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Question for the mechanics about oil analysis

If you haven't viewed my thread about my son's problem with his Veloster here's a brief breakdown.
The catalytic converter failed at 39000 miles which, from a best guess, caused backpressure on the engine causing the engine to spin a bearing causing a knocking sound. Same issue happened again 9000 miles later only the knock isn't as bad as the first time. No CEL when the cat fails and no stored codes. There was no knocking sound prior to the cat failure but there is noticeably a knock in the engine now that really shows up as the engine gets warm and the oil warms up.

I'm trying to figure out what is causing the cat failure and if it has spun a bearing again. I'm considering having a full engine oil analysis done but I'm not sure it will tell me what I want to know. My thinking is, if there is a spun bearing or cylinder damage due to the back pressure, higher amounts of metals and carbon from the back pressure would show up in the oil along with possibly fuel.

What does the PP brain trust say? Would this be a good first step in determining what happened and possibly what's causing the cat to melt down? I know in heavy equipment when there is an engine issue, the first thing they do is send out oil for analysis.

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Old 09-02-2020, 01:26 PM
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A couple things I can think of that can cause a cat to clog up. One is contamination, like with excessive oil. Rare.

The one I've personally experienced was from running too lean so the cats got hot and melted.
That was on a POS ford ranger (redundant), where the primary fuel pump in the tank was really weak.
It provided enough fuel pressure for the injection at idle, but under load it would lean out and melt the two cats.
Did it twice before it was properly diagnosed, then I dumped the POS and got something better.

BTW if you spun a bearing, you don't need oil analysis. You'll be able to see the glitter in the oil.
Oil analysis is useful to determine if a bearing is kinda thinking about getting ready to fail.
Old 09-02-2020, 01:40 PM
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My Jeep Wrangler ate a couple cats until we discovered #1 & #2 injectors were swapped.
From the factory!.

Switched the two injectors, and it's been fine ever since.
Old 09-02-2020, 03:20 PM
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Originally Posted by Dantilla View Post
My Jeep Wrangler ate a couple cats until we discovered #1 & #2 injectors were swapped.
From the factory!.

Switched the two injectors, and it's been fine ever since.
I gotta think they would have caught that when they did the new short block after the first cat failed. Just checked and forgot to mention after cat 1 failed, they installed a new short block.
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Old 09-02-2020, 03:24 PM
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The only other thing I can think of that may potentially eat cats is oil with high levels of ZDDP.
Couldn't hurt to send a sample off to Blackstone for analysis. Even better if you send them a virgin sample of the oil you used along with.
Old 09-02-2020, 04:08 PM
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There were some 1.8 Toyota engines that did this back in about 2000-2002,typically in the MR2 There was no cure, only prevention by owners stripping out the guts of the precat so that the internal bits that would break up were not there any more to so do.After 2003 Toyota changed something to prevent this happening
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Old 09-02-2020, 11:02 PM
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I'm going to run a sample over to Blackstone in Ft Wayne. I figure for $30 it can't hurt to have the oil analyzed.
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Old 09-03-2020, 04:10 AM
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Quote:
Originally Posted by sammyg2 View Post
BTW if you spun a bearing, you don't need oil analysis. You'll be able to see the glitter in the oil.
Oil analysis is useful to determine if a bearing is kinda thinking about getting ready to fail.
Yup.

Because helicopters are essentially thousands of parts flying in close formation, oil analysis is done at regular intervals as a preventive action.

Oil analysis is phenomenal, especially tracking results on individual aircraft over time. Full spectrum: engines, transmissions, hydraulics.

For $30 bucks, however, I'd do it just because it would be interesting to see the results.
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Last edited by Seahawk; 09-03-2020 at 04:38 AM..
Old 09-03-2020, 04:27 AM
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Originally Posted by sammyg2 View Post
The one I've personally experienced was from running too lean so the cats got hot and melted.
That was on a POS ford ranger (redundant), where the primary fuel pump in the tank was really weak.
It provided enough fuel pressure for the injection at idle, but under load it would lean out and melt the two cats.
Did it twice before it was properly diagnosed, then I dumped the POS and got something better.
I saw a turbo Thunderbird lose timing, and after driving the cat was cherry red...full retard maybe, causing uncombusted fuel to burn up in the cat?
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Old 09-03-2020, 04:36 AM
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Yep, that would do it too.
Old 09-03-2020, 05:06 AM
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I touched on my thoughts as to why the cat is melting down but they assured me that the engine management is so sophisticated that if there is even a slight misfire it would set a code. I said "the cat plugged twice on this car and this thing didn't throw a single emission related code. Are you sure the engine management is as sophisticated as you think it is?"

