TIT/CDT guage needed (I think)

[M20Kid]

The TIT/CDT guage in my 231 seems to be reading low - actually the TIT side appears to read low, the CDT appears approximately correct. Does anyone know if this guage is repairable? Alternatively, does anyone have a spare sitting around that they would be willing to part with?

By was of trouble shooting, I replaced the probe a few months back because it had a broken wire coming off the lead. After changing the probe I do get a reading but it's always lower that the EGT reading I see on my EDM-700. I believe that compression in the exhaust stack should cause at least a small temperature rise and so a lower temperature on the TIT tells me it's reading low. I've never seen the TIT guage read more than the low 1500 dF regardless of leaning.

[fluffysheap]

Lots of people experience the JPI reading higher than the factory gauge. I wouldn't chase this problem, I just use the JPI TIT gauge to keep the TIT under 1650, which is about 1575-1600 on the factory gauge. I actually usually aim for 1575-1600 LOP, which for me happens around 30" and just under 10 GPH. I am not sure if this means I have 50 degrees of margin or 125, but I'm glad to have the JPI.

I don't know whether the actual reason is that the factory gauge is old and has deteriorated, if the factory gauge always read low, or if the JPI installation disrupts the reading on the factory gauge somehow.

I suspect the factory gauge is just not as accurate. The readings tend to converge over time, which is in line with what it says in the JPI manual, that the factory probe is more massive and takes longer to heat up.

[M20Kid]

Thank you for the input! In my particular case I only have the EGT on the JPI but not TIT. Do you have any idea what the typical spread is between the EGT and TIT readings on the JPI? Obviously I don't want to burn the turbo but I want to run LOP if I can get there safely.

[fluffysheap]

My TIT is usually about 100F hotter than the EGT, although because of the EGT spread that is approximate. Maybe it is better to say it is about 50-75 hotter than the hottest EGT. You could also get a TIT gauge installed. I would rather have a JPI gauge than a brand new factory gauge.

[M20Kid]

I agree. I just had the JPI-700 installed and I did not choose the TIT option; now I wish I had. I didn't know the TIT guage was so inaccurate until I saw the actual EGT readings on the new JPI. I guess I can have TIT added but the cost would be greater now than during the initial installation and I'm sure the monitor would need to be removed and sent back to JPI to add the extra functionality. Sigh ...

[jwilkins]

I just replaced the ship's gauge TIT probe; even with the new probe it reads about 100 degree lower than the JPI.

Dan at Lasar has the probes (not compatible with JPI or Alcor probes) AND has a guy who can repair / rebuild the original gauge.

Lasar parts:

(800) 954-5619

[M20Kid]

Thank you! I replaced the probe recently; prior to that the guage didn't work at all. Now it reads lower than the EGT reading on the JPI. Did you have Lasar rebuild your guage or have you learned to live with the discrepancy?

[kortopates]

I'd be surprised if you'd need to send back the monitor, but obviously the TIT sensor would need to be added.

JPI documents in the users manual that their gauge reads ~100F above the factory massive TIT gauge. That said, the factory gauge is the one with the legal redline limit of 1650. But I personally avoid operating above 1550F TIT based on my higher reading JPI, which is accurate. I just don't trust the factory TIT.

Using 1550-1575F as a TIT target limit on my JPI (which would 1450-1475 on the factory TIT), I can run all day at 70% power 80F LOP (11 GPH, 32.5MP, 2400 rpm). That's my personal LOP limit as I can't get to max 78.6% cruise power without exceeding my personal TIT's comfort level, but max cruise LOP is still within the factory TIT red line.

[231LV]

I agree. I just had the JPI-700 installed and I did not choose the TIT option; now I wish I had. I didn't know the TIT guage was so inaccurate until I saw the actual EGT readings on the new JPI. I guess I can have TIT added but the cost would be greater now than during the initial installation and I'm sure the monitor would need to be removed and sent back to JPI to add the extra functionality. Sigh ...

not having TIT is an inconvenience but not a problem . To run LOP, simply dial back your prop rpm to 2500, close the cowl flaps and reduce your ff to 10 gph or less...you will be running well into the LOP side probably getting about 68 percent power...CHT's will run about 370-380 on the hottest jug....ff will give you a pretty reasonable idea of where you are on the power curve...push it up over 10 gph and you will likely see CHT go through 400-410......keep hottest jug below 380 using ff and you will be gold.

