Wing tank fuel sump/CHT Guage

[Carl Thuringer]

I recently purchased N8111Y, what a great bird. I have two questions. The first is in regards to the tip tanks, does anyone have a suggested tool for the fuel sump, a standard fuel sump tool does not seem to cut it. Next question is my CHT gauges to not seem to be functioning, any suggestions on what to check?

[N3322G]

Hi Carl,

Welcome to Comanche ownership.

On the tip tank sump - I'm sure you've read that you sump through the belly and at the tip tank itself. Our tip tanks sump perfectly with the standard sump tool. So far, this is the first time I've heard that anyone has had a problem like this for the Comanche tip tanks ... been around them for a few decades. Maybe if they haven't been used in awhile, they need cleaned ? Perhaps others will chime in with ideas.

wrt the CHTs. Unless it has changed, FAA regs say that if a plane has cowl flaps, CHT readings must be on display at all times. There was a mechanic that felt he was above the FAA and removed the Piper CHT probes when he installed JPI monitors. This of course made my Twin unairworthy in the eyes of the FAA. I got this fixed by putting a 5050A JPI probe on and flying to Air Parts of Lock Haven where they replaced the mechanics sloppy two different incorrect probes and calibrated them with the original gauges. This may or may not be your problem.

Today there are gauges that are certified to replace the factory CHT functions so that is another option to the above.

So, 1st I'd check to make sure you have probes connected - if not, you can get replacement probes but they also have to be calibrated with the gauges.

Hope this helps and please post again once you find the problem.

[Carl Thuringer]

Thank you Pat, I appreciate the advice. I will take another look at the tip tank sumps. I have the bird in the shop for the CHT's now. It will be interesting to see what the story is.

[Carl Thuringer]

After some investigation it turns out that the CHT probes need to be replaced. Any suggestions as to where one might find CHT probes?

[N3322G]

Carl,

Suggest contacting Air Parts of Lock Haven http://www.airpartsoflockhaven.com/contact.html They are an ICS advertiser. See the Home page of this website for the link to many Comanche parts suppliers.

You may know Lock Haven was the original manufacturing location for the Twins.

[Zach Grant L1011jock]

Carl,
The tip tank drains are somewhat problematic. You need a fairly sturdy item to push the spring loaded pin up to sump the tanks. It is an interesting arrangement in the tip tanks that should be brought up. The tips don't have a sump any more than the wing tanks do, but they do have an finger screen that rests on the drain valve and surrounds the fuel pickup line that runs vertically down to the bottom of the tank. When you push up on the sump drain on the tip, you are actually lifting the screen and allowing any crud or other stuff to enter the drain and hopefully be removed from the tank. I say hopefully, because what happens more than not is that if the tip drains haven't been used in many years (or even if they were used yesterday), something will get stuck in the drain, and it will not shut off all the way which can lead to a large flow or an annoying drip or something in between. The drains are replaceable and are available from JL Osbourne but they are a real PITA to remove as they are usually stuck pretty good. Draining the tips from the cockpit will eradicate anything liquid (or anything small enough to get through the finger screen) from the tips that can get sucked up by the engines as long as you drain a significant amount of fuel (the run from the tips to the fuel strainer is a long one!). A small mirror and a flashlight will show you the condition of the finger screen and if there is anything being retained outside of the screen. I would suggest looking before draining and ending up with a big headache, expensive too if you loose a bunch of dead dino juice before you can get it shut off.

-Zach

[Carl Thuringer]

Thanks for all of the advice. Here is where I am at with the CHT, both of the gauges read exactly half of what they should read, around 160 deg off. If only one side were doing this I would not be so confused. But both sides being equally inaccurate has put another spin on this.

[Richard Lanning]

Right after I bought my plane I had a tough time with the tip tank drains. They were difficult to open and they leaked and on a number of occasions took a lot of probing to get them to shut off. Trip to the mechanic found them to be in need of a lot of TLC. Now they work fine.

I use a GATs jar. When they were hard to open I got an electric connector and crimped it onto the GATs jar probe. This allowed me to apply enough pressure on the drain pin without it slipping off which I suspect you are experiencing. Just be careful if you use a GATs jar you don't accidently dump the electric connector into your tank. I made mine snug but not so snug I couldn't remove it. Somewhere along the way I lost it (sure hope it isn't in my tank) and have not really needed since the drains were cleaned up.

I do have a question that maybe you or someone else on the thread can answer. I have CHT/EGT probes on all cylinders. There is also a 7th probe which clearly shows OAT on the CHT display but I am also getting a reading on the EGT display that in flight usually is around 115-125 degrees. I thought it might be carb heat but when I apply carb heat it does not change its reading unless maybe it is the inlet to the carb. Just wondering what temperature is being displayed. Gives me one more thing to worry about when I fly.

[Carl Thuringer]

Thanks for the tips on the fuel tanks. I am working on the CHT's for a Twin Comanche so I am about as familiar with the Comanche as I am with the Twin Comanche, learning more and more every day.