Leaking Antifreeze

[akarmy]

Wondering how the rest of you have your overflow bottle's setup? Mine is mounted high on the left side of the firewall in what I think is the standard location for the series 7 and supersport. What I'm finding is a puddle of fluid on the hanger floor after flying. When looking I see the path of it coming down the firewall from the bottle. My suspicion is the hole in the cap. I'm one who's known to do a bit of horsing around with my Kitfox and I'm wondering if the zero g (momentary at best) is squirting fluid out the top of the cap? I have an 1/8" hole drilled into the cap I presume as a vent. If that's the problem maybe we need something more sophisticated to vent the bottle.

How about the rest of you?

[Dave S]

Hi Andy,

With our S7 912ULS - same setup with the overflow bottle - never had any leakage out of the bottle.

The hole in the cap of the overflow bottle has to be there for pressure equalization due to fluid expansion, changes in air pressure with altitude & temp.

Overfilling could be a possibility. I set the coolant level at just a bit above the minimum line on the bottle when cold. The coolant expands quite a lot with heating. Filling to the MAX line when cool is not necessary and provides no benefit - except maybe making the nose heavier by 6 oz.. Even if some blows overboard in flight due to overfilling - there would probably be enough cool down by the time you glide to a landing and taxi back to the hangar so it wouldn't look too full at that point.

Other possibilities could include the integrity of the overflow bottle, cap seal to the overflow bottle and/or the hose attachment at the overflow bottle from the spider tank. A rivet or other fastener wearing into the tank could make a hole in the tank.

My comments relate to the overflow bottle - assuming that is where the leak is coming from.

For the record - I did have a little leakage from the radiator hoses during extremely cold weather - typically a drop or two clinging to the joint of the rubber hose and aluminum pipe - adjusting the hose clamps a bit takes care of that. This never happened after flying - only after an overnight cold soak. I still have not warmed up to the screw clamps - eventually I plan on getting some spring clamps like on the hoses to the heads with the hope that spring clamps are better at self adjusting with material expansion/contraction.

I am not real sure what horsing around is and I don't know what effect that has on the KItfox design related to coolant leakage.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp

[HighWing]

I flew 900 hours in my first Model IV and had overflow issues from time to time. It was always after I "topped up" the coolant in the bottle. I found that if I put more then an inch or so at the bottom, it would expand and blow out. The early bottles were probably 8 oz wash bottles and the larger Rotax bottles supplied now will catch a lot more fluid, but I still suspect that you are filling it too high.

Keep in mind that the bottle is to catch excess when the engine is hot, so practically, anything in the bottle to keep the system from sucking air after cool down is enough. You just don't want to see an empty bottle with a cold engine.

[akarmy]

I found that if I put more then an inch or so at the bottom, it would expand and blow out.

I think that may be it. Mine was running almost empty (cold) so I gave it a couple of inches in the bottle (new style) and over a number of flights it has emptied itself down to say 1/4 - 1/2 inch level.

Thanks!

[wildirishtime]

... so this overflow bottle, should my Kitfox 5 be drawing BACK in from that bottle when the engine cools or not? (or is it just an 'overlow catcher')?

I installed the new 1.2bar rad cap, but whenever I run the engine up to upper end of normal temps (taping over the rad) it pushes OUT into the overflow and when I check my black "reservoir" where the spider of coolant lines divide on the top of the engine, and it's only 1/2" up from the bottom of that tank!

What's the story here? How is it supposed to be, and how can I test it on the ground? If I look inside the black reservoir, the fitting for the overflow bottle tube appears well above the thermostat seal....so I'm having trouble visualizing how it works... isn't the thermostat seal SEALING TIGHT when cold?

Thanks! ~Wild

[Dave S]

Wild,

It is supposed to suck coolant back in to the system on cool down - the overflow bottle is not just a catcher.

A couple things to think about.

1) If the system is working correctly: A person will fill the spider tank to the top with the engine cold - put on the radiator cap - top off the overflow bottle to at least the cold line. If all is well - a couple hot/cold cycles should result in the coolant being sucked back into the system so the engine/spider tank has no airspace - usually some coolant gets sucked back to fill 100% and a person needs to top off the overflow bottle again and all is well after that with predictable cold and hot volumes showing in the overflow bottle.

2) If the system is not working correctly - a) if the coolant is boiling in the system (overheating) it may push out so much that you could get the effect you are indicating - depends. In an overheating situation - it is possible to blow out the overflow completely and end up with a very small amount of coolant in the bottom of the overflow bottle with air getting sucked back instead of coolant. b) You mention a thermostat???? do you have a thermostat in the system in addition to the normal radiator and coolant line plumbing?

