Hello all,

I recently changed my cylinder head (clearwater cylinder head) on my 01 xj with 98k miles after it cracked. Afterwards, the oil pressure would drop to 0 at hot idle. After replacing the fram oil filter and putting in 10w-40 I have about 10 psi at hot idle. I do notice more vibration than before the oil gets hot at idle but otherwise no problems. I have heard that running with low (below 13 psi) oil pressure is okay, since at idle there is no load and the oil film on engine internals sticks around for a few minutes. Can anyone verify this? I would just like to hear thoughts about the relative safety of idling with below spec oil pressure.

Thanks

 

what prompted the head swap ?

 

I have been driving mine for over 2 years with 4 psi. Very busy daily driver in all types of traffic, from city to 70mph highways and many times pulling a trailer. No problems yet. Runs great,uses no oil and gets good gas mileage. It was annoying to see the gauge dip to zero and hear the check gauges chime but i have pretty much blocked it out now.

 

5psi per 1000rpm is safe from what i was told. I have the same problem with the vibrations and low oil pressure. I'm at 7psi when I'm at a hot idle. Accelerate slower when it's low or pop it in neutral so get the pressure up before going.

I ruled everything out so I'm 99% sure my cam bearings are shot. I'm just waiting for it to blow up so i can replace it.

 

^^^

If you determined your head was cracked due to coolant seeping into the oil, the ethylene glycol has likely eaten away at your bearings. This is the big reason head cracking is a problem. If it doesn't make noise and still runs alright just keep driving it. Either the body will rust away or the engine will tell you that a rebuild is needed (not via catastrophic failure, pressure will continue to fall or it'll develop new noises)

 

Yeah some 4.0s had problems with the cam bearing walking out of the journal which will cause VERY low pressure. I suspect that I have the same problem but after 30k miles I don't worry about it anymore. The engine will "talk-to-you" when it is time to rebuild/replace, so just drive it until you hear noises. Just because the pressure is low does not mean the engine isn't getting lubed. Oil is still flowing throughout the engine or it would blow up.

 

I'm doing some "googleing" on the idea of coolant eating the bearings. I just learned of the idea here on the forum. Might be that the long term exposer from a cracked 0331 is worse.

Found this;

I dont know if I can agree with you on eating bearings.... BUT, the very nature of Ethylene glycol.... Ethylene by its self. is comprised of Carbon, Hydrogen and Chlorine.....

This is from a MSDS site on Ethylene glycol
Strong oxidizing agents. Reacts violently with chlorosulfonic acid, oleum, sulfuric acid, perchloric acid. Causes ignition at room temperature with chromium trioxide, potassium permanganate and sodium peroxide; causes ignition at 212F(100C) with ammonium dichromate, silver chlorate, sodium chloride and uranyl nitrate.
the combustion process makes sulfuric acid, hydrochloric acid, and Phosphoric acid.. that why Engine oil contains calcium as a acid neturalizer.....
and since Ethylene glycol is chlorinated... Hydrochloric acid is a very real possibility.....
Wheather produced in amounts great enouf to do significant damage.. well I dont know... but it would have to be a greater amount that the calcium of the engine oil could adsorb....

OK, I'm convinced;

Acid Formation and Bearing Damage
Under normal operating conditions, ethylene glycol oxidizes to form organic acids such as glycolic acid, oxalic acid, formic acid and carbonic acid. Typically the reaction rate doubles for each 18°F (8°C) in temperature. These acids contribute to secondary and tertiary effects as further described. However, their presence alone in lubricating oil can jeopardize bearings and other frictional surfaces. The corrosive conditions can pit the clad surfaces of the lead/tin overlay of journal bearings, promote rust on steel and iron surfaces, and tarnish cupric metals of bronze and brass. One study found that even a small coolant leak in a large integral gas engine/compressor was enough to severely corrode engine steel and copper surfaces.

This link has a bunch> http://www.machinerylubrication.com/Read/193/oil-glycol