oil temp capillary

[pmel22]

Hi anyone have any pictures or advice of the correct way to route the oil temp capillary? I am installing a new rochester gauge after the electric replacement failed. I have a 56 172. Thanks

[pmel22]

Thanks, he asked me to start it and then he would come in and check it..do you remember what hole it goes through. I have an opening toward the top where I believe the old tach cable went through, that was converted to electric also. Thanks again

[pmel22]

Thank..I will see if that will work ..btw I purchased a panel overlay from you, it looks great, thanks again

[Bruce Fenstermacher]

Depends probably on your model and serial number. While not approved, sometimes the IPC can give clues how things are suppose to be. Here is figure 57 of the B model IPC with the grommet parts removed and labels as to what went through the hole from the parts list.

From Fig 57 B model IPC

The above picture is the same as fig 39 in the A model IPC

Not so clear is fig 34 from the 48 IPC below.

Fig 34 48 IPC

fig 34 48 IPC.png (15.04 KiB) Viewed 25838 times

Looking at it I think the locations are the same in all models.

[cessna170bdriver]

Make that "early" B-model, Bruce. I'm not sure when they started, but my '55 model has the battery on the left. However those firewall penetrations make sense to be on the right in that they are straight forward of the instruments they go to. In the photo below, the oil temp capillary is the smaller black line coming through the same hole as the large electrical cable. The hole in the firewall has to be large enough to insert the sensor bulb from the inside. (I hate drilling extra holes in perfectly good airplanes, so I also used this hole for the electrical cable when I upgraded to a 50A alternator).

[n2582d]

Pete, Attached is a labeled copy of the early C-172 firewall. The late C-170B and the early C-172 firewalls traded positions for where the throttle, 'P' leads, and oil temperature gage line penetrated. Mile's plane was ahead of it's time as it matches the early C-172 configuration. Bruce meant to label "Oil Temperature Gage Line" instead of "Oil Pressure Line" on his IPC illustration.

Click twice to enlarge

Oh, and some of you ragwing owners may have missed S.L.N.-69 dated 6-16-48:

Production Improvement recommended for Model 170 airplanes in the field Serial Numbers 18000-18050, inclusive.
...

5. Tachometer Drive Shaft Routing.
The tachometer drive shaft and the oil temperature indicator line are routed through the firewall through two identical holes, one located at the center line of the firewall and the other hole about 4 1/2 inches to the right of the center line hole. The oil temperature indicator line should be routed through the center hole and the tachometer drive shaft through the hole on the right side of the firewall. This routing was reversed on some of the airplanes delivered prior to Serial Number 18050. Some reports from the field have been received of tachometer drive shaft failures and tachometer malfunctioning. The correction of this routing, therefore, is recommended in the field to prevent further similar occurrences.

[ghostflyer]

As previously stated check the calibration before fitting it. We have had 4 Rochester (new)gauges checked and found a 40 degs variance between them. Went back to the supplier who contacted the manufacture and was told its with in limits . All showing colder that what they should have been . One owner wanted to start blocking off the blast tubes . The digital laser temperature gun told another story . Most of the electrical temperature systems are very good with variances of less than 6 degs . We swear by EI instruments , they are very robust and very accurate .

[pmel22]

you guys are awesome!!!! thanks very much!!

[frasergu]

Anyone know the correct "o" ring for the oil temperature capillary adapter, original factory fitting into the engine?
Thank You
GC

[Bruce Fenstermacher]

o-ring? Do you mean the copper ring that goes between the adapter and the accessory case? AN900-10. This is found in X30014 Illustrated Parts Catalog for the C-145/0-300 figure 9, item 27.

There is no 0-ring. the adapter goes through the AN900-10 into the case. The capillary goes through into the adapter. The adapter nut is screwed tight into the adapter holding in the capillary. Do not over do the tightness of the adapter nut. You can split the adapter.

FYI Adapters and their nuts are matched. There are different bevels used. If replacing an adapter one must make sure they get one with the same bevel as the adapter nut that is on their capillary.

[GAHorn]

One of the best treatises on this subject of capillary-type Oil Temp gauges was produced by Neal Wright of our sister Assoc'n "The Int'l C-120/140 Assoc'n".
Neal was kind enough to share and I was given permission to share with our Members, but want to emphasize that it's not our work...so please do not re-publish or hand-out without permission.
TIC170A Members will find it in the MX Library: http://cessna170.org/forums/viewtopic.php?f=26&t=13893

Non TIC170A Members should seek this info by joining Us or The Int'l C0129/140 Assoc'n. https://www.cessna120-140.org/

[frasergu]

Thank You, we installed a 5/8" plug there with the copper gasket you have provided the information for. This sealed the engine for transport to and from the engine test stand after overhaul. There was an o-ring in there when I took it apart, and then it was lost. Maybe that is why the previous owners had so much oil leaking?
Thanks
GC Fraser

[GAHorn]

Thank You, we installed a 5/8 NPT plug there with the copper gasket you have provided the information for. This sealed the engine for transport to and from the engine test stand after overhaul. There was an o-ring in there when I took it apart, and then it was lost. Maybe that is why the previous owners had so much oil leaking?
Thanks
GC Fraser

The synopsis is this: Prior to 1998 Scott used oil temp probes with a bulb which inserted into an adapter-nut, and the bulb had a flat flange (integral copper) which matched the flat flange bed inside the adapter nut. The adapter nut is what screws into the engine using a copper crush gasket. (PN AN900-10)

After 1998 Scott changed the flange on the bulb to a flared (conical) flange, which requires that the older adapter nut not be used... instead a matching, internal, (conical) flared-flange adapter nut must be used. In every case, the AN900-10 crush gasket fits between the adapter nut and the engine.

NO gasket or O-ring is used between the bulb and the adapter nut. A snug fit is all that's required. (In fact, if you overtighten the bulb-nut into the adapter nut you will shear the bulb-flange and create an oil leak...sometimes the leak being so big as to lose all the engine oil in the next flight.)

Old Style FLAT flange

New Style FLARED flange

To reiterate.... you MUST use the correct bulb and adapter nuts which are made for each other or you will have a leak. DO NOT MIX THEM. You MUST use an AN900-10 copper crush gasket between the adapter nut and the engine.

[n2582d]

I have what appears to be an original oil temperature gauge, p/n 0411017, with the Cessna logo on it. What's interesting is that the bulb style doesn't really match up with either Scott style; the nut end is flat where it contacts the capillary bulb and the bulb is flared where it contacts the adapter.

[GAHorn]

That may be an early Rochester unit made for Cessna. It also had a matching adaptor. (Original enthusiasts can have an instrument shop silk-screen the Cessna logos on any gauges.)