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Oil temp issue- need your help

9Abuilder

Member
Boy, do I feel stupid! Today, I was taking off, with my oil temp reading 210 degrees. I wanted to stay in the pattern, so I turned on my landing light. My oil temp warning came on and the temp reading shot up to 330 degrees! I immediately landed, turned off my landing light, and the oil temp went back to 210 degrees. I tried my taxi light and got the same immediate high oil temp. A very good friend told me to check my secondary ground wire from the engine block to the firewall. I really don’t think I have a secondary ground from the engine block to the firewall and I have no idea what he is referring to. I’m flying a 9A and my engine is an O-320 D1A. I have an AFS 5600 EFIS, with a single AFS radio and 2-axis auto pilot. Please help!
 
Engine or sensor ground

It’s not clear if you’re the builder or not. It is clear that current loads impact your oil temp sensor readings, which suggests the sensor, which is typically grounded through engine, is not well grounded. That suggests the engine and/or the EFIS is not well grounded, which is where the grounding strap comment comes from. That the landing light causes the change might suggest there’s more than one grounding issue in play. Arizona seems to have a relatively high concentration of talented builders. I’d suggest you find someone to give you a hand with an electrical inspection, firewall forward and back. It’s probably something simple, especially if this is a change in behavior, corrected in an afternoon for a few dollars in wire. You might have to wait until they come home from up north. :)
 
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Ground wire

I think your friend is probably referring to one of the two main earth cables on the engine side of the firewall. Typically there is a brass bolt through the firewall with one heavy lead going to the battery negative terminal and another heavy or braided lead going to the engine case. You could start by checking that these leads are intact and secured at both ends.
 
Same issue

Hi, I had the same issue on a non-RV.
Erratic oil & cylinder head temps.
The engine ground strap (a flat braided wire) connector clamp was loose on the engine mount... (yes, on a certified plane...)
After cleaning the area and correctly tightening the clamp, all is well.

Good luck with your investigation
 
I also would suspect a ground issue. You MUST have a ground strap (braided wire) between the engine and airframe. You must have something, otherwise you wouldn't be able to start the engine. If that connection is poor (loose, corossion, etc.), return current starts looking for a better path.

Start tracing the current path from the landing light Neg terminal all the way back to the battery Neg terminal. Somwhere in that path is some resistance and the electrons are finding a better way back to the battery via your oil temp sensor.

Larry
 
I also would suspect a ground issue. You MUST have a ground strap (braided wire) between the engine and airframe. You must have something, otherwise you wouldn't be able to start the engine. If that connection is poor (loose, corossion, etc.), return current starts looking for a better path.
...
What Larry says is where I would also look. It's also recommended by the gurus to have two ground straps - just in case. If you only have one, might be worth it to add a second to two different locations on the engine and the airframe.
 
Like others said, you should find out what's happening with the engine ground, but if you want more reliable oil temperature sensing, you could install a two-wire sensor as specified in the installation manual.
 

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Oil temp issue- please help

Thank you to everyone who replied to my need for help. I added the grounding cable from the firewall to the engine block and all systems are working perfectly.
You guys are great!:D
 
Thanks

I had been struggling with a fluctuating oil temp on my MGL EMS for a couple of months. Oil temp kept running high also. Stumbled on this thread and it was exactly what was wrong with my system! Thanks everyone! Gotta love this group!
Cheers
 
Oil temperature sensor ground - Titan engines

Very similar to this thread, related to single wire temperature sensor grounding on a Titan engine with oil filter angle mount (Mine is a 340, but I think most other models have this, or similar filter adapter).

When I wired my Dynon EFIS system, all was well except for no oil temperature reading, with the system saying no signal at all. We checked and rechecked the wiring; all was good. Decided the sensor must be bad, but it checked ok with a meter (reading from body to center electrode). Engine grounds looked good and everything else was working. Finally, tested from the sensor body to several ground points and there was no connection -- well, several million ohms.

Cause: The temperature sensor body is threaded into a nice angled oil filter adapter. The oil filter angle adapter that Continental/Titan uses is essentially an extension on the accessory case, solidly bolted to it with 4 through bolts. Of course, there is a gasket at the base, and powder coat on the outside. The 4 through bolts are fitted with washers under the heads that don't necessary scratch through the powder coat, resulting in an effectively insulated oil filter adapter, and thus no ground for the oil temperature sensor. After tracing wires (and maybe cussing a bit) for the better part of a day, it simply took a little scratching paint under the head of a bolt. (well, 2 for safety)

If you have this issue with a Titan, give that a look. I suppose it applies to other situations where you would think a component JUST HAS to be grounded to the engine (but isn't)

Ted
 
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