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Discussion Starter · #1 ·
I have an 81 CJ-7 with a 258 of unknown mileage. It doesn't rattle or smoke but it shows only 3 - 5 psi when hot. The guage is a new mechanical one that reads the same as the two electric ones befor it. I have installed a high volume pump and replaced the rod bearings w/stock while I had it apart. I didn't plasticguage the old bearings 'cause I had the new ones anyway. The old ones didn't look to good so I assumed that was the problem. It wasn't. I gained a pound or two of pressure at idle at most. This jeep doesn't make any "bad" noises yet still I am concerned. Anyone have any thoughts on this?

Thanks, jay2jeeps

Bad politicians are elected by good people who don't vote

 
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Discussion Starter · #2 ·
Mine goes from 10 to 40 with new bearings. You should have 10lbs for every 1000 rpms. One thing to think about, did you get the pick up tube in securely in the oil pump? Also, bleed the gage line because air compresses more that oil. If the lifters are screaming, and your not overheating, you should be OK.

 
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Discussion Starter · #3 ·
mines gauge reads about 35 on idle, and about 50 or maybe less when driving


(\/)ikey 1988 Wrangler Laredo 4.2L w/5spd Manual
1995 Wrangler 2.5L w/ 5spd Manual
 

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I have a 258 in my 78 CJ and when I start mine up in the morning I get almost 60 (20w50 oil too). When it warms up I normally have
about 12-15 at idle. What weight oil are you using? You may want to try a thicker oil if youdon't live in a cold climate. Here in Fl I run
20w50 all year except for January and February. Those months I use 10w40.

Alec

 
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Discussion Starter · #5 ·
I know of CJ's that have had the same reading as yours (including my own) for years, with no problem. The key is that you want a 10 lb increase for every 1000 rpm. I'm probably gonna change my mains to see if that is it, but many will tell you its normal. I think Granville King (I think that's his name) author of the second Jeep Owner's Bible, has been quoted on this as well.

Phil Baird 83 CJ7
www.off-road.com/~pbaird
[email protected]
 
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Discussion Starter · #6 ·
Most likely your engine is getting old...like the rest of us. If your rod bearings were worn, then the mains are most likely worse...and most likely the cause of poor oil pressure. Without doing a rebuild, about all you can do is run a heavier weight oil and not abuse it. Short of a rebuild, there is nothing you can do to solve the problem. And to be honest, 5psi at hot idle is not that bad...as long as you get about 10psi per 1000 RPM as the others stated...i.e., at 3000 rpm you should have about 40psi.....

If you live in a warm climate then run 20w50 oil....winter time, 10w30. Don't waste any money on oil additives like Slick 50....they are just gimicks.

John......southern CA
84CJ7,3"lift,32"BFG,4.11's,ARB,Solid Axle's
 
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Discussion Starter · #7 ·
Something not suggested is change out your oil pressure sending unit. I just did mine and before it went from 5-20 now it goes 5-40. still is lower then I'd like but it is closer. Also try hooking up a mechanical gauge to see what it is truely running at. It seems that 1. these engines tend to put out low pressure over time and 2 the guage sucks.

Brent

 

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With a high volume pump on it .....you should have almost 60 psi at cold start and around 40 psi at warm idle ......with probably 55-58 at road speed........you're not even at half that.....( I have one and the stock oil pump has about half the vane area that the HV unit has)....normal would be around 12-15 warm idle........around 40 at cold start and 23-25 at road speed..........
BTW-what is the pressure at road speed?........you didn't say......


........tap a new oil pressure location......there's got to be another one somewhere on the motor.

GeeAea


 
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Discussion Starter · #9 ·
I have a 84 CJ7 that I bought used years ago with 39,000 miles on it. At idle the pressure dropped off to 5 psi. Replaced the electrical gage with a mechanical, same thing. Calibrated the gage to make sure it was reading right. Installed a high volume pump and while the pressure, cold, started off at 60psi at 3000 RPM it still dropped off to 5 psi at idle. I now have 89,000 miles on the engine, 6 Rubicon runs and numerous other trips. The engine doesn,t clatter,(lifters) or knock, (bearings). It also doesn't burn oil. I won't be pulling it apart until something drastic happens. When I do it will get rod, mains and most definitely cam bearings. Probably a 4.0 head also. My suggestion is: drive it.

 
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Discussion Starter · #10 ·
Guys, a lot of DUMMY lights on automobiles do not indicate low pressure until 3 psi.
Now if you have an engine that is running low on pressure, and you overheat-- say to 230 degrees F.----- You are going
to have instant damage--- and the end of the engine in a minute of two.

I have a newly rebuild Buick V6 that runs at 37 psi cold-- the oil pressure relief valve keeps it down under 40 pounds at an idle.

Then when hot at idle it drops to about 17 psi. But when hot lugging, while doing crawling at 300-500 rpms in low range-- crawling it drops to
about 5 psi----SCARY! Then even with only 5 pounds, when reved back to 2000 RPMs it has 35-40 pounds.
I would not put in a heavy oil pump because it strains the distributor drive gears, and wears it out-- and timing gets to be a problem.

I have had a lot of engines that were at 5 psi when at hot idle, and only at about 10-20 psi
at 2000-3000 rpms-- and they ran for tens of thousands of miles--- and on disassembly, nothing unusual!
No one likes to see low oil pressure! Having high pressure is like an insurance policy. But if you got 15 pounds
at 2000 rpms, the bearings are not going to burn-up.
But if you only get less 9 pounds at 2000 rpms when hot-- or lower -- your engine is not in shape and could go bad shortly.
If you change oil very often, it MIGHT help the engine live longer.
Sometimes even with new pump gears, a worn oil pump housing causes lowered pressure.
Sometimes a whole new pump (housing too) does not help.---- Other times it is only a worn-out pump and not the crank bearings causing low pressure.
If you are below 9 pounds and you hear chattering when you rev the engine up to 2000-3000 rpms --- and hear the lifters ticking and all that sound that is the soul of the engine
saying "this is the end---- mate".

Oil thickeners--- do they help? Like two cans of STP in the crankcase? I'd say only if you are trying to hold your engine together for the last couple of thousand
miles.

So to sum it up, some engines run and run with pretty low oil pressure--------- but you got to have a little to keep them alive.


SRR

 
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