How to diagnose worn rod bearings

[Matt.S_951]

Hi all.

I need advice for how to tell if my rod bearings need to be replaced.

Background: my car is a 2.8L stroker with a big turbo and all the other normal addons. It also has a big front oil cooler and a baffle plate in the oil pan. The engine was built in 2002 and has been in a few cars since then. 3 years ago it went into my car and has been used for about 5 De's a year. I bought the car last fall.
I don't know when the last time the bearings were changed.

In normal street driving, oil pressure stays high. Because of the oil cooler, oil temp stays at about 120 c on the street.

I did a de last weekend. Car ran great, but I was to busy driving to look down at the oil pressure. On track the oil temps reached about 200 c.

Before everyone says the obvious, I know I should replace the bearings. Problem is I have 3 De's coming up, and I'm not sure I have the time to do the bearings before then.

I am hoping someone can give me pointers on how I can diagnose the condition of my bearings. For example: with oil temp at x, and rpm at y, oil pressure should be z. I realize that all of my mods make this a difficult question.

Thanks for the help

[smudo]

According to owners manual with warmed up engine/oil at around 5000 rpm. the oil pressure should be around 4 bar. With hot oil temperature it might be lower. 120 C on street and 200 C at track seem to be really high oil temperatures.

[kdjones2000]

I think that 200C is pretty normal for these cars under racing conditions.

Here is my 944 Spec (NA) car's oil temperature during our last race as Las Vegas. Oil temperature was up to 200C.

[smudo]

I didn't know that as I do not have oil temperature gauge in my 951. Good to now when you choose oil for 944 that is driven on a track from time to time.

OT: With may daily driver I have never seen more than 108 C ( while driving in Germany on autobahn for 300 km in a 85 - 125 mph range.

[divil]

Hi, I usually just lurk here

But I had to chime in on this...200 degrees C is ludicrously high. You want to be around 105 - 120 degrees C. In other words, 220 - 250 F

It's worth reading this thread with some input from a few very well known 944 pros.

In particular:

So – the answer is really anything over 230 is not optimum. Anything over 250 not good. Anything over 280 and you might as well use stale beer as a lubricant!

(They are talking about Fahrenheit)

[Matt.S_951]

My street driving oil temp might not be accurate. The temp gage only goes down to 120, so it could really be anything less than that
Does anyone have any other recommendations besides 4 bar at 5000 rpm?
Anyone know whether the engine being a stroker would affect this spec?

Thanks.

[smokintr6]

You guys need to double check your oil temperature units. 200C is almost 400F, which is waaaayyy waaaaaaaaayyyy too hot! 250F is sort of a cutoff for good synthetic oil. The guy who was around 100C on the track is probably reasonably close.

You are a good candidate for sending an oil sample to blackstone labs. They will be able to tell you if there are elevated levels of copper etc etc in the oil. You probably need to do the maintenance soon-ish just so you can figure out exactly what you've got. If you're paying attention you might be able to catch the low oil pressure at the track before you window the block, but you never know.

[DannoXYZ]

The times I've replaced rod-bearings that turned out to be completely worn out or have less than 100-miles left, there we no changes in oil-pressure that indicated failure. Only sure way to diagnose is to pull the rod-caps and inspect.

Only takes about 1-hr to hang the engine and pull the oil-pan. Much less effort than doing engine or swapping in replacement engine.

[kdjones2000]

Originally Posted by divil

Hi, I usually just lurk here

But I had to chime in on this...200 degrees C is ludicrously high. You want to be around 105 - 120 degrees C. In other words, 220 - 250 F

It's worth reading this thread with some input from a few very well known 944 pros.

In particular:



(They are talking about Fahrenheit)

Good points.

That gauge is in degrees F, I just forgot about that and assumed C.

[divil]

Originally Posted by DannoXYZ

The times I've replaced rod-bearings that turned out to be completely worn out or have less than 100-miles left, there we no changes in oil-pressure that indicated failure. Only sure way to diagnose is to pull the rod-caps and inspect.

Only takes about 1-hr to hang the engine and pull the oil-pan. Much less effort than doing engine or swapping in replacement engine.

1-hr? To remove the oil pan, I had to:

- remove the intake and a few turbo fittings
- remove the crossover pipe
- support the engine
- remove the crossmember/rack/control arms (i.e. disconnect tie rods, ball joints, caster blocks, steering joint, PS lines)
- remove a few heat shields
- move the AC compressor out of the way
- remove 22 bolts

Even now having done it before I think it would take me 5-6 hours! My hat is off to anyone who can do this in 1 hour.

[333pg333]

It had to be in F no C. You wouldn't have a factory gauge in the US with C temps. Even so, you should make sure you have a decent oil if you're DE'ing the car. Not wanting to start another oil thread but you need something with a decent film strength otherwise you will spin a bearing. 20w/50 with somewhere between 1200-1500ppm of ZDDP is recommended.

[Pete R]

Where the sensor is taking the reading will vary the oil temp quite a bit too. I never had a gauge but my 951 would get insanely hot on track days. I would lose a lot of oil pressure. (even with 20-50 Amsoil race oil) A larger oil cooler was next on my project list before I sold the car.