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How Hot Is Too Hot?

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Pops

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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.
Had a similar problem with a Buick 215 V8 engine in the rear of a VW bug with the radiator in front in the spare tire area with air ducts to the radiator and long runs of coolant pipes to the rear engine. Hard to get and KEEP the air out of the system. Ended up puting bleed ports in different points and also had to open these ports about every 3/4 months to bleed air that would get trapped. Just a change the oil additional job.
 

Pops

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Looking ahead, I would say you will have a regular burp the coolant system on a regulator schedule after so many engine run hours.
 

Hot Wings

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Time for customization.
If not practical then..........

@ the OP:
Also consider using vacuum to bleed the coolant system. It is a very effective method for suborn systems but does require some not so common equipment. A siphon feed undercoating gun can be used for a vacuum source in a pinch.

Don't apply vacuum to an already warm system.
 

delta

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Perhaps you could elevate the tail and pressure check the system with the bleed port open to get the air out. The chance that you cooked your engine is doubtful. Once she's broke in, it'll run even cooler. If ground running on a hot day eventually becomes a problem you may have to figure out where to put a fan.
 

BJC

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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.
Lift the tail.

Edit As Delta said.

BJC
 

wsimpso1

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If the heads were not covered with coolant, they can get way hot there and boil the coolant. Question then becomes what is likely to be failed. Biggy is to look for headgasket type failure issues. Oil and coolant mixed, oil or coolant in the combustion chamber, etc. To have this failure either the gaskets were cooked/ over squeezed (head and block expand more than the head bolts) or head warp from head going above creep temp. Both can result in head bolt torques being relaxed. Check all of this by examining oil and coolant closely, putting air pressure in the sparkplug holes and listening for air in the cooling system, and then checking head bolt torques. Low head bolt torques most likely mean a teardown issue. I would check with an engine shop that knows LS' and ask what the torque for in use head bolts should be at, then ask how they would check it.

Even if a gasket or head bolt issue arises, I suspect that a good engine shop can inspect your disassembled engine, check for issues, and tell you if they can salvage the engine or not. You get to compare their price with a new crate...

Prevention - being covered well above. My comments are +1 on good bleeding - level the engine for the job, bleed valves at all high spots, etc. But number one is to know how much coolant is needed to fill the engine, radiators, hoses, tanks, etc. Then when you fill, have that much mixed coolant and keep at it until it all goes in. If you have a quart to go, there is still a big slug of air someplace.

Comments on air cooled engine oil temps need to be taken with a grain of salt. Let's remember that the Lycoming oil comes from the sump, then the pump, filter, cooler, past the temp probe, through the galleries, then it drains back to the sump. The oil comes from the cooler before you get to the probe. Oil temp on Lycomings is thus post cooler, and sump temps are significantly higher than the number from the probe. So if Lycoming says "danger" at 245 F, they are saying "danger" when the sump is a lot hotter than 245 F ... I have no idea where GM put the probe in the LS, but that is worth some research and a probe with an alarm. I would not worry terribly over engine oil getting to 300 F for a few minutes. Sure, change it and the filter and the oil analysis is a good idea for this and the next few oil changes.

In automatic transmissions, we consider torque converter out temps (hottest place in an automatic tranny) of 300 F to be the death zone, but only because the friction modifier dies quickly there, and the friction elements will shift rough or shudder after that. The rest of the oil and lubrication is fine with the friction modifier converted to the smell of a cooked steak...

Billski
 
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TXFlyGuy

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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.
We are doing this also. Hope it’s not too little, too late.
Both my engine tuner and his dad are concerned. 275 F was not the hottest part of the engine, so we have no idea how hot it actually got.
The MoTeC coolant temp sensor is at the rear of the engine, which is the lowest part. All of the boiling took place in the most forward part (the highest elevated) of the engine.
 

Hot Wings

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Check all of this by examining oil and coolant closely, putting air pressure in the sparkplug holes and listening for air in the cooling system, and then checking head bolt torques.
I'd also pressurize the (known full) system from the coolant side and watch the pressure under static temperature over a period of an hour or more. This will detect small coolant leaks and help locate their source.

Checking the head bolt torque will only be useful for a significant reduction in torque or clamping pressure. The friction of the static bolt, even at reduced clamping pressure, will make accurate determination of true existing torque little more than a guess. Final torque, other than torque and turn or torque to yield, should always be reached while the fastener is in motion to eliminate this error.
 

