Oil Thickness/Rod Knock?

[MrwassmanNA2T]

So I switched to 15w-50 Mobil one synthetic last oil change from 10w-30 castrol synthetic.

Figured the car has a decent amount of mileage on it and maybe the tolerances aren't what they used to be, right?(~140K, ok not that much)

Well, after cruising for awhile (maybe 20 min+ in some warmish weather, 85+), I get a noise that sounds like knocking. This is from about 15 in/ vaccum all the way to boosting situations. So through out the 1000-3000rpm range pretty much. Then it goes away I think, then again i was fearing for the mains so i didn't boost to much.

Does it make sense in anyway that this could cause a lack of oil being able to get to the mains and rod journals? I am just trying to fit peices together.

I personnally think it kind of Does NOT make sense because it is after the oil gets hot, which in turn should make it thinner.

Input is gratefull.

BTW, i am dragging the car on saturday

[SATAN]

um doesnt it get thicker after it gets hot. You need the thinner oil for the cold startin situations.

sounds like you are one your way to spinning a bearing. I'll put money that if you are spinning a bearing that it is a rod berring and not a main.

[MrwassmanNA2T]

ahh, yes, just kinda realized that, had my thinking backwards.

Um, lets hope not, for it to spin, it would have to be pretty dam thin.

[Jason84NA2T]

What is your oil pressure reading cold/hot?

If it is indeed a rod knock (which is what you describe there) and you have good oil pressure, you can probably assume it was probably damaged due to starvation or contamination on the part of a previous owner. The reason I say this is because these engines don't seem to ever develop rod knocks easily. I drove one for 3-5 miles on the highway with NO oil pressure and it showed no substantial bearing damage when I tore it apart.

[SATAN]

MrwassmanNA2T wrote: ahh, yes, just kinda realized that, had my thinking backwards.

Um, lets hope not, for it to spin, it would have to be pretty dam thin.

No, just wore out. that is always the first sign of a spinning bearing berring whatever. you can hear it "rattle" with slight load up to about 3k 3500 rpm? but under full load you hear nothing right? YUP :wink:

I heard mine start to do that and kept a VERY close eye on my oil. but still after a while it was done.

Have you ever changed the head gasket and not changed the oil afterwards maybe?

[Andrevas]

[quote]SATAN wrote:

ahh, yes, just kinda realized that, had my thinking backwards.

Um, lets hope not, for it to spin, it would have to be pretty dam thin.
No, just wore out. that is always the first sign of a spinning bearing berring whatever. you can hear it "rattle" with slight load up to about 3k 3500 rpm? but under full load you hear nothing right? YUP :wink:

I heard mine start to do that and kept a VERY close eye on my oil. but still after a while it was done.

Have you ever changed the head gasket and not changed the oil afterwards maybe?

the only headgasket swap was with the ported heads added during the turbo conversion, and the oil was changed for that since he swapped pans for the turbo one.

[SATAN]

Hmm, cause I know a lot of times people will do a head gasket and some coolant will get down in the oil sometimes, People dont really think anything of it but...

Dunno but I think we can all agree a rod rattle wont go away on its own.

[Firehawk]

I never have had any problems using different viscosity oils, so you can rule out that problem.

[jjewell]

castrol gtx high mileage 20-50. by far the best oil i have used in my z. i've had both mobil 1 and valveline full synth break down on me in just around 1500 miles to the point i would use up to 3 quarts in little time at all. now i do the normal 2500-3000 mile oil change and i can take out all 5 quarts that i put in. and no there are no massive leaks anywhere that 3 quarts of oil will go. the mobil 1 was in the 300 and the valveline was in my 350z which has 25,000 miles on it. 2 cars same problem. no more synthetics for me thanks.

[ShamWow]

jjewell wrote: castrol gtx high mileage 20-50. by far the best oil i have used in my z. i've had both mobil 1 and valveline full synth break down on me in just around 1500 miles to the point i would use up to 3 quarts in little time at all. now i do the normal 2500-3000 mile oil change and i can take out all 5 quarts that i put in. and no there are no massive leaks anywhere that 3 quarts of oil will go. the mobil 1 was in the 300 and the valveline was in my 350z which has 25,000 miles on it. 2 cars same problem. no more synthetics for me thanks.

What are you talking about?

Are you saying that you ran synthetic in your 300zx and it lost three quarts, and you ran synthetic in your 350Z and it lost three quarts...But then you switched both to Castrol High Mileage, and now you dont ever lose any oil when you do your 3000 mile changes? So in your opinion MrwassmanNA2T's synthetic oil fried his bearings?

Im not trying to be a jerk, i just dont understand your post, or why its posted here.

On a side note, you lost 3 quarts of synthetic oil in 1500 miles once with your 300zx and once with your 350z? Something just doesnt seem right there...

-Mike

[jjewell]

2 cars same problem and only with synthetics. the 300 happened with about 1500 miles on the oil in summer. the 350z with 25,000 miles on the engine did the same thing but after about 2000 miles . what i think happened was the heat broke the oil down and blew right past the rings and got burned in combustion. both cars only did it in the summer that i know of. i never gave it enough time to even make it to the winter without changing back to conventional oil. i only know what i have experienced first hand. alot of people will argue this because synthetics cost more so they must be better. i don't run the high mileage oil in the 350 just a good quility conventional oil because the engine doesn't have high mileage. when you pull a drain plug on a cold engine and the 2 quarts of oil that are left in the engine piss out of it thinner than water you know somethings wrong.

[SATAN]

That............................ it is rediculous

[Andrevas]

jjewell wrote: 2 cars same problem and only with synthetics. the 300 happened with about 1500 miles on the oil in summer. the 350z with 25,000 miles on the engine did the same thing but after about 2000 miles . what i think happened was the heat broke the oil down and blew right past the rings and got burned in combustion. both cars only did it in the summer that i know of. i never gave it enough time to even make it to the winter without changing back to conventional oil. i only know what i have experienced first hand. alot of people will argue this because synthetics cost more so they must be better. i don't run the high mileage oil in the 350 just a good quility conventional oil because the engine doesn't have high mileage. when you pull a drain plug on a cold engine and the 2 quarts of oil that are left in the engine piss out of it thinner than water you know somethings wrong.

you're doing something really wrong to get that result with Mobil 1, especially in a Z33.

[MrwassmanNA2T]

Well, since switching to the thicker oil i have a zero oil leak/burn now somehow. It has been 1000 miles and it is still slightly overfilled. Has yet to make the sound since that day....

[SATAN]

Hmm, well just make sure you keep and ear on it.

Ive got rod rattle in my 240sx that I've had for over a year. The owner before me n2o'd it and fuxored it up I believe. but other than the rattle it does fine. rattle hasnt gotten worse, BUT, that doesnt mean it wont.