Low oil pressure problem

[79cj]

I am a new member to this forum and am glad to be in this. I'm having a problem with my '79 CJ5 with a AMC 258 i6 / 4.2l . It has a oil pressure gauge that isn't electric, instead it has a plastic oil line that runs directy to it. Recently I've been noticing that as I've been driving it, the oil pressure drops. The longer I drive it the more the pressure seems to drop. I have always changed the oil at the right intervals and I don't believe that I have a sludge problem. Can this be an oil pump problem, I thought these pumps either worked or not, so I'm not sure what is happening with mine.

Any ideas!

Thanks,

79CJ

 

[JR74CJ5]

:ww: to the site!

Have you checked the line for a leak?

I don't have much knowledge with that type of gauge, so hopefully someone else will pipe in soon

 

[LongHorn]

I am a new member to this forum and am glad to be in this. I'm having a problem with my '79 CJ5 with a AMC 258 i6 / 4.2l . It has a oil pressure gauge that isn't electric, instead it has a plastic oil line that runs directy to it. Recently I've been noticing that as I've been driving it, the oil pressure drops. The longer I drive it the more the pressure seems to drop. I have always changed the oil at the right intervals and I don't believe that I have a sludge problem. Can this be an oil pump problem, I thought these pumps either worked or not, so I'm not sure what is happening with mine.

Any ideas!

Thanks,

79CJ

Good News & Bad News:

The Good News is;
You have a mechanical oil pressure gauge, generally considered to be more accurate & reliable than the electrical type.

The Bad News is;
The problem you describe sounds like a common occurrence in old worn out engines as the oil heats up & becomes thinner, the oil pressure drops off.



It's time for a rebuild.

 

[79cj]

Hi All,
Thanks for the info and welcomes!

I hope I don't need a rebuild; this engine has 94,000 on it and has been well cared for. My oil has always been relatively clean when I change it.
I would like to explore other possibilities before the rebuild one.

Here's what I've been wondering -

Can these oil pumps wear out?

Do these pumps have a pressure release spring or some such think that may be weak?

I've never replaced an engine’s oil pump, but I've never had a vehicle this long either. I've had this since '85.

My oil has always been pretty clean even when I've gone to change it. I haven't ever had to add oil between oil changes.

Also, I wanted to share some pics of this Jeep, but I don't know how to install them on this site, so any info on that would be helpful.

Thanks,

79CJ

 

[LongHorn]

Hi All,
Thanks for the info and welcomes!

I hope I don't need a rebuild; this engine has 94,000 on it and has been well cared for. My oil has always been relatively clean when I change it.
I would like to explore other possibilities before the rebuild one.

Here's what I've been wondering -

Can these oil pumps wear out?

Do these pumps have a pressure release spring or some such think that may be weak?

I've never replaced an engine’s oil pump, but I've never had a vehicle this long either. I've had this since '85.

My oil has always been pretty clean even when I've gone to change it. I haven't ever had to add oil between oil changes.

Also, I wanted to share some pics of this Jeep, but I don't know how to install them on this site, so any info on that would be helpful.

Thanks,

79CJ

I suppose you could have a bad oil pump, they usually last about as long as the rest of the engine though.
My suggestion would be to try a new mechanical gauge, just to see if that's the issue.
The AMC V8 has an aluminum oil pump housing that wears out sometimes, but that's not applicable to the "AMC 258 i6 / 4.2l ".

 

[JR74CJ5]

Also, I wanted to share some pics of this Jeep, but I don't know how to install them on this site, so any info on that would be helpful.

Couple different ways...

Here's a good instructional post: http://www.jeep-cj.com/forums/f16/how-attach-images-post-1270/

 

[73CJ]

Sounds like a worn motor. If you change the pump, it probaly won't make any difference. I suspect the main and cam bearings are worn. When hot at idle it drops to Zero?

 

[MN CJ7]

A few ideas.....

Summer temps should use 10w-40
the use of thinner oils in summer can lower the oil pressures

There is a built in oil bypass by the oil filter..... If I remember right there is a spring there, and if not assembled right or if the spring does not have the right tension... it can lower the operational oil pressure. It allow oil to bypass the system and the result will be lower pressure.

95,000 miles on a AMC 258 i6 / 4.2l is not a lot of miles... These have goen 50% more and still run well. A simple compression test would tell you the health of the engine. Since your oil is clean, well cared for, and does not burn oil... I do not think this is a tired engine. This simple test will give you peace of mind and confirm your suspesion of a healthy engine.

