quick question for you smart guys out there

[night_crawler]

I have an 89 jeep cherokee. about a week ago i was having a problem with the oil pressure dropping to absolute 0. I replaced the oil pressure sending unit and it didn't seem to help any. So not wanting to pull the pan off for the 3rd time i took it to my mechanic and he said the oil pump pick up line was clogged. My question is.
What should the psi read at after driving for about 20-30mins?
As of right now, when it's a cold start up it reads 40 then at a stop light it reads about 10ish and while driving it sits roughly at 20.

[AZRockRunner]

That will vary depending on the jeep. I have owned ALOT of XJ's and they are all different as to what the gauge reads. I have had some that stay at 40 PSI driving and not drop below 30 at idle to jeeps that never reached above 20.

You really should replace the pickup unit, there cheap and easy to do and then use a mechanical gauge to get accurate readings.

Just my .02
:dunno:

[FuzzyD]

dido on the mechanical guage. theres a lot of things that effect oil pressure, were and tear, how well its been maintained, ect. you could just have a bad guage or a bad wire somewhere

[RCP Phx]

Oil pressure is also effected by the type/weight of the oil.The oil filter can also play into it!

[iwannadie]

Just thought I would ask since the topic came up.

How do you guys feel about running a permanent mechanical oil pressure gauge? I've read a lot of pros/cons about it but I still think it sounds like a good idea. Most of the cons involve the idea of running hot pressurized oil into the cab and the fitting fails you spray oil. Then people swear that the modern electrical sending units are great and not like it was in the 70s when mechanical was a must back then.

Also, what is a good mechanical gauge tool? I don't want one from harbor freight but I can't seem to find one on like summitracing. It's either the $10 job from harbor freight or like $150 for higher end.

[AZRockRunner]

I run ALL mechanical gauges on mine with copper lines and NOT the cheap plastic line that comes with some. I have some plastic line for a field repair if needed but I don't worry about the copper failing.

[5-90]

Any suspect gage reading should be verified independently, PARTICULARLY ON RENIX. The IP gages are known to lie, even when everything else is working fine (ex. my voltmeter reads about 15.5VDC, although my actual alternator output - as measured - is about 13.4VDC. So, I just made a mark with a grease pencil, and use is as a "relative state-of-charge" indicator.

(My oil pressure sensor is fed through a T fitting, the branch of the T has a "dry-break" connector for plugging in a mechanical gage as part of annual inspections.)

If you lose oil pressure, you'll hear it! Other causes of a "false low" pressure reading:
- Failed/failing sensor
- Failed/failing gage
- Wiring fault
- Small debris clogging sensor port
- Small debris clogging passage to sensor

And just about all of these can be checked without pulling the sump off of the engine yet again (I do sympathise, the sump is a pain to pull at stock height. Three inches or better of lift make it ever so much easier...)

[iwannadie]

(My oil pressure sensor is fed through a T fitting, the branch of the T has a "dry-break" connector for plugging in a mechanical gage as part of annual inspections.)

I've read about your setup before and was considering the idea of running the same setup with a dedicated cabin mechanical oil pressure gauge.

I'm liking the idea of using the copper tubing not the cheap vinyl that come with most gauges.

I don't have any symptoms of low oil pressure, just like the idea of more gauges just incase.

[5-90]

I've read about your setup before and was considering the idea of running the same setup with a dedicated cabin mechanical oil pressure gauge.

I'm liking the idea of using the copper tubing not the cheap vinyl that come with most gauges.

I don't have any symptoms of low oil pressure, just like the idea of more gauges just incase.

Bending copper tubing is a pain, and susceptible to vibration. Use proper reinforced low-pressure hydraulic hose (WP somewhere around 150-250psig) and you'll be fine. I don't like that Nylon tubing either.

[tbburg]

What kind of oil filter you running? 'Buddy of mine just had his Blazer start acting up. Turned out it was a failed filter(you guessed it - Fram)

Nothing wrong with a full time mechanical gauge. It's a good idea to put a fitting with a small orifice in the block, so if you do have a line break/gauge failure, all the oil doesn't pump out before you have a chance to shut it off.
Copper does work-harden in a high vibration environment, and can crack over time, so it's a good idea to have a flexible line between the engine and firewall.(Not entirely necessary, I know,..)