Mechanical oil pressure gauge.

I’m installing a mechanical oil pressure gauge, by putting in a brass “tee” fitting along with the oil pressure sending unit. I’ve got a brass tee, a 3’ grease fitting line (rated 3600 psi) a reducer fitting and a oil filled pressure gauge. Total cost is $25. I asked the guy if this gauge was appropriate for this use and he said yes. Working pressure will be ~50 psi. Is this gauge ok or do I need an automotive one?

Also, the gauge has an instruction on it to cut off a rubber seal a the top, which I find is odd.

Jim

I'm doing the same thing ... using a car oil gauge kit I got from Auto Zone, about the same cost (minus the T, I've got to find of those).

I got everything at Greenline Hose and Fittings, in Vancouver British Columbia. They have been very helpful for me in the past. There should be a similar outfit for you where you are (FL), I would imagine. These places are Industrial concerns and sell hydraulic hoses and various fittings for liquids and gases. Seriously, I was stunned that this set up was only $25.

Don't use a brass nipple to connect the tee to the block. They can fatigue fracture. Use steel there.

Thanks Ski. I can make that change. Everything is only hand tight right now. Any thoughts on the gauge?

Jim

IF you install a Murphy Switch Gauge you can set it to any pressure , below which it can ring an alarm.


About $45, plus the alarm.

JDCAVE said:

I’m installing a mechanical oil pressure gauge, by putting in a brass “tee” fitting along with the oil pressure sending unit. I’ve got a brass tee, a 3’ grease fitting line (rated 3600 psi) a reducer fitting and a oil filled pressure gauge. Total cost is $25. I asked the guy if this gauge was appropriate for this use and he said yes. Working pressure will be ~50 psi. Is this gauge ok or do I need an automotive one?

Also, the gauge has an instruction on it to cut off a rubber seal a the top, which I find is odd.

Jim

View attachment 94182

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It makes me happy to see you used a quality line to connect the guage. I have had those copper capillary tubes break and leak oil.

Gauge looks fine. Liquid filled so that damps pressure pulses. Range might be a bit high (100psi) but that's ok.

You can get a steel machined nipple from a hydraulic shop for a couple bucks, well worth it. I have dealt with an engine with wiped bearings from when a cheap nipple fractured. Once the thing broke off, it lost the ground for the oil pressure alarm, so alarm never sounded. Not pretty.

Yup, thanks Ski. I’d rather learn someone else’s lesson. Everything is closed this weekend, so I’ll pick one up Monday. The nipples on the grease whip is brass as well. Are those a concern as well, or just the brass tee?

FF: I still have a low oil alarm that is attached to the ignition switch. It sounds when I turn on the ignition and when I shut down the engine.

"FF: I still have a low oil alarm that is attached to the ignition switch. It sounds when I turn on the ignition and when I shut down the engine."

That will let you know when the oil pressure is below 5PSI or whatever it was set for.

A Murphy Gauge will allow you to set your gauge to any setting , so if you normally see 40PSI cruising you can set the gauge to say 35PSI and not wipe the engine at cruise RPM.

They make mechanical temperature alarm gauges too.

Hi JD,

I also put in a mechanical oil pressure gauge this summer. It was a Bosche from Advance Auto Parts, $19.95. I used a brass tee but will change to steel after reading Ski's advise.

Pressure was dropping as the engine ran. Turned out to be a bad sender. I replaced the sender but like the belt and suspenders of mechanical and electric.

Rob

Ski's advice to use steel rather than brass is wise advice. With the weight of that sensor and of the hose being supported by the nipple portion threaded into the block, engine vibration will work harden the brass and it will fracture. I know this from experience. NO brass!

The brass tee is ok. The nipple where it screws into the engine is the concern, it should be steel.

Ski in NC said:

The brass tee is ok. The nipple where it screws into the engine is the concern, it should be steel.

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This explain me why my oil pressure senders are screwed into a brass tee, itself screwed into a iron nipple, itself screwed in the engine block. I was wondering why the builder did that

L

Jim:

Have you figured out how you’re going to mount the gauge? We bought a Equus dual panel mount (part #: 9922) when we did ours. We also added temperature when we did the oil. Equus also makes a single and triple mount.

Larry: I thought I’d just “tastefully” mount it on a piece of starboard, afixed to the beam supporting the hatch combing. I will use a bracket to hold the gauge at the position of the reducer fitting. This fitting is fairly thick stainless and can easily hold the gauge in a rigid position.

