues as I can: Redoing my dry compression test, doing a wet compression test, check for rod knock by hand cranking the cylinders and checking play, check for play in the thrust bearing while operating the clutch, checking my work on the sparkplugs I replaced.

My questions are:
1: As anyone heard these sounds before, especially intermittently like this?
2: Does anyone have any suggestions to the root or where I should look?
3: if not, would you add any diagnostics to my list?

More info about the state of the car:
- Currently showing codes P0135, P0135p and P0136p
- I/C on ODB shows CAT, O2, HO2 and i think EVAP as 'Not ready' after driving..
- I did a hot dry compression test the day i bought it: ~210, ~210, ~90, ~90, ~180 (i have a blown head gasket on my mind bc of adjacent cylinders.. but i have minimal white smoke so i'm worried it an even worse problem)
- I then replaced the plugs with non-oem plugs (I now have a set of volvo plugs on the way). Torqued to about 17, but i have super simple torque wrench, I did used anti-sieze.
- Oil change, non-oem filter and 5-30 oil (also have a OEM filter on the way). I didn't pay great attention to the quality of what came out, but i think there was definitely some particulates.. I wish i had inspected.
- Flushed my coolant system, made a mess.. I didnt notice oil or metalic look, but I also didnt inspect this super closely and it's a yellow/orange coolant already.. Also wish i had inspected this.
-Replaced Thermostat (non oem, another mistake, have OEM on the way!)
-Replaced Coolant temp sensor (non oem, i'm so dumb, have OEM on the way!)
-New ait filter
-full tank of 93 octane with Lucas High Milage fuel treatment
*(All service was done before i drove it and noticed this sound)

Other notes
-Timing belt done at 140k
-Haven't looked far enough back in service record to find PCV system being done, so i have the kit on the way
-Seems like it was well maintained up to 180k, then the record becomes less clear, but seemed to mostly focus on the brakes.
-New exhaust (im not exactly sure what) was done in april
-Oil was low when I bought it, coolant seemed to be a little high above top lines.

Any other info i should provide? i'm hoping to dig more into the maintenance records tonight!

P.s. also I do need to figure out this O2 sensor issue, as it's causing a Check Engine light and i live in MA so i wont pass inspection. But i want to make sure the motor wont explode first!



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Re: Intermittent low knocking from engine bay, heard when hot and at idle - s70 NA Manual

Post by clifford06 » Thu Sep 26, 2019 7:28 pm

Greetings and welcome ! I say your brother inlaw might be correct. I had a similar sound before my amazon purchased water pump went bad ! From your video , it seem to come from the right / passenger side of motor . Sounds to me like water pump fan is wobbling . I could be wrong , but pull timing belt cover and give it a look . Check to see if timing belt tensor has play . If it does replace ASAP !

You have entered the the " black hole " of Volvo ownership . Your time , patience and wallet will be tested.
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Re: Intermittent low knocking from engine bay, heard when hot and at idle - s70 NA Manual

Post by smacknab » Thu Sep 26, 2019 8:47 pm

Hey Clifford thanks for the welcome and for the tip.

I had assumed they did the water pump with the timing belt, but you prompted me to look closer. I just went through the first owner's records again and I see atleast two timing belt changes (weird intervals of 101k miles and 141k miles) with tensioners and pulleys listed but no mention of the water pump with those services. I'll check on it next!

And yes, already it's become a bit of a black hole I've noticed. Everyone likes to say 'labor is most of the cost' but when you're fixing everything the parts add up quick.



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Re: Intermittent low knocking from engine bay, heard when hot and at idle - s70 NA Manual

Post by clifford06 » Thu Sep 26, 2019 9:10 pm

We have to fight this battle together . Water pump was probably not changed because it was not leaking . Time has caught up with it. Check it before you lose your DIY project to a head rebuild due to bent valves caused by a locked up water pump .
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Re: Intermittent low knocking from engine bay, heard when hot and at idle - s70 NA Manual

Post by clifford06 » Thu Sep 26, 2019 9:23 pm

Owning a Volvo is like dating a stripper. The first date is awesome ! Every minute after can be costly ! I have no knowledge of stripper behavior ! Just sayiing !! :wink:



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Re: Intermittent low knocking from engine bay, heard when hot and at idle - s70 NA Manual

Post by abscate » Fri Sep 27, 2019 12:14 am

What do you on the second date after all the car paint is removed?

Op..that sounds accessory tome , not In the engine. Try removing SERP belt and seeing if it is still there


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Re: Intermittent low knocking from engine bay, heard when hot and at idle - s70 NA Manual

Post by smacknab » Sun Sep 29, 2019 12:33 pm

Just swapped the timing belt, tensioner, idler pulley and water pump. Same problem as of right now. I also put in the OEM thermostat and coolant temp sensor too.

Any other suggestions? I've got the OEM fuel filter, plugs and the pcv kit to do still. Was gonna get the O2 soon!

Anyway, if anyone has some other thoughts that'd be great!

Thanks



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Re: Intermittent low knocking from engine bay, heard when hot and at idle - s70 NA Manual

Post by abscate » Sun Sep 29, 2019 12:49 pm

AC compressor clutch. Try cycling AC button when noise is prese[not to see \if it changes

YOur harmonic balancer or crankshaft pulley could be loose. You can usually track down a noise to wtin a cm or so using a hose as a stethoscope

The sound does remind me of my bad AC clutch
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Re: Intermittent low knocking from engine bay, heard when hot and at idle - s70 NA Manual

Post by bronco » Mon Sep 30, 2019 4:44 am

I've heard a sound like that before coming from a solenoid near the throttle body
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Re: Intermittent low knocking from engine bay, heard when hot and at idle - s70 NA Manual

Post by smacknab » Mon Sep 30, 2019 7:44 pm

Thanks for keeping the suggestions coming. I ended up bringing the car by a Volvo Indy in my area owned by two super nice guys (Superior Auto in Salem MA) who were reccommended by a guy in the parts Dept at the dealer (who exclusively has owned s70's lol). They were kind and patient and fair with the price.

They had it for the day and said they poked around the accessory belt and drove it for some errands and suggested the alternator clutch. They said it's 'a one way clutch' so its probably free wheeling when it's not under load and that could be where the sound is coming from. They also suggested I replace the serp belt tensioner pulley. They added that the sound would get much worse before it actually fails (not sure exactly how much worse).

Anyway, writing this out, I do kind of feel like if I was more patient and used the tube in the ear method, I might've been able to narrow that down. But I will say they have calmed me down from thinking the worst in terms of internal engine damage. I'd say considering that I've owned the car for a week and this is all very new to me, having a Volvo mechanic say the car is in pretty good shape made me feel alot more confident in what I'm trying (learning/hoping) to do with the car!

Also, i added photo of my new timing belt sticker I filled out myself! A very rewarding feeling, if a little optimistic.
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