Bill-Higdon

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If not practical then..........

@ the OP:
Also consider using vacuum to bleed the coolant system. It is a very effective method for suborn systems but does require some not so common equipment. A siphon feed undercoating gun can be used for a vacuum source in a pinch.

Don't apply vacuum to an already warm system.
I use a similar vacuum method to get the air out of my VW Rabbit & Quantums, also the water cooled VW Vans have this issue until completely blead.
 

TFF

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Since the engine is backwards, I would first look at the back of the heads. I think LS intakes are dry, so you will need to machine a port in the back of each head. Maybe a special freeze plug with a fitting. I would T them into a manifold. Leveling is a stop gap, but you can’t check it anytime. The t manifold could be easily opened and checked.

Having a shop take it apart and measure everything and correct it might make a better engine. Even if you buy another, you will have to know how to modify it.
 

TXFlyGuy

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My engine tuner will do a borescope on the engine, checking for scuffing of the pistons and cylinders. Plus the cold/hot comp checks.
Next week we should have some answers. Plus the results from the oil analysis.
 

proppastie

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I had a bad head gasket on my car, it would put air into the coolant system, never could bleed it......as was said "oil in the coolant." need a bleed port highest point or perhaps the vacuum coolant trick. That it boiled over after you shut down is a plus but why is it that hot,.....need to figure out what is wrong....cars do not boil over after shut down,.....are you talking to any other TFX guys? do their engines boil over after they taxi in and shut down? If you do not fix the problem, you will just ruin a new engine.......Your problem is not bad sensors, your problem is there is something wrong with your setup, or a bad engine part., bad timing, etc. This is not your local garage where you replace parts till it finally works because you do not have a stock setup......
 
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TXFlyGuy

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I had a bad head gasket on my car, it would put air into the coolant system, never could bleed it......as was said "oil in the coolant." need a bleed port highest point or perhaps the vacuum coolant trick. That it boiled over after you shut down is a plus but why is it that hot,.....need to figure out what is wrong....cars do not boil over after shut down,.....are you talking to any other TFX guys? do their engines boil over after they taxi in and shut down?
On one occasion, it did boil briefly after shutdown. No coolant expelled.

Two other times, the engine started shooting coolant 5 feet into the air, and then it was shut down immediately.

Why is it hot? We guess not enough airflow thru the belly scoop / radiator. I was told to keep the engine at or above 1800 rpm to help get more air flowing.

A few other T-51 owners report similar issues, with getting extra warm during extended taxi times.

This could have been avoided if the person who installed the coolant temp sensor would have done it correctly. We thought everything was fine, with temps reading 120 F, then going up to 155 F. But that was a lie...with the boil over soon after hitting 160 F.
 

mcrae0104

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Comments on air cooled engine oil temps need to be taken with a grain of salt.
I fully agree with this. A Lycoming is a very different animal than TFG's water-cooled LS. I only brought it up to illustrate the point that the CHT (or coolant temp) limit is not the same thing as an oil temp limit. It's not really the central issue here. Good luck sorting it out, TFG.
 

TXFlyGuy

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What do the others say what is different from the few .....or do all have the problem and only a few talk about it.......
Some claim they can taxi around for 45 minutes, no problems. Others say they had to pull over at Oshkosh and shut down due to over heating while taxiing in.

A friend who owns/flies a real P-51 just told me..."It's a get off the ground quick airplane. They don't even fly if it's above 92 F."
 

proppastie

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I am thinking if something was wrong it most likely is you had a slug of air in the coolant system, if you did not warp the heads and now have a head gasket problem you still need to get all the air from your system. With my head gasket problem when it was a small leak (before it got worse) I had good compression. The plugs were real clean was leaking into the cylinders not the oil....and the pistons were pushing air into the coolant, along with a little oil which collected on the cap which is the highest point. As it got worse missing until the water burned off. Finally so bad I could not start and water shot out of the spark plug hole as I was checking for spark.
 

BBerson

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I put a simple round automotive coolant guage with a one piece bulb and 5' cable on my car. Worked 20 years so far. No place to screw in the bulb. Just clamped the bulb to the head.
 

TFF

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While you are just taxing around, I would rig up an electric fan on the radiator or leaf blower. Not for flight, but guarantee air is flowing through the radiator on the ground. I would get it sorted with the engine in the plane now. If you buy a new one, it will not be the one experimented on.
 
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