direct reading oil temp gauge sluggish response

  • john hilton
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1 month 3 weeks ago #3432 by john hilton
Replied by john hilton on topic direct reading oil temp gauge sluggish response
Steve
well, we both are over thinking this matter of gauge not reading
today I rapped the gauge and on my second rap--lo--it jumped to life
I had thought my 182 vibrated enough to keep the needles free.
not so apparently.
as you say, sometimes the simplest solution should be our first action.
thanks again for your help
John H

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1 month 3 weeks ago #3430 by john hilton
Replied by john hilton on topic direct reading oil temp gauge sluggish response
thanks Steve,
I had suspected that your experience with the temp gauge was "normal",
yet my rebuilt gauge, and associated line/bulb, seems not to have fixed the problem.
I will take a few test flights to see if the problem persists, and if so,
ask my mechanic to do the boiling water test.
more later,
John H.

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1 month 3 weeks ago #3429 by STEVE ELLS
Replied by STEVE ELLS on topic direct reading oil temp gauge sluggish response
Hi John,
You should see some indication within minutes after starting the engine. Unless you're flying in an extremely cold environment.
Your mechanic can easily test the oil temp system by removing the bulb end of the capillary tube and submerging it in boiling water.
You should see the needle move almost immediately.
In addition to "testing" the system, this task will show where 212 deg F is on your oil temp gauge face. I did this in my C-182 and put a white dot on the face as a reference.

If the temp gauge needle doesn't move, your mechanic needs to send it back and get one that does.
You can do the boiling water test prior to installation to see if the "new" gauge system works.

Let me know what you find.

Steve

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1 month 3 weeks ago #3425 by john hilton
Replied by john hilton on topic direct reading oil temp gauge sluggish response
Steve,thanks, my original question was on the sluggish oil temp gauge.
sorry about the reference to oil pressure.
my mechanic replaced the oil temp gauge with a rebuilt gauge and to me the sluggishness seems to persist.
should I see some oil temp indication within 20 minutes or so of flight?
again, sorry for the reference to oil pressure,
the question here seems solely due to lack of any reading for the first hour or so of flight, and any thoughts on why this happens
John Hilton

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1 month 3 weeks ago #3423 by STEVE ELLS
Replied by STEVE ELLS on topic direct reading oil temp gauge sluggish response
Hi John;
I'm having trouble with your reporting.

So let's start from scratch. In the beginning you said the oil pressure gauge was sluggish, correct?

I suggested blowing out the tube. Did your mechanic do that????

If there was a leak in the hose/line between the engine and the gauge, it would have easy to discover since oil in your engine should be around 40 -60 psi when the engine is running. The idle oil pressure is lower, but there's still pressure in that tube/line. Any hole would cause a large leak.

Both the oil temperature and oil pressure gauges are Bourdon tube-type gauges, because there's a sealed chamber in the gauge that changes shape with different pressures.

The hose/line from the engine to the gauge is not called a Bourdon tube; it's simply a small copper tube (there may be a short flexible tube between the engine and copper tube) to connect the engine oil pressure to the gauge.

When ever there's a question about engine oil pressure, the first job is to verify the engine oil pressure. This is done be connecting what we call a direct reading gauge directly to the oil pressure outlet port on the engine.
A direct reading gauge just a mechanical Bourdon-type gauge (you can buy one that will work for testing at any auto parts store) that's separate from the aircraft oil system gauge. Disconnect the oil pressure hose/line at the engine, and connect the direct reading gauge in it's place--Then run the engine and check the OP reading on the gauge.
If the OP readings are normal on the direct reading gauge, this eliminates an actual oil pressure problem with the engine.
If the hot idle oil pressure is below 10 psi, this is an indication that there's wear in your engine. Normal OP in cruise should be between 30-60 psi.

When you say your oil temperature now doesn't work, that's worrisome. The oil temperature system is what's called a capillary tube system. A liquid is enclosed in the temperature bulb that's installed in the engine. As the oil temp increases, the liquid in the temp bulb and closed capillary tube expands, causing a higher pressure in the capillary tube. The other end of the capillary is directly connected to a Bourdon-type gauge that changes dimension as the pressure increases.
The following is right out of the service manual:
"15-43. OIL TEMPERATURE GAGE.
15-44. DESCRIPTION. On some airplanes, the oil temperature gage is a Bourdon tube type pressure
instrument connected by armored capillary tubing to a temperature bulb in the engine. The temperature bulb,
capillary tube and gage are filled with fluid and sealed. Expansion and contraction of fluid in the bulb with temperature changes operates the gage. Checking capillary tube for damage and fittings for security is the only maintenance required. Since the tubes inside diameter is small, small dents and kinks, which would be acceptable in larger tubing, may partially or completely close off the capillary, making the gage inoperative.
Is is possible that the capillary tube may have gotten kinked somehow??

I have attached a couple pages that further explain Bourdon tubes and how they work.

Steve
Attachments:

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1 month 3 weeks ago #3421 by john hilton
Replied by john hilton on topic direct reading oil temp gauge sluggish response
Steve
my mechanic installed a rebuilt gauge with a fluid/gas? filled bourdon tube line
no oil in this lime I suspect
now? still no oil temp indication
and, now I also get no oil pressure read indication
(although my idiot lites show I have oil pressure and on shutdown the hot engine indicates hot oil)
thought you might like to see my follow up
thoughts?

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