258 W/low Oil Pressure

Had some low oil pressure issues yesterday for the first time ever. Could barely get 10 PSI on the highway at probably 2,500 RPMs. At idle dropped to almost zero.

Of course I did some internet research and from what I've read I should first verify the oil pressure with a mechanical guage and use that info to determine whether my sending unit is bad. If it checks out them maybe a replacement oil pump. Read a little about using a high volume, or perhaps high pressure, oil pump. Also read some stuff that said if the pump is too high volume, then the suction from the oil pan will outrun the oil that can drain back into the pan and will pump the pan dry.

Question...is it very hard to change out an oil pump on this motor?

Comments on whether I should just get a stock replacement oil pump? Or upgrade and if so...to what?

 

all it takes is dropping the pan..
keep it simple and keep it stock.. it lasted you this long....

Sealed Power 224-41198

 

If you had zero oil pressure, the lifters would clatter. Do you notice that the engine noise is worse now? Plus, this sort of thing does not suddenly start up - it's a gradual decline as the bearings get more and more worn.

What brand of oil filter?

Low oil pressure is not a common complaint for the 258, unlike the AMC V8s. They run a iron oil pump in the oil pan that is driven off the bottom of the distributor. The engine should get very tired before it starts running out of oil pressure. Any TSM covering the 258 will show you how it goes together, like here: http://oljeep.com/gw/74_tsm/1A-SixCylinderEngines.pdf This shows you how to measure the oil pump to determine if it's worn out.

The oil is supposed to drain back faster than the pump delivers it to the top of the engine. Sometimes you see bad drain-back when the sludge is so bad that it blocks the return holes in the cylinder head. Then the valve cover fills up with oil and starves the oil pump. (Unlikely! with modern detergent-base oils). Take a look under the valve cover - there are holes in the head that go back straight down through the block to the pan.

With the looong stroke of the 258, I'd expect you to need rod bearings before the oil pump wears out. Usually you'd hear that - and low oil pressure would be a symptom of the oil draining out through the hammered bearing. If this is the case, an oil pump is going to do nothing for you. Rebuild time.

Do the mechanical gauge first.

 

Thanks Tim. It's hard for me to believe the thing needs re-building. It just runs too good. No valve clatter or any other noise even when the gauge reads zero. No smoke at all. Never smoked as long as I've had it. Never used a drop of oil. I've had it over 10 years and might have put 10,000 miles on it...probably less. The engine was rebuilt before I bought it. Now...I did just finish replacing the lifters and push rods. Not sure whether or not that would have anything to do with it. I do recall my brother having me spin the engine over with the valve cover off so that he could see oil coming up through the pushrods and he said everything looked good there. It has fresh oil and filter in it and I'm fairly sure it's a Fram filter. Not 100% positive on that though. And, it is full of oil.

 

The standard orange Frams have a reputation for making oil pressure low. Bad drain-back valves or something. Wix is better, or Napa (which is also Wix?). What kind of oil? I run the 15W40 Shell Rotella T in the Jeeps. Delo is also popular. Both diesel oils, approved for gasoline engines too.

 

Another thing is to smell the dipstick. If the fuel pump is leaking into the crankcase, that will dilute the oil with gasoline and the oil pressure will drop. Oil level will be way high too.

 

That's good information Tim. I will check the dipstick for odor. I can say the oil looked very clean. Not black at all. Looked like i'd just poured it out of the bottle. Hard in fact to tell where it was on the dipstick because it was translucent. But it seemed to have the correct consistency.

Honestly I have no idea what oil is in it. Probably just picked some off the shelf. So you're recommending Shell Rotella T - 15W40? I will remember that.

 

Slight update.

I replaced the fram filter with a Penzoil filter. I had great pressure when I cranked it. Fluctuated with RPM from 30 - 50 at times.

Took it for a drive to Wal-Mart in Magee...about 15 miles down the road. Oil pressure dropped to around 15 on the highway and then slowly to around 10 at highway speeds. So...I decided to change the oil with Castrol 20W-50 while @ Walmart. On the return trip I managed to maintain 15 psi for about the whole trip.

Since I had the good pressure with the cold oil and new Penzoil filter, I'm guessing my sender is probably fine. And since I managed to maintain about 15 on the 20W-50 Castrol on the return trip from Magee I'm thinking now it may be time to drop the oil pan and replace the pump and see if that helps.

Still not ready to consider that the engine needs re-building. Like I said...the engine just runs too good. Nice and smooth. Not a drip from underneath, and no smoke at all. Clean tail pipe.

My brother even suggested that the oil pick up tube could have possibly dropped into the pan. Thoughts on that? He said with a full pan of oil the pump will still pick up some oil so it could still be pumping oil to the top of the engine (evidence from when we had the valve cover off and checked the new pushrods and lifters we installed).

 

Don't guess - measure. Summit Racing® Analog Mechanical Gauges SUM-G2934 Cheap; a worthy addition to your toolbox.Hook it up and run it into the cabin temporarily so you can see the pressure.

Occam's razor says the answer with the fewest assumptions is the most likely one. A single assumption that your gauge is lying to you answers everything. No noises, engine seems strong and healthy, but the gauge reads low ... don't throw parts at it until you know. And I also think that a new oil pump won't help, even if you have low pressure. The oil pump is not a problem area for the 258.

Oil pickup tube falling off would likely give you no oil pressure, not low pressure. It would have to fall off just enough so that oil uptake is reduced but not eliminated. Seems unlikely.

 

A friend used to sponsor and build race bikes and wondered why the cams kept going away so called the company that he got the cams from. Use Kendall oil. I used to get oil from him. I was up at my local speed shop and asked about Kendall oil, They still have it. Not really easy to find. but it seems to do better than anything else out there.

 

Lots of 258s out there with low pressure, but like Tim said, they will clatter if that is the case. As easy as a 258 oil pressure port is to get to, I'd double check it with a mechanical gauge if it's not clattering. Lots of old timer Jeep mechanics have told me that a 258 will run at 5-10psi at idle forever as long as you get adequate pressure at higher RPM (IE sloppy bearings vs junk pump)

That being said, 258s are pretty durable and will generally tolerate low pressure for a much longer time than something like a SBC. At least two of mine have idled below 10psi all the time without any major problem other than they had a ton of clatter (Incidentally, they were never a form of transportation I relied on either). The one I pulled out last year idled at 3 psi running 15W-40 in October, in Maine. It ran fine, but it admittedly made me a little nervous, and when combined with the rediculous amount of blowby (with both valve cover openings hooked to manifold vacuum it still pushed oil out the valve cover gasket and dip stick tube) and given that I was swapping a T18 and 2.46:1 D20 anyway, I opted to swap engines. </unrelated anecdote>

 

Before I got too far into anything else, I'd definitely check the sending unit with a mechanical gauge of known quality. Cheap, easy insurance against spending unneeded time and energy chasing the trouble. I've had 258s that were worn out, and if they had super low oil pressure, they clattered. Good luck!

 

The gauge in the wife's fluctuates when it heats up to the point that it says zero pressure checked with a known good gauge it's fine. The replacement sender didn't fix it I'm guessing the gauge itself is bad. I'm running it till it totally fails.

 

Though I know nothing about high quality parts...the PO bragged to me that this jeep has the high dollar VDO gauges. I now that's not the sender, but...supposedly I have decent gauges.

I agree with you all and will check the sender before dropping the oil pan.

Thanks fellas.