I think it's not sensing a misfire and raw fuel is being dumped into the cat causing the cat to overheat and melt down. The tech said when he pulled the O2 sensor and started the car it blew chunks of the cat out the O2 sensor port.
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Old 09-03-2020, 05:12 AM
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Call me dumb, but I still fail to see how a plugged cat, could cause a spun bearing ? I would think you would have all sorts of driveability issues , low power, and knocking long before bearing damage would result .
But, Hyundai.....
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Old 09-03-2020, 05:38 AM
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First, quit starting and driving the damn thing. If you've got what you think is a rod knock, an oil analysis is useless. Pull the pan and look at the rod end. If you have excess clearance, pray that the crank journal isn't ruined. If you see that the rod end or crank journal is darker than the others, that is a sign that excess heat was involved and I'd suggest you look for an oiling problem. If you end up pulling the motor apart, check that cylinder's piston top for detonation signs.

Examining the cat will tell you if it failed from heat. That's usually from excess raw fuel in the exhaust.

The two problems may or may not be related but the cat failure was probably a result, not a cause.

I should probably mention that the oil viscosity that should be used is dependent upon the designed bearing clearances, so it's possible that one of the bearing clearances wasn't right to start out with, or maybe the wrong weight of oil was used at some point.

Last edited by javadog; 09-03-2020 at 06:01 AM..
Old 09-03-2020, 05:58 AM
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Another name for Oil Analysis is Tribology
Three elements of analysis are typically done:

Chemistry
Viscosity
Contamination

It all relates to friction & wear

Its all slippery
https://www.ggbearings.com/en/company/tribology
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Old 09-03-2020, 06:01 AM
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Quote:
Originally Posted by cabmando View Post
I think it's not sensing a misfire and raw fuel is being dumped into the cat causing the cat to overheat and melt down. The tech said when he pulled the O2 sensor and started the car it blew chunks of the cat out the O2 sensor port.
I'm leaning this way too.


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Originally Posted by fastfredracing View Post
Call me dumb, but I still fail to see how a plugged cat, could cause a spun bearing ? I would think you would have all sorts of driveability issues , low power, and knocking long before bearing damage would result .
But, Hyundai.....
Agree. I can see lots of related issues, but not a spun bearing.
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Old 09-03-2020, 06:41 AM
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Originally Posted by fastfredracing View Post
Call me dumb, but I still fail to see how a plugged cat, could cause a spun bearing ? I would think you would have all sorts of driveability issues , low power, and knocking long before bearing damage would result .
But, Hyundai.....
Oh yeah there were all sorts of driveability issues when the first one went. It completely shut down. This isn't the cat plugging over time. It happens all at once and without warning. One minute it's cruising along just fine, the next the engine shuts down. Extreme back pressure would be my guess as to why the engine is getting hurt. This time around it failed about 1/2 mile from home but apparently not quite as bad as the first time because it still ran but sounded really weird (nowhere for the exhaust gases to go).

Here's what happened to the Kia's with the 1.6L engine. Sounds really familiar.
High exhaust gas temperatures may damage the catalytic converter, possibly resulting in abnormal engine combustion and damage to one or more of the engine’s pistons as well as possible piston connecting rod failure. Piston damage may result in an engine stall, increasing the risk of a crash. A broken connecting rod may puncture the engine block, allowing engine oil to escape that may contact the exhaust, increasing the risk of a fire.
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Last edited by cabmando; 09-03-2020 at 10:15 AM..
Old 09-03-2020, 09:54 AM
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Originally Posted by javadog View Post
First, quit starting and driving the damn thing. If you've got what you think is a rod knock, an oil analysis is useless. Pull the pan and look at the rod end. If you have excess clearance, pray that the crank journal isn't ruined. If you see that the rod end or crank journal is darker than the others, that is a sign that excess heat was involved and I'd suggest you look for an oiling problem. If you end up pulling the motor apart, check that cylinder's piston top for detonation signs.

Examining the cat will tell you if it failed from heat. That's usually from excess raw fuel in the exhaust.

The two problems may or may not be related but the cat failure was probably a result, not a cause.

I should probably mention that the oil viscosity that should be used is dependent upon the designed bearing clearances, so it's possible that one of the bearing clearances wasn't right to start out with, or maybe the wrong weight of oil was used at some point.
Not driving it. It's at the dealer. But you might be onto how I can prevent this from happening again... just stop driving it.

If it's over fueling an oil analysis will show this.

Can't examine the cat, it's a part of the manifold so the only way to view the top side is cut it apart from the manifold.

The two problems are definitely related. The short block has 9000 miles on it and didn't make a knocking sound before the cat plugged up.

5w20 is what goes in the car and it gets changed at shorter intervals than the manufacturer recommends.
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Old 09-03-2020, 09:59 AM
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Right or wrong move, $30 seems cheap enough. I'll have the results back tomorrow. Maybe I'll scan and post to see what the brain trust has to say.
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Old 09-03-2020, 01:24 PM
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Rod reversal.

At least that is a problem with recip compressors, I would think it could apply to engines too. maybe.
Old 09-03-2020, 01:47 PM
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Maybe I'll scan and post to see what the brain trust has to say.
You might want to do the same here.

It's basically the Pelican Parts for motor oil related info/tribology nerds.

Old 09-03-2020, 04:10 PM
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