Subaru Outback Forums banner

1 - 17 of 17 Posts

·
Registered
Joined
·
98 Posts
Discussion Starter #1
A while back (mid January, about 3500 miles ago), I did an oil change on my '99 OBS and put Mobil 1 Synthetic 5W-30 in. The vehicle had ~39,000 miles on it at the time. Being as I had just purchased the vehicle 1 month prior, I have no idea what type of oil used to be in it. However, ever since then, I have had a knocking noise between ~1400rpm and ~1900rpm when the engine is not at full operating temperature. It doesn't matter if it's 15 degreees (F) out, or 80 degrees (F) when I start the car...the noise is the same. Like I said, the noise all started when I switched to synthetic oil. I have checked the oil level, and it's right at the full mark on the oil dipstick....not overfilled, and not underfilled.

So, my question is this: what can I do to get rid of the noise? This is the first time I've run synthetic oil, and I've heard that once you switch to synthetic, you can not switch back. Is that true in my case, even though I've only had it in there for one oil change? If I can't switch back to regular dino-oil, can I switch to a synthetic-blend, or is that also a "no-no"?

Thanks for the help everyone!
Matt
 

·
Registered
03 H6 OBW & 06 WRX Sportwagon
Joined
·
17,572 Posts
From what I've read in several forums I'd consider the following items;

1. MANY soobs have piston slap. It is usually noticeable after startup and goes away/reduces when engine is warm. Better quality/higher viscosity oils usually reduce the sound. Consensus is it does not reduce engine life/quality and, though there are exceptions, Subaru will do nothing for it on warranty.

2. MANY soobs have bad TB tensioners that SOME report sounding like a knock and reducing with engine warmup. Best inspection is to look for a 'rubbed' spot on inside of TB cover. Fix is to replace tensioner.

3. Most reports about switching between oil types are that going from dino oil in a 'high' (whatever that is) mileage engine to syn can create some leaking seals. Some say this is not true. I suspect it can happen in an engine that was somewhat neglected. Never heard of any problems going from syn back to dino. You have a subaru, it's gonna leak oil eventually anyway.(they mark their territory!)

4. You could try a heavier weight oil(in summer anyway - given your location) But you should confirm it is piston slap and not some other issue.

let us know what you find out OK?

Carl
1 Lucky Texan
 

·
Registered
Joined
·
98 Posts
Discussion Starter #3
Carl,

Thanks for taking the time to respond. :) Here are my responses to your responses:

1. MANY soobs have piston slap. It is usually noticeable after startup and goes away/reduces when engine is warm. Better quality/higher viscosity oils usually reduce the sound. Consensus is it does not reduce engine life/quality and, though there are exceptions, Subaru will do nothing for it on warranty.
While I tend to agree that this is piston slap, I never heard the noise before I changed oils. And now, everytime I give someone a ride, they ask "Wow! Is your car supposed to make that sound?". It's kinda...I don't know...embarrasing. :(

2. MANY soobs have bad TB tensioners that SOME report sounding like a knock and reducing with engine warmup. Best inspection is to look for a 'rubbed' spot on inside of TB cover. Fix is to replace tensioner.
TB tensioner? The only "TB" I can think of is Throttle Body....and I'm pretty sure there's not a tensioner on there, so I must be wrong. What is the TB?

3. Most reports about switching between oil types are that going from dino oil in a 'high' (whatever that is) mileage engine to syn can create some leaking seals. Some say this is not true. I suspect it can happen in an engine that was somewhat neglected. Never heard of any problems going from syn back to dino. You have a subaru, it's gonna leak oil eventually anyway.(they mark their territory!)
Actually, my OBS doesn't leak oil at all. At least, if it does, it is pooling up somewhere, and hasn't yet spilled over. I haven't had a drop of oil on my driveway since I've owned this car...well, except for where I spilled oil during the last oil change! :rolleyes: hehe

4. You could try a heavier weight oil(in summer anyway - given your location) But you should confirm it is piston slap and not some other issue.
Yeah, without being able to definitely confirm that its just piston slap, I'd rather not just put heavier weight oil in. Plus, that wouldn't fix the problem during the winter, so I'd rather figure out something else to do.

Thanks again for your help!
Matt
 

·
Tokyo's between my toes
2001 Wintergreen Outback 5MT
Joined
·
6,684 Posts
TB would be timing belt.

I've never heard of a synth oil bringing on piston slap, that sounds strange.

I don't see why you could not switch back to dino oil or a synth/dino blend.

In my experience of putting synth into various older cars, the synth will find a way past seals to leak where dino oil would not. I attribute that to a better penetrating ability. Perhaps, by the same token, your synth is behaving like a thinner oil than the 5W rating would suggest.
 

