oil pressure dropped

[scrambler]

Last weekend I was driving on the freeway doing about 65 and my jeep shuttered and then started making a loud ticking so I pulled over and turned it off. Started right back up. The ticking was a lifter and the oil pressure which is usually between 20 and 40 now fluctuated between 10 and 0!!! Not really sure where to even start. I really don't want to replace the oil pump but gotta do what ya gotta do. Any other ideas on what might have happened? It is the AMC 258 i6 / 4.2l , 1981 scrambler. Also it still starts and runs just has the lifter knock from time to time.....(had to drive it home )

 

[CJ]

Did you pull the valve cover and look? You may have loose as heck rocker allowing the oil pressure to bleed off via the lifter.

I broke a push rod on my V8 one time, popped the lifter out of the bore and the oil pressure dropped to zero...

 

[crscrkcj]

Shouldn't be hard to figure out. Just pull valve cover and look for what's not the same. Suspect lifter or rocker broke. Saw a solid lifter shoot through the hood of a Chrysler once. Was not a good sign.

 

[biohazard cj]

i was just checking out a amc forum i saw this and it might help both of us a little.



I'd say this is a typical oil pressure reading from an AMC V8 after the engine has suffered a cooling system failure. My suspicion is that the iron oil pump gears inside the aluminum housing are fine during normal temp heat cycles, but when temps go too high the thermal expansion rates become incompatible and the clearances get loose; it seems the gears chew into the aluminum housing surfaces. I've even noticed the lips of the iron gear teeth even get ground away, having an irregular notchy look from biting into the aluminum case. More severe, when this happens to the oil pump, the next thing is you'll hear bearing noises, probably from the rear main and rod bearings. (don't overheat the AMC V8) An AMC V8 like this is likely to throw a rod (usually the 5/6 journal, more rare 7/8 for some reason) if sustained high rpms are demanded from it. (It'll still run fine for hundreds of thousands of miles otherwise). 20lbs of pressure at idle, in my experience, is normal for the AMC V8 that hasn't been overheated. First off, I'd say to go to 20-50w oil and filter change to continue running engine for street duty -but avoid high rpm if you notice bearing noises. Second, you might be able to restore better pressure by servicing the pump on the engine. Remove oil pump cover/filter adapter, inspect gears and housing. If the gears are worn put in better ones, and if the cover is scored restore the surface to smooth. (See amc oil performance mofication setup) -I'd say the low oil pressure is usually a combination of a loose oil pump and worn bearings, most likely from a cooling system failure- Fram used to make one of the best oil filters for AMC's, along with AC/Delco, but Fram was bought out (I think in the mid-nineties) by another corporation who cheapened the oil filter product line to a lower standard. Apparently TRW was part of the deal, and now their forged aluminum pistons for the AMC V8 are become unavailable -good pistons for a high rpm AMC 304 /360 if you can find 'em though; I've used 'em in a 360 built for 7200 rpm cam and kit and they were flawless. (I used the Iskendarian cam and kit with Rhodes variable lift anti-pump up lifters and it worked great for me; smooth idle and wild "drool bucket" high rpm power!) OK I'll shut up! -great work guys on this AMC Forum!

 

[scrambler]

Alright I pulled the valve cover and nothing was broken. About four of my lifters were bone dry while all others were soaked with oil and had the small puddles on them. I started it with the cover off and everything looked good. Still had about ten psi oil pressure. One thing I did notice is that my valve cover wasn't very tight. There were only three of the nuts/bolts holding it on that were, all the rest I took of with my fingers. Do ya think its the oil pump then?

 

[scrambler]

Anybody got any good ideas before I tear the thing apart?

 

[surfbum]

collapsed lifter maybe?? .... is there lots of play in one of the pushrods/rockers? Could your filter be partially plugged, restricting the oil flow? Just some things to check before dropping the pan.

 

[CJ]

You have a tough one to diagnose, unfortunately it's going to take more digging into. A shot bearing could be bleeding off pressure also. I would rebuild the oil pump before I dropped the pan. It's usually a hour or two job.

 

[86 CJ]

Keep it simple...Drain your oil and replace your oil filter FIRST...This has happend to me twice, including three weeks ago, it was the brand new filter (FRAM=)that had 110 miles on it. I went from 0psi to 50 when I replaced it If that is not it it might be your pump inside your oil pan, you will need to drop your pan and replace that. If that its not it, it might get more complicated up in your valve cover....Good Luck!!!!

 

[TDHofstetter]

Check the pressure relief spring - that may have broken, or the relief plunger may have stuck open. It's behind a plug very near the oil filter.

 

[scrambler]

"it was the brand new filter (FRAM=)that had 110 miles on it"


This one was brand new too thats why I haven't thought that it was the problem but now that you say that I think it was a FRAM filter.... I'll have to try that and see how it goes. Pisses me off cuz I just changed the oil and used synthetic.... expensive mistake

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[TDHofstetter]

So... you suspect the oil filter is completely plugged (including the internal pressure bypass - these filters are on the pressure side of the pump, not the suction side) and simply hanging onto 50+ psi? If the filter is plugged, that could only mean it's FULL of SOMETHING. Whatever that SOMETHING is, it would have been living in the bottom of the oil pan until it got sucked into the filter... in which case any brand of filter would have done the same thing.

That ignores the internal bypass, though. What might have jammed that? I've never seen one jammed. Could happen, I suppose... or worse, the passage leading out of the filter might be plugged, in which case all the oil galleries would be very suspect. I'd worry very hard about the whole motor if I found a condition like that. Good way to gall & spin a rod bearing or main bearing, or eat a lobe off a camshaft, or wreck a cylinder wall or...