Rattling dipstick
Thread Starter
Joined: Sep 2002
Posts: 63
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From: Essex, UK
Rattling dipstick
Checking out the club C152 yesterday, I remembered a story my instructor told me of when a dipstick which hadn't been tightened properly had started to rattle, thus causing the student to panic, thinking the engine was on its way out.
Question is, would an unsecured dipstick result in a reduced oil pressure showing on the gauge?
[BTW, I'm not one of the "tighten it till it strips" brigade]
Question is, would an unsecured dipstick result in a reduced oil pressure showing on the gauge?
[BTW, I'm not one of the "tighten it till it strips" brigade]
Official PPRuNe Chaplain
Joined: Apr 2001
Posts: 3,498
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From: Witnesham, Suffolk
Depends on the engine, I suspect. But since the pilot checks the oil and secures the dipstick on her preflight, it won't happen, will it 
I don't know if it would blow oil out of the dipstick tube on the Arrow engine - it's a long tube sticking right up to the flap. Never tried it.
My pet hate is when folks do the dipstick up so tight that I can't undo it without getting my hands filthy - or getting out my leatherman to grip it.
I don't know if it would blow oil out of the dipstick tube on the Arrow engine - it's a long tube sticking right up to the flap. Never tried it.
My pet hate is when folks do the dipstick up so tight that I can't undo it without getting my hands filthy - or getting out my leatherman to grip it.
Why do it if it's not fun?
Joined: Jul 2001
Posts: 4,782
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From: Bournemouth
My initial suspicion would be No.
In an engine with a wet sump, the dipstick is inserted into the sump, which is relatively low pressure anyway - the oil having gone through any number of tight spots before being released back into the sump. In many engines, the sump is vented to the atmosphere anyway, so a loose dipstick would not make any difference. The oil pressure is measured in a completely different place, close to the pump.
In an engine with a dry sump, the dipstick is inserted into the oil tank, which is completely separate from the engine. So it's very hard to see how it would make any difference to the measured oil pressure at all.
Realistically, apart from rattling, the only difference a loose dipstick would make might be a little bit of oil escaping. It wouldn't affect the engine until lots of oil has escaped.
I'm not going to volunteer to try this, though, just in case I'm wrong!
FFF
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In an engine with a wet sump, the dipstick is inserted into the sump, which is relatively low pressure anyway - the oil having gone through any number of tight spots before being released back into the sump. In many engines, the sump is vented to the atmosphere anyway, so a loose dipstick would not make any difference. The oil pressure is measured in a completely different place, close to the pump.
In an engine with a dry sump, the dipstick is inserted into the oil tank, which is completely separate from the engine. So it's very hard to see how it would make any difference to the measured oil pressure at all.
Realistically, apart from rattling, the only difference a loose dipstick would make might be a little bit of oil escaping. It wouldn't affect the engine until lots of oil has escaped.
I'm not going to volunteer to try this, though, just in case I'm wrong!
FFF
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Joined: Aug 2001
Posts: 2,414
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From: Europe
Sounds like the aviation variation on the urban legend tale.
I would be surprised if you could hear a rattling dipstick over the din of the average aviation engine + propellor + unsilenced exhaust.
The untightness or even absence of the dipstick would not result in a lower reading of the oil pressure; that is until the engine oil has departed!
FD
I would be surprised if you could hear a rattling dipstick over the din of the average aviation engine + propellor + unsilenced exhaust.
The untightness or even absence of the dipstick would not result in a lower reading of the oil pressure; that is until the engine oil has departed!
FD
Joined: Aug 2000
Posts: 2,681
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From: Just South of the last ice sheet
FD and FFF are correct, a missing oil filler cap will make no difference to your oil pressure. The engine crankcase has a breather to allow any accumulated pressure build up from combustion gasses passing past the piston rings and valves to vent to atmosphere. If you left the oil filler cap off then you would merely be providing another route for the pressure to be relieved.
Very little oil would exit through the missing filler cap in straight and level flight unless the hole is located in a low pressure area which could cause the oil to be sucked out. Usually the filler cap is located in an area of slightly higher than ambient pressure due to the air being stuffed into the front of the cowling to cool the engine down, so oil being sucked out wouldn't be a problem. However, the usual warning of "don't try this at home children" applies
PS, as FD says, the chances of hearing a dipstick rattling over the general cacophony of an aero engine are non-existant.
Very little oil would exit through the missing filler cap in straight and level flight unless the hole is located in a low pressure area which could cause the oil to be sucked out. Usually the filler cap is located in an area of slightly higher than ambient pressure due to the air being stuffed into the front of the cowling to cool the engine down, so oil being sucked out wouldn't be a problem. However, the usual warning of "don't try this at home children" applies
PS, as FD says, the chances of hearing a dipstick rattling over the general cacophony of an aero engine are non-existant.
Joined: Mar 2002
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From: Biggleswade
Over ten years ago now, I checked the oil level pre-flight, but failed to secure the dipstick properly on my R-R C-90 powered light aircraft. The flight was only 15 mins. There were no cockpit indications - noise or oil pressure - but the amount of oil lost, only a few cc's, went a long way in staining the fuselage side. There was no way I could miss it on the after flight, or the next walk-roound!
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