Rotax radiator

[rhtrudder]

Should the overflow tank on my 914 be vented , mine is sealed , wondering if that would put undue pressure on the plastic line from the cap to the plastic tank as mine blew a hole in it,

 

 

[skyfox1]

Should be vented otherwise it won't return to the radiator it will create a vacuum and won't be drawn back as it cools

 

 

[rhtrudder]

Looks like previous owner lost original cap and replaced it with a Castrol oil bottle lid, I did think it had to be vented otherwise everything would be under pressure ,

 

engine done 1400 hrs, lucky to get this far, hope there's no more damage

 

 

[Downunder]

A 3mm drill bit in the cap should fix it nicely.....

 

 

[M61A1]

Looks like previous owner lost original cap and replaced it with a Castrol oil bottle lid, I did think it had to be vented otherwise everything would be under pressure ,engine done 1400 hrs, lucky to get this far, hope there's no more damage

There shouldn't be any damage as long as when you check your coolant level on your pre-flight, you remove the pressure cap and check the contents of the system, not just glance at the overflow.

 

 

[rhtrudder]

There shouldn't be any damage as long as when you check your coolant level on your pre-flight, you remove the pressure cap and check the contents of the system, not just glance at the overflow.

Lots of screws to get to the cap, easy to see the bottle, never had any trouble with the cooling system before, maybe the oil cap leaked enough air to still breath , have drilled the 3mm hole which could have caused a disaster , my CFI said it's the simple things that will kill you , lucky this time.

[M61A1]

Lots of screws to get to the cap, easy to see the bottle, never had any trouble with the cooling system before, maybe the oil cap leaked enough air to still breath , have drilled the 3mm hole which could have caused a disaster , my CFI said it's the simple things that will kill you , lucky this time.

Simple things indeed....coolant in the overflow bottle is not an indicator of coolant in the system. Your choice.

 

 

[rhtrudder]

Indeed, thanks for pointing out the bleeding obvious

 

 

[skyfox1]

You really need to make a better inspection point to access the radiator cap like M61A1 said over flow doesn't mean the radiator is full ,how do you access the oil tank does it have a seperate inspection point .

 

Cheers Geoff

 

 

[rhtrudder]

My problem wasn't that the radiator was low on fluid , the overflow tank had the wrong cap which came under pressure and blew the tube , I have changed the fluid at the service intervals but never had to top it up, my point was that a simple small hole in a the cap was all that was needed, I never picked up that it had the wrong cap. Flew it tonight with no overheating so all good, discovered that with a torch and mirror I can check fluid level through the oil inspection hatch, thanks everyone for your interest.

 

 

[M61A1]

Indeed, thanks for pointing out the bleeding obvious

Sorry, that wasn't intended. One of the problems with internet chatty things is that you don't know what level of experience you are dealing with. There people out there who may think that it's acceptable just to look at the overflow level. I don't think that it's adequate.

For the record, my overflow tank on my 582 is an aluminium drink bottle with a screw on lid. I drilled two holes in the bottle, near the top. One hole has a tube from the radiator which goes all the way to the bottom, so that the radiator can draw back the coolant as it cools, the other has a tube that goes in the top only and runs down (zip tied) the engine mount and clear of the airframe.

 

Also, if you can get the coolant cap off, but cant see it, you can stick a finger in it and feel the level.

 

 

[rhtrudder]

I think it might be a smart idea to get the original cap from floods, the oil cap screws on with the right thread , has no tube to direct coolant away so would end up on the battery.

 

 

[skippydiesel]

Simple things indeed....coolant in the overflow bottle is not an indicator of coolant in the system. Your choice.

Hi - I have a small inspection " hatch" right side upper cowling, which facilitates oil level checking and visual inspection of the coolant overflow/serge bottle.

 

The bottle is translucent, so the green coolant level can be seen without removing the lid.

 

I have marked the cold coolant lower level on the bottle, so a quick check with the metric eyeball tells me if levels are normal - system full of coolant.

 

The lower level also allows me to keep a check on coolant loss which, in a well maintained engine, should be very slight/negligible.

 

I usually open the hatch after an "opp" and again a quick check will show the hot, upper, expanded, level of the coolant. The upper level may vary slightly with cooling system temperature.

 

The observed coolant at or very near the cool/low level mark and the rise to the upper hot levels and back down as the engine cools, strongly indicates situation normal.

 

I agree that periodic inspection of coolant level at the "cap" is a good practice but doing this, at other than service intervals (cowl removal time), is impractical in my installation.

 

In short, I must rely on the coolant in the overflow bottle as an indicator of the condition of the entire cooling system.

