109jb

No worries.  I know a lot of people would just go with what is known to work, which in this case would be insuring a thermostat is installed and blocking off the radiator as required.  I tend to overdo but it is at least always a fun trip. Since I'm getting a close by hangar soon I should be able to finally start whittling away at the list of changes I want to make to the plane. I'll be sure to post my results with this.

That is absolutely going to happen. As I said before I suspect that the engine doesn't have a thermostat.  If it doesn't then that would explain what happened during my cold weather flight. I couldn't check because at the airport I'm keeping it at I didn't have tools or a catch pan to drain coolant to check. I haven't been back out there since that flight. That place (a friends strip) is 30 minutes away but the good news is that the airport 5 minutes away called Friday and had a hangar open up.  I will first put the new one I have on my counter in  and as soon as I get a good day weather wise I will head down and move the plane to its new apartment. Any mods will happen after it gets to its new home.  I had always planned on re-doing the cooling system because although it works and doesn't leak, the workmanship isn't the best.

I disagree with the thought that the small hole in the thermostat is for flow. Sure, the fact that it is there means that even with a closed thermostat there will be a tiny amount of flow but that ain't why its there. It is an old wives tale that it is for flow, and it is really only to prevent an air pocket forming around the pill of the thermostat. If an air pocket forms, the thermostat will not open at the correct time. As a matter of fact many thermostats come with a "jiggle valve" in that hole. The purpose of that valve is to let air escape, but not allow water flow during operation.  Also, in the case of my airplane with the cylinder head facing up I have the 3/16" vent line connected to the top of the head which provides a flow path for the coolant bypassing the thermostat anyway. This line is also really only to purge air.
If I wasn't respecting it I wouldn't have posted about being concerned about it in the first place. My concern about the water temperature is the whole point of starting this thread.
I found the spec for the inlet vs outlet temp in the Rotax install manual. Optimum is pump inlet temp 5 to 9 deg below the head outlet temp with an 11 deg maximum differential. The manual refers to it as a radiator inlet to radiator outlet temperature, but what really matters is what the engine sees. So with this information I could put the secondary thermostat on the water pump side with a 155 thermostat and a 160 degree stat in the head giving the optimum differential. The secondary valve would operate like a mixing valve blending the hotter water flowing through the heater cores with the colder water flowing through the radiator. 
 

I don't know about other Kitfoxes and can only speak about the one that I have but I've also been thinking about going to a larger tailwheel on my Kitfox IV. This thread prompted me to do a little W&B check. I currently have the 6" Matco solid wheel tailwheel that matco says weighs 4.75 lbs. The 8" wide pneumatic dual fork is 8.3 lbs for a difference of 3.55 lbs.  Running some W&B scenarios, adding 3.55 lbs at the tail would basically reduce the amount of weight I can carry in the baggage area by about 20 pounds. Now this is for a Rotax 582 powered Kitfox IV so probably one of the lightest engines and most tail heavy configurations. To get the full baggage carrying capacity back I could relocate the battery from its current spot behind the seat to the firewall. That would get it back to being able to carry full baggage and load up pilot and fuel to max gross.  So for me that would be what is needed. 

Drilling a small hole in the thermostat has nothing to do with flow. It is to allow air to escape when filling the system.

I'm sure you are right about the engine thermostat making things work for the engine as you have a lot more experience with the 582 than I do.  However, I'm not just thinking about the engine staying warm but also myself staying warm. Like you, I also like to keep things as simple as possible unless there is a clear benefit for doing otherwise.  In the case of the secondary thermostat I see the potential benefits and disadvantages as follows:
Benefits:
1. Controlled flow of heated coolant through heater cores (ie: Better heat output)
2. Isolation of the radiator will help maintain heat within the engine. 
Disadvantages:
1. If the secondary thermostat fails closed, the radiator will be isolated and unable to cool the coolant.
The only disadvantage I see is the potential failure of the secondary thermostat in the closed position.  Failure in the open position wouldn't be a problem and the only other issue would be a leak. I'm not worried about it leaking, so that leaves the closed failure. The most common failure mode for a thermostat is to fail open, so this mode would be essentially no different that not having a secondary thermostat.  If it fails closed, then the flow to the radiator will be blocked. While not as common a failure mode, it has to be considered. In my case, with 2 fairly large heater cores would still be in the flow even with a stuck closed secondary thermostat. Although I can't prove it, I feel that the heater cores with the fans running would be large enough to allow the engine to be operated at a power setting that would allow sustained flight.  This airplane doesn't need a lot of power to stay aloft. 
Basically, at this point I still see enough potential benefit and not enough disadvantage that I'm still leaning toward including the secondary thermostat.
 

