View Full Version : Motor idling smoothly, but is very loud.

05-07-2008, 10:03 AM
98 240 SE w T25 Bottom Mount - Ran pretty good before I did any work. Occasionally smoked and clutch was slipping. Sounded like a stock KA with an exhaust at idle.

Random thoughts (updated):
I did pressure wash the engine bay also. Maybe I got some water in the fuel lines? I capped them off pretty good, but it was just a thought. How would the car run if a little water got in the lines?

Main Problem - Idle sound:
When the car starts, it sounds like I'm trying to compress liquid or something. Even though it cranks and runs ok. The idle is extremely loud, almost like an old school V8. I'm not talking the exhaust, just the sound of the motor idling. You have to raise your voice to really talk while its running. The idle itself is around 8-900, doesn't stumble, raise, or fall. Its kind of hard to describe, but it just seems like a deep resonating rumble. It also sounds and feels pretty normal to rev it up, even though I've only revved it up to about 3000 RPM, the motor sounds as expected. Just a little more vibration than usual. But I have yet to actually drive the car. I've just done this while its been in neutral .

One more note: Whenever you turn the car off, it shuts off kind of hard. Almost like its being forced to stop or something. Way harder than my other engines.

Problems - Coolant/smoke:
I've determined that the coolant seals in the T25 are shot. The exhaust literately was pouring water out of it and smoking a lot after it warmed up. So I clamped off the water lines running from the T's to the turbo. 90% of the smoke stopped and after evaporating a bit of the old leak, there wasn't much liquid in the tailpipe either. Also, this turbo had never been watercooled as far as I know. So I think its safe to assume that the seals are shot in the turbo. Lucky me I have a Garrett T28 waiting to put on.

Other possible issues:
One of my motor mounts is loose.
The downpipe hits the bottom of the car pretty much the whole time.

Other things I've checked/changed:
I replaced the spark plugs with some NGK BKRE6 (or whatever the part number) gapped to .30
The coolant and Oil still look clean after idling for about an hour. (Headgasket sounds like its good to me)
Compression tested it and got 150/155 across all 4 cylinders.

Questions and possible other issues:
Could having a new clutch, bad pilot bushing, or the procedure of installing them affected the sound of my engine at idle? I did everything by the FSM. But could the actual parts change the sound of the engine.

Could I have warped something in the process of taking off my intake/exhaust manifolds (even though I removed them the way the FSM states)?

Could the belts be too tight? Could it be a bad spark plug wire? *scrtaches head* Suggestions?


So I recently took the motor out of my car to replace the clutch and the oil pan. While the motor was out, I pressure washed it down and painted the block (only the block). I had pulled all components and brackets off the motor in the process.

The clutch:
After which, I replaced the clutch with an ACT Extreme Pressure plate and 6 puck sprung disc. Replacing the pilot bushing and throwout bearing with the one ACT provided.

Turbo coolant lines:
I ran 2 custom made hardlines ( I made using some 3/8" brake line) from the turbo around the back of the block to the heater core in, and heater core out.

Oil pan:
My Oil return bung was way too low so I got a new pan welded up with a fitting farther back and at the very very top where the lip is at.

Replaced all the oil with Royal Purple 10w30 and transmission fluid with Royal purple also. Coolant was just generic stuff.