TKS Fluid Level Indication Problem

[Yooper Rocketman]

As promised, here is a report on a TKS problem that appears to be pretty common and expensive to repair. My level indicator starting acting up on start up, staying a zero sometimes, then reading normally after getting up to cruise altitude. One time doing this was with my maintenance shop owner on a medical flight after an approach into Houghton, MI in some serious icing. We taxied out to leave and the fluid level stuck at zero. We were about to call my kid (going to college there ) and have him bring over his car (well actually my car if you know what I mean) when we decided to taxi the plane a some more jerking it a bit left and right, and the level went back up to our known amount.

So, during last years annual, being done by my maintenance shop ( I was too busy with my project ) they asked me if I wanted the level indicator system repaired. I told them to call and see what it likely was and give me a quote to fix it. Well, CAV Aerospace told them it was the sender, which was $800 and that it was a real bitch to change. My quote came in at $2,000, so I deferred to fix at that time.

This year I decided to do my own annual. To clarify, my hangar partner and best friend is an A&P, another friend is an IA, and I have been doing owner maintenance under these two for over 20 years. Both this IA and the one owning the maintenance shop have said they would sign off my experience for my A&P license, as I have all over 5,000 hours of documented aircraft maintenance experience. So, I decided to tackle the fuel sender during the annual this year and called CAV to see if this could be a fluid logged float. The tech support guy said yes, and it COULD be repaired if I was willing to try it.

I pulled the sender out, based on his instructions, and found the design is lacking to say the least. The float is two parts, the inside support member is plastic and resembles a miniature bar bell in shape. Then a composite sleeve slides over the the plastic support, over an o-ring on each end of the plastic "bar bell". When I slid the sleeve off, I got a lap full of TKS fluid. We found new o-rings, just a few thousands bigger, and reassembled it. The original factory assembly has some PRC wiped on the ends as well. I resealed with a better Locktite product called Hysol, which is used in composite construction in the aerospace field.

The removal took about 3 hours, and reassembly was about half that time. It probably took longer to calibrate the sender than to install it. The quote from my maintenance shop was based on what CAV told them, and I do not fault them at all for covering themselves. I know if it actually took less time, he would have charged less as well. I have that kind of relationship with him. But, most shops are going to quote this job high, especially if they talk to CAV before doing it.

Just wanted to share with other TKS owners that this repair can be done for a lot less than most shops will quote.

[BorealOne]

Good to know! Thanks for the post!

Sent from my iPad using Tapatalk

[aviatoreb]

Thank you Tom.

 

That is a very interesting discussion - and I am planning to find this very thread again if I ever need it.

 

There is no specific preventive maintenance though, but a good inexpensive repair.

[Nathan Peterson]

Tom,

Did you take some pic's while you were working?  Thank you.

 

Nate

[Yooper Rocketman]

Tom,

Did you take some pic's while you were working?  Thank you.

 

Nate

No, thought of that after the repair was done. I am still using one of those (came over on the Mayflower) flip phones, so unless I think about it and grab my camera, it's not going get snapped.

[M016576]

Outstanding info, thanks!

[M20R]

How hard was it to remove and reinstall the sender?

[Yooper Rocketman]

How hard was it to remove and reinstall the sender?

First you need to drain the tank. I pulled the hose off the filler neck (from the back side )and stuffed it through an access hole in the bottom of the fuselage, catching the fluid in a jug with a paint filter in the neck. Once empty (well mostly empty) I popped the back seat out and a few of the taped in aluminum access panels. There are 5 screws holding the sender in, which are not too bad to remove. I also removed the wiring harness, but be careful, there are some little metal tabs that bridge the screw holes to the center plug. They could be lost really easy. I marked orientation on the sender to the tank, but with 5 holes, not sure you could miss install it anyway.

The difficult part is the fact that the factory ( or installer) uses PRC on the gasket. I was warned it would be a challenge getting the sender broke free from the tank, and access is very limited. The CAV Aerospace tech said he used an angled set of needle nose pliers to work and break the seal. I used several different dental picks with 90 degree tips on them. He said you will likely distort the flange, but just get it out and then straighten it once you have access to a vice or bench (which I did). We made a new gasket out of gasket material and, like I said, calibrating the sender for reinstallation took longer than the actual install. The transmission of fuel level from the sender to the wiring is done magnetically, so orientation of the wiring / electronic module to the actual sender determines proper level indications through out the sweep of the float.

I suspect the total job took me 5 hours.

Hope this is what you were looking for?

[N177MC]

Thanks to this old post I was able to repair a faulty TKS level gauge.

Just what the OP said: The floater is hollow and can leak, so when filled with tks fluid it does not float very well giving very low or somewhat erratic readings.

Be forewarned - it is a bitch of a job in an Ovation that was exasperated by the fact that the rear seat airbag modules are mounted directly over the sender unit and it took more time getting it's mounting bracket out then the rest of the job combined !

Also, I drilled out a couple of the cherry max rivets holding the left seat pan, just in the corner so that I could lift it and bend it back to get direct acces from the top to pry off the sender from the tank.

[hypertech]

Any info on how this calibration procedure works?  My float was repaired as a pre-buy item but I've always been skeptical that the amount in there matches what it says.  I wonder if it needs calibration.

[N177MC]

10 hours ago, hypertech said:

Any info on how this calibration procedure works?  My float was repaired as a pre-buy item but I've always been skeptical that the amount in there matches what it says.  I wonder if it needs calibration.

Well the MM shows a "calibration table" and gives Ohm readings for the various quantities, but it gives no info on how to actually modify the reading output.

Probably best just to fill it incrementally and not the reading to get an idea of any delta and make a note of it .

On second thought, you might be inclined to simply bend the floater rod to make adjustments.