I don't see how the secondary thermostat could do any different than the primary thermostat.. If there were  only the primary thermostat in the system and the scenario you describe happens where the radiator liquid gets too cold, even the primary opening would allow for your "slug" of cold water.  Since it doesn't happen with a single thermostat system, I fail to see how it would be any different with the second thermostat in there.  
Additionally, the flow through the heater cores  is unobstructed and when the secondary thermostat opens, it opens in response to the heat of the coolant around the thermostat pill.  In other words, it doesn't go from closed to full open like a light switch. This behavior would tend to modulate the flow through the radiator and it would mix with the coolant from the heater cores on the opposite side moderating the temp of the coolant going back to the engine.  Quickly thinking about it seems that this would be even better than without the secondary thermostat since without it, most of the coolant flow is going through the radiator due to the fact that it has larger hoses, and has a straight path rather than having to run through tees. The radiator is the path of least resistance. That right there sets it up so that it cools faster than wanted.
All that said, lets assume what you describe is possible. Again quickly thinking about it I think it can easily be countered by installing the secondary thermostat in place of the return tee rather than the supply tee. Facing the thermostat pill so it faces the engine means that once again the flow through the heater cores is unobstructed and the thermostat pill would be in the continuous flow through the heater cores and would open if the returning coolant got too hot. Conversely, it would close if the coolant got too cold. The problem I see with this is selecting the right temp thermostat.  On the supply side the primary and the secondary thermostats would only be a few inches apart in my installation and therefore I could use a 160 deg thermostat for both the primary and secondary.  With the secondary on the return side, its thermostat should be a lower temp one since the coolant has lost heat running through the heater cores/radiator. But what temp??  
I got the 175 jets just in case. The shipping is a killer and I decided to play  it safe. I agree that I will probably never use them but if I do need them I have them.
When I was descending I was at about 45 mph indicated and I was keeping as much power as I could in , but with just me on board it took very little power before I wasn't descending anymore.  I'm sure I could have slowed it down more but since I have so few hours in the airplane I was not comfortable doing that just yet.
I'm not sure I even have a thermostat in it right now, but I ordered the OMC 160 degree stat for the engine. If I do wind up using the secondary thermostat I will use a 160 there if its on the same side as the engine thermostat.
I'm not opposed to blocking off the radiator if that's what it takes.  I am even thinking that what I may do next year is put the fiberglass radiator duct that Kitfox sells on my airplane and put a door on the inlet like a carburetor butterfly. I don't think it will come to it but if I have to I'll block the radiator.
I think the reason that the hot water heaters aren't working up to snuff is precisely because of the reduced flow through the cores. With flow going through the radiator as the path of least resistance, there isn't much of the engine heat making it to the heater cores. The secondary thermostat would solve that and should make the heaters work much better. I know it worked on my father's UTV.
 
Thanks for the responses. Don't think I am totally discounting them. Your responses allow me to think through the situation so I can make a better informed decision which way to go. Nothing is carved in stone so to speak yet.

Looked at your heat muff build and it looks good. Would be really easy for inspections.

