rotax 912 uls high cht

[jaybhansen]

I have read that I should purge the trapped air in the coolant system. What I can't find is instructions on how to do this. Any help would be appreciated.

[h&jeuropa]

Jay,
Be sure the expansion tank on the top of the engine is the highest point in the system.

You should also have a coolant overflow bottle connected to the expansion tank. The connection from the neck of the expansion tank should go to the bottom of the overflow bottle. The bottom of the overflow bottle should be below the top of the expansion tank.

With the engine cold, fill the system so the expansion tank is full to the top. Be sure there is coolant in the overflow bottle, perhaps half full. Run the engine up to temp and let cool down completely.

When the coolant heats up it will expand into the overflow bottle. When the coolant cools down, it will draw coolant in from the overflow bottle.

You may have to add coolant to the overflow bottle and get things hot and cool down a couple times. Eventually, the expansion tank will be completely full and the overflow bottle will have some coolant (maybe 1/4 full) when cold.

I never open the expansion tank unless the engine is cold and it is always full to the top. My coolant check on preflight is that there is coolant in the overflow bottle and I monitor that the level stays the same every preflight.

Hope this helps.

Jim Butcher

[JBPILOT]

Maybe you should explain your high CHT's. What are you seeing and when ? Sitting on ground, flying, warm day etc ?

[John-G]

Jay-

I'm curious .... are both your left & right cylinder heat temps reading high ... or just one of the two? Prior to engine start, are both the CHT readings displayed about the same?

If only one of the two temperature displays are reading high, you may be looking at a possible wiring/connector issue or even a bad sensor.

Another thought ... if both your CHT readings are high and this is a RV-12 you purchased from another owner, it's possible the previous owner installed the winterization kit Van's offers for the RV-12. The winterization kit includes a fixture that allows a removable plate to be installed in front of the upper portion of the coolant radiator ... this plate partially blocks airflow to the coolant radiator, thus generating higher water temperatures. If you are not the original builder, check to make sure the air blocking plate is not installed in front of the upper portion of the coolant radiator.

Be sure to let us know what the root cause of your issue when you find out.

Happy flying,

[rvbuilder2002]

Originally Posted by jaybhansen

I have read that I should purge the trapped air in the coolant system. What I can't find is instructions on how to do this. Any help would be appreciated.

When newly filled, there can be some air entrapment.

Weighting the tail down so that the tail tie down is held to the ground and shaking a wing tip up and down slightly while the cap is off of the expansion tank can sometimes help.

[NinerBikes]

Jay is building his own RV-12, this is a new one, I believe.

[jaybhansen]

new (even though it took me 4 years to build) 11.4 hobbs. I noticed both cht's being high on my last flight away from the airport. Then Tuesday during runup. By the way, on my taxi back to the hangar I blew my left tire. Airplanes are fun.

[Harvey L. Sorensen]

Mine did the same. I told a friend about it and he asked if I was using distilled water and I was not. I drained everything out and put in distilled and I lost around 15 degrees. I still cannot believe that. but time and the water must have been the cure.
RV-12, RV9A, 1939 Piper J-4, Cessna 150. sold the 9, J-4 am selling 150 keeping the RV-12.

[crashley]

Hi how hot are they getting and what is the oil temp

[jaybhansen]

It turns out that my cooling radiator was very low (empty). What I don't understand is that my overflow container still was half full. Isn't is supposed to supply more coolant when the radiator is lowering?