Jeep Enthusiast Forums banner
1 - 20 of 21 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
1991 Jeep YJ 4.0L I6.. I turn the key to on and the gauge goes up a little past 40psi. Stays there until I turn the key to start the jeep. Then it goes straight up to 75psi while idling. When you press the gas peddle it creeps a bit more than 75psi then returns. I just replaced the sender unit and the oil pump so the relief valve is working, thats why it sits at 75psi. I also tested it with a mechanical oil pump. Thats how I know it went higher than 80 psi with the peddle. I changed the oil too with the pump and made sure it was full. I did see everything was covered in black sludge when I removed the oil pan. Does this mean there are most likely oil passages that are blocked? Is there an easy way to clean these and where exactly are these "passages" that I have read about. Are they through the block or the push rods? Or maybe its something else?
 

·
Premium Member
Joined
·
11,008 Posts

·
Typical /f12 Hooligan
Joined
·
6,936 Posts
I agree with Fish. More than likely you are getting a false reading. That said, you claimed to have tested with " a mechanical oil pump".

I would like to dwell on that statement. How did you test with a mechanical oil pump? Or do you mean you replaced the electronic oil pressure sending unit with a mechanical oil sender and hooked up a mechanical gauge and got the 80 PSI reading?

Need to know exactly what happened on that sequence of events.

Now.. cleaning out a sludge filled engine/oil pan is fairly easy and straightforward.

When you changed the oil pump and had the pan off, you stated you had sludge. If the oil pan gasket is new (I assume) and no rear main seal leak, simply substitute one quart of ATF +4 for one quart of oil on your next oil change. Use "cheap oil" and a good filter. After driving with the ATF in there for 75-100 miles, drain the oil, add in fresh oil, fresh filter, and call it cleaned. You may hear louder than usual valve train initially. If you use a high zinc oil like Castrol GTX Classic or the motor oil of your choice with a Zinc Additive Package you will help prevent wear on your lifters and cam as well as help to quiet down the clatter.

OR

You can buy a marketed engine oil cleaner product. Just follow the directions. Either way, these old engines really need the zinc in conventional oil.
 

·
Premium Member
Joined
·
4,654 Posts
I fully agree with putting a quart of ATF in the oil. ATF is still approximately a 10 wt oil. Some of the engine crankcase flushes pour like water.
 

·
Registered
Joined
·
736 Posts
It's a YJ, probably a good chance it's a glitch in the gauge. Oddly, mine would peg sometimes to 80, othertimes not, but pretty twitchy, lol. And if my music is louder (no subwoofer, just 2x 6.5 and 2x 6x9 component speakers, so not a slouch, but not "bumping" either, and it still moves a tad with bass.

It drives me nuts, and I may try a new sensor one day- no, actually I'm gonna order it now, lol.

I also had a tick, used Marvel Mystery, got better, this last time, I used Sea Foam, Autozone didn't have MM that week. Tick went away. Point is, my oil has changed, do you think the gauge changed? No. Still a crackhead of a gauge.

I wouldn't over think it. Watch your temp gauge, listen to your engine (I do everytime I start it up and everytime I come home with music off in my car port). And your probably gonna be fine.

Do your other gauges move wierd? Are they also showing wierd signs? Could be that ribbon in the back? They used to sell new ones, but have been discontinued. But you could try cleaning it.
 

·
Registered
Joined
·
736 Posts
Oh, while we're on it, and this may help OP as well. What is considered "normal" in terms of PSI?

At idle, my gauge will be around 40 PSI. But I've read that it should read 10 PSI for every 1k RPM? that seems low, but just my uneducated guess.

People say the oil gauge is broken alot, but, um, compared to what? Lol
 

·
Premium Member
Joined
·
4,654 Posts
10PSI per 1k of RPMs is an old rule of thumb that works pretty well. It is a baseline that indicates that you have enough oil pressure. Most engines that have tight tolerances though will have more than 10 PSI at idle which is less than 1k RPMs. Too much oil pressure can be bad. The rubber o ring that is you oil filter gasket will only survive so much pressure. Some of the 80s Chrysler 4 cylinders could have that condition when cold. Like 80 or 90 psi IIRC and you hear a little pop noise and oil down the road and run out of oil very very quickly. Been there, done that.
 