Yep. I was thankful that I keep the airplane at my friends grass strip right now with very little traffic to worry about.  I made my approach knowing that if I had to add power I could risk a cold seize. fortunately I planned the approach well and never had to add power except to taxi in which I did after letting it warm up again.
I figured it was a stuck open thermostat. It never even occurred to me that the engine might not have a thermostat installed and I only found out this evening that they shipped without them. I didn't have a drain bucket to drain the coolant or I would have checked it. 
As for the cabin heat, I think the secondary thermostat will solve the problem of keeping enough heat in the engine. I went ahead and ordered one, and I ordered a new thermostat for the cylinder head. Once installed, if the secondary thermostat is closed and the engine is still cooling off with the heater fans running I may have to shut the cabin heat off for a descent or something but I don't mind turning off heat for short periods anyway. I take the approach that when I fly I dress for the outside conditions just in case I wind up in those outside conditions.  I don't think that will be the case though. Time will tell. 
If the above doesn't work then I will consider a heat muff approach, but I'm not real fond of them from almost being killed by one in a 1969 VW Beetle when I was a kid. Over the years I've also worked several accidents with NTSB that were CO related. I'm not totally against heat muff type heaters, but if I can avoid I will.  If I do go that route I will definitely have a CO detector in the airplane..
The larger jets are ordered. The stock 165 jets with needle raised full up works in all regimes except power on descents. I ordered 170 and 175 mains. The chart says 170's will work down to -4 deg F which should be enough but I got the 175's too.
Hopefully my plan will work out. 

I found it. Hopefully this will work.
Kitfox_Pack_News_July1990.pdf

Both the square pump and round pump and several others have been made for many many years. I've had both over the years on snowmobiles. I have the square one on a 2001 Arctic Cat in my barn right now. The square one is 31 liters per hour and the round one is 35 liters per hour. Both are genuine mikuni.

So you have a size comparison, here is what those look like on a Kitfox IV. They are mounted on the 8" Douglas ATV wheels.
 
 

I love the airplane.  Mine is a Kifox IV 1050 with a Rotax 582 for power. The logs say it is 560 lbs empty, but I haven't re-weighed it yet.  I've only got about 15 hours in it so far. I've been very busy with work and have had a few things that slowed me down. I've been working on "fixing" things too.  Nothing that is really "wrong", but stuff that isn't up to my standards.  
As for actually flying it, here are my impressions:
I love the performance that can be eeked out of 65 hp. The takeoff and climb performance is great as is the landing performance.  That said, I'm at 600 ft MSL field elevation, so those at higher altitudes may disagree.Mine is definitely pretty close to neutral in yaw. It isn't difficult to keep the ball centered, but does require constant "butt awake" time. I have read that enlarging the rudder improves this dramatically. I plan to do this mod but may not happen until next spring. I'm planning to go about 8" taller and 2" wider on the rudder. I'll add an aerodynamic counterbalance horn on top so I don't have to modify the vertical stabilizer. I have the stock landing gear running the 8" Douglas wheels and 21X12X8 smooth ATV tires and it seems fine. Maybe a little narrow but pretty well behaved. Just make sure you don't land in a crab and all will be fine. I may build a new gear but his one is fine for now. I'd guess the ATV tires make it behave a little better than if it had smaller tires. I also have the 6" solid tire Matco tailwheel and I am looking at converting over to an 8" pneumatic tire. I'm a former machinist and have a shop, so  will probably make a new fork that will accept the larger tire. I added dual brakes and they are weak. Mine currently has the stock rudder pedal geometry, so this will be getting changed. I added dual brakes, and should have fixed the geometry then, but I didn't think it could be as bad as it is. I can't hold more than about 3/4 throttle. The good news is you can't lock the brakes, but you also won't be getting much brake help if it starts going a bit sideways. My recommendation would be to ditch the MC-1 master cylinders and go to MC-4's so that the geometry can be fixed. I'm going to do this mod soon. There are plenty of threads about improving brake effectiveness but it boils down to the geometry between the pedal and the master cylinder. Many have said that the elevator on these earlier IV's isn't powerful enough but I haven't had any problem. As I said I have the 582 which is one of the lightest options, so I think those running out of elevator may be the ones with heavier engines on the front and hence a more nose-heavy airplane.As for flying, I've been doing a lot of takeoff and landing practice. I started off approaching at 60 mph with 0 deg flap. I've now worked down to 50 mph approach with 1/2 flaps and that seems to work much better.  I've mostly been 3 pointing it but it seems to wheel land fine. I'm just rusty having been out of flying for too long. She ain't gonna win any races, but then again I don't think anyone who buys one is buying to go fast.I like to fly for fun and have stayed away from strong winds. About the most I've had it out in is maybe 15 kts quartering headwind.  It seems to me that the airplane handles the wind while flying fine, but it is so light that taxiing may be more of a problem sometimes.  I certainly would not take this airplane out in the kind of wind I've had my Sonerai in.Bottom line is that it is a fun, well performing, fair weather airplane as far as I am concerned. It will definitely get into places other airplanes can't/shouldn't.  

