I have a SeaRey with a 912ULS engine. About a year ago I changed from a Rotax 914 to the 912ULS. I reused the Rotax 914 exhaust with a modification where the turbo was. On the 914, the EGTs were in the normal range (1200-1400's) but with the 912 ULS, with the EGT probes in the same holes, so the same distance from the exhaust, the EGTs both read about 400. This started immediately after installing the engine but I just haven't been motivated to address it until now. CHT's and oil temps are normal around 200 and the engine is running well and smooth. The probes have a gray appearance when inspected. I replaced one of the 2 probes and no difference. I checked the EMS setting and it is set to K-type sensor. I do use more oil than one would expect from a Rotax, about 2.5 oz/hr, but it isn't showing up on the probes. Anyone have an answer? I sure don't seem to. Thanks.
Low EGT
- Thread starter Mazerbase
- Start date
A bit stumped here - EGTs are indeed Type K if they're ours, and there wouldn't be any major change in probe configuration (as far as EGTs go) between those two engines.
Albee
Member
Re-check wires and connections? Thermocouples are extremely weak voltage sources, weak connection/damaged connections or wires could conceivably result in low readings. My ancient Westach probes would read low for a while just before the wires broke entirely.
Thanks for the suggestion. I've looked at the wires and connections but haven't checked the resistance on them. I suppose I should. It just seems odd that both sides would do the same thing at the same time to the same degree. If it was the wiring I would expect some difference in the degree of failure between the 2 probes.
Well, I decided to make another attempt at figuring this out and it gets a little stranger. I pulled the new probe from the engine while cold and applied a heat gun. Strangely, the right probe, the older one, read -23 and the new one read 500-ish. I looked at the EMS sensor setup and erased both EGTs and reentered them, forced a network reboot, and, surprise, the L EGT read 86 (about right for ambient) and rose appropriately with heat. I replaced the right probe with a new probe and it also read ambient and rose appropriately with a heat gun. Eureka I thought. So, I pulled the plane out, started the engine, looked down and 2 red Xs on the EGT temps! I re-forced a network reboot and still 2 red Xs. I shut down the engine and pulled the plane back in. On a lark, I turned on the master and both probes read an elevated temperature consistent with a cooling exhaust. So, I left the master on, pulled the plane back out, and started the engine. 2 red Xs again after the engine started. When the engine was shutdown, the Xs disappeared and the temperatures appeared appropriate again. I am beyond lost on this. Anyone got an answer for this?
rkorff
I love flying!
Hows the ground strap grounding engine to airframe? Did you remember to clean a spot of paint under the ground strap on the new engine block? Think I’d look at that first.
rkorff
I love flying!
We’re talking about miniscule voltage and amperage - millivolts and milliamperes. Ground path with engine not running is not shared with engine electronics. When it is running, it’s a common path. Could cause resistance changes to EGT sensors. Just throwing out a common problem area that hadn’t been mentioned before. My two cents. Take it for what it’s worth.
Still narrowing down the issue. Today I hooked up a K-type analog EGT display to the R EGT. Unfortunately, the display doesn't have numbers on it but, according to the manufacturer, the graduation with the asterisk is about peak EGT. When I brought up the power, the analog EGT rose appropriately but, surprise, there was an indication on the Dynon for the R EGT. So, I pulled the connector and checked the continuity and found it was good. But, even with the connector pulled, the Dynon EGT is showing ambient temperature. Is there a fault in the EMS?
Albee
Member
Did you get this resolved? Sorry but I guess I checked out of the thread before seeing your picture. I'd expect near-ambient on the EMS with the probe disconnected.
Thermocouples produce a voltage proportional (almost) to the difference between the two ends of the alloy wire pair. So a zero voltage at the thermocouple pins on the EMS is saying the EMS and the probe are at the same temperature.
Thermocouples produce a voltage proportional (almost) to the difference between the two ends of the alloy wire pair. So a zero voltage at the thermocouple pins on the EMS is saying the EMS and the probe are at the same temperature.