Still No Oil Pressure

I've read several posts where people have experienced a cracked cyl head. symptoms of slow loss of coolant and reduced oil pressure. Oil pressure would drop after the head warms up (which causes the metal to expand and the crack to widen allowing the leak).

as far as i can tell no loss of coolant, but I am not running it for long periods of time either...

I do know that no oil in coolant, and no coolant in oil...

exhaust had no cloud... like no white/blue smoke... some condensation on the ground, but once it got warm that stopped...

My hand in the hot exhaust for a few minutes (I know... burns... but hey...)
resulted in nothing "slippery" like no oil/coolant residue burning off...

I did not start to sniff the exhaust, so don't worry about that...

FSM talks about pressure testing the block with air... also a black light dye to check for external leaks... worst case I could have a dealer pressure test to see if there is a crack somewhere...

But not jumping the gun yet... oil pressure check and compression check first... (well... I could compression check, then prime pump since all plugs pulled, then oil pressure check)

See what those results are, and go from there...

Rockn93YJ wrote:

I've read several posts where people have experienced a cracked cyl head. symptoms of slow loss of coolant and reduced oil pressure. Oil pressure would drop after the head warms up (which causes the metal to expand and the crack to widen allowing the leak).

Bill, I think you might of hit it on the head.. I was talking to a buddy about my overheating problems and he said the 4.0 is well know for cracked heads. He originally thought that was my issue but we believe its the clutch fan.

I think your theory about the crack expanding when its hot might be a factor.

If you turn it off after loosing pressure will it build back up when started or do you need to let it cool down first before the pressure resumes.

I vote for a cracked head as well. I had a TJ that would lose oil pressure but only after it was hot. At stops the pressure would drop very low (not low enough to throw the light but just above it) and when revving it would pick back up to the 40+ zone. I began smelling coolant as well and dumped it.

Went to Salvo Tuesday and picked up a quart of Lucas Oil additive...

Picked up the compression gauge, and oil pressure gauge (well... splurged for the oil/temp/volt combo cluster to mount on the roll bar... evenly gradiated numbers MUCH better then guessing what the F the hash marks are trying to represent. )

I primed the pump per Bill's instructions... wow... I can see why to pull the plugs... it cranks right over with no load...

All the plugs looked good... just changed them a few months back so they were still newer looking... none fouled out or crudded up.

Did the compression test... #6 (Firewall) was at 85psi to 90 tops. The rest were at 90 psi to 105 tops. These were all while it was still hot (oooow my forearms in tight spaces.. )

Next came firing it up...

At idle... 10 psi of oil. Revving came out to almost the basic 10 psi per 1000 RPM (2K RPM = 20, 2500 = a little over 25, etc)

Not sure how it matched up to dash gauge because I have not done the T yet...

As the engine got hotter the idle psi would drop out closer to 5... always steady, not pulsing (pulsing would indicate sucking air I think... steady equals constant flow, just low pressure).

So the cracked head idea really seems to fit... not that I am thrilled about it, but at least we are getting somewhere.

I would guess no coolant/oil loss or mixing because it has never run longer than a 15 minute burst, then at least an hour to cool...

Oh yeah... if its hot and I restart... low pressure, but steady. I also did compression cold, then hot to see if maybe the temp was causing a change in the compression too... not much difference, so I think I can assume no lower block damage (though maybe still main bearings).

I have done quite a few head gaskets, so its nothing new... probably spend the weekend scouring Crazy Rays for a head assembly... then spend some time cleaning it up, lubing all nice and purdy, and give it a whirl...

Save up some cash for the $500 new head assembly (with roller rockers for longer life)... and if it is still running strong by then, continue to save up for the Golen 4.7 stroker for the next time I have a :lllgh: moment.

Wait... before I go running out for all that... should I pull my head (sounds soooooooooo dirty) and check for a crack first... think I would be able to see it? And if 6 (firewall) was off kilter on compression compared to the other 5 then may it be in that area?

Might as well check all the push rods too... make sure none are bent, etc. And check the pistons for slop...

Wow... this is turning into a good overhaul... between, the motor, the lift, the tires (haven't forgotten yet Nester... still itching to get them on there...) the flat fenders... I don't think there will be a system I hadn't touched before the next run I make...