Pretty hard to diagnose a system from afar; but, it doesn't sound like everything is working correctly with the radiator taped up. Might want to consider if the temp gauge is calibrated and be sure it isn't misleading you. Don't know where the location of your probe is but it is not impossible to have the probe/gauge say OK and have some boiling going on. What are you using for coolant - that can have an effect on boiling point?

Just a couple ideas to think about; but, a person needs to be the one looking at the machine to figure it out for sure.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp

[wildirishtime]

...yea that was a typo, my last sentance should have read:

doesn't the rad cap seal SEALING DOWN TIGHT when cold?

I tend to open the spider tank and stick my finger in on a normal day,
and I feel water about 1" down from the top top edge, and never saw
any transfer to or from the overflow bottle.

...but after taping over my rad and achieving 200deg temps on my
CHT probe (thus actually getting some cabin heat now!) I was pushing
water out of the vent hole in the overflow bottle. When I then checked
my spider tank when cold, none of the fluid pulled back in.... thus
leaving only 1/2" in the spider tank and a full overhaul bottle.

Thoughts? methods to test? I suppose I should pull the overflow line
off the spider tank and suck with my mouth to make sure fluid will pull back in. Does that overflow tube need to be FULL of coolant? Or
can air pockets exist in the tube going to the overflow bottle? Seems like even with air it SHOULD suck back in when it cools....

Lastly, it's 50/50 Dex.

Thanks guys! ~Wild

[Monocock]

Hi there. I had a similar problem with my set up so thought I would let you know what happened.

Firstly I bought a new 1.2 bar rad cap and the coolant still would not suck back into the spider from the overflow bottle when she cooled off after flying.

Next, I checked for any blockages in the pipe from the spider to the overflow bottle and confirmed it was clear. I knew it must be because the coolant was travelling to the overflow when she was warm as it should, but not back the other way.

I figured that there wasn't any pressure being held in the spider and that as the coolant gradually cooled after flying, it wasn't able to get back to the spider from the overflow. So, I gave the top of the filler spout on the spider (where it meets the pressure seal on the rad cap) a really good clean up. There was a very slight crust of congealed coolant which came off after a rub with some WD40. This solved the problem and now the coolant sucks back to the spider when she cools off and when I pre-flight her there is coolant right to the top in the spider each time.

I would also suggest that if this works for you, that you make sure the rad cap is seated in exactly the same position each time you put it back on (ie have the engraved "1.2 Bar" words always pointing the same way). The pressure seal seems to do a better job if it is in exactly the same place all the time and you will see there is a slight indent in the seal where it fits on the spider mouth.

Hope this works for you too.

[wildirishtime]

Thanks for the reply. Can someone explain exactly what seals and what opens when it's hot at and cold. THe upper 'lip' seal must be sealed to PULL from the overflow tank, but does that spring and lower seal on the rad cap expand DOWN and UP based on temperature as well as a 1.2bar pressure release??

An exact understanding of it's operation will help me troubleshoot it.....

Lastly, can I heat the spider tank with a heatgun to test the push/pull of coolant? Anyone done this?

~Wild

[Monocock]

AIUI, there are two seals. One is permanently sealed to stop water escaping the spider tank, whether hot or cold.

The second seal is the one I mentioned above. It sits on the lower ledge that you can see when you look into the top of the spider tank filler hole. The spring mounted seal on the rad cap butts up on this ledge. As the water heats up and the pressure builds, this spring contracts, allowing the seal to be broken between the circular rubber seal on the end of the spring and the ledge inside the filler hole. Coolant expands out of the side hole in the filler neck and travels to the overflow bottle. While this is happening the main seal is holding (or should be holding) the overall pressure in the system.

When you shut down, the spring will still be up and will very slowly go back down as the coolant drops back to ambient temperature. As the coolant cools off, it retracts in size, and the excess coolant from the over flow bottle returns to the spider tank via the side hole in the filler neck. All being healthy, by the time the coolant has cooled right off, you should have a full spider tank and a level in the over flow bottle the same as before you flew.

If there is a poor main seal in the rad cap, the system will loose pressure soon after shutdown, thereby not providing the pressure to allow the over flow coolant to be sucked back.

Are you sure you're not checking it too soon after shutdown? In the summer I find it can take as long as 24 hours for the coolant to properly travel back to the spider tank, especially if I have a dust cover over the top cowl that keeps the heat in the engine bay while it sits in the hangar. As soon as you open the rad cap, you will loose any sucking pressure and will then need to manually top up the spider tank and perhaps even siphon some from the over flow bottle.

Does this make any sense?!!!!!