oil pressure question

Cacti_Ken · Posted: Sat Dec 22, 2007 10:45 am Post subject: oil pressure question

A post was started concerning oil pressure on another forum, on which I replied with my concerns but didn't get any responce to it.

So let me ask here.
I have a couple of questions relating to oil pressure.

With a newly rebuilt engine and a new oil pump, what should one expect the oil pressure to be when engine is operating above 1000 rpms'. I am not being specific on the rpms, but I figure a 1000 rpms is a good number to get peak oil pressure.

Concidering that the oil pump is regulating as it should and the oil passage ways are clear, normal, and not obstructed.

Can a higher than normal (what ever that is) oil pressure be bad for the engine. I realize that there are things and conditions that control the oil pressure. If the pump is operating as it is supposed to be, then basically I am asking how much pressure would be too high or not good?

Hope my questions make sense .
thanks
ken
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wesk · Posted: Sat Dec 22, 2007 11:17 am Post subject:

Ken,
The big problems with high oil pressure are forced leaks and the danger of blowing flexible hoses. Also excessively high oil pressure results in higher oil temps which shortens the life expectancy of the oil and in turn forces the water temp up.

The book is quite clear in the low and cruise limits. 10 PSI minimum at idle and 30 to 35 PSI at cruise RPM about 1800 to 2000. The variations between 600 RPM idle and 2000 RPM cruise are not straight line so interpolating the intermediate pressures are impossible. An acceptable industry high is 45 to 60 PSI. I would be uncomfortable with a 2000 RPM pressure of 51 PSI or higher.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

Cacti_Ken · Posted: Sat Dec 22, 2007 11:46 am Post subject:

Thanks for the info Wes.
I don't know how accurate the gauge I was using back when I got this engine running, but I recall at least 80psi on it.

I'm going to try and get a known good guage and measure it again. Since I am retired I don't have access to test gauges and test instruments anymore. Maybe I can get one of my friends that still work there to check calibration on a gauge for me.

ken
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davem201m38 · Member Joined: Jan 22, 2006 Posts: 429 Location: UK

I recently picked up an industry type gauge that works directly off the oil in the gallery pressing against a diapghram (darn, I can't spell the word!) in the gauge, is very accurate.
I discovered that it wasn't my gauge or sender that wasn't working but it was my engine that was running at about 5psi or less! which didn't really register on the 60 psi gauge/sender or the 120 gauge / sender.

Thing is it's ran at this pressure and been FLOGGED by me on European motorways and Brit motorways since I got it up and runs fine, doesn't use oil, if it wasn't for it getting water in the oil I'd leave it alone!

Just goes to show how robust these little old units are!
Try and pick upone of these simple test gauges.
All the best,
Dave

Cacti_Ken · Posted: Sat Dec 22, 2007 6:29 pm Post subject:

What I am using on the jeep is the 24volt sender an gauge. The sender is used and the gauge is new. I don't think it is displaying the truth. But then again I never checked it against a good gauge. I was satisfied at the time that at least I did have oil pressure which was good enough for me. Right now it has close to 450 miles on it.
But at this time I don't know what the real pressure is.
I am going to find out as soon as I can.
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wesk · Posted: Sat Dec 22, 2007 10:26 pm Post subject:

Any quality direct reading gage can be installed in the threaded port the electric sender uses. You can even assemble a short piece of hose to the port and the gage. Usually a 0-100 PSI gage with 5 pound increments or better is best.

You can order this one from McMaster-Carr for $11.30

Cacti_Ken · Posted: Sun Dec 23, 2007 10:34 am Post subject:

Sounds good, One is on order.
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davem201m38 · Member Joined: Jan 22, 2006 Posts: 429 Location: UK

Yeap, thats more or less it. Mine has a length of flexy amoured hose and and an a-dap-ter to screw it into the block to get it to the same thread size as the sender which I think is very close to BSP taper? anyway. A highly experienced heavy mechanic told me the gauge would be more accurate if I filled the hose with oil.
There are several threads here someplace about my woes as I tried to trace my problems with my oil pressure till I got this gauge.

I found that as I swaped gauges and senders I created earthing faults and other faults. Actually finding out I was running 5psi or less was a relief .

Cacti_Ken · Posted: Fri Dec 28, 2007 2:40 pm Post subject:

I received the gauge that I order and have placed it at the end of the line going to the oil filter in the first two photos. Photos 3 & 4 are with the gauge in line to the filter.

At idle rpm

At higher Rpms

At Idle RPM

AT Higher RPMs

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wesk · Posted: Fri Dec 28, 2007 3:16 pm Post subject:

Well looks like you have plenty of pressure. The "T"d hookup verifies the oil filter's restrictor is doing it's job. You're a bit high for idle but then we don't know if you are idling at 650 or 1000 RPM. I'd say you have a very tight engine. I just love those large readable dials.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

Cacti_Ken · Posted: Fri Dec 28, 2007 7:08 pm Post subject:

I put the gauge on the oil filter line because it was easier to get to. Do you recommend putting it at the oil sender port for better determination of pressure?
Looks like to me the overall pressure with the oil filter in the circuit is roughly 30 psi at higher RPM.

I don't have a way to tell what the RPMs are but I'd make a guess they weren't higher than 750 at idle.
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35th Inf. Reg. "CACTI" 4th I.D. VN
Amateur Radio K5XOM

wesk · Posted: Sat Dec 29, 2007 12:21 am Post subject:

Anywhere along that main left oil gallery is fine.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

sergeantfirkus · Posted: Sat Dec 29, 2007 9:26 am Post subject:

Ken:

I defer to the masters! Sometimes a guy need to think outside the box which obviously you do.

I of course bent over the fender and tee-d a fitting in down by the sender to hook up a gauge to verify my oil pressure too.

Didn't even think about putting the TEE up by the filter. Of course there is no challenge in that, no steering or exhaust to work around while bent over!

I'm doomed to continue dragging my knuckles thru the dirt.....

Greg V.
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1951 M38

wesk · Posted: Sat Dec 29, 2007 10:18 am Post subject:

The "T" reading is the reading that is being picked up by the M38's pressure sender. The dead end 50 PSI reading is not a realistic or useable working oil pressure figure. Also do not leave the oil filter out of loop for long on the early chain drive cam engines. An electric gauge connected to the stock location that reads 50 or more PSI is usually the result of a bad sender or a plugged oil gallery. The latter is dangerous to your engine's health.

The reason for many recent overhauls not registering much more than 30 PSI at higher RPMs is usually worn lifter bores and/or worn cam journal bores assuming all other oil clearances have been brought into tolerance during the regular overhaul procedures. If you want that 45 PSI reading at 2500 RPM then oversize lifters and special bushing of the cam journals will be needed.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

Cacti_Ken · Posted: Sat Dec 29, 2007 12:05 pm Post subject:

Greg, don't feel bad. I have busted my knuckles many times and realized later I could have done it different.

I made the decision to dead head the pressure into the gauge on my curiosity of what the pressure would be and only run the engine long enough to take photos. And which later determined that the oil filter is working.

I was dissapointed in that the highest pressure obtained after I Tee'd the gauge in line was just under 30 psi at higher rpms on the rebuilt engine.

I looked at the itemized list of worked the rebuilder did on the engine.
He didn't replace any valve lifters, so as you commented that maybe where the engine is losing some pressure.
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Tropical Veteran
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Amateur Radio K5XOM


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