I’m looking to trade my '95 dodge ram 1500 with someone for their '95 grand cherokee. The GC has 190k miles on it, my truck has 155k.
I noticed when test driving the GC that the oil gauge follows the rpms of the engine. I.e. when idle the oil gauge is low-mid level. When i raise the RPMs, the gauge indicates there is more oil pumping, then when i go back to idle it drops back down too; in other words it looks like the oil jumps with RPMs.
I’ve never seen this type of behavior before, is this a sign of typical behavior for a jeep GC, a bad gauge, maybe an oil leak?
Engine is a
It could be a wore out oil pump,main bearings,rod bearings or cam bearings. It could run like this for a long time or die next week. Now having said that I have fix this problem by just replacing the oil pump. But I can do this work myself and I know how to check for bearing wear. Me I would keep looking.
What ARE the pressures?
Oil pressure increasing with an increase in RPM is not a sign of a problem as long as the pressures are appropriate. And if they are appropriate it’s a good thing. The harder the engine is pounding sideways on the rod and crank bearings, the more pressure you need to keep a pressurized oil barrier between the metal of the rods & crank and the metal of the bearings.
The Oil Pump Is Driven By The Engine. The Faster The Engine Runs The Faster The Pump Runs And An Increase In Oil Volume Pumped And Pressure Is Normal, New, Used Or Otherwise. The Oil Pump And Oil Pressure Gauge Are Apparently Working.
CSA
Right. Perfectly normal. I forgot to say that, didn’t I? I guess I wanted to be sure the pressure is adequate before saying it’s good.
You should see about 10psi of oil pressure for every 1000rpm’s
Current gauges are just approximate indicators. If a hot engine has oil pressure indicated at approximately 1/3 the sweep of the gauge at idle and moves to 2/3 at 3,000 rpm there is usually no need to be concerned.
These are great answers and, such as Rod Knox answer, confirm my observation.
It certainly makes sense that it would fluctuate if the pump is driven by the engine; I just never seen such behavior in any other vehicle before.
Thanks so much.
This is the way an oil pressure gauge SHOULD work, but I’ve seen cars where apparently if the oil pressure is good by an electrical signal the needle goes to one place and just stays there. In those cases I think it’s basically just receiving an electrical signal similar to the signal sent to an idiot light. I’ve noticed this on my mom’s Mercury Grand Marquis. As soon as the engine starts the oil pressure gauge goes to the half way point and never moves and has done this since the car was new.
I’ve got a mechanical oil pressure gauge hooked up to my '88 Escort, it reads about 20-25 psi at warm idle and increases and decreases with rpm’s as I go through the gears. Once I’m in 4th gear (4 speed) the oil pressure at approximately 2000-2500 rpm (no tach) and 55 mph is 55-60 psi on a warm engine. If the engine is cold the pressure will likely be higher, because the oil is cold/thick. When I start my Escort on a cold engine the oil pressure usually goes to about 75-80 psi and gradually drops as the engine/oil warm up.