95 Legacy Engine Noise

[Guest bogriver]

Ok...95 Legacy 196,000mi on the clock.

 

I recently took a trip, about 800mi, and after the trip

noticed the engine would make a knocking sound

when the engine was fully warmed up, at idle.

 

If I would increase the rpm to about 3000 the noise would

go away. Lower the rpm's again and it would return.

From a cold start no noise. At highway speeds or driving

at any speed the sound is not heard, or at least not noticeable.

 

The engine has had regular maintenance all it's life.

I use a Subaru oil filter and 10-40 oil. It does not use any oil

between changes. I have NOT replaced the oil pump.

 

Anybody have any ideas before I conclude it's a connecting rod or main bearing? Almost sounds as if it's a oil supply problem...but, that's probably wishful thinking

 

 

Thanks,

Bogriver

[Guest Legacy777]

Yeah I would tend to agree with you about the oil supply. Either the pump needs replaced. Or on these pumps there's a backing plate with O-ring and the screws that holds the backing plate on come loose, so you loose oil pressure, which could be happening.

 

If you want to know for sure, you'll either have to tap into the oil pressure sender, and try to interpret the signal voltage to a pressure, or get a different sensor to tap into that location.

 

If it is the oil pump you'll need to pull the timing belts and all that stuff off.

[Guest bogriver]

Josh,

 

Thanks for the reply.

 

Yeh, I had planned to test the oil pressure first.

The service manual says 43psi at 5000rpm, do you know

what the typical Subaru oil pressure is at idle?

As I believe the oil pump is a fixed displacement pump, with

a pressure relief valve, which should give you a lower

oil pressure value at idle.

 

Thanks,

Bogriver

[Guest Legacy777]

unfortunately, no I don't really know what the pressure should be at idle.

[Guest LeoneTurbo]

This is what my FSM says:

 

Flow at 600 rpm:

4,2L @ 98 kPa (1,0 bar)

 

Flow at 5000 rpm:

42L @ 294 kPa (3,0 bar)

 

Oil pressure relief valve operates at 490 kPa (5,0 bar)

 

These are for SOHC engines, DOHC engines run higher oil pressures. Sorry - I don't have US quantities.

[Guest Frag]

Haynes gives between 14 to 26 psi at 2000 rpm and 34 to 46 psi at 4,000 rpm.

I think these figures are very conservative.

I have a mechanical oil pressure gauge and get 55 psi at 3000 rpm (my regular crusing speed).

[Guest bogriver]

Thanks everybody for your info.

I will check the pressure this weekend.

 

Thanks again,

 

Bogriver

[Guest bogriver]

Well...I checked the oil pressure.

 

It looks OK,

75psi @ 3000

35psi @ Idle

 

Still puzzles me as to why the noise is not there until the engine reaches normal operating temp, and, does not seem

to be getting worse. Still...sure sounds like a bearing to me

as I have had the lifter tap on and off with every Subie I have

had for the last 15 years.

 

Oh well, now my search for a engine begins.

I hope to find a used "low mileage" (80,000mi or less) one.

 

Thanks again to all for the help and info.

 

Bogriver

[Guest Frag]

Just curious Bogriver, you certainly did not take those reading at engine operating temp did you?

And about the noise, why dont you look into the possibility of a faulty belt tensionner before buying a new engine. Some posters have described the noise it makes as resembling a bottom end knocking sound.

I guess you would have to remove the belt covers to have a look at that.l

[Guest bogriver]

The oil pressure measurements were taken at normal operating temperature.

 

I had given the belt tensionner a thought, but the noise

emanates from the back, and not the front of the engine.

 

And still I ask...why when warm not cold??

You would think any clearances would be at maximum

during a cold start.

 

The only explanation I have is the

increased viscosity of the oil when cold is enough to

compensate for the increased bearing wear. When the oil

heats up and viscosity decreases it cannot compensate enough for the bearing wear (clearance) even though

the clearances have decreased somewhat due to the increased temperature of the engine after warm-up.

 

Just my thoughts...

 

Bogriver

[Guest 1 Lucky Texan]

HEY Bogriver! You just suggested your own next step!

 

Put in some 50W oil as a test of your theory! Cheap and easy compared to some other inspection/disassemby procedure.

 

Carl

1 Lucky Texan

[Guest Strakes]

Just a thought from way out of left field...

 

Did you illiminate pre-ignition/detonation? The subaru engines love making carbon build-up. This leads to detonation, that sounds like knocking. Also, this kind of knocking requires a hot engine, to have heated up the carbon to a point that it causes the detonation.

 

There is a "water" cleaning method that works great if you think your car's knocking noise is a result of carbon build-up. Here's a link that may help if you think it is because of carbon build-up:

 

www.bbs.legacycentral.org...water+tick

[Guest bogriver]

Well I did some tests...

 

I did the water trick to remove any excess carbon build-up.

Verified that it actually worked, by borrowing a friends

scope and scoping each cylinder through the spark plug

holes. The engine looked great, minimal deposits on the

piston and virtually no deposits on the valves.

The original hone marks were clearly visible.

This I find amazing on an engine with nearly 200K miles on it.

I then pronounced the engine clean and installed a new set of NGK V's.

 

I still have the slight knocking sound when the engine is warm.

It still does not make any sound when cold, and, when it does

make the knocking sound increasing the RPM's makes it go away. Also, if I put the trans. in gear and apply the brake

to slightly "load" the engine the sound disappears.

 

I am still stumped!!

 

I then pulled each spark plug wire off on at a time while the

engine was making the noise, NO CHANGE!

Most mechanics I have talked to say this is a decent test

for bad lower end bearings. I do not get any double slap noise. Three independent mechanics have come to one conclusion...they would not condemn the engine just yet.

 

At this time I have not yet spent the money for a mechanic

to look at the car in detail, I might be headed in that direction though.

 

Does anyone have any more ideas as to what this noise could be?

 

Thanks,

Bogiver

[Guest Setright]

It could your one of your catalysts, the first is right there at the back of the engine, and these things can make some strange noises. My catalyst number two, under the cabin, has started a death rattle, and is making all sorts of noise that sound as if the engine is shaking itself to bits...

 

Funny though, I replaced it due to rust in Feb 2002, and had it changed again under warranty because it started to rattle. I am now fighting with the dealer to have this second one replaced FOC again!