2.5l engine

[FFF]

This has been discussed many times on this forum, but I have not found a
definitive answer:

The sound of the 2.5l engine in my GT is perfectly OK until it hits around 3000
RPM. At this point, a certain harmonic roar develops that blends into a smoother
sound above 3200 RPMs. This is slightly more noticeable with the engine under
higher load.

is this:

1. universally accepted as normal?
2. indicative of a problem with the crankshaft/harmonic balancer?
3. an ill-fitting exhaust?
4. a sign of aging crankshaft bearings?

I am pretty happy with the performance of the engine otherwise - don't have any
of the dreaded piston slap. The gas mileage is pretty poor compared to my old 2.
2l MT - it seems to get only 19 mpg (mixed city & HWY). in city traffic more
like 16, at which rate I could as well be driving a Jeep Cherokee (hiss!). Does
that seem normal?


florian

 

[Edward Hayes]

My 2000 Forester AT & 2.5L engine doesn't have what you describe. Has this
done this new?? Could you be more descriptive and maybe answers will come.
ps There is no harmonic balance and it certainly doesn't sound like bearing.
My first guess is air intake system leaking. eddie

 

[FFF]

My 2000 Forester AT & 2.5L engine doesn't have what you describe. Has this
done this new?? Could you be more descriptive and maybe answers will come.
ps There is no harmonic balance and it certainly doesn't sound like bearing.
My first guess is air intake system leaking. eddie

In reply to this:

The engine in question is the 2.5l DOHC (with hydraulic lifters, AFAIK).

The roar is definitively a low harmonic resonance, like two cycles of vibrations
overlapping at 3000 RMP and blending into an overall louder sound than expected
from how the motor sounds below 3000 RPM. It doesn't sound like a hum -
definitively more like a roar.

My guess was off center rotation of something in the engine - perhaps pulleys or
crank shaft center bearing.
There's no hiss or similar from the air intake, but I'll try.

Here are other threads about this symptom:
Forester Engine Vibration: <http://makeashorterlink.com/?F3E551BF6>
Question about engine vibration: <http://makeashorterlink.com/?X5F512BF6>

florian

 

[FFF]

My 2000 Forester AT & 2.5L engine doesn't have what you describe. Has this
done this new?? Could you be more descriptive and maybe answers will come.
ps There is no harmonic balance and it certainly doesn't sound like bearing.
My first guess is air intake system leaking. eddie

Oh, and I don't know if it's been doing this since new.
That 96 GT Wagon and I are just getting to know each other (bought used at 139k
miles three weeks ago).

florian

 

[Verbs Under My Gel]

This has been discussed many times on this forum, but I have not found a
definitive answer:

The sound of the 2.5l engine in my GT is perfectly OK until it hits around 3000
RPM. At this point, a certain harmonic roar develops that blends into a smoother
sound above 3200 RPMs. This is slightly more noticeable with the engine under
higher load.

is this:

1. universally accepted as normal?
2. indicative of a problem with the crankshaft/harmonic balancer?
3. an ill-fitting exhaust?
4. a sign of aging crankshaft bearings?

I am pretty happy with the performance of the engine otherwise - don't have any
of the dreaded piston slap. The gas mileage is pretty poor compared to my old 2.
2l MT - it seems to get only 19 mpg (mixed city & HWY). in city traffic more
like 16, at which rate I could as well be driving a Jeep Cherokee (hiss!). Does
that seem normal?


florian

I'm not sure about the noise. Have an independent mechanic give it a
listen. As for the fuel consumption, I've never done worse than 21
mi/US gal, and I routinely see 27 mi/US gal in mixed city and highway
driving. This is with a "Phase-II" (SOHC, roller rockers) 2.5l MT
with 37,000 mi.

 

[FFF]

I'm not sure about the noise. Have an independent mechanic give it a
listen. As for the fuel consumption, I've never done worse than 21
mi/US gal, and I routinely see 27 mi/US gal in mixed city and highway
driving. This is with a "Phase-II" (SOHC, roller rockers) 2.5l MT
with 37,000 mi.

