AMC 304 Oil Pressure Issue

[Span24]

Fellow CJ Lovers,

I recently purchased a restored 79 CJ5 /AMC 304 which was reported by the seller to have only 22K original (engine) miles. He delivered the Jeep to me so the engine was already warmed when, at the time of delivery I drove it about 20 miles with no problems other than (what was described as) a non-functional stock electric oil pressure gauge. The engine ran and sounded fine other than not idling in 1st gear 4-low. The seller indicated that the oil pressure gauge was not working because the ground was not connected and that the idle problem was due to the idle being set too low.

The day after closing the deal on the Jeep I started it up cold and noticed a very prominent tapping like that of a poorly adjusted rocker. After a few moments and some throttle exercises the tapping simply vanished. It did not fade but abruptly stopped. I thought that perhaps it was a sticky valve?

After checking out the oil pressure gauge and (indeed) finding that the ground was not secure I managed to get it properly grounded. However, the gauge still reads zero but bounces to 5-10 PSI only rarely. I tested the gauge by grounding the sensor wire to the frame which pegged it. Because of this I believe the gauge to be functioning.

I started the Jeep again this morning and the tapping was there. Again, following a few throttle exercises it went away, all the while the gauge read zero. If I allow the engine to idle for a period it will start tapping again until I pump the throttle. I'm not sure if it continues when the engine completely warms up.

Where should my testing go from here? I am thinking that I need to know what the pressure is using a mechanical gauge. I'm thinking that if the pressure is good then either something is sticking on the top end, or a lifter is bad, or the bearings are worn. I remember a very long time ago a friend cut the top off of an old set of GM valve covers to adjust the rockers on Chevy small blocks. If I had a set of those I'm thinking I could see what the oil looks like on top. These days however, getting my hands on a set of spare valve covers for this old AMC 304 doesn't sound practical.

Although I'm hoping for a bad sending unit and a sticky valve or rocker I am very much concerned that the tapping may be from lack of oil pressure and that the oil pump is failing or worse, that a lifter is bad or the main or cam bearings are worn.

Any thoughts/advice is appreciated!

Michael

 

[Torxhead]

Having noisy lifters after the engine has been warmed up is not a good thing. I agree with the mechanical gauge plan as a good place to start. I purchased a mechanical gauge for testing use only, just to see where it is at. My pressure is rather low at least the valve lifters don't clatter. Using a good detergent oil like a Rotella T can help also, even a low mileage engine can clog up its oil passages.

 

[mtnwhlr]

I would agree that a mechanical gauge would the place to start. You need to know for sure where the pressure is before tearing into anything else.

 

[Torxhead]

I would agree that a mechanical gauge would the place to start. You need to know for sure where the pressure is before tearing into anything else.

As there could be tired electrical componets like the gauge or the sensor.

 

[Span24]

Well I grabbed a mechanical gauge from the local O'riellys and hooked it up. I find that I am getting a pretty constant 45-50 PSI so I'm pretty sure I can rule out a worn oil pump and/or bearings. However, now I am facing the prospect of a stuck valve or bad lifter. After warmup it does seem to subside.

It purrs like a kitten when it isn't tapping!

Thoughts?

 

[Hedgehog]

Sounds like a great place for a quart or so of Marvel Mystery Oil, I'd use 2 full quarts, topped off with thin oil.

 

[Lumpy Grits]

What weight oil is in it now?
Who's oil filter?
Do not ever trust OEM, AMC electric oil gauges.
Change the oil to either 15W40 Shell Rotella or 20W50 Castrol with a Wix(NAPA)oil filter.
LG

 

[Saddle Tramp]

X 2 on the above advice. The AMC V8 oiling system is notorious for having a temperamental oiling system in part due to the aluminum case (the timing chain cover) that the pump gears live in as it is prone to wear. Go mechanical, use the Mystery Oil, and then switch to the Rotella; see how that goes.

 

[Span24]

What weight oil is in it now?
Who's oil filter?
Do not ever trust OEM, AMC electric oil gauges.
Change the oil to either 15W40 Shell Rotella or 20W50 Castrol with a Wix(NAPA)oil filter.
LG

I'm unsure of the current oil weight. I've not had it long enough to change the oil . It currently has a K&N Oil Filter. Any reason to change?

Going tonight to grab Rotella 15w40, new K&N filter, and 2 quarts of Marvel Mystery Oil.

 

[Span24]

X 2 on the above advice. The AMC V8 oiling system is notorious for having a temperamental oiling system in part due to the aluminum case (the timing chain cover) that the pump gears live in as it is prone to wear. Go mechanical, use the Mystery Oil, and then switch to the Rotella; see how that goes.

Mechanical gauge is in and functioning!

Are you thinking I should just drain 2 quarts of the current oil and replace with Mystery Oil for a few hundred or change everything out completely with the suggested and run through a typical oil cycle?

Any real harm in switching oil viscosities at this point? I'm not sure it matters though as I have no way of knowing what the current oil is.

Also, any problems with including Mystery Oil in the fuel system as well? I've heard that it does wonders on injected engines though I'm not sure of any benefit to this old carbureted set-up.

