Really weird cooling issue today with no resolution

[C5Engineer 1170]

Well I had my first ever cooling issue today. I went out to try and fly on the last day of the year and the weather was absolutely perfect. She fired right up and I let it run in the chocks a little longer than I normally do since it was only about 30 degrees out. As I was taxiing out a buddy of mine came in thru the gate and he was waving frantically at me. I figured I was either dragging a fence behind me or something was wrong with my plane. I shut down and jumped out and coolant was pouring out from under the cowling!!! I turned the key back on to check the temp and the gauge was reading zero. Backing up a little bit I just installed this Westach water temp gauge 3 days ago. I did a run up but didn't fly and it worked perfectly. Anyways I pushed the plane back to the hangar and pulled the cowling.

I found nothing obvious. Another important note is that the lower rad hoses going to the belly radiator were cold as well as the bypass hose. I couldn't tell if the water came from the cap or the overflow bottle. The overflow bottle was only about 1/3 full but it had been shut down 20-30 mins at this point. I cleaned everything up and topped off the fluid and fired it up. Kept staring at the temp gauge and it never came up at all. The lower hoses warmed up and no fluid was flowing into the overflow bottle. I could put my hand on the head. I ran it at 4000 rpm for 15 minutes once and 20 minutes the second time and no leaks and no evidence it was overheating. The temp gauge stayed at zero so in between runs I swapped my old gauge back in which was still working when I pulled it out, it was just jumping around while I was flying or at full power. It didn't move at all either.

The only thing I can think of is the thermostat didn't open. This is the coldest day I've flown it with this new set up. What really has me baffled is the water temp gauge. I shot all the wires and checked and double checked everything and like I said I tried my other gauge. I can't help but think the two are related. I know if the sender is not covered in water it won't read but I don't see how I could have air down there at the bottom of the head. It didn't seem like it took that much water to top if back off after it was leaking so I guess it could have some air in the system.

I'm at a bit of a loss on this one guys. Any thoughts on what happened or what is still happening? I would of flown it in the pattern if I would have had a working gauge. Do senders go bad? I would of thought they would go full scale if it did. My dad told me to ground the wire from the sender and it should go full hot if the sender is working. Sorry for the story I just wanted to get in all the things I felt were pertinent.

[Fly-n-Low 181]

Senders do go bad, and I have had them also work the opposite in the range. Example an oil pressure gauge that worked backwards until I changed the sender...

I think the sender would read steam if it was that hot. Do you have an infrared temp gun? They are pretty cheap now. I use mine from anything from checking bearings, temp of engine blocks/heads, a/c work, oil coolers, etc, etc.

Mine has a laser to sight with. That way you can follow the hoses, thermostat housing, head, block, etc.

[C5Engineer 1170]

Just seems awfully coincidental that it happened at the same time the system spewed fluid for no apparent reason. 

[gregpro50 64]

Sounds like an air bubble in the coolant system.

[C5Engineer 1170]

I will pull the pump plug and try the tail lift trick next time out.

[C5Engineer 1170]

Any other easy ways to test the sender besides grounding it and seeing if the needle goes full deflection?

[Av8r3400 1179]

Multimeter connected with sender in a pan of water on the stove.  Check resistance at different temperatures.

Cross check with a cooking thermometer.

[Knuckledragger 135]

I wonder if there was a chunk of ice in the belly rad lines...

If so, the water did indeed come from the overflow bottle (more technically, the 'expansion tank').  Then as the system cooled and contracted, 2/3 of the fluid in the bottle got sucked back into the system.  This is to be expected.  Given the hypothesis that the belly line was plugged with ice: the thermostat would open as normal, but no circulation would take place allowing a rapid rise in temps and pressures in one specific area.  This would lead to the release of pressurized fluid into the overflow/expansion tank (AKA Puke Tank).

I'm glad your buddy came with his arms!  Under this scenario, your engine would have suffered an overheat condition and possibly seized.

Since it was below freezing, I would include a few squeezes of the radiator hoses especially around the belly radiator to check for frozen lines in your pre-flight checks.

