I have a 1984 cj-7. The oil gage only reads about 17 lbs until you get going, but even then it won't get over about 40 lbs of pressure. The jeep seems to be running fine. How would I know if the oil pump is bad or if the gage is bad? Also, if it's the oil pump, are they very hard to replace? Thanks for any help.
While it sounds like your oil pressure is OK beep, I have to respectfully disagree with you Daddy. IMHO, "some" oil pressure is not enough (back me up here Horatio). There are lots of nooks and crannies in the engine that will not get enough/any oil of the pressure is low. It is asking for trouble not to address low oil pressure.
So how do you know if its the gauge or what, esp. since they are notoriously inaccurate?
There are stand-alone, mechanincal oil pressure gauges that can be hooked up to the engine in place of the oil pressure sender. Any decent shop should have one. This is the way to tell. But even if it's low, it may not be a bad pump. I'm 99% sure my ridiculasly low pressure is a result of too much bearing clearance, since the previous owner appears to have done a so-so job of rebuilding the engine. A new high-volume pump, from Melling, is going in today, as a temporary fix until I can rebuild the engine at some point in the future.
So check it out, and if you have a real 17 psi @ idle and close to 40 while gunning it, you are better off than most, and in fact good to go as long as it stays in that range.
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Your probably right, the engine is probably worn. Put some viscosity thickener in it (stp or the like) on the good side Jeepdaddy is right, 17 at idle, while a little low is still acceptable. an OLD rule of thumb is 10 lbs pressure for every 1000 rpm. Many stock pumps run a 40lb bypass spring.
I think there's truth is all that's said here but feel I should elaborate a little. I didn't literally mean "as long as you have a some oil pressure your okay". I can see how someone could read that to be "5 psi is okay" or "5 - 10 psi from idle to 4000 rpm is okay". I should have said what jeepdaddy2000 said. If it's a LITTLE low on a mid to high milage engine, it's normal. And, as CJeep said, most oil pressure gauges aren't very accurate.
I believe that the gauge is just there to tell you if something is really wrong. If you are used to seeing 40psi day in and day out and all of a sudden you look down and see 5psi while at highway speeds, you probably have a problem. You should stop and check things out imediately.
If you are used to seeing 40psi and you look down on a hot day after being stuck in traffic, and see 35 psi, I wouldn't be alarmed. We use common sense here and realize that the hotter the oil gets, the less viscosity it has and the lower the pressure will be. Engine RPM plays a big role here too.
Remember too, the older your engine is, the older your gauge and sending unit is too. I'm sure that my gauge worked better in 1985 than it does now. Mine kinda bounces around a little like most old gauges do. I don't really like it, but I'm not worried about pressure because of it.
My 2 cents.
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I would have to just state my thoughts. The 304 has an external oil pump, this is very easy to replace, because you don't have to drop the pan. The bottom plate is right next to you oil filter. If you take that plate off you will see to gears, those actually cause the oil flow. There is a gear replacement kit for 15 - 20 bucks. Make sure the cover plate isn't worn with groves, replace the gears and the bypass spring. Should take no more than 1 hour to do. In addition the books call out that the 304 should have 30 psi at 2500 to 300 rpm. So I have to agree with above roughley 10psi per 1000 rpms. Later....
One more thought.I used a threaded copper tube with a T fitting on my V6. One side of the fitting is attached to my preasure gauge and the other is connected to the idiot light.I wanted the light because it is difficult to monitor the gauge while wheeling.If the pressure gets below 6 lbs the light goes on and that is a lot more noticable than seeing the needle drop.I learned the hard way,I lost a motor with 15000 miles on it when the oil line to the gauge went south and I didn't notice until the lifters started clattering!