Cold start knock

[Sniepster]

Originally Posted by Ultramaroon

It's early rod knock. Takes a couple seconds for the oil to pump up and hit the bearings from a cold start. Relying on thin film lubrication until then, and it's when worn journals will be most obvious.

Sorry. Sucks.

Early rod knock? Is there even such a thing? If a rod is spun wouldn't the knock be always present?


I'm finding it really hard to believe it's rod knock as the car has had the recall done 20.000 miles ago and has had zero issues. If not a blocked oil passage what else could cause rod knock?

Also the car has had a new short block replacement at around 40k miles, now the odo reading 70k miles.

[fableluke]

do you know where in the engine bay that sound coming from? have you got someone else to turn on the car while you record/watch/listen to where that sound is coming from? It might narrow where the issue is coming from, or it might not, probably wouldn't hurt to check, though.

[Ultramaroon]

Originally Posted by Sniepster

Early rod knock? Is there even such a thing? If a rod is spun wouldn't the knock be always present?


I'm finding it really hard to believe it's rod knock as the car has had the recall done 20.000 miles ago and has had zero issues. If not a blocked oil passage what else could cause rod knock?

Also the car has had a new short block replacement at around 40k miles, now the odo reading 70k miles.

It happens. Late in its life, my Eclipse knocked whenever I skipped pre-filling the oil filter after a change. Still ran fine for tens of thousands of miles right to the end.


Come to think of it, @Opie mentioned something about the timing chain tensioner preload being critical. If not preloaded enough, the chain slaps until it pumps up. I think that's only potentially an issue after a reassembly. Seems like an outside shot but might as well mention it.

[Sniepster]

Originally Posted by fableluke

do you know where in the engine bay that sound coming from? have you got someone else to turn on the car while you record/watch/listen to where that sound is coming from? It might narrow where the issue is coming from, or it might not, probably wouldn't hurt to check, though.

Unfortunately the sound is present for less than a second so it's hard to investigate, and it is there only if the car has been sitting for at least a day...

[Sniepster]

Originally Posted by Ultramaroon

It happens. Late in its life, my Eclipse knocked whenever I skipped pre-filling the oil filter after a change. Still ran fine for tens of thousands of miles right to the end.


Come to think of it, @Opie mentioned something about the timing chain tensioner preload being critical. If not preloaded enough, the chain slaps until it pumps up. I think that's only potentially an issue after a reassembly. Seems like an outside shot but might as well mention it.

IF bearings turn out to be the issue, is there any preventive maintenance i could to do avoid a spun rod? Change the bearings?

I will be changing the oil soon to 5w30 anyway.

[FrickingReallySlow]

Worn timing chain? tensioner needs to take up more of the slack until oil pressure meets amount of slack needed to be taken up.

OP how many miles on the engine

Originally Posted by Ultramaroon

It happens. Late in its life, my Eclipse knocked whenever I skipped pre-filling the oil filter after a change. Still ran fine for tens of thousands of miles right to the end.


Come to think of it, @Opie mentioned something about the timing chain tensioner preload being critical. If not preloaded enough, the chain slaps until it pumps up. I think that's only potentially an issue after a reassembly. Seems like an outside shot but might as well mention it.

[Ultramaroon]

Originally Posted by Sniepster

IF bearings turn out to be the issue, is there any preventive maintenance i could to do avoid a spun rod? Change the bearings?

I will be changing the oil soon to 5w30 anyway.

If it's a rod bearing, and it's knocking on cold start, the downhill slide to a hard failure will be quick. I'd love to be wrong, believe me. I suggest having it properly diagnosed before sweating too much. The best, and least expensive course would be to replace the worn [bearings, not journals] before the crankshaft [journal] is scored.

Let us know! If I'm wrong, then we can put that info into our collective forum knowledge base.


edit: Used Oil Analysis will clearly show elevated soft journal metals if one is scuffed.

[NoHaveMSG]

A UOA will help tell you if it is the rod bearing. Should be showing excessive amounts of material. Bearing can be bad without being spun.

[Sniepster]

Originally Posted by Ultramaroon

If it's a rod bearing, and it's knocking on cold start, the downhill slide to a hard failure will be quick. I'd love to be wrong, believe me. I suggest having it properly diagnosed before sweating too much. The best, and least expensive course would be to replace the worn journal(s) before the cranshaft is scored.

Let us know! If I'm wrong, then we can put that info into our collective forum knowledge base.


edit: Used Oil Analysis will clearly show elevated soft journal metals if one is scuffed.

When i'll be taking it in for the oil change tomorrow i'll have the guys at the shop have a look to get their opinion.