 

[Hedgehog]

If you had a better history on the oil currently in your Jeep I'd suggest removing a couple quarts and replacing with Marvel Mystery Oil. Since you really have no idea about the oil you have I'd find light weight oil that you can afford and add the Mystery Oil. Marvel Mystery Oil was one of the very first oil products that is designed to clean your engine while running. I's use light oil for the flow or purging through the engine. I wouldn't go more than 500 miles with this mixture, less if your ticking clears up. For everyday driving I use relatively heavy, but an old time standard 20W50, like the tractor/diesel oils 20w50 still has the chemicals in it an old design engine needs to live a long life.

Marvel Myster Oil is frequently used by the gallon in diesel trucks with hundreds of thousands of miles on them. It's an old time product, but is still hard to beat. ...... and that smell always brings me back to my fathers work bench in the barn and his gun shop, a smell that you'll never forget.

Yes, deffinately change the oil filter. Unlike their air filters the K&N oil filters aren't reusable. I always change the oil filter when changing engine oil.

 

[Lumpy Grits]

Run the 15W40 WITHOUT the MMO. At this point I'm think'n you want a heavy oil to rid yourself of the 'ticks'.
Wix was AMC, OEM filter and still one of the best made.
OIL is the cheapest thing you will EVER put into and engine.
I've run 20W50 Castrol for 29 yrs w/Wix filter. NEVER have been inside the engine other than to reseal the v'cover a couple of time.
LG

 

[Hedgehog]

Thousands of vehicles use MMO and some don't believe in it. Your "tick" likely won't go away, miricles just don't seem to happen much anymore, but it might with a good oil change.

Good luck my friend......

 

[Lumpy Grits]

Been use'n MMO for over 50 yrs.
Everything from guns , airtools, sewing machine and reloading press lube.
My think'n was we can always put the MMO in later-Lets have the OP try the 15W40 'full-strength'.
MMO is for the most part, mineral oil.
I use 1oz per gallon in stored gasoline for my lawnmowers, chainsaws and generators.
Respectfully,
LG

 

[mtnwhlr]

Been use'n MMO for over 50 yrs.
Everything from guns , airtools, sewing machine and reloading press lube.
My think'n was we can always put the MMO in later-Lets have the OP try the 15W40 'full-strength'.
MMO is for the most part, mineral oil.
I use 1oz per gallon in stored gasoline for my lawnmowers, chainsaws and generators.
Respectfully,
LG

 

[Hedgehog]

When I get a vehicle that I have no history on I feel better FLushing the engine with oil I know. No, I don't leave it in there for a long time, maybe a few hundred miles of light driving. When new oil goes in I know where I'm starting from. I have heard that it isn't good to flush a truly dirty engine because oil passages can get plugged. I'm not really convinced in the truth in that though.

 

[Span24]

I stopped by my local O'riely's and picked up a WIX filter, a gallon of MMO, and 2 gallons of Castrol GTX 20w50. Will be changing the oil out tomorrow.

Interestingly, it was my initial intention to purchase Rotella 15w40 as suggested here but everything I found was advertised for diesel engines. Excuse my ignorance but is this because of the weight or is their oil specifically designed for diesel engines which can not/should not be used in gasoline engines? Because I did not know, and the store employees could not give me a believable answer, I went with Castrol.

Is it appropriate to run this weight on a regular basis? I will remind you that I live in the cool midwest where the temps average 85 in the summer and 15 in the winter.

I'll post again when I get the oil changed.

 

[Saddle Tramp]

I stopped by my local O'riely's and picked up a WIX filter, a gallon of MMO, and 2 gallons of Castrol GTX 20w50. Will be changing the oil out tomorrow.

Interestingly, it was my initial intention to purchase Rotella 15w40 as suggested here but everything I found was advertised for diesel engines. Excuse my ignorance but is this because of the weight or is their oil specifically designed for diesel engines which can not/should not be used in gasoline engines? Because I did not know, and the store employees could not give me a believable answer, I went with Castrol.

Is it appropriate to run this weight on a regular basis? I will remind you that I live in the cool midwest where the temps average 85 in the summer and 15 in the winter.

I'll post again when I get the oil changed.

The difference between the diesel rated oils and the gas engine oils all comes down to additives or more importantly the lack thereof. There have been a few disagreements over the technical aspects between the two on this board in the past but primarily zinc and/or other additives have been removed from the typical gas engine oil where diesel oils due to the heavier nature of the engines have not been stripped of all the good stuff that helps with lubrication to the same extent. The reason given for the change is stated to be in the interest of pollution control but somewhere I know money comes into play and may really be the motivator. Google it and you will find different opinions.

 

[steve1973]

Your 73 would have started its life with a Stewart Warner mechanical oil pressure gauge. Keep in mind that oil pressure is also a measure of friction. You want it in spec, not to high, which would decrease efficiency and decrease the heat removal function that oil also serves.


Sent from my iPhone using Tapatalk

 

[Hedgehog]

Good point, a lot of guys don't know it, but oil is a major portion of the engine 's cooling system. Engine oil essentially grabs up heat that develops in the nooks and crannies inside an engine and moves it to another place to cool. Granted the thought that hot engine oil actually cools is a relative thing.