Ca you run both an elec. and a mechanical oil pressure gauge on a 258?

[marc]

Has anyone ever run both a mechanical and an electric oil pressure guage on a 258 off the same access, maybe with a T?

[tgreese]

Yes, it will work. As you suggest, use a tee.

[bigun]

I have done it for temp gauge

[tgreese]

Sp. I have done it on my J10 and my CJ-6. The J10 has the original gauge and a switch for an electric fuel pump. The CJ-6 is a V8 but same idea - I have a mechanical gauge and a switch for the electric choke.

IMO it makes no sense to run two gauges long term, but it would work. Add a tee and use the same port for both.

[will e]

In my other old car I have a mechanical oil gauge under the hood. I can see it from the cab with the hood lifted. Yep, just use a T.

[marc]

Not looking to hook it up permanent but I need to diagnose the classic engine heats up and oil pressure drops to the white marker or below in gear at idle hot. But is is inconsistent sometimes higher or lower. I did get the gauges running with the point of comparison with the addition of the little circuit to replace the burned out voltage regulator. Now the oil and gas gauges seem to change by about 15 to 20% depending on their mood. Twice they both read zero for awhile. Some connection is likely loose. I want to establish if in fact there is a sufficient oil pressure. Having both would will allow me to have some point of comparison to the original meter.

[tgreese]

Good plan!

[Stuka]

Not looking to hook it up permanent but I need to diagnose the classic engine heats up and oil pressure drops to the white marker or below in gear at idle hot. But is is inconsistent sometimes higher or lower. I did get the gauges running with the point of comparison with the addition of the little circuit to replace the burned out voltage regulator. Now the oil and gas gauges seem to change by about 15 to 20% depending on their mood. Twice they both read zero for awhile. Some connection is likely loose. I want to establish if in fact there is a sufficient oil pressure. Having both would will allow me to have some point of comparison to the original meter.

If the oil pressure truly dropped to zero, you would most likely hear a lot of lifter clatter. But verifying with a mechanical gauge is certainly the right move. The stock oil pressure gauges are uh... unreliable at best.

[threepiece]

I had a sending unit crack one lucky day. This was in my restored Wagoneer. The unit was made with a part that was plastic or perhaps phenolic of sorts. I was lucky because it happened just before I drove up my driveway at home. I noticed a large puddle of oil after parking it. Had it happen while rolling the freeway the story would have ended very differently.

For this reason I only use direct reading gauge plumbed with all steel lines or no gauge at alL

[marc]

threepiece, do you use a standard mechanical oil pressure gauge or is it something special that can use steel tubing and how do you bring it through the firewall? And what kind of connections does it use, flare, compression or what? I have been looking for a gauge with more low end resolution to watch the changes in oil pressure. Thanks, Marc

[tgreese]

With a mechanical gauge, you typically have your choice of plastic (nylon) lines or copper. Both are a standard tubing size, and use similar fittings. When 3-piece says steel, I would guess he means braided steel lines. Something like that would be fine - it all fits together with plumbing fittings. I presume you could find 1/8" steel line in place of copper. This has the advantage of not accumulating work-hardening with vibration, like aluminum or copper would. Steel is unique in this respect, lasting indefinitely as long as its stress limit is not exceeded.

I'd suggest this: https://www.summitracing.com/parts/sww-82323

JMO - I've had good luck with both the nylon and copper installation kits. When I used nylon, I sheathed its entire length with vacuum hose. Might fail after a few decades, if installed properly.

[marc]

Tim, I was thinking of this gauge, https://www.summitracing.com/search/par ... ter%202179 as it seems to have a greater resolution, going to 0-60 psi, at lower pressures. I am curious as to how the oil pressure drops as the engine heats. BUT, I don't know about the relative quality of the manufacturers.
Marc

[tgreese]

Don't know about the maker. It's only 1.5" in diameter - that's small. Is that what you want? Not a name brand. S-W, Autometer, VDO

You can get the Stewart-Warner with a 0-80 full sweep. Summit sells its own gauges in a larger format https://www.summitracing.com/parts/sum-g2934 - fine for a temporary setup, and more visible.

