2.5l engine

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: Question about engine vibration:

florian

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

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

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

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

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

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

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