·
Registered
03 H6 OBW & 06 WRX Sportwagon
Joined
·
17,572 Posts
sorry - yes Timing Belt.

As oils go, I've read (maybe at www.bobistheoilguy.com) that M1 products are on the thin side (in terms of centistokes for new product). Um - what oil had you (or previous owner) been using? What drain period? Did you have this car last spring?
If you do change it out, Donot be shocked by it color - synths are very good at suspending/removing varnish and it may be darker than your old oil. Its a good thing.
 

·
Registered
Formerly 04 Outback 3.0R VDC, now 2011 Mitsubishi Pajero GLS DiD
Joined
·
1,617 Posts
Hmmm could it be that the synthetic M1 cleaned the engine a little too well, removed varnish from the cylinder wall and that small extra tolerance created piston slap that is audible?
 

·
Registered
Joined
·
194 Posts
Well, to answer your most obvious question. Yes, with modern synthetics you can go back to a dino oil. It might be worth your while to try it. If the noise goes away let us know.

I have changed to synthetics in a few mottors with ~100,000 miles. I have had no problems yet.
 

·
Registered
Joined
·
98 Posts
Discussion Starter #9
Jondalar said:
Hmmm could it be that the synthetic M1 cleaned the engine a little too well, removed varnish from the cylinder wall and that small extra tolerance created piston slap that is audible?
Yeah, that's kinda what I figured it is. I think I may switch back to dino oil and see what happens. Actually, maybe I'll just go to a synthetic-blend first and see if the noise goes away. I'd rather run synthetic than dino, so a syn-blend might just have to do it for me. However, I've had it with this noise, and want to get rid of it, so staying with pure syn just doesn't seem like an option to me anymore.

Thanks for all the opinions/help, everyone! :D

Matt
 

·
Registered
Formerly 04 Outback 3.0R VDC, now 2011 Mitsubishi Pajero GLS DiD
Joined
·
1,617 Posts
How about an additive? Used to be very common to stick a can of STP or Bardahl or Wynn's into the engine. Just make sure it's compatible with synthetic oil. :D
 

·
Registered
99' OB Ltd 2.5 SOHC
Joined
·
19 Posts
I switched to M1 at last oil change (98K) too. The engine respones much quicker than before but is also noisey than before. Is this the common problem when using synthethic?
 

·
Registered
MY99 3rd Gen Outback GX, 2004 Lexus RX330 Sport Luxury
Joined
·
242 Posts
Which M1 did you use Kmwan ? I presume 10w30 ? This grade of Mobil 1 is a pretty thin 30w (10cSt @ 100 C) so a bit of extra engine noise is the norm for thinner viscosity oils.
 

·
Registered
Joined
·
98 Posts
Discussion Starter #13
I'm using Mobil 1 5W30 in mine....at least, I'm pretty sure that's what it is. Can't remember offhand, but I have the container at home.

Matt
 

·
Registered
Joined
·
181 Posts
For my last oil change I switched to Castrol Syntec Blend 5W-30. What do you htink the oil change interval should be??? Any ideas?

tbert
 

·
Tokyo's between my toes
2001 Wintergreen Outback 5MT
Joined
·
6,684 Posts
I would think it would depend on the kind of driving you do - city stop-and-go, or open highway.

When I ran synthetic in the Escort, I changed it twice a year - once when it was time to plant daffodils in the fall, and again when the daffodils were blooming in the spring.

:D
 

·
Registered
'99 OUTBACK AT Green
Joined
·
14 Posts
Ski4Ever said:
A while back (mid January, about 3500 miles ago), I did an oil change on my '99 OBS and put Mobil 1 Synthetic 5W-30 in. The vehicle had ~39,000 miles on it at the time. Being as I had just purchased the vehicle 1 month prior, I have no idea what type of oil used to be in it. However, ever since then, I have had a knocking noise between ~1400rpm and ~1900rpm when the engine is not at full operating temperature. It doesn't matter if it's 15 degreees (F) out, or 80 degrees (F) when I start the car...the noise is the same. Like I said, the noise all started when I switched to synthetic oil. I have checked the oil level, and it's right at the full mark on the oil dipstick....not overfilled, and not underfilled.

So, my question is this: what can I do to get rid of the noise? This is the first time I've run synthetic oil, and I've heard that once you switch to synthetic, you can not switch back. Is that true in my case, even though I've only had it in there for one oil change? If I can't switch back to regular dino-oil, can I switch to a synthetic-blend, or is that also a "no-no"?

Thanks for the help everyone!
Matt
I have a simimlar problem after having my OB serviced on Friday, I had a noise that they could put their finger on but after they changed the oil it is now very pronouced did you find the actual problem
 
1 - 17 of 17 Posts
Top