I am soooooooo glad I didn't let this beat me... and so VERY appreciative of all the help guys.

"Did the compression test... #6 (Firewall) was at 85psi to 90 tops. The rest were at 90 psi to 105 tops. These were all while it was still hot"

With the compression test did you let it cycle about 3 times before reading the compression? Should be getting readings between 120-150 psi


"At idle... 10 psi of oil."
Not too bad, should be 13 so a small leak somewhere

"Revving came out to almost the basic 10 psi per 1000 RPM (2K RPM = 20, 2500 = a little over 25, etc)"
at 1600 rpm or higher the pressure should be 37 to 75 psi.

"As the engine got hotter the idle psi would drop out closer to 5... always steady, not pulsing (pulsing would indicate sucking air I think... steady equals constant flow, just low pressure)."
Heat expansion of metal would cause any leak to worsen.

"So the cracked head idea really seems to fit"
It does fit but it may not be all that is wrong so definitely check the bearings first.

"should I pull my head"
All the pressures were quite low so I would repeat the test making sure to cycle 3 full times on each and get a reading again.

I would highly recommend first checking the main bearings and while you are in there replace the oil pump with a stock replacement just to make sure the short oil pickup isn't adding to the problem. Then check the oil pressures again. The compression test showed low readings across the board so if it was done correctly then it would suggest more extensive wear for all of the cyl to be leaking. Start small since you have time now before replacing the head. You may actually pull a cracked head from the junkyard and still have the same probs.

I will check the compression again... Laurie was trying to help turn it over, but she can't reach the clutch to push it all the way in... yes... she is that short...

the gauge ticked over 2 or 3 times... it did pressure slightly higher but then held at 90. never over 120 though...

Since I am tearing it all down yet again I am thinking yank the motor and put it on a stand.

I think it may be a lot simpler, quicker, cleaner, and safer to just pull it, spin it any way I need it to set it all back up.

New clutch/throw out bearing when I button it back up... for one less thing to worry about since it has 60,000 on it.

And do it all right the second time

Hey Bill,

What is the name of that wonderful engine book you have, and where can I get a copy...

It may be handy to have for referance with this adventure...

The book is Mopar Performance parts JEEP ENGINES 3rd edition part number P5007161. they may have a new issue by now. You can borrow mine if you want. New says like $30 I can send it home with Von this weekend if you live near him.

Gotta re-do the compression test... wife never put throttle at wide open... closed the whole time... she couldn't do both pedals at once.

I was too busy watching gauge to notice.

I will set hand throttle full open, and try again...

According to diagnosis though... wouldn't a cracked head result in 2 cylinders being low in reading, showing them to be about the same value?

depends on where it is cracked. could blow into the water ports or an adjacent cyllendar. I'm not entirely convinced it is a cracked head, I still have hope it is something simple like a bearing.

I like bill's idea of putting a stock oil pump on it and see what happens it alot less work that pulling the whole engine. the compession gauge should hold the pressure until you release it so you can do the test yourself. Pulling the motor is a lot of work if you need a picker and a stand I have one you can use.

RETESTED -

OK... so after it sat awhile here are the numbers... HUGE difference.

The oil readings were off because I guess the engine had not cooled enough before testing the new meter (I installed it after the compression testing so motor was still warm).

From a cold start I had 40 psi constant at idle. Once the temp got to around 170 (new temp gauge)... the psi dropped to about 20.

10 minutes later it dropped to the low 5 to 10 psi range.

I revved it, built pressure back above 40, and I kept it there for about 2 minutes...

No knocks, pings, clangs, bangs, backfires, sputters,etc.

If I had given the keys to one of my neighbors, or buddies at work, no one would ever guess it has a problem from listening to it.

I let it idle to settle down and make sure it was up to temp for compression... and just observed under the hood...

One thing I picked up on that I did not notice before (usually test from passenger side... this time I was on driver to work the throttle body).

I am getting a shrill whistle... the best way to describe it is like a turbo on one of those import tuners... wait... Jeep forum... how about... a small child running around screaming that high pitch ear piercing banshee wail...

Only this is not loud, does not change pitch or volume when throttle changes, but does seem to start and stop at times...

If I had to guess I would say it is sucking air someplace...



There were also puffs of smoke every few minutes... not a huge cloud, and no definitive source... someplace in the front of the motor, but the fan dissipates it so I can't see from where...

