banner graphic
Airport Webcams
Who's Online
8 registered (bb174890, theboys3, ak172guy, xcfire, magman, California Flyer, DA900DVR, EdW), 110 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Newest Members
Dinji0311, wing guy, Shamir, drew2219, Marksta
7633 Registered Users
Top Posters
Bargain Bob 127154
vettdvr 7035
Cessna Dude 6628
Rusty Rudder 5885
California Flyer 5081
Willie 3930
Clyde Cessna 3447
wrecksum 2704
Joeman434 2555
Don Tedrow 2542
XP Driver 2333
Peedie Montgomery 2301
Ward Holbrook 2269
oilwell1415 1906
ytodd 1884
Nightowl 1826
Nintendo Pilot 1718
Glenn Darr 1708
November X-ray 1690
RodneyHooverCFI 1645
Lee T. Hargic 1633
Jim_1 1594
Pilawt 1553
Bigdoggh 1538
EdW 1349
Shuswap 1225
Showboatsix 1141
Pilot110 1116
Propduster 1103
Awkward Bird 1049
Top Posters (30 Days)
Bargain Bob 1983
Joeman434 94
vettdvr 81
Willie 63
Don Tedrow 54
Peedie Montgomery 53
Rusty Rudder 47
N5479R 46
Desert Hawk 45
3hawks 44
California Flyer 37
XP Driver 34
JD Casteel 33
Pilot110 31
Curious1 31
Viper_96 29
Newpilotoldplane 26
magman 25
SunDog 25
Flyboy712 24
Flubber4.0 20
Wayne R 14
cadcap 14
EdW 14
Kentucky Captain 14
Kinhop 13
Jim_1 13
bnt1983 12
Shuswap 12
flynhi 12
Topic Options
#17839 - 01/05/11 10:39 AM Hobbs Meter Pressure Switch
mames Offline
New Member

Registered: 12/31/10
Posts: 11
Loc: OK
Just wanted folks to be aware of what recently happened to me and my 1969 172 Lycoming O-320. I experienced a failure of the Hobbs meter pressure switch located at the front top of my O-320. Oil poured out of it and luckily I was on the ground and became aware of the problem before takeoff. There’s not much of a sicker feeling than to see oil coming out of the bottom of the cowling. Luckily, I just had to remove the part, plug it, and add one quart of oil. I got by lucky, but it could have been a lot worse. It's worth keeping an eye on this part, although not being a mechanic I'm not sure what can be done other than regularly checking for any leakage. Of course, one might evaluate whether they even need a Hobbs. When mine failed oil poured out. Also, the part is just above the large hose that takes air to the muffler shroud for cabin heat. I noticed oil also went into this hose and muffler shroud, not a lot but I still removed and cleaned it out. Just wanted folks to be aware of this potential issue.

Top
#17851 - 01/05/11 12:11 PM Re: Hobbs Meter Pressure Switch [Re: mames]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/24/10
Posts: 7035
Loc: Slidell La
I totally agree. The oil sending unit looks like a car application and if the gasket fails on a car it just leaks but IFR, VFR or just wheels off the ground makes it a really bad thing.
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

Top
#17867 - 01/05/11 03:44 PM Re: Hobbs Meter Pressure Switch [Re: vettdvr]
EdW Online   content
Club Sponsor
Gold Pilot

Registered: 11/21/10
Posts: 1349
Loc: Just east of Graceland
I recently had to rebuild an O-360 for the same reason. The engine was still running when he passed my hangar, but sounded like a John Deere tractor. After having to have the case and accessory case overhauled by DivCo, he wound up with two connecting rods, the hydraulic pushrod units, and the tubing/accessories off the original engine. That $25 item wound up costing him a bundle!


Edited by EdW (01/05/11 03:45 PM)

Top
#17878 - 01/05/11 06:14 PM Re: Hobbs Meter Pressure Switch [Re: EdW]
steve71e Offline
Second in Command

Registered: 02/22/10
Posts: 172
Loc: Atlanta, Ga
The fitting on the engine case suppling that line for the pressure switch or even the actual direct reading oil pressure gage should be a "restricted orifice fitting" which means if you do have a switch, hose or gage failure it will make a mess but greatly reduse the amount of oil flowing out of the leak and give you time to get down before you get below the minimum allowable oil amount in the sump (2.75 I believe on an O-320). The fitting should have only a tiny, tiny hole allowing oil to pass through.
_________________________

Top
#17880 - 01/05/11 06:23 PM Re: Hobbs Meter Pressure Switch [Re: steve71e]
Rusty Rudder Offline
Diamond Pilot

Registered: 02/26/10
Posts: 5885
Loc: NorthEast
On the 1982 P model, that hobbs sending unit is up under the Co-pilots dash panel, and when it leaks the oil goes onto the floor mat on the Co-pilots side. Very noticeable right away...
_________________________
Take-off's are optional, landings are manditory



Top


Cessna172 Tribute
THIS MONTH'S SPONSOR
Special thanks to:
You!
Thank you for making this site great
Fredericksburg TX '15 Countdown
September 25-27, 2015 T82
Today's Birthdays
aoatley
Member Map
Where in the world are the Cessna 172 Club Members?

View the map

Helpful Links
100LL Price Finder
AD Directory
Aging GA Aircraft
Aircraft Directory
Airplane Report
AirNav
Airport Facilities Directory
AOPA
Aviation Weather
Barnstormers
BaseOps
C172 History
Cessna
Controller
Crash Records
DUAT Voyager Planner
DUATS
FAA
FltPlan
Flight Aware
Flying Tools (Files)
Google Earth
Ground Speed Records
National METAR Map
Sky Vector
Trade-A-Plane
Uvalde Flight Ctr
All the Webcams
Shout Box

AOPA
AOPA
Weather Lookup
Airport code:
(separate multiple codes with spaces)

List of stations