It’s shame this grease whip has brass nipples. I will see if they can make up the equivalent with steel nipples

Jim

The hose with brass nipples should be ok too. The problem with the brass is the nipple that screwed into the block must support the mass of the tee, sender and some of the hose. And in an environ where it is lively with vibration. The brass nipples tend to also be thin wall. If you could find a thick wall nipple, that would be ok too. The hose ends probably have thick wall fittings (small hole in center).

Ski in NC said:

The brass tee is ok. The nipple where it screws into the engine is the concern, it should be steel.

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The fitting in the picture is an all-brass street T. That's why I said NO brass. A brass T fitted to a simple steel nipple works but more simple alternative is a steel street T.

catalinajack said:

The fitting in the picture is an all-brass street T. That's why I said NO brass. A brass T fitted to a simple steel nipple works but more simple alternative is a steel street T.

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Thanks Ski, Cat Jack. I’m going to get a steel street tee, for sure, and if they can make up a hydraulic hose with steel nipples, I’ll get that otherwise I will use the hose with brass nipples for now.

Jim

Jim,
i doubt you will have any problem with the brass hose fitting ends. The hose is rated for high pressure and so must the end fittings be, usually more than the hose they are attached to.. THey will be thick enough to stand up.

As Ski said it is the brass nipple between the engine block and the brass TEE where the problem lies. Engines vibrate and the brass in that application won't last partly because the nipples are typically a thin wall and a close or short nipple is nearly fully threaded which weakens them even more.

A FORGED fitting or a HEX nipple would be a lot better than a close or short.

Better is change the nipple to a hydr. steel nipple and a steel hyd TEE.

Well, I decided to go all steel with the hydraulic line. I was on the fence on it but went ahead anyways. It was considerably more expensive, with the change over to the steel tee and the hydraulic line being another $28. They had to make it up with fittings and a hose one size up, Hopefully it’s not too heavy. It will certainly need more support than the grease whip with brass nipples.

Hi Jim, you should be fine to leave the rubber seal intact for the pressures you are measuring and the accuracy required. The gauge is measuring the differential pressure between the pressure entering the Borden tube from the gauge port and the atmospheric pressure on the outside of the tube. A liquid filled gauge requires the gauge case to be sealed to prevent the fluid from escaping during shipping and hence sealing the gauge from receiving the atmospheric base reading required to enable a true measurement. Just pry the grommet sideways a little to allow the internal pressure to stabilise with the atmospheric pressure of the day if you require an accurate measurement, but it should never change more than 3 psi. Temperature changes can also make a slight difference to a sealed gauge but not very much. If you ever notice the needle move of the stop at rest the grommet needs burping. Or ..............you could just cut the rubber seal off.

BeeJay said:

Hi Jim, you should be fine to leave the rubber seal intact for the pressures you are measuring...

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Update: I’ve got it all put together, steel street T, new oil temperature sender, hydraulic line and mechanical gauge. All is running fine, except slight differences of 3 psi between the two. I guess, it’s the same as having two clocks...You never know what the time is...

So I try and pierce the seal at the top of the gauge and end up pushing the whole thing into the gauge to reveal a hole of about 1/2”. WTF? I’ve sealed it for now with electrical tape. It works fine as the guts of the operation seem to be contained in a cylinder inside the gauge. I’m going to get another rubber grommet to seal the gauge. If the whole thing fails, I’ll just get another gauge as they are cheap enough.

Jim

Looks nice. I don’t know what cutting the rubber plug is all about. There should be a rubber plug in the top of the gauge where the liquid (probably glycerin) was put in.

I had an oil pressure switch try to kill me once. I was flying a Cessna 172 and had landed at Ft. Lauderdale to go through customs.

As I was getting ready to leave I had the engine running while I listened to the radio. A guy came up, banged on the door and pointed down. I shut down, got out and there was all of my oil on the ground under the airplane. The diaphragm in the switch had burst and all the oil had been pumped out through it. If it had burst ten minutes later, I’d have been a glider pilot pretty quick.

Any chance you can use a pair of tweezers to pull the plug back out? I'm thinking it might interfere with the guage operation as the tube/gear rack moves.

Thanks “C”. I sealed it for now with a tapered plastic end cap. It seems to be working for now. The VDO gauge at the helm is stable at about 55 psi and the mechanical gauge above the engine is reading 54 psi. If it happens to stop working down the line, I will just replace it. It was only $13.



Jim

Well done, something else to add to my tasks list lol

L