  • Wow
Reactions: fishadventure

·
Premium Member
Joined
·
4,654 Posts
I corrected your grammar. No charge.
Nope, mineral spirits pour slower than water. I stick to my guns. Some of them are very high profit garbage products that are watered down mineral spirits.

They do more harm than good.

The sad thing is that the residue and left over flush in an engine that is trapped in places, like on top of rocker arms around the bridges for instance. Just had the valve cover off my 4.2 last night. A good amount of oil remains inside of the valley in the top of the rocker arm let alone in other places in the engine. I had not even run the Jeep in a couple of days and a good puddle of oil remained on top of each rocker arm.

Trying to get to the point with a clear explanation.

We have mop buckets at work filled with mineral spirits. We mop up oil spills with mops and mineral spirits. A good clean bucket of it will make a floor clean as a whistle and dry in minutes. A bucket of it that has been used and used and diluted with oil over and over will still do a good clean up, takes longer to dry, maybe even into tomorrow, but the floor is not slippery and will still completely dry given enough time.

The moral of the story is. The engine flushes break down the new oil that you put into them. Badly.
 

·
Registered
Joined
·
736 Posts
Ah crap, now you guys are gettin me all paranoid!!! Lol.

Sigh, ok, I'll read the Sea Foam SDS, I have a feeling I'm changing oil this weekend....

I followed the instructions. But I don't mind changing the oil, if it is for the better. Hell, I guess I'll learn something. I get tired of learning sometimes, lol.
 

·
Typical /f12 Hooligan
Joined
·
6,936 Posts
I see Isopropanal? Is that bad?

Wow, also see alot of "flammable", that doesn't sound to good for an engine, even if it is mixed in oil. 1 valve cover leak and you could have a bad day?
The point of @Boojo35's concern isn't that you will explode the jeep. The point was that formulation directly destroys oil. Even draining the oil with the mineral spirits leaves some of that product in the engine. The new oil is also adulterated and weakened by those products.

ATF4+ is a lubricant and detergent. The detergents are mild enough for soft metals and seals. It will break down the sludge while still providing lubrication. It's not a perfect scenario for engine protection to run a quart of ATF, but it will do the job without issues. Once the ATF adulterated oil is drained, any remaining ATF in the engine will again mix with the new oil and continue to lubricate and clean. The main difference is the ATF works with the oil, mineral spirits work against it.
 

·
Registered
Joined
·
736 Posts
The point of @Boojo35's concern isn't that you will explode the jeep. The point was that formulation directly destroys oil. Even draining the oil with the mineral spirits leaves some of that product in the engine. The new oil is also adulterated and weakened by those products.

ATF4+ is a lubricant and detergent. The detergents are mild enough for soft metals and seals. It will break down the sludge while still providing lubrication. It's not a perfect scenario for engine protection to run a quart of ATF, but it will do the job without issues. Once the ATF adulterated oil is drained, any remaining ATF in the engine will again mix with the new oil and continue to lubricate and clean. The main difference is the ATF works with the oil, mineral spirits work against it.
That makes sense, Sea Foam is supposed to break apart carbon and other stuff left over, sometimes from old oil. But if it breaks down old oil? What does it do to new oil? Lol

I hadn't thought that all the way through, but yeah, you guys are right.

Ok, I still have the Sea Foam in there, maybe 200 miles on the Jeep, oddly, my oil sensor is working better? Lol, wierd,anyhow, I'll do another oil change.

Doesn't bother me that much. I am stock piled in filters and oil. And I like it. I am always finding something to do on the Jeep, kinda clears my mind, even if it's something that is frustrating. Keeps me off the News and other negative things in the world, lol. Should name my Jeep Zen or something.
 

·
Registered
Joined
·
736 Posts
Have you been considering something … violent?!
DON’T DO IT, MAN​
🤪 GO BUY SOME MORE BRAKE SHOES
Lol, just thoughts..... just kidding. Meh, nothing I can do about it, just sadness all over, energy crisis in EU, Construction slowing down- can't get electrical components, generators, etc. Politics in general causing divide, and more.

The Jeep and reading about engines keeps my head clear and intrigued/interested. It's why I bug guys like you and others with ridiculous theories/questions, lol. You guys help keep me sane as well.

News: "We may see a nuclear war....."

Me: "I'm gonna go find that squeak in the Jeep now...." 🤣
 
1 - 20 of 21 Posts
Top