 

 

[rhtrudder]

You would think if the cold level in the overflow bottle dropped away there would be a problem

 

 

[skyfox1]

I never trust the over flow bottle l always check the radiator for being full,you just don't know if it has pulled the water back in to the radiator to the safe level.

 

 

[M61A1]

You would think if the cold level in the overflow bottle dropped away there would be a problem

You can lose all the coolant in the radiator and still have the same level in the overflow bottle.

 

 

[rhtrudder]

You can lose all the coolant in the radiator and still have the same level in the overflow bottle.

you are right , my radiator set up holds about 2.5 litres which would have to empty out through the lid, and I guess some could be left behind when the engine cooled down.

 

 

[M61A1]

you are right , my radiator set up holds about 2.5 litres which would have to empty out through the lid, and I guess some could be left behind when the engine cooled down.

Just suppose a hose, a fitting or even the radiator was leaking and not the lid. If a hose was leaking it could drain the coolant on the ground while sitting for a few hours and you'd never know.

 

 

[skippydiesel]

Yes you can have a "catastrophic" failure of the radiator and still potentially have coolant in the overflow bottle.

 

If your installation allows easy access to the "radiator cap" over the top of the engine, go ahead check it in your pre-flight inspection.

 

I still stand by my earlier statement

 

"I agree that periodic inspection of coolant level at the "cap" is a good practice but doing this, at other than service intervals (cowl removal time), is impractical in my installation.

 

In short, I must rely on the coolant in the overflow bottle as an indicator of the condition of the entire cooling system."

 

After an embarrassing number of years mucking about with all sorts of internal combustion engines, I am convinced that the by monitoring the coolant surge/overflow you haves a good indication of the integrity of the entire liquid cooling system. This is not perfect but then what is.

 

You would think if the cold level in the overflow bottle dropped away there would be a problem

Not quit sure what you mean by this. I apologise if my interpretation is wide of the mark.

 

It would seem you do not know how this sort of radiator works.

 

First of all you need to understand that the coolant will boil at approximately 100 degrees centigrade at sea level pressure. (I say approximately because of the glycol & other inhibitors present.)

 

Water boils at lower temperatures at altitude. The higher the altitude the lower the boiling point.

 

Boiling water turns to steam and steam is not a good cooling medium.

 

Early liquid cooled engines had cooling systems open to atmosphere & required frequent "topping up" as the water boiled off.

 

From about he early 1940's or so, liquid cooled engines use a sealed cooling system, keeping the coolant under pressure to prevent boiling.

 

Water (coolant) expands as it is heated.

 

The expanding fluid must be allowed to go somewhere or the cooling system will rupture or if fitted with a spring loaded pressure cap "blow off" .

 

In the old days the radiator was only filled to just above the internal core/fins. This left a space, in what was called the upper radiator tank, for the expanded fluid to fill. On cooling the old system went into negative pressure often collapsing (non reinforced) coolant hoses in the process (usually the lower radiator hose). The cap was often hard to remove, due to the negative pressure and many people on seeing the coolant well below the top of the radiator, topped up the system, only to have the excess blow off.

 

The Rotax 912/914 range of engines (in common with most modern liquid cooled engines) has a serge/overflow tank & a two way pressure cap.

 

As the coolant heats up so it expands. The expanded fluid is released by the two way cap, into the serge/overflow tank.

 

As the coolant cools, after shut down (or as the engine cools when in cruise flight) the coolant is drawn back, past the two way cap, into the cooling system/radiator.

 

Modern engine cooling systems require that they be filled to the very top (preferably leaving no or very little air gap) and a small amount added to the serge/overflow tank.

 

For the overflow tank to work properly, there must be no air gap between it and the radiator coolant. (any small amount of air present will be blown through on your first engine start/warm up after refilling the system, leaving no air gap/bubble)

 

The overflow tank must be open to atmosphere to work correctly (usually a small 3mm hole in the cap will suffice)

 

If you fill the overflow tank to the top, it will overflow, to waste, when the engine starts to warm up.

 

This system allows for a relatively small (light weight) cooling system in which pressures both positive and negative are better controlled and very little coolant is lost over the service interval of the system.

 

SO!! if the Rotax cooling system has been correctly installed and serviced, the level of the fluid in the serge/overflow tank will indicate the general health of the system.

 

If there is a:

 

• Leak the cool level will slowly get lower (depending on leak rate)
   
   
  
• A blown head gasket the level will drop very fast and there may be bubbles rising in the overflow tank.
   
   
  
• Oil contamination, a seal has gone somewhere.
   