I was already planning a UOA and ordered a Blackstone kit a while ago.

I'll keep you guys updated on my findings.

[Dzmitry]

Originally Posted by Ultramaroon

It's early rod knock. Takes a couple seconds for the oil to pump up and hit the bearings from a cold start. Relying on thin film lubrication until then, and it's when worn journals will be most obvious.

Sorry. Sucks.

Trying to understand this more. Does the oil always take a couple seconds to hit the bearings on cold start? Thought it might be quicker even with its thickness.

Or is this because you are saying he already has some kind of damage and therefore slowing down oil flow in some way?

[Sniepster]

Originally Posted by Dzmitry

Trying to understand this more. Does the oil always take a couple seconds to hit the bearings on cold start? Thought it might be quicker even with its thickness.

Or is this because you are saying he already has some kind of damage and therefore slowing down oil flow in some way?

+1

I am also quite perplexed as to how would this happen. It is 5w40 after all, not a thick-ass 10w60 racing oil.

And i find it weird the issue has started happening during the hot summer months (when the oil is already warm and should flow quite well) and not during the freezing temps in winter.

[Ultramaroon]

Originally Posted by Dzmitry

Trying to understand this more. Does the oil always take a couple seconds to hit the bearings on cold start? Thought it might be quicker even with its thickness.

Or is this because you are saying he already has some kind of damage and therefore slowing down oil flow in some way?

Originally Posted by Sniepster

+1

I am also quite perplexed as to how would this happen. It is 5w40 after all, not a thick-ass 10w60 racing oil.

And i find it weird the issue has started happening during the hot summer months (when the oil is already warm and should flow quite well) and not during the freezing temps in winter.

Anyone with an oil pressure gauge will confirm. It takes over a second for the oil to reach the journals after the galleries have drained. This is normal and referred to as transition from boundary, to hydrodynamic lubrication. Boundary lubrication is fine as long as heat generated by working the lubricant doesn't cause the temperature to rise - and viscosity to lower - to the point of allowing contact between the journal and bearing surfaces. Boundary lubrication is the dominant mode in applications where slow-moving parts are lubricated with grease.

The problem with worn bearings is that the gap is wide enough to allow the cyclic loads to overcome the boundary. We get that hammering effect. That's where it all goes to shit.

[Ultramaroon]

Another correction before I get slammed. Boundary lubrication isn't necessarily only for cases where relative motion is slow. It's just that the lubricant must be able to withstand the heat generated from being worked.

[Dzmitry]

Originally Posted by Ultramaroon

Anyone with an oil pressure gauge will confirm. It takes over a second for the oil to reach the journals after the galleries have drained. This is normal and referred to as transition from boundary, to hydrodynamic lubrication. Boundary lubrication is fine as long as heat generated by working the lubricant doesn't cause the temperature to rise - and viscosity to lower - to the point of allowing contact between the journal and bearing surfaces. Boundary lubrication is the dominant mode in applications where slow-moving parts are lubricated with grease.

The problem with worn bearings is that the gap is wide enough to allow the cyclic loads to overcome the boundary. We get that hammering effect. That's where it all goes to shit.

Gotcha. So boundary lubrication is happening on cold start if I understood that correctly. The wear of the bearings is bad enough that the proper oil lubrication actually lacks on cold start. In which case it causes additional wear on the parts.

I had this sound on my shitty old Mazda6 back then. Slightly for a different reason which is why your explanation confused me a bit at first. I was well aware of what the sound was of course. I had bought it used and didn't know any better as I was young. But the engine already had leaky head gaskets. Minor for some time but that developed into major within a year. I was adding 5 quarts of oil per week at one point.

But in my case, it was because the oil was leaking out so quickly, and sometimes I would get down to probably a couple quarts before I added a bunch more. When it would get very low, that was the sound I experienced. Always cringed and drove like a baby when it would happen. It was amazing how many times I got it to happen though, and that engine still lasted some how. I probably drove like that for several months before finally finding another car and selling this one off.

The car sat for a while before I sold it. I got it to start when a guy came to check it out, and that sound came on for a solid 5-6 seconds on the initial start lol. Then it calmed down and it was good. He was like oh that's not good! I told him it had an oil leak and he will need to be topping it off with oil. Didn't tell him how much But I sold it for like 300 so I wasn't trying to screw him over haha.

On a rant here... anyways the reason I brought up the story is because I didn't think there would be any lubrication issues unless the oil was low enough or something. Didn't know that wear on parts would cause the oil to actually lack flow. But the more I think about it, it's kind of obvious and makes sense.