Gauges are not all that accurate, bounce them around for a few years. So I would look further here too. The block mount is a 1/8 NPT thread..... go get a 100 PSI liq filled gauge, the farm stores sell these for $12 and get a brass adapter to neck down the 1/4 NPT gauge mount to the 1/8 NPT and screw it into the block. Then ck you engine oil pressure on start up and operational temps. Gauges are 2, 3, 5% accuracy. Bounce them around for a time and 10-15% could be the error.... So try this first and see if you have something to address or not.

Do the oil press test with a new gauge, Then do the compression test.

If we need to look further after the "gauge & compression tests".... I will try and find the write up on the oil bypass and the modification to make it work properly. I know this adjment can make the pressure too high and too low... Did you take this apart or made mods to this is also a good question??


Last idea.... if you bent a rod, or lost a rod, the lifter could have come out of pocket... This would interrupt the oil path internal to the engine.... This would also lower the oil pressure. This would show up in the compression test above.

 

[79cj]

Sounds like a worn motor. If you change the pump, it probaly won't make any difference. I suspect the main and cam bearings are worn. When hot at idle it drops to Zero?

When I start driving my pressure is about 60psi while going down the road and 20psi when idling. If I drive it for an hour or so it ends up at about 30 on the road, and when I stop for a light or something and have it at idle it goes down to about 5psi or even a little lower. This scares me !

I am using 10-40.

I thought I put a post with a picture in this forum yesterday and I don't think it showed up so I must have not done it right. Wish I could learn more about how to do that correctly. I'll try adding it to this post to see what happens.

 

[LongHorn]

When I start driving my pressure is about 60psi while going down the road and 20psi when idling. If I drive it for an hour or so it ends up at about 30 on the road, and when I stop for a light or something and have it at idle it goes down to about 5psi or even a little lower. This scares me !

I am using 10-40.

I thought I put a post with a picture in this forum yesterday and I don't think it showed up so I must have not done it right. Wish I could learn more about how to do that correctly. I'll try adding it to this post to see what happens.[/QUOTE

Are you positive you have 94,000 miles & not 194,000?

 

[CJ]

~~~ I thought I put a post with a picture in this forum yesterday and I don't think it showed up so I must have not done it right. Wish I could learn more about how to do that correctly. I'll try adding it to this post to see what happens.

This image? It's there at the bottom of your post.

 

[MN CJ7]

Pictures..... posting to forums


The easiest way is to sign up for a free picture sight like
Photobucket.com
They offer a free service for uploading your pics to the web. Set up a few folders and then use the LINKs to show the pictures on help forums and emails and craigslist..... Its a great service and its free. FOLDERs on www.photobucket.com will help you find pictures when you want to use them again....

Then on Jeep-CJ.com you copy just the LINK and put it in the picture button tool on top of the posting block.... The link will show in your verbage and when you hit SAVE it will put the picture in your post.... Odd thing to do the first time or two but then its get to be old hat...

Engine pics are best from top, right and left sides. Carbs and Distributor are all good topics for the pics too....

 

[CJ]

Or... By using the gallery at this site you don't need to use any links to outside sites. All you have to do is click on the 'Insert an Image' link in the 'My Gallery Images' box and you can just click on the thumbnails to inset images into you post.

 

[73CJ]

Yup thats exactly what mine did. I driest tried an oil pump,but thatdidnt help. New bearings and a reground crank fixed it.

Not what you wanted to hear but

Mine never made it to 90000 either. They were hard miles.

 

[1986cj7]

When I start driving my pressure is about 60psi while going down the road and 20psi when idling. If I drive it for an hour or so it ends up at about 30 on the road, and when I stop for a light or something and have it at idle it goes down to about 5psi or even a little lower. This scares me !

I am using 10-40.

I thought I put a post with a picture in this forum yesterday and I don't think it showed up so I must have not done it right. Wish I could learn more about how to do that correctly. I'll try adding it to this post to see what happens.[/QUOTE

Are you positive you have 94,000 miles & not 194,000?

I've got 240000 on mine and oil pressure is 60 starting out and 25 at idle after heating up but goes up as the rpms of motor goes up. The po said he didn't rebuild the motor, and was running 33' with stock 2.73 so who knows how many miles are on it. I don't think the motor is woren out. Most likely a guage problem. And maybe I'm just lucky with my motor.