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Factory EGT, CHT, oil temp probes for IO-470K engine

1969 E33 CD-1212, IO-470-K

So, this question is about the factory onboard temperature probes for Oil and CHT. I'm trying to research, partly to educate myself... and partly to be able to speak the same language as my mechanic.

The onboard oil temp probe is showing erratic readings - it seems to be reading ambient air temps. It appears to be located under the oil cooler, while a secondary (going to an EI UBG-16 engine analyzer) is located in the top of the oil cooler. First, is there a way to troubleshoot the factory oil temp probe? I've searched the IPC and can't find a reference for a replacement part number, where should I be looking? And second, is there an advantage to relocating the secondary probe to the boss under the prop governor?

Likewise, the onboard CHT gauge is not anywhere close to what is being displayed on the secondary engine analyzer. Are CHT probes generally interchangeable between manufacturers, or do I need to find an adapter to fit or piggyback the factory probe with the EI CHT probe? What even is the original part from Beechcraft? Is there a procedure for troubleshooting CHT probes and gauges? Again, my IPC skills appear to be lacking.

Marshall Herington

Model: Bonanza E33
Aircraft Serial Number: CD-1212
Posted 1/17/2021 - 1 month ago

Replies Sort

The oil temp probe is reading the amount of resistance to aircraft ground and provides that OHM reading to the gauge to show oil temp.
A quick way to test is to remove the wire from the probe and ground the wire. The gauge will go full scale. Remove the wire form ground and gauge will go full scale opposite direction.
If the works correctly then most likely you have a bad oil temp sensor.
The sensor is in the IPG FIG 62, Item #22
P/N 1512926 Avstat in CA 818-780-6032 shows one available.

The CHT system operates the same as the Oil temp system, sensor is reading resistance to ground.
The sensor is in the IPC FIG 47, Item #39
P/N is 1514340 Avstat also has one available.

Bob Ripley
ABS Technical Advisor

Posted 1/20/2021 - 1 month ago

Factory EGT, CHT, oil temp probes for IO-470K engine