Compression Results:
1 (Radiator) - 175
2 180
3 160
4 160
5 170
6 (Firewall) 160

I guess next week I will start with the bearings and pump again...

For now I'll just note the banshee whistle and smoke puffs as another not quite normal occurrence, and continue on the rebuild.

As strange as this sounds I am upset I broke it, but proud of the fact I am fixing it myself... done a lot of small engine rebuilds, and engine swaps... the basics to car motors (head gaskets, motor mount swaps, exhaust, carb tuning, timing, etc)... but never a full one motor rebuild...

This is actually kinda fun at the same time.

Zen and the art of Jeep repair...

Tony, I gave the jeep engines book to Von. Give him a call or PM to arrange picking it up from him if you like.

cool... thanks bill...

Tony, i talked to a guy that i worked with who used to work at adams jeep about 10 years ago.
Without actually seeing the motor, he said that you probably damaged the cam bearing and probably some other ones. Especially if you found some metal shavings in the oil after your drained it the first time.
Just thought id let you know

yes, tony i have the book at my house. i can hold on to it until you want to pick it up. or i can give it to kathy since you know were she lives. just let me know

Sean... no metal found anywhere... but I was gonna start with main crank bearings and the front/rear seals (think puff of smoke may be front seal behind timing cover)

If that doesn't get it then off with his head... inspect lifters, rockers, springs, etc. At that point redo intake gasket in the event that is my whistle/scream (sucking air?)

After that... then cam shaft bearings...

If I get to that point (which hopefully not)... well.... time to stroke it... because the entire motor will have to be pulled, and every component already messed with, so why the heck not...

Send the block out to be decked and honed, then bored .060 over if it is solid...

Send the head to be ported, and pressure tested for cracks...

New pistons, rings, Comp Cams cam, roller rockers... ( I have been doing A LOT of homework on this and found several builds all under $2,000... the most expensive part is the machine shop work...)

Expensive... well... yeah... it will be... but at this rate it may be awhile before it is back on the road anyway between trying to get the lift in and everything else...

Hopefully this week I can drop the pan, replace the main bearings, seals, and pump... and be done with it... if not...

well thats good news. I thought you saidthat you did find some metal. Good luck with the rebuild. I hope it was just the main bearings.

Think twice before you stroke the motor on your jeep. Then talk to Bill about it.

Tony, the stock 4.0 is plenty of power for a trail rig. bore and stroke is not worth it and you could save a lot of $ just replacing the motor with a stock unit.

Tony, My engine was a rebuilt from Advance Auto got it for under a grand and it has plenty of power.

mdcj7 wrote:

Tony, My engine was a rebuilt from Advance Auto got it for under a grand and it has plenty of power.

A complete 4.0?!? That's pretty sweet. I knew they were pretty cheap to rebuild - didn't realize you could get a rebuilt motor for that "cheap"

Tony...i agree on not dumping that much coin into the 4.0. It's the one thing Jeep got right!!!!!!!!

I've been at the point of dreaming of the stroker as well but bill and nester have successfully talked me out of it. There's always the V8 dream but I'll stick to the 4.0 and keep my drivetrain alive.

Von - You can give the book back to Bill next time you see him... I got a copy off eBay for $5 (with a Jeep Haynes manual)...

So now I have the FSM year specific to Black N Blue, the Jeep Engine Book, and the Haynes book...

Lots of cross referencing, pictures, and info...

I did some more trouble shooting... engine book talked about pulling the radiator cap once the engine was at temp (thermostat open) and watch for bubbles on compression... nothing... so in theory no head leak...

Looking over the repair (and my dad's second set of eyes) going back to the oil pump as Bill suggested...

It is going to be a royal pain in the butt again, but well worth it if thats all it is.

Dad and I went to Crazy Rays... he needed a hood release cable, I needed a steering column for the dakota (still driving hot wired for now which was fun explaining to a very understanding officer when I went to pick a friend up from the bar at 1AM...)

A motor (complete) would run me $200, found 2 2004 Grands, but sever front end damage (too risky) and everything else had 150,000 or more.

Haven't had time to do much more... Saturday I plan on really tearing into it again and go from there...

status? found you a motor with under 100k miles from a 98 TJ $200 I think.

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