Dancing Oil Temperature

[Andy]

I'm seeing a sporadic to frequent problem where my oil temperature "dances" between 140-200 in flight. Movement of the gauge needle is fairly fluid once it starts and the gauge seems to stabilize at higher values (200- 220) when my temps get up there. Mostly this seems to happen after flying a two hour cross-country leg, but I have seen it once or twice right after start, and then it quit before the run-up checks. My mechanic and I ran resistance checks of the wiring to the gauge and the gauge and they seemed to be okay. But then I flew yesterday three short flights (0.5 to 0.7 hrs) in succession and the oil temp system performed nominally. My mechanic thought the problem was in the sending unit until yesterday's flights. Has anyone seen this before? Where do we need to look?

 

Thanks.

[S3flyer]

Has all the earmarks of the sender going bad or one of the other grounds being loose. You can pick up the VDO sender for about $25 from an auto parts store.

 

[whoops -- should've read closer. No pressure problems here. Guess I was juxtaposing my oil pressure symptoms of a couple months ago ]

[Tad Olmsted]

I'm seeing a sporadic to frequent problem where my oil temperature "dances" between 140-200 in flight. Movement of the gauge needle is fairly fluid once it starts and the gauge seems to stabilize at higher values (200- 220) when my temps get up there. Mostly this seems to happen after flying a two hour cross-country leg, but I have seen it once or twice right after start, and then it quit before the run-up checks. My mechanic and I ran resistance checks of the wiring to the gauge and the gauge and they seemed to be okay. But then I flew yesterday three short flights (0.5 to 0.7 hrs) in succession and the oil temp system performed nominally. My mechanic thought the problem was in the sending unit until yesterday's flights. Has anyone seen this before? Where do we need to look?

 

Thanks.

 

Andy,

Ive seen it plenty of times. The connector on the oil temp wire usually is the problem. If it has red plastic on it then it is original from FD and needs to be changed. These connectors are cheap and not installed all that well from the factory. Same goes for your CHT sensor wires.

Also an oily/dirty connection at the sensor will give erratic readings. Just clean it and make sure it is a tight fit on the sensor. I have never seen an oil temp sensor fail.

Last thing is to double check all the grounds behind your EMS and look for corrosion and security.

 

This should fix your problem

[Roger Lee]

Hi Andy,

 

The temp probes rarely go bad. 95% of the time it is a bad wire or connection. Make sure that the connector on the probe is crimped well so it has some resistance when you try to move the connector back and forth on the probe end. Then pull on the wire and see if it comes out of the connector. I just had one of these and the wire inside the connector was hanging by a thread. Then in the instrument panel tighten the ground where they come through the firewall. Loosen the top nut then tighten the one at the far back then re-tighten the front one. Depending on how your grounds come through the firewall make sure you put a wrench on any ground coming through the firewall and if you have a grounding block tighten that main ground screw and its 4 smaller screws. These grounds are considered loose until a wrench has been used. Hand tight and wrench loose. These temp probes and pressure senders are very sensitive to poor grounds and are the first items to show up when a ground or connection is a little loose.

[Runtoeat]

Andy, Tad and Roger (miss anyone?) suggestion to check the wire is a good one. I just had your concern. My oil temps would fluctuate with the needle oscillating. and then just quit. I found the wire connected to the sender had broken inside the insulation so it wasn't apparent. This wire runs from the engine block then routes 3 or 4 inches to the oil temp sender. It is unsupported and eventually the wire fails due to vibration. To fix it, a new connector was crimped/soldered to the wire. Also, I added two layers of shrink wrap which included coverage of the connector and then runs up the wire a few inches to reinforce the wire and prevent vibration from breaking the wire again.

[Tad Olmsted]

Andy, Tad and Roger (miss anyone?) suggestion to check the wire is a good one. I just had your concern. My oil temps would fluctuate with the needle oscillating. and then just quit. I found the wire connected to the sender had broken inside the insulation so it wasn't apparent. This wire runs from the engine block then routes 3 or 4 inches to the oil temp sender. It is unsupported and eventually the wire fails due to vibration. To fix it, a new connector was crimped/soldered to the wire. Also, I added two layers of shrink wrap which included coverage of the connector and then runs up the wire a few inches to reinforce the wire and prevent vibration from breaking the wire again.

 

Awesome!

 

One thing guys forget to do is stretch a wire when checking for continuity, good catch and good fix.