   
  
• The coolant level does nor rise on engine warm up you are low on coolant for a range of possible reasons headed up by a major leak or failure to correctly fill the system & purge air.
   
   
  

 

 

The above "off the cuff" explanation is I hope close to correct.

 

NOTE: Any variation from normal levels of coolant must be cause for immediate investigation failure to do so may cause loss of engine/aircraft/life

 

 

[skippydiesel]

Just suppose a hose, a fitting or even the radiator was leaking and not the lid. If a hose was leaking it could drain the coolant on the ground while sitting for a few hours and you'd never know.

Its called a pre flight inspection ( & walk aground) - I would have thought mandatory.

 

Any liquid on your aircraft belly/cowling, on ground under aircraft is cause for serious concern this could be oil, fuel or coolant (or I suppose rainwater or pee). Corrective action before further flight might just be in order.

 

 

[M61A1]

Its called a pre flight inspection ( & walk aground) - I would have thought mandatory.Any liquid on your aircraft belly/cowling, on ground under aircraft is cause for serious concern this could be oil, fuel or coolant (or I suppose rainwater or pee). Corrective action before further flight might just be in order.

I'm guessing that you have a concrete hangar floor. We have places a plenty around here where you wouldn't know if that was your coolant on the ground or not if you didn't physically check.

Yes, a pre-flight is mandatory.

 

 

[skippydiesel]

A serious leak of coolant on the ground should be obvious. (As Rotax recommend Castrol coolant, which is green, I will stick to this colour.) Green steaks down fuselage/belly, pooling of coolant around the engine cowling, green drops from under the cowling, green liquid on the ground (earth or concrete) - all a bit of a "give away".

 

Unexplained drop or rise in temperature, while in flight, is a concern that should have you looking for the nearest airfield or decent paddock. Luckily a Rotax 912/914 will run for a long time without coolant, especially at reduced power.

 

The condition of the coolant in the overflow container is just one of many indicators of engine health.

 

If your aircraft is stabled on an earth/grass or gravel floor consider placing an impervious membrane/tray under it, to catch any liquid (fuel/oil/coolant/hydraulic fluid) that me be escaping from its lawful container.

 

 

[rhtrudder]

I put a lot of faith in my gauges, after start up which is when I picked up the initial problem, and climb out ,not all,but most of these problems seem to occur when the engine is running.

 

 

[skippydiesel]

I put a lot of faith in my gauges, after start up which is when I picked up the initial problem, and climb out ,not all,but most of these problems seem to occur when the engine is running.

Most of must rely on our engine monitoring and flight instruments to inform us of our aircraft's well-being at any given moment and enable us to "manage" the situation effectively. Gauges/monitoring systems can fail/give false information and we must be prepared for this situation by being able to cross check with other information sources so as not to jump to a conclusion that might evolve into a disastrous situation.

Yes most failures will occurs during an operation and probably during high power/climb situations. This is when all systems are under the most stress/demand, so stands to reason if there is a weakness, this is when it will show up and failure occur. Other flight situations may have their own challenges (icing at low power, nose wheel failure on dodgy landing, etc)

 

Pre-flight checks are in large part reading the history of the aircraft, that is what anomalies are evident, that may indicate a future problem. This is why knowing the normal level for the coolant in an overflow bottle is a vital piece of information, if you are to make informed judgements about the condition of the cooling system.

 

 

[zodiacpilot]

Hi - I have a small inspection " hatch" right side upper cowling, which facilitates oil level checking and visual inspection of the coolant overflow/serge bottle.The bottle is translucent, so the green coolant level can be seen without removing the lid.

I have marked the cold coolant lower level on the bottle, so a quick check with the metric eyeball tells me if levels are normal - system full of coolant.

 

The lower level also allows me to keep a check on coolant loss which, in a well maintained engine, should be very slight/negligible.

 

I usually open the hatch after an "opp" and again a quick check will show the hot, upper, expanded, level of the coolant. The upper level may vary slightly with cooling system temperature.

 

The observed coolant at or very near the cool/low level mark and the rise to the upper hot levels and back down as the engine cools, strongly indicates situation normal.

 

I agree that periodic inspection of coolant level at the "cap" is a good practice but doing this, at other than service intervals (cowl removal time), is impractical in my installation.

 

In short, I must rely on the coolant in the overflow bottle as an indicator of the condition of the entire cooling system.

Sorry Skippy, if a preflight doesn't include inspection at the cap, you need to 'change your installation'. If not, one day you WILL be looking for somewhere to land with a cooked goose! Experience talkin'.