I have a Kitfox IV 1050 that the W&B says weighs 560 pounds empty. Thinking about some of my flights with my instructor I think we were probably 100 lbs over gross once or twice and the airplane performed fine. This was back in warmer weather about 85 deg F at 600 ft msl field elevation. Performance wise with the 65 hp Rotax 582, I didn see a problem. 
The manual for my airplane says it is stressed for ultimate loads of +5.7 g, -2.85 g at 1050 lbs. So if we ran this airplane at 1200 lbs without any mods it would be good for an ultimate load of 5.7*1050/1200 = 4.99 g and -2.85*1050/1200 = -2.5 g. With a 1.5 safety factor it would be good for +3.325 g, -1.66 g. A little below what the FAA considers a "normal" category airplane which is +3.8 g, -1.52 g. Another way to look at it would be to say it is still good for 3.8 g, but with a 1.3 safety factor rather than 1.5.
The other consideration is performance which could be the limiting factor on gross weight, but as I said, from my little flying of a Kitfox with just 65 hp I just can't see this as an issue, at least at lower density altitudes.
 
I too want to get amphibious floats at some point. I have read that when it was Denny Aircraft that there was a document that authorized a float equipped Kitfox IV 1050 to operate to 1200.  The mention of this document came from John McBean on a post over on the TeamKitfox forums, so I believe it is real. I have searched for this document, but have not found it anywhere. If anyone has this document I would like a copy.  Even so, I will likely at some point do some strengthening mods on the airplane.
As for the comments that the max gross weight is set in stone by the original builder, I don't buy it.  I won't get into it but IMO, the official aircraft file is the one in OKC, and even if a FSDO did save some paper about a homebuilt it doesn't matter. For one, even if this is the case, there is about a 0.0001% chance that the paper at the FSDO will ever see the light of day even if something happens. Second, I have all the paper submitted for the Sonerai that i built and not one piece of paper says anything about weight. There is nothing about weight in the file from OKC either.  My Sonerai was inspected by a MIDO inspector and the MIDO office he worked at closed. What do you think the chances are that they could even find any paper on my airplane if it ever existed. Bottom line, the weight is set in phase 1 testing and if you want to change the "authorized" weight it it is just a matter of re-entering phase 1 and verifying it and record it in the aircraft records. Now whether that new weight is safe or not is another question.
In my opinion, I am not concerned about performance at higher weights, and if I happen to exceed the 1050 once in a while I'm not concerned about structural strength, but if I were to operate above 1050 regularly I would do some mods including beefed up carry  through tubes, strengthened strut attach and heavier struts. None of these are particularly hard for someone with some welding experience.  
I have my fire suit on

Now that I have a new battery and can actually start my engine, I'm back to deciding whether or not to get a clutch. The only thing stopping me at this point is the fact that you cannot turn the engine by turning the prop.  On sleds and this 582 I have always done piston checks for various reasons by looking in the ports while rolling the engine around. With no engagement to the prop and no pull start, I don't see a easy way to accomplish it. Seems to me that one would have to pull the gearbox to rotate the engine. So, for you guys with clutches, how are you handling things like checking the pistons when looking through exhaust ports? 
Oh and that possible deal on the 912 fell through.

Thanks. Already has synthetic gear lube in it.  I think the main problem was a battery not really intended to start engines. 