[Tad Olmsted]

WOW, look at the posts Roger and I left. They are only a minute apart, so we must have been typing at the same time. We both gave the same remedies almost word for word. Only a few word differences and I am told I am much better looking

 

We must have ESPN ... now that's funny

[chanik]

This sort of oily-patina on the fuel pressure spades combined with loose faston connectors was causing my flaky fuel pressure sender readings as well. Those had red sleaves too.

[Andy]

This sort of oily-patina on the fuel pressure spades combined with loose faston connectors was causing my flaky fuel pressure sender readings as well. Those had red sleaves too.

WOW! Thanks to everyone who responded. We'll go check these out and I'll let you know what we find out.

 

Andy

[mocfly]

Guys,

After many of the same problems with dancing gauges i wanted to share what i have found. Our CT has experienced issues with dancing oil pressure, oil temp going to the peg and cht following suit. I have read and re-read every post related to this and the common thread is grounding issues. We had a number of people work on our plane and it was on the field at Fondulac where the issue was finally found and resolved. The back story is a saga and i would like to leave it at that.

 

After following the advise of Roger Lee, John Hurst and the many members who have posted about grounding issues, i removed, polished and tightened all the grounds.

 

Here is a pic of a typical connection and its shape. This is the base connector at the starter solenoid. (img 00471)

 

Trying to get to the ground bus made me remove the radio stack and the picture of the connector with the pin out of place(img 0051) was one thing which was noticed along with the ground loop wire not being connected to the bus.(img 00501) Can you imagine how surprised i was to see this. I then removed all the connectors and reinserted them carefully checking that the connector was fully engaged.

 

The third picture is of the engine instruments in flight after the cleaning and reconnection of the grounds. (dscn0198)

 

I am having the prop re-pitched and hope to see the oil temp down in the green.

 

I can't say how much this group has helped me to diagnose and fix this issue which has plagued us for almost a year now.

[Roger Lee]

Howdy Mocfly,

 

I'll tell you what I see. If you found any ground very loose and especially off my vote says it was done during the firewall blanket install. I have seen this a few times where the mechanic does not get everything back where it goes or doesn't connect it. The second thing I would highly recommend to anyone with an aircraft in a humid state is to spray all your electrical terminals with Boeshield T-9 which will shield your electric contacts from corrosion. It is clear and has a paraffin base which will block out all moisture. It was designed for Boeing with just that type of thought in mind.

 

p.s.

If any one post pictures don't forget to re-size them.

[Roger Lee]

Howdy Mocfly,

 

I'll tell you what I see. If you found any ground very loose and especially off my vote says it was done during the firewall blanket install. I have seen this a few times where the mechanic does not get everything back where it goes or doesn't connect it. The second thing I would highly recommend to anyone with an aircraft in a humid state is to spray all your electrical terminals with Boeshield T-9 which will shield your electric contacts from corrosion. It is clear and has a paraffin base which will block out all moisture. It was designed for Boeing with just that type of thought in mind. I used it in my last business around lots of salt water and it does a great job. It can be used to spray metals else where and gives the same protection.

 

p.s.

If any one post pictures don't forget to re-size them.

[rookie]

Roger/Tad

 

It was only a mater of time before I ran into the same oil temp/cht temp problem that others have had. Both went goofy on a recent x-country. I totally agree with whoever commeneted on how Mickey Mouse these connectors are. Fortunatley I remembered this post and knew where the problem was and how to fix it.

 

What are these connectors called and where do you buy them? I want to install new ones, the right way.

 

al meyer

[Tad Olmsted]

Al,

I use the ones from fastenal. They cost a bit, but last. The sleave is maluable and not brittle. I think the brand is Wurst???

Also guys, never use thread tape or dope when installing a new oil sender. Only use loctite 222, the housing is the ground through the pump.

[chanik]

You can get a lifetime supply here for $3

http://www.allelectronics.com/make-a-store/item/1125/1/4-QUICK-CONNECT-FEMALE-RED/1.html

But make sure you get a crimp tool or have a multi-tool with crimp pliers. Just crunching down the barrel onto the wire with ordinary pliers is a good way to make a bad connection.

 

Cheap one here http://www.google.com/products/catalog?q=crimp+tool&hl=en&rlz=1T4GGLL_enUS386US386&prmd=ivns&bav=on.2,or.r_gc.r_pw.&biw=1680&bih=892&wrapid=tlif131439369976310&um=1&ie=UTF-8&tbm=shop&cid=3395507352410042552&sa=X&ei=YQ5YToa7IcniiALJ-pG8CQ&ved=0CI0BEPMCMAE#

Often you can find these as kits with the crimps in Lowes or Home despot or auto-parts stores.