I just did a couple of recent cross country flights of 4hours each leg at 17k ft and had the ff dialed back to about 9 gph with hottest jug showing 371and oil temp at 190...KTAS was 173

[M20Kid]

Thanks 231LV! I'm heading out for a flight in a few days and I'll try that same thing. I'll also keep the other information in mind that the TIT is likely 75 ~ 100 dF hotter than the highest EGT reading.

I'm very excited to be able to explore the LOP side of the house, I've been burning too much gas for way too long.

[fluffysheap]

370 seems pretty hot for CHT if you are LOP.

By way of comparison, I did a recent cross country flight in my 231 - 2500RPM, FL210, 30" MP, just below 10GPH. I have no idea how many degrees LOP this is. TAS worked out at about 170KTAS. At lower altitudes, say 12K, I get about 150KTAS at that fuel burn. My airspeeds always seem to be about 5-10 less than everyone else, not sure if my airspeed gauge is slow or the plane is. Well, also, I had full fuel and about 270 pounds of passenger and baggage, so that will make a difference. All CHTs were between 290 and 320, and the TIT (measured by JPI) was around 1580-1600.

[jwilkins]

re: "Did you have Lasar rebuild your gauge or have you learned to live with the discrepancy?"

I replaced the ship TIT probe, but did NOT have the gauge rebuilt. The JPI manual states that the ship gauge TIT will vary by up to 100 degree from the JPI gauge. They explain it as a difference in construction of the two probes. That does not make sense to me if you allow the two probes time to stabilize, but they specifically state you can expect a difference. I use the JPI as the gauge to monitor; since it's the higher I feel it's safer to use the higher reading gauge.

BTW I just had the JPI / EDM 830 display installed to replace the 800 display. You can trade in the old 700 or 800 display. I'm really pleased with the new 830 display and being able to see almost everything I want without pushing buttons. I think it's one of the most cost effective 'upgrades' I've done on an airplane.

If there is room around the old 700/800 display the installation is minimal; the hole size gets increased from the 2+ inch hole to the 3+in std hole size. Cabling is the same so you just need to plug it in if the old cable has an extra 2 inches of slack.

It's a really nice upgrade to have all those parameters displayed on one screen without cycling through the display.

Jim

[jlunseth]

I believe the aircraft is unairworthy if the TIT is not working. I am pretty sure it is a required instrument under the Type Certificate, you could find the Type Cert. on the FAA site and check. I am pretty sure the CDT gauge is also a required instrument. There are redlines for both in the manual, so the gauges need to be working properly. Get thee to an A&P.

PS it might be cheaper and faster to have your A&P contact JPI and upgrade the 700 to a 711, which can be STC'd as primary for TIT and some other things. The 700 may not be used as a primary instrument, and if the primary instrument (the factory gauge) is out, you are grounded.

[jwilkins]

I agree that required gauges must be working. I do not know of any specification on calibration, and, since the JPI specifically states that their probe may vary in displayed temp from the original massive probe, the probability of having the two agree is not high.

Arizona Aircraftsman has a calibration tester so they can get an indication of the accuracy of the probes after installation. Just as with your compass, you could placard the instrument with a correction factor. If I did not have the JPI I probably would send the ship gauge out for calibration. Since I have both, I can watch the offset between the ship gauge and the JPI. If the offset remains consistent it is an indication that the precision is under control.

One thought that just occurred to me: JPI states that their indicated TIT temperature may vary by as much as 100 degrees from the ship gauge due to probe construction differences. When they supply a 711 kit, certified to replace the ship gauge TIT, do they use the same probes? If I remember correctly, the difference between the 711 and 700 is hard coded limits and an annunciator for the 711.

I agree you need a functional TIT and CDT when the type certificate and operating limitations reference them. You want the readings to be accurate and precise. However, I believe you can placard the instrument for an offset if you have a method of testing it, as AAC does.

Again, if I had ONLY the ship gauge and it were reading more than 25 or 30 degrees off, I probably would send it out for calibration. If it starts drifting more, without an additional indicator, you won't know that the offset is changing.