I made a decision.
My old battery is a 18 AH 12180 AGM battery that is found in older jump start packs, emergency lighting, UPS, etc. It gives no indication that it is bad other than it can't crank my 582 fast enough to start at 20 deg F. I couldn't find a single spec for this battery regarding CCA, HCA, PHCA, or anything similar. 
I decided to go with a EXT18L AGM motorcycle battery for now for a couple reasons.  One is that this is the same battery I have in my bike and it has been in there for 4 seasons so far and still cranks the big 1700 cc twin over just fine. I start the bike every couple weeks in the winter and it is in the unheated section of my barn and it has no problem withstarting the bike even at temps as low as 0 deg F. Spec wise, the EXT18L is 340 CCA, 20 AH, 18 lbs.  I really debated about the PC680, but decided that the double CCA (170 for the PC680) was worth the extra weight. The PC680 is 15.4 lbs and the battery that I'm replacing is 12.5. If the engien starts when I want it to the 5.5 pound weight gain will be fine with me. Price came in there a little as the EXT81L is about 1/2 the price.  I had to make a new battery tray to accommodate the larger size but I figure the EXT18L is as large as needed and if I ever want to go to a PC680 I can simply install it. I made the tray such that I can put in any battery the same size or smaller than the EXT18L.
Today isn't a great test since temps here are in the 40 deg F range, but with the new battery the engine cranks over about 600 rpm compared to 350 at best with the old battery. Those were tests with the gas turned off to see how fast the cranking was. The test with the old battery  was after it was fully charged from a tender, and the new battery was as received after buying it. The voltmeter read 12.2V on the new battery so this wasn't even fully charged.
This isn't a condemnation of the PC680 in any way.  The old battery was an unknown in terms of cranking amps and I just decided to maximize cranking amps. It could very well be that the generic 12180 battery is very weak on CCA, and it isn't really intended to be a starting battery as far as I'm concerned. The PC680 is a 170 CCA battery and that may well be plenty. I don't see why it won't, but if the EXT18L battery doesn't last I'll probably try the PC680 or a LiFePO4. The LiFePO4 EarthX batteries are just too high price for me right at the moment. Perhaps down the road.

My Kitfox IV has them too. In addition to my Kitfox, I fly a Sonerai IIL that has wings almost entirely riveted together with SS pop rivets. The SS pop rivets have a higher shear strength than a same diameter AN rivet.
I would be more worried about dissimilar metal corrosion between the aluminum and steel tubes 

That's too bad. It looked like a decent airplane that would not have taken a lot to get back in the air.

I know that felt great!!!!!

My Kitfox IV with 582 weighs 560 according to the logbooks. I haven't re-weighed it but I can't see where any additional weight would have been added after the original build.  At that weight it performs fantastically. With 2 on board with about 1/2 tanks (26 gallon capacity), 70 deg F, at 700 ft field elevation the climb after takeoff is about 1000 ft/min. It isn't fast, but I didn't expect it to be. I'm still feeling mine out but I figure it will be about a 90 mph cruise the way it is. What really impresses me is the takeoff, landing and climb performance. Its a blast challenging myself on short takeoffs and landings. I just bought mine earlier this year and have been flying it only since October.  Weather, family obligations and work have kept me down to only about 15 hours in it so far but it is definitely a fun airplane.
As far as the logs, it really isn't as big a deal on a homebuilt as it is on a production airplane.  Production airplanes have to show AD compliance, time limited parts, etc. A homebuilt, especially one with a non-certified engine doesn't have AD's and are pretty much always "on-condition". The only drawback I see for yours is that you may not have a good handle on the time that 2-stroke has on it. They are 300 hour TBO, so you might want to plan for an overhaul sooner rather than later. As long as you have the things you already listed you are fine with just a new condition inspection.
I see in your signature line you are also building a Sonerai IIL. My Kitfox is the same colors as yours and I built a Sonerail IIL completing it in 1992. For a variety of reasons/excuses, I only have about 350 hours on it to this day, but it will be back in the air next spring (no cabin heat). Along the way I converted it to a single seat. Here it is with 2 of my excuses for not flying it more.
Your Kitfox looks great.  Hope it is as nice as th pictures show.

Its serial number 1420 which is before mine at serial number 1488, so it is going to be a 1050 gross weight model IV Kitfox

Looks like a very nice airplane undoubtedly 2-stroke powered. Looks like he lives in Florida. If I was closer I'd have to consider it.

yep. That's exactly what my research showed. In warmer climates they look great, but not so much for cold weather ops