Hi all:  I have a 1993, 240 wagon, 

B230F engine, auto-transmission, 140,000 miles.

I'm in the process of building a homemade

Oil Pressure Gauge for my car.

This would allow me to temporarily mount

the gauge inside the vehicle to monitor oil pressure as I'm driving (need

this for another problem I'm working on).

I have a 100 psi gauge.  I will attach

an 8 ft. (96") reinforced rubber "fuel line" hose to it.  3/16" I.D. 

Fairly thick wall thickness.

It will then be attached to the engine

where the Oil Pressure Switch/Sensor is and routed through the firewall

/ bulkhead.

I plan on pre-filling the 8 foot hose

with engine oil before I attach the gauge to it.

QUESTIONS?

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1.  Will this length of hose (8 feet) effect the reading?

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2.  Because the hose is rubber (and could flex and expand slightly)

will this effect the reading?

Any assistance or ideas would be appreciated.

Thanks ...  Mr. Tool  (Two 1987

240 Wagons, One 1993 240 Wagon)

I picked up a mechanical oil pressure gauge from the local auto parts store for about $25. It came with all the fittings and plastic tubing . On the block end, the gauge kit had a male 1/8" pipe thread. Fortunately, I had an old broken idiot light oil pressure sender that I modified by breaking off all of the plastic, drilling out the center, and tapping it to 1/8" pipe thread. I just screwed that into the block, screwed the end of the gauge's oil line into the hole I tapped on the old sender, ran the line through a hole in the firewall and hooked it up.

I've had it in for about 4 months now with no problems. And I didn't prefill the tube. Doesn't seem to spike the gauge.

Well, not for watching your oil pressure, but Neal, aren't you 'Mr. Tool' too? I mean the publisher of some very helpful toolmaking plans?

I want to thank you somewhat publicly for providing me and others with a wonderful use for our spare 2" rigid conduit couplings;-)

All told (and no, I haven't begun) your contribution was a great experience, and I thank you for it, my nice solid ride and hosting the web page.

Art, thanks for the mail and the picture. I've been called a "tool" before, but never "Mr. Tool". It made my day to see that someone actually built and used the sucker.

Would you mind if I added your picture to my website? I didn't have a digital camera when I was using the tool on my car. When I was putting the website together, that's the one picture I really wanted to have.

Of course I'll add your name to the list of credits on the site.

Thanks again.

Neal, I can send you that pic and several more so you can choose for yourself. The images are much larger and more detailed than the one I posted. You might want to contact me off list dhxc5c2@hotmail.com if you don't want many megs in your mailbox later tonight. Thanks again!

Wow, Gary's response was impressive. Mostly I'd have worried about the clamp on the gauge end coming loose and spraying oil all over your interior.

But I recall once when I was plotting as you are I found an aftermarket oil pressure gauge for about what you'd pay for line and shipping from Grainger. The one I have came with a 1/8 plastic pressure hose something like the line I'd like to find to repair a WaterPik, which for some product liability reason Teledyne won't sell. Check the shiny chrome section of the auto parts chain store. Or maybe K-mart?

STOP!

Don't use fuel line for oil pressure! Instead go to an industrial supply house (like Grainger) and get the right length of 1/4" (or 1/8" if possible) hydraulic hose which is MEANT for elevated temperature oil. It'll cost you 10 bucks or so, but it'll be much safer than fuel line which is typically not suited for temps much over 100F. Make sure the gauge you use is capable of 100 psi or more.

As to your question about the length of the hose and its flexing affecting the readings, the short answer is "not enough to be concerned with." This is a non-flowing application, so the hose diameter and length really will only affect the rate at which the pressure readings change. I work in an aerospace fluids lab (air to 1200F & 3500 psig, oil to 350F & 7500 psig, and we routinely use 1/4 lines for static pressure measurements; I think most mecanical pressure gauges used for automotive applications are 1/8" diameter. As far as the flexing of the line, this actually works to dampen out sharp pressure spikes (I wouldn't expect any) and preserve the Bourdon tube movement in the gauge.

Good luck!