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How Hot Is Too Hot?

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TXFlyGuy

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Full disclosure: My new LS376/495 engine got hot. Not once, but 3 times with boil overs. The MoTeC shows we hit 275 F. But our coolant temp readout never went above 165 F. The sensor is not accurate, and that is part of the problem.

As soon as we saw signs of over heating, the engine was shut down.

No water in the oil. The oil smells like new. No white smoke in the exhaust. And the compression still feels good. We will do another hot and cold compression check.

Any thoughts? Is the engine "cooked"?
 

proppastie

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Timing, bad thermostat, kink in coolant hose.mixture? Color of plugs?
 

TFF

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My list from easy to hard is nothing of importance to head gaskets to warped head. Your probably ok but once you get the temps under control make a coolant consumption note until you feel good about it. You need to check what ohms sensor you have and it that is how the gauge calibration is. The other thing to note is where you take the reading. The regular thermostat is going to be 208F. I would probably set redline at 220.
 

TFF

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It might take time to see if there is damage. Might take a while to really know. You just have to realize you took some life off it for down the road.
 

TXFlyGuy

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It might take time to see if there is damage. Might take a while to really know. You just have to realize you took some life off it for down the road.
There are zero obvious, tell-tale signs of overheat damage.
We did a prop pull-through, to feel each cylinder and get an idea on compression. It still feels good.
Another compression check will be done, first cold, then hot.
The previous cylinder numbers were 180 psi for all 8.

My reading finds that temps of 280 F are certain permanent damage, pistons / cylinders. Even a single one time overheat will do this damage.

We know that my engine hit 275+ three times. Each time with a major boil over.

Yes, we thought we were being cautious. And the coolant temp readout was in the 150-160 range most of the time. Never over 165-170F.
 
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TXFlyGuy

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Found this...

300 degrees F.

It's generally accepted that petroleum-based engine oil starts oxidizing (breaking down) around 240 degrees F (115 degrees Celsius), while full synthetics, such as Rotella T6, can handle temperatures above 300 degrees F.
 

Mcmark

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Lycoming doesn't get upset until the oil temps exceed 245 for a while. Many of the aerobatic guys have called to discuss worrisome temps of 220 and the techs respond, "call back when it gets over 245".
 

mcrae0104

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Found this...

300 degrees F.

It's generally accepted that petroleum-based engine oil starts oxidizing (breaking down) around 240 degrees F (115 degrees Celsius), while full synthetics, such as Rotella T6, can handle temperatures above 300 degrees F.
Oil temp and CHT (or coolant temp) are not the same. Did you read coolant temp or OT at 275?

For example...

https://www.lycoming.com/content/leaning-lycoming-engines said:
During normal operation, maintain the following recommended temperature limits:
  • Cylinder head temperatures – 400˚ F. or below.
  • Oil temperature – 165˚ F. – 220˚ F.
 
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Hot Wings

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It might take time to see if there is damage. Might take a while to really know. You just have to realize you took some life off it for down the road.
Thatone

Lots of variables starting with - Why - did it overheat and where are the sensors located that are correct and the location of the incorrect one(s). What is the designed system pressure and was it really getting to that pressure/temperature before boil over? How long after shut down did the boil over last before the system quit venting? That information can tell you what kind of temperatures were actually reached and how heat soaked the internals were.

My remote, don't know anything about your particular system, thought is:
There is probably no significant damage. The lack of external and internal coolant leaks is a good sign. Internally the first things that seem to give up due to high short duration overheat are piston rings. They can have good compression, both static and pumping, but will allow increased oil consumption.

Oil degradation is cumulative - chronic, not acute. Based on you observations I'd probably use the old oil until I figured out the cooling system, then change it.....but I'm cheap.
 

wsimpso1

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First and foremost, how did you know you got to 275+ F figure? Was this a sensor thatł you have a correction for? Have you checked your calibration? Distilled water boils at temperature based upon yourambient pressure, so you can check it readily and improve your estimate.

Next did it boil over while running or after shut down? Did it boil over with the cap holding pressure, or after the cap was opened? If you know the glycol % and the pressure during boil over, you can find that boiling point temperature. If you lost only a little of your coolant then the coolant got to whatever the boiling point of your glycol % and cap pressure would allow, perhaps different from 275F.

Now to the locations of the sensors. Were they submerged throughout, or were they uncovered. Uncovered, they can lie to you badly.

So, if the top water kept the heads covered, your engine might be OK.

If you lost most of the coolant, that uncovers the heads, and that can be bad indeed for the engine.

Let's wait for the rest of the info.

Billski
 

TXFlyGuy

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At first, we suspected an air bubble in the coolant system. So we ran the engine several times letting it warm up, then shut down for cooling. Coolant was added each time after shut down in an effort to bleed the system.

The sensor was an AC-Delco, which we thought worked just fine. But it did not. The temps were in the 140-155 F range most of the time, but it went up to 165 F at the boil over. We have since corrected this with a new sensor that the G3X will accept.

Time from start up to over heat was typically 12 to 15 minutes of ground running.

When the engine got hot (275 F coolant temp per the MoTeC), it was shut down, and the boil over which spewed anti-freeze out of the overflow 5 feet into the air, lasted about 0 to 3 minutes. You could actually hear the bubbling / boiling taking place in the front end of the engine. Much like a pot on a stove with violently boiling water.

The MoTeC does not have oil temps so we are not sure about that. Most of the sensors that were installed did not work with the Garmin. We have since rectified that.

During a ground run, I went back and placed my hand into the radiator exhaust, at the aft belly scoop area. There seemed to be plenty of air flow, with a large volume of hot air being discharged.

Recent advice says to keep the rpm's at or above 1800 during ground ops to keep extra air flow going through the radiator.

I am debating the option of just ordering a new LS376-495. Not sure this engine can be trusted now.
 
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TFF

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With a complex cooling system, there needs to be bleed ports at certain points to make sure there is no air in the system. Open the bleeds, put coolant in and once the first bleed starts purging, close it off. Move on to the next until the top. There has to be a bleed port as the highest point of the coming system. A car is usually the radiator cap, but I have cars that it’s on the engine.
 

TXFlyGuy

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With a complex cooling system, there needs to be bleed ports at certain points to make sure there is no air in the system. Open the bleeds, put coolant in and once the first bleed starts purging, close it off. Move on to the next until the top. There has to be a bleed port as the highest point of the coming system. A car is usually the radiator cap, but I have cars that it’s on the engine.
There is a bleed port on the front of the engine. But the engine is reversed, with the bleed port at the aft side in our installation. This is the lowest point on the engine. We sit at about 13 to 14 degrees nose up. So the air (if there is any) is trapped in the forward end.
 

TFF

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A friend is helping with a VK 30 with the last single Continental Voyager engine. They have to pull a vacuum on the system and fill it like a Freon system for AC. The only way they can fill it as designed.
 
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