Oil For Oil Filled Gauges?

[HAP]

Ordered some replacement guages due to the old ones started leaking through the crazing on the faces. The new ones did not come filled, so I was wondering what whould be the best type of fluid to fill them with. I really do not want to go through the trouble of draining the old guage fluid into the new ones as I know they will will come up short in quantity and I would still end up needing to top them off with something...

Thanks,
HAP

[Rich Carlstedt]

I believe they use Glycerin for the liquid, which is available at drug stores

Rich

[CCWKen]

+1 on the glycerin. The gauges I bought came with directions. As I recall, you're suppose to leave a small air gap for expansion. A small air bubble is barely visible at the top of my gauges.

[garagemark]

I use aviation compass fluid..... which I believe is a glycerin based fluid ( I just happen to have a couple of short quarts from rebuilding several compasses for some aviation friends).

[HAP]

Thanks for the speedy feedback. What do I look for in the drug store? Is there only one type?

[lane]

You ask the druggist.

[Thruthefence]

Here's an MSDS for "Airpath" compass fluid. A very common general aviation part.

http://www.emedco.info/rtk/common/wcd00004/wcd00445.htm

SECTION XII - Ingredients/Identity Information
Ingredient # 01
Ingredient Name C10-C13-ISOALKANES, ODORLESS MINERAL SPIRITS *94-3*
CAS Number 68551177
NIOSH Number 1006441IS
Proprietary NO
Percent N/K
OSHA PEL N/K
ACGIH TLV N/K
Recommended Limit 400 PPM

"I knew a guy" who has serviced scores of compasses over the years with Jet-A, right out of the sump, filtered through a coffee filter for extra QC.

[Black_Moons]

"I knew a guy" who has serviced scores of compasses over the years with Jet-A, right out of the sump, filtered through a coffee filter for extra QC.

I thought jet fuel/diesel could end up growing microbes and otherwise 'going off' if stored long enough? (One would assume eventualy getting cloudy/gelly)

[JoeLee]

I think there are different viscosities of glycerin used depending on the preassure range of the gage. Higher reading gages use the thicker stuff. You won't find a choice of viscosities at the local drug store but what they sell will work just fine in most gages. Just don't put regular oil in the gage as it will yellow the dial.

JL..................

[garagemark]

I indeed bought my compass fluid by the quart from Airpath. From looking at the MSDS, it might not be glycerin based, but it works quite well throughout my temperature range.

Some of my gauges are in a very cold environment, but the viscosity doesn't seem to change much between hot or cold; I get no needle bounce at any time. It might not be the "correct" stuff, but I'm good with it.

A quart cost me $5.75 in April.

[boslab]

I beleive the compass oil is the same oil [mineral] as supplied for vacuum pumps, i just filled some pumps after service and it was the same spec oil, its clear btw, not like ordinary oil, i asked one of the fitters what was in the damped gauges as a damping fluid and he thought it was silicone oil but it turns out its the same spec as the vacuum oil i use, needless to say there will be a few bottles of Edwards High vacuum oil being poached from my workshop!, little bottles of gauge oil were about ten times the price!
mark

[Thruthefence]

"I thought jet fuel/diesel could end up growing microbes and otherwise 'going off' if stored long enough? "

The "bugs" will not live in straight kerosene. There must be free water in the tank, such as will occur from condensation in the tank ullage. They actually live in the water globule, and feed off the kerosene. It's their waste products, and little dead bodies that foul the mix. The detritus they leave can be corrosive to the tank structure in aircraft as well as fouling filters & such.

This product:

http://www.conntect.com/fueladditives/biobor/

or something similar, is routinely added to the fuel farm tanks to minimize the bug problem.

I can't imagine enough free water getting into a whiskey compass to breed an infestation, as they are not open to atmosphere, any more then they would infest a quart bottle of compass fluid, that may sit on the shelf of an instrument shop for 10 years.

A "guy I know" told me all this stuff.

[HAP]

Just picked up some glycerin from CVS. They had a hard time trying to locate it in the store. Finaly found it in the beauty section... $5.86 out the door for a 6 oz bottle.
Thanks for all of the help.
R,
HAP