[67GMC]

You've probably already seen several posts about the accuracy of the stock gauges. Not sure I would be too concerned about sporadic readings from the stock gauges. A set of autometer gauges (water temp/oil pressure/volts) will go a long way and you will most likely get more reliable readings. On my '84 I've seen the oil pressure get pretty low when the Jeep is hot and sitting at idle. Max pressure is always at cold engine and typically goes down when the oil heats up. The mechanical oil pump flow increases with increasing RPM. The increased flow encounters resistance in the engine making pressure.

[marc]

How low is "Pretty low" oil pressure, my oil pressure after 40 minutes running, goes down at idle in gear to the top of the white range on the stock gauge. I assume this is ~10 psi +/-. Going to look for parts to tee off a mechanical gauge.
Marc

[tgreese]

Without a third gauge, you have no way to check the accuracy of both the gauge and the sender. You have to assume one is accurate and test the other. The TSM tells you what the nominal performance is, ie 10 psi results in a sender reading of 35-38 ohms, and this should provide an indication of 10 psi on the gauge. You should put the year, model and equipment of your Jeep in every post. If you put it in your signature file, it will always be there. I would point you to a specific TSM, but I don't know what the specs of you Jeep are.

Anyway, you can assume that the sender is accurate and substitute the nominal resistance from the TSM, and that's what the meaning of the markings is. That's probably the more accurate way to calibrate using what you have.

[marc]

Something definitely is going on with the stock gauges and/or senders on my 1984 J10, put 9 gallons into an 3/4 empty 18 gallon gas tank and filled it both according to the gauges and the filler. On the hunt for a local source for a resistor to test the gauge. A while ago, i did put in the little homemade unit that replaces the CVR which had fried. Possibly that is the source of some of the varying readings.
Marc

[tgreese]

Order from Mouser. Shipping will be maybe $10, ten times the price of the parts. You could buy a 100 ohm potentiometer and dial in the resistance you need. Then clip it to the sender wire and ground. Buy clip leads from Amazon.

Here's a group of 3 on Amazon. Prime too, if you have that. Cheaper than shipping from Mouser. https://www.amazon.com/TWTADE-Potentiom ... ref=sr_1_3

Or buy a resistor assortment. https://www.amazon.com/Resistor-Toleran ... ref=sr_1_4 Way more than you need, but the price is low. Check my article linked below for making other values by putting resistors in series or parallel.

What's your location? There are still a few electronics stores around. Maybe someone in your area can advise.

Here's my article about building a gauge tester on earlyCJ5.com http://www.earlycj5.com/xf_cj5/index.ph ... er.143458/ I expect you will need to register there to see the pictures in full-size. You don't need a special tester - you can use clip leads and resistors. If the gauge responds correctly to the resistor values clipped in to replace the sender, replace the sender. If not, the problem is in the gauge.

[marc]

For my 84 J10, built a variable resistor box with a 100 Ohm Potentiometer. Calibrated it with my volt-Ohm/tach for 0 psi, 10 psi, 60 and 80. The most unnerving result was that at 36 - 37 Ohms, after initially showing 10 psi on the gauge, it repeatedly rose to 20 psi on the dash gauge. My interpretation is that when showing 20 psi the truck could be operating on 10 but when it heats up that drops dramatically, which implies that it is operating on next to no oil pressure when hot? Next step is to put the oil pressure sender on a tee and install a mechanical guage to get an actual measure. Got the numbers from the TSM but need to confirm that they are for my model..

[marc]

Friends, installed an over the counter mechanical oil pressure guage from O'Rielly's off a street tee with the electrical sender as well. Cold starts at 60 PSI and runs at 50 street or highway on the mech gauge. The dash gauge shows forty to start and drops to 30-35. After driving 40 minues including 3o+ minutes at freeway speeds, the oil pressure on the mechanical gauge at idle in drive was a skosh higher than 10 PSI and 13-14 idling in park. Next outing, I will check the idle rpm. Rechecked it on the return trip and that ten+ PSI was holding steady. The dash gauge was going into the left hand white zone. It seems to me that this is marginal but acceptable for now?