RobertE

Might running at low CHT glaze a cylinder?

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I’m burning oil in a couple of cylinders despite only 300 hours SMOH.  I properly broke in the engine.  But here I am with a couple of cylinders with a problem.  I routinely run LOP and have cylinder temps around 320F.  Might that have produced the problem?

 

 

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I have similar CHTs as you have reported... even colder in the winter...

But, that didn’t cause any cylinder issues... on my IO550... (not terribly helpful for this discussion)

Possible Next steps... get pics from inside the cylinders looking to see where the cross hatchlings went...

Cylinder surface wear is typically caused by high CHTs... See if you can tell if it is a surface challenge first than move on to a ring inspection if needed... loss of an oil ring has a tendency make oil escape...

Got a dental camera?

PP thoughts only, not a mechanic...

Best regards,

-a-

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Low CHTs shouldn't be a problem unless due to running at very low power. Glazing is usually a break in issue, but it might happen if the engine were consistently run at very low power. Glazing is caused when the combustion pressures are too low to seal the rings properly and hot combustion gasses leak past the rings and bake the oil on the cylinder walls. I'd investigate further to determine the source of the problem. A borescope and compression test are good places to start. Glazing should be evident in a borescope inspection if it's present. Is there a lot of oil on the belly? If the rings are leaky, combustion gasses pressurize the crankcase and oil usually gets forced out the breather.

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Edited by PT20J

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12 hours ago, RobertE said:

I’m burning oil in a couple of cylinders despite only 300 hours SMOH.  I properly broke in the engine.  But here I am with a couple of cylinders with a problem.  I routinely run LOP and have cylinder temps around 320F.  Might that have produced the problem?

Did the increase in oil consumption happen suddenly, or increased slowly over a period of time?  What was the oil consumption after break in, and what is it now?

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And did break in result in a noticeable lowering of CHTs ie positive evidence your rings seated? 

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To answer both questions, as to break in, I got the normal indications - elevated CHTs in all cylinders initially then declining to normal, accompanied by plugs that showed no oil.  As to oil usage after break in, it was never all that low - probably about 7 or 8 hours per quart.  It is now down to about 5 and it seems to have gotten there slowly.

As I’m replaying all of this I’m wondering if, in fact, I didn’t do a completely thorough job of break in and am now, slowly, seeing the consequences.  

I plan to make a couple of long-planned trips then have the two offending cylinders pulled to take a close look.  I’m going to feel mighty stupid if this was a self-inflicted wound.  I’ll report back with findings in about a month.

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7-8 hours per quart is very high for newly broken in cylinders.  I’d expect at least 10-12, especially with fresh oil. Since it started high and gradually got even worse it’s probably a break in issue.  Broken rings would be a relatively sudden increase in oil consumption, and too coincidental for two cylinders simultaneously. 

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1 hour ago, Cyril Gibb said:

7-8 hours per quart is very high for newly broken in cylinders.  I’d expect at least 10-12, especially with fresh oil.

What data do you base that on? And, why would increased oil consumption after 300 hrs be break in related. 

Oil consumption normally increases slowly over hundreds of hours as engines wear. If it increases significantly over a short period, something has changed and further investigation is warranted.  

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8 hours ago, PT20J said:

What data do you base that on? And, why would increased oil consumption after 300 hrs be break in related. 

Oil consumption normally increases slowly over hundreds of hours as engines wear. If it increases significantly over a short period, something has changed and further investigation is warranted.  

I agree.  It also depends on what type cylinders the OP has.  If they’re chrome, 7-8 is pretty good.  If steel, then probably average or slightly below.  Mike Busch has some good reading on oil use vs different types of cylinders.  Chrome average around 5hrs/qt.  

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9 hours ago, Ragsf15e said:

I agree.  It also depends on what type cylinders the OP has.  If they’re chrome, 7-8 is pretty good.  If steel, then probably average or slightly below.  Mike Busch has some good reading on oil use vs different types of cylinders.  Chrome average around 5hrs/qt.  

Good question re:chrome cylinders.  I hadn't thought of that.

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