Edited 1 Jan 2016 by Knuckledragger

[Av8r_Sed 82]

I vote for air trapped in the system.  Is your thermostat drilled with a bypass hole?  The hole allows for purging air from the system when the thermostat is closed.  It might also allow the thermostat to heat and open quicker with the little bit of flow it allows.

 

[Emory Bored 61]

I'm not sure what the temp was at Vacaville yesterday but I know that my hangar doesn't freeze at 20F or even lower unless it sit's that way for weeks.  Sun on the hangar door keeps things 20F warmer than the outside.  Tough to imagine coolant with anti-freeze in it freezing up inside a hangar.  

[C5Engineer 1170]

I'm not sure what the temp was at Vacaville yesterday but I know that my hangar doesn't freeze at 20F or even lower unless it sit's that way for weeks.  Sun on the hangar door keeps things 20F warmer than the outside.  Tough to imagine coolant with anti-freeze in it freezing up inside a hangar.  

There was frost on the truck but it wasn't very cold. I am going out again tomorrow to mess around with it. A new sender is $18. Will try that next. I think that they are related somehow. Way to much coincidence that after 3 motors and 400 hrs the sender died at the exact same time the engine blew coolant. Anything is possible but I am skeptical and really hoping I find the cause. Nothing worse than a problem you can't duplicate and wondering when it's going to happen again. 

[C5Engineer 1170]

Thought of one more piece of the puzzle. Last week I swapped water temp gauges from an old CPS one to a Westach. The back was identical. I test ran it but didn't fly but it worked perfect. It was also working as I taxied out yesterday. 

[Knuckledragger 135]

I'm not sure what the temp was at Vacaville yesterday but I know that my hangar doesn't freeze at 20F or even lower unless it sit's that way for weeks.  Sun on the hangar door keeps things 20F warmer than the outside.  Tough to imagine coolant with anti-freeze in it freezing up inside a hangar.  

Good points.  We lose perspective down here in Florida.  People here break out the parkas when it dips down into the 50's.

Way to much coincidence that after 3 motors and 400 hrs the sender died at the exact same time the engine blew coolant.

Agreed.  I'm now in the air in the system camp, and I suspect a bad thermostat.

[C5Engineer 1170]

I emailed Rotax Rick to see what he does with the T stat during a rebuild. I imagine probably nothing. Going to replace my rad cap too. 13lb I believe?

[thebriman 69]

i used a 13lb cap on mine last year.  

[thebriman 69]

i used a Motorad T-13R cap btw

[C5Engineer 1170]

Mine had a Moto Rad T7 on it. Guy cross flowed it over to another cap but I am thinking its 7lb too. I did everything I could think of to burp out any air including tipping it up almost on her nose. I've now ran it 4 times from a cold start with no issues. Still no temp indication. I am replacing it with a Westach one this weekend. Perhaps the Westach and Falcon are not compatible? I will report back.

[C5Engineer 1170]

All fixed up. I cross checked the part number and the cap that was on the Kitfox parts I picked up for my conversion was only 7lbs and it was old. I put in a new 13lb cap. I swapped the sender out for a Westach one and fired it up and temp gauge came right up. No leaks. So I think what I had was a combination of a bad cap and an incompatible sender. Can't say for certain but appears that Westach and Falcon senders are not compatible. Weather was terrible so I didn't fly but I wiped down the whole plane, cleaned the windows and fixed a couple small things. Never been so excited to see water temp Great day at the hangar!

 

Edited 10 Jan 2016 by C5Engineer

[lostman 198]

Glad to see you worked that out quickly. 

[TJay 1041]

Nice Pocket knife next to the water temp!

[C5Engineer 1170]

Nice Pocket knife next to the water temp!

I keep my knife and 0-15 psi pressure gauge on the right side of the panel. 

[Av8r3400 1179]

Did you ever get anywhere with the "Ghetto Cowl" project?

[C5Engineer 1170]

Did you ever get anywhere with the "Ghetto Cowl" project?

Nope. Conditional due in Feb so it's time. WX is finally deciding to be winter here so that helps. 

[KFfan 151]

Thanks for passing on info on the resolution

 

Lou