Case study:

The 98 is running about 15 lbs at hot idle ( should be within spec), when running higher rpm it goes up to around 40. Okay this should be normal. I haven't checked it with a mechanical gauge yet but will soon. I hooked my scanner up and it reads oil pressure ( which is where I get my figures). I'm wondering if it reads from the dash gauge?

Interesting fact though the 99 runs around 40 all the time at hot idle, when given more rpm (cruising) it goes up to around 50 or so. No noises out of either of them. Just kinda stumped how they are not even close to each other on the readings? Plan on throwing a mechanical gauge on them both to see for real. Any ideas? Thanks

 

Sending units are notorious POSs.

 

alot of it depends on maintenace.... my 97 has 190k on the engine and runs at 22lbs at idle, 50 psi at 1600

previous engine with 150k ran at 11 lbs idle, 37 psi at 1800 rpms. both of them were verified with mechanical gauges... as you can see the one with higher mailage was more than likely better maintained. plus you got too take into account different oil filters and different oils in you're case.

if this is just occuring out of the blue check or replace the sending unit with a mopar one.

 

Mine runs at 40 at idle and 60-65 driving, verified with a manual gauge.

 

Oil pressure is not a constant. Too many variables. A oil pressure gauge is just a very crude method of verifying you have (possibly) oil flow. Since it would be impractical to install flow sensors on every bearing the oil gauge measures how much restriction against flow you have. As a margin of safety oil pumps produce more volume than needed and that is what creates pressure. In other words pressure represents how much oil IS NOT being delivered! Case in point; when a cold engine is started oil pressure oil pressure is very high but the thick oil is barely getting to where it is needed but once engine warms up and the oil thins out pressure goes down but oil flow goes way up. 0 psi with adequate flow will lubricate a bearing. 1/2 psi will lift a column of oil 2 feet high and that is enough to get oil to the rockers. There have been many an engine destroyed by monkeying around with thick oil or additives in an attempt to get pressure up.....pressure = restriction.

 

big badon, low oil pressure can indicate a problem with the system too.... like bearings that are out of tolerance and that may give up in a matter of miles and destroy the crank calling for a full rebuild + crank. an engine needs oil pressure. i dont believe anything less than 7lbs at idle is sufficient, at cruising speed 20lbs may be sufficient for an engine to last.

that said the op does not have an issue unless these specs occured all of a sudden and is rapidly decreasing in pressure.

 

The best thing to do if you have any oil pressure concerns is VERIFY! Just go to any auto parts store that rents tools and get a oil pressure gauge and connect it where the oil pressure sending unit is connected and then you have some place to start looking if the pressure is to low. You will really never know if you don't verify.

 

Restriction = Delta P I build things hydraulic.

 

Exactly right low pressure is usually the result of a worn engine and all the pressure in the world will not add life to the engine. Pressure is not needed to lubricate an engine as long as oil is flowing to where it needs to go. Oil pressure is used as a means to measure engine wear.

 

That is correct and pressure is the result of restriction I'm retired from mechanical Engineering.

 

That's one heck of an idea, Robert!!

 

Yeah! I have no idea how I figured to try that. I just pulled that one out of nowhere... LOL

 

And it was so well received!! LOL.