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Oil gauge Problems

2225 Views 18 Replies 7 Participants Last post by  CJDave
Anyone else have problems with their factory oil gauge? At idle I'm at about 50psi, and giving it a little gas makes it jump to 75 psi. No engine problems at all, so I figure the gauge is just off. How can I fix this?


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How about a little more info? Is it 50psi cold idle ...... or all the time ( it should be less when hot - same with the high end pressure ). After you give it a little gas does it hang up at the higher pressure or return to the lower one? What weight oil are you using? What year and model (so that someone here knows what type of sending unit you have - electric - mechanical - electronic - etc.) with what engine? Is it an OEM gauge or after market?
I have a high volume oil pump ..... and even when the motor is cold I only get to about 58 psi ..... that's what my pressure relief appears to allow ...... I may go a little above that if I hit highway speeds before being warm ..... but 75psi seems a little on the high side to me ......

MIne did that just before it quit working all together.


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I have the same deal. My Oil gauge starts out at low, but while driving it jumps all over. At a stop on a level surface is the only way to get a semi-accuratte reading.


/wwwthreads_images/icons/wink.gif I see from Grif's profile that both of his Jeeps are 93s. That means the 4.0, and usually they are pretty consistent on oil least mine is....not over 50, and warm idle at about 25. You can certainly see the Chrysler influence in the oiling system over the early AMC engines. Chryslers have always had stellar oil pressure. I don't trust the senders all that much, and before I put the ranch up for auction I always check that. It's a lot easier than rollin' in a set of bearings. /wwwthreads_images/icons/crazy.gif I always like to try the 98 cent solution first.....just a habit...that's saved me thousands of dollars and tons of grief. /wwwthreads_images/icons/tongue.gif/wwwthreads_images/icons/wink.gif

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my wife's CJ-8 had oil pressure that changed with RPM and engine temp. (also had some electrical needle spikes) it slowly got worse (more erratic/extreme readings) i didn't believe it was the engine, so i replaced the factory electrical guage and sender with a mechanical guage and tubing, now my oil pressure is more stable, i believe it's also more accurate.

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Oil Pressure gauge S terminal - Purple wire from sender
Oil Pressure gauge middle terminal - Black wire (Ground)
Oil Pressure gauge right terminal - Red wire (Ignition-on hot 12v)

The oil pressure sending unit is on the engine block and looks like a small 2 X 3 inch filter with one terminal. There may be another sender plumbed in the same area that has two connectors. It is an oil pressure switch that is supposed to close below 4 psi to activate a dash warning light in some speedometer clusters.

To be sure the problem is not the gauge, you can momentarily short the wire from the output of the Sender to ground. If there is no resistance, your gauge should read 80 psi. DO NOT hold it for long in this position. If the needle does not move from zero psi then, either the wiring (open circuit) or the gauge is bad. If it does move, the sender unit is bad.

It is very common for the sending units used with the 258 and 232 engines to be inaccurate. Make sure you have a good connection to the sending unit.

It is easiest to test the sending unit by temporarily plumbing in a good mechanical gauge.

Pressure (PSI) Resistance (ohms)
0 234-246
20 149-157
40 100.5-105.5
60 65-69
80 32.5-34.5

Jeep CJ Gauge & Sender Diagnostics
by John Foutz

/wwwthreads_images/icons/crazy.gif It's a JEEP thing! 1985 CJ7 /wwwthreads_images/icons/crazy.gif
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I love getting on on the 'ol "oil pressure reading" discussion.

My opinion is that electric gauges aren't accurate. If it reads anything, you have pressure. If it reads nothing, you may have pressure. The best way to check is either replace it with a mechanical, or buy a cheap mechanical for $10.00 and hook it up temporarily just to see if you have pressure.

Loose nut behind the wheel
Another right-wing conservative.....
I'd have to agree with LEVE. My experience has been the same. My idle pressure is just under 20 lbs with a new oil pressure sending unit. Altho, it doesnt get much higher than about 25 lbs at highway speeds and I'm running 35" tires with 4.10s... so I think that's about right. I do, however, have higher oil pressure at startup....somewhere in the range of 35 - 40 lbs.

That's been my experience....

85 CJ8,258,Weber32/36,4" BDS lift,4.10,35"tires,f/r lockers
Huummmm .... Say, 85 CJ-7...
You should give the author credit when you paste copyrighted text and images from another site....
... being a computer pro you should know that. It is also common courtesy.
You have good intentions my friend, but bad manners.

EDIT: OK, thanks for credit tag, guy.
BTW: My Diagnostics are limited up to 1986 CJs. The YJ & TJ gauges are a whole different story.

OK, kidz....
Let me remind you that a high volume oil pump is a real bad idea in most cases.
Such a pump can cause the following problems in a new or tight engine...
1.Without a large capacity pan you can be sucking your oil pan dry.
2.The high pressure pump might try to send your distributor through your hood.
3.Extra high pressure will make your block's internal bypass open, sending unfiltered oil to your bearings.