Wow. Where does that difference com from? The manual transmission alone? I like
shifting - in fact, I miss it. Maybe I'll go and make my GT the only '96 around
that has a manual gear box...

florian

 

[Dominic Richens]

The sound of the 2.5l engine in my GT is perfectly OK until it hits
around 3000 RPM. At this point, a certain harmonic roar develops that
blends into a smoother sound above 3200 RPMs. This is slightly more
noticeable with the engine under higher load.

Have you thought of heat-sheild rattle? I had similar symptoms, I googled
the net and found lots of complaints about rattling heatsheild and took it
to my dealer who removed it - noise gone!

 

[FFF]

Have you thought of heat-sheild rattle? I had similar symptoms, I googled
the net and found lots of complaints about rattling heatsheild and took it
to my dealer who removed it - noise gone!

No, I checked the exhaust pipe and heat shields for rattle because of a clunking
sound when driving across small bumps, but nothing was loose there. It's also
not really a rattle - more like a oscillating whooo.. whooo.. whooo that
smoothes out beyond 3200 RPMs.


florian

 

[Stu Hedith]

No, I checked the exhaust pipe and heat shields for rattle because of a clunking
sound when driving across small bumps, but nothing was loose there. It's also
not really a rattle - more like a oscillating whooo.. whooo.. whooo that
smoothes out beyond 3200 RPMs.


florian

I had a 98 GT auto and got 24-25 mpg regardless of how i drove. As for
the sound, the whooo...whooo... makes me think maybe tire noise.
Despite being aligned within specs and rotating tires, I had 2 sets of
tires wear unevenly on the edges (don't know if it was feathering or
scalloping) and the tire noise was relentless at low speeds. Once I got
above 30 or 40, there was enough other noise to drown out the tire noise
which was at a higher frequency by then. I was starting to think i
might have had a bad bearing. I put a new set of snow tires on one
winter and the noise was all but gone.

Stu

 

[GTT]

Wow. Where does that difference com from? The manual transmission alone? I like
shifting - in fact, I miss it. Maybe I'll go and make my GT the only '96 around
that has a manual gear box...

florian

Dunno, but I have an almost new Forester and I get regularly 23 around town
and 28 on the highway! And it's an AT.

 

[FFF]

Dunno, but I have an almost new Forester and I get regularly 23 around town
and 28 on the highway! And it's an AT.

That's the SOHC 2.5l, I assume. Is there a big difference in the AT between
those generations?

florian

 

[Edward Hayes]

There should be NO measurable difference in those vehicles. Same gearing and
power/torque levels. eddie

 

[FFF]

There should be NO measurable difference in those vehicles. Same gearing and
power/torque levels. eddie

Turns out the engine is at 125 compression (175, I believe is factory spec).
And that's even, on all cylinders - I am not happy at all.

florian

 

[Edward Hayes]

There is only one correct way to check compression besides having a good
gage with a tight seal. All spark plugs removed and throttle blocked wide
open. The engine starter must crank at ???? rpms. Suspious that all
cylinders are the same max pressure leads me to believe measurement is
faulty. I did not see the original post so are there other issues?? This
condition could be caused by a mis-indexed cam timing belt. Let us know what
you find out. eddie

 

[FFF]

There is only one correct way to check compression besides having a good
gage with a tight seal. All spark plugs removed and throttle blocked wide
open. The engine starter must crank at ???? rpms. Suspious that all
cylinders are the same max pressure leads me to believe measurement is
faulty. I did not see the original post so are there other issues?? This
condition could be caused by a mis-indexed cam timing belt. Let us know what
you find out. eddie

I am counting on my mechanic's gauge and ability to measure correctly. You're
right that the equally low compression is very likely a measuring mistake. I do
have some coolant loss (even though no white fog coming out of the exhaust at
startup), and the coolant is "dirty". A symmetrical head-gasket failure on both
sides could also kill compression in that way, but how likely is that?

As I wrote; I am not terribly impressed by the performance of the engine and
downright disappointed with its fuel economy. Is that consistent with low
compression?

florian