HJC

I got the rod knock and in a foolish attempt to make it to the dealer, the rod snaped an oil blew out of my exhaust. Now I got pretty much a new engine but am concerned about what caused it.

The dealer paperwork says:

• #4 rod broken
• no signs of oil discoloration
• found wear and scoring in camshaft area of cylinder heads and camshafts (grooved/scored)

Does this give any clues to weather or not it was oil starvation, detonation, or other causes? I really wouldn't want this to happen again.

As for the history of the engine, I found the oil level really low twice! This was around 10,000 miles ago. Filled it up and it ran fine. I checked and filled oil every gas fillup after that point. I had 50K miles on it with oil changes every 3 months (Mobil 1 5w30).

sigma pi

iTrader: (6)

dirty and low oil will do the cam thing

rod knock i dont know

wrxisthebest

iTrader: (15)

ya.. make sure ur oil is changed every 3000 miles with good oil and a new filter...

another thing to find out would be if u had water in ur oil...it wouldnt discolor the oil... but rather make it a lil milky....

but water usually just bends rods lol

Chocoholic005

There are lots of possible causes for your problem. Low oil will cause the scoring on your camshafts and crank. Its not the only cause but in your case its the most likely. My guess is that this scoring on the crank caused excess friction between the rods and the rod journals causing piston slap, which put extra stress on the piston/rod and caused the break. I would have thought the skirt of the piston would have gone first but go figure. Your crank also may have been out of balance which doesn't help things.

meilers

I agree, it must have been actual piston slap; you're not making enough HP to break a rod by that alone, and that usually happens only on pushrod engines. You must have had a damaged camshaft which in turn put unequal forces on the rods and caused a piston to hit the top of the cylinder.

HJC

Thanks for the replies. I'll be keeping an eye on the oil levels every fill-up now.

Anti-hero

Did you know they took out the additives in the oil that protect the engine?
ZDDP is almost absent in all modern sm rated motor oils.

Try running Amsoil or Mobil 1 even or use the stp additve(red bottle) BG or the like.
Some here are dead fast against additves so do some research before picking one.

I run Lubro moly oil in the subie, if its good for porsche its good for the subie.

The hot rodders that run flat tappets are complaining about the crap oils being made safe for catalitic converters..

yanimaya

hey HJC, can you please tell me how much was that cost you to change engine?

loccomoffo

Have you had this car since new? If not maybe the previous owner used to rev the **** off it. And the current con rod failure is a fatigue failure. Ask the mechanic if he still has the con rod, a failure due to excessive force will show signs of the metal bending/yielding, a fatigue failure gives a clean brittle fracture. Well clean as in quiet flat, the surface will be rough, kinda like its covered in tiny crystals.

Some nice fatigue fracture pics here:
http://en.wikipedia.org/wiki/Fatigue_(material)

Where did the con rod break btw?

Lack of oil wouldn't have caused this, if you caused any serious damage 10k ago you would have heard the big end bearings slapping. Was the engine overheated at the time the con rod failed? Maybe the piston ceased?

Meilers we talking V8 pushrods here? I'm not following your logic

The cam issue is a different story, mainly from running very low oil levels and not changing oil filters would be the best guess. Once again have you had the car from new?

As for oils and additives, the most important thing about the oil is its viscosity. The fancy additives and synthetics stop oil from thickening up due to oxidation from temperature. That’s why you can double the mileage between oil change outs when using synthetics. Personally I prefer dino oil as changing it out twice as often also gets rid of all the particulates which wear the engine. And I prefer to leave the additive mixing to the oil manufacturer’s technicians, otherwise you're just going blind with no idea of benefits. If you're really serious send the oil off for oil analysis, they'll tell you which additives you’re running low on. But then again you might as well just buy new oil and same yourself some $$.