Okay "big boys"/wwwthreads_images/icons/smile.gif.....I again bucked convention on this. I have had a high volume oil pump in my '99 TJ from about 3000 miles. It's had ZERO oil consumptionl in 4500 miles (7500 on it now -synthetic and still going) and still appears clear...some of this can be attributed to a new clean motor w/o all the blowby but the priciple reason is that the oil is refreshed so much more often that it doesn't see the severe heat that fatigues it.....pressure is higher and ..yes I'm sure the distributor is taking on additonal load......but....IF THE DISTRIBUTOR DOES FAIL's a snap to replace ......bearings ....blow-by (I guess blow by doesn't exist with NON high volume pump motors) and such are not quite as easy.
High volume oil pumps are available for almost every domestic motor made ...... I have yet to see any with a warning sticker saying "don't buy me because I'll only hurt your manufacturer only builds me for practice and likes to waste his time and money paying people to do it and remember everything OEM or equivalent is the only way to go (including exhaust, suspension, tires, carbs, body height, shocks, etc.) BECAUSE THEY KNOW BEST.
You can cry "the sky is falling" all you want Chicken Little and you can live with 15 psi at a warm idle .....and do your 3000 mile change interval ....and will more than likely, inspite of your best efforts, end up with typical engine wear. But that's not good enough for me..........for any ONE bad event regarding a highvolume oil pump ....I'll show you a junk yard full of "sad stories" because of poor lubrication.....not half of them due to neglect. Many in this forum will flog their motor in extreme conditions .....they've spent tons of cash on extreme upgrades to thier tires/shocks/springs/wheels/gears/axles/shafts/trannies/transfer cases/lockers and "on board air ...all to accomplish acts not meant for mortal vehicles .......yet you treat the lubication system as though it was a common passenger car driven under normal just doesn't add up to me.

GeeAea - praying for dispensation for crimes against the common oil pressure guild
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You have made some very good points. All valid!
Since you have made such a good point as to the merits of lots of oil volume (and I agree whole heartedly with you), and you have made the point of spending tons of cash on other upgrades (also true) then may I say one should follow through with this train of thought as to the high volume pumps.
The distributor is the least of the worry. The dry sump syndrome IS.
If your engine can handle a high volume pump (Both Hesco and Clifford advise against using one and instead recommend a heavy duty or blueprinted unit) then I'd say "go ahead!" BUT I would NEVER leave it at that!
Please notice in your Summit and other hot rod catalogs there are pages full of deeply or widely expanded and baffeled oil pans. These are designed to complement all those high volume pumps for exactly the reasons I gave in my original post. Plus the extra volume helps keep your oil temp down.
Ideally, an off roader with a high volume pump would want a pan whos side/s are enlarged horizontally AND properly baffeled. Going head first down a 30 degree incline with a high volume pump will most likely put most of your oil up top and in the front of your engine and very little to none at your pick up screen. Such pans are usually designed to also lower the sump's oil level thus decreasing oil frothing at high RPM or extreme angles therby decreasing oil blow by into the the upper ventilation areas.
Food for more thought.

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Hehe, I don't remember this type of discusions in at the old BBS. I think I've learned more here in the past week than all summer long with my friends.

93 YJ, 4.0L, Tuffy'ized interior
Here's what I did. Ihave an 85 CJ7. The oil gauge was registering about 20PSI at freeway speeds which scared the hell out of me. Hooked a mechanical guage to it and the pressure was fine. I then replaced the sending unit. It still didn't work. Replace the gauge. Still no luck. This really annoyed me as I sank about $45 into this little problem. Last weekend I installed an Autometer mechanical gauge. It took about 20 minutes tops and it works perfect! The gauge is also the perfect size to fit in the stock hole. Hope this helps and I wish I had done this a long time ago. Also, I replaced the volt meter with one from Autometer as well. It fits perfect too.

It must have been the pepperoni pizza last night ..../wwwthreads_images/icons/smile.gif ....I'm just sensitive when it comes to my high volume oil pump ...oh I love it so!/wwwthreads_images/icons/wink.gif Summit and Clifford are a high performance application you could literally send all the oil into the top of the motor before it could return to the sump -( I've actually seen this happen ..this was before a lot of the advanced pan technologies were developed for market and had not reached the public)......hence they sell sump extentions and deeper pans with the windage trays and such - they also have a reputation to uphold ...and one or more hot rodders spinning their cranks because of a high volume pump running the sump dry ....and they have to advise against it. But I don't anticipate pulling 8000 rpm or speed shifting the TJ anytime it the near future so I think that my principle concern will be my distributor wear. I'm banking on the high flow characteristics of synthetic oil to spare it the high torque needed to turn the higher volume of oil.

.........and what was that about that guys gauge......????/wwwthreads_images/icons/smile.gif

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/wwwthreads_images/icons/tongue.gif How, oh I ask you HOW...can I not comment on this. There was a lot of truth in what has been said here...all of it; and in my not so very humble opinion, one of the posts brushed against THEE critical factor in maintaining good oil pressure over a reasonable RPM range, and at various engine temperatures, and that factor is.........blueprinting. Yep, if the pump is actually what the engine designer intended, you'll be fine. The problem is.....very few are. We all know how bad the AMC V8 family is for oil pressure, well an outfit in Oregon takes your front cover, and reworks it to PERFECT specs, and that ends your oil pressure trouble at RPM and at idle. The rest of the engine clearances don't matter much if the pump is sloppy and won't pump warm oil./wwwthreads_images/icons/wink.gif

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