oil pressure issue or no issue ?

[oldscot3]

I've been sorting out little mechanical issues on my recently aquired cj2a and finally have been doing a little driving. I've noticed oil pressure is good on cold start up and remains good (between 40 and 60 psi) during driving, however, when the engine is up to temp and allowed to idle the pressure drops to about 5 lbs. Does this sound like my engine bearing clearances are too wide, or is that still acceptable for these old flatheads?

[gmwillys]

That is about par for the course as far as oil pressure at idle while warm. Our 2A holds between 5 and 10 psi depending on ambient temperature, with SAE 30 wt. Oil. Last weekend with the temperature in the low 100's, the L134 was running close to 5 psi on the gauge.

[oldscot3]

thanks, that eases my mind a bit... and now I can devote my full time to worrying about drivetrain noises.:confused:

[bmorgil]

gmwillys is right on. The spec for minimum safe oil pressure is 6 lbs at idle (600 rpm) and 20 lbs at 2000 rpm (35 mph). 35 psi is listed as normal at 2000 rpm. The relief valve is set for 40 psi. I can tell you with a freshly rebuilt motor at idle with hot oil, 6 is all I can get. This is not uncommon as gmwillys points out. The cam is the primary culprit. It only has one tight clearance bearing. The rest of the camshaft journals run on the bare block. This sprays a lot of the oil pressure out onto the crank. As the block wears this gets a little worse. The thing to put your mind at ease is these little L134's are some of the first pressurized lubrication engines. Engines in the 1920's, 30's and early 40's frequently were lubricated via "splash". No oil pressure at all. I have heard many accounts of little to no visible pressure on the gauge at idle on a hot motor. I would first say you must check this with a good large scale test instrument. 6 psi is hard to measure accurately on a 2 inch gauge. Second always use a high Zinc oil that has excellent film strength. If you get readings in the 60 psi range when warmed up, you might want to be sure you are running the right SAE weight oil. At 60 psi a lot of oil is by-passing via the relief valve. Not necessarily a good thing.

[oldscot3]

Apparently my engine was rebuilt (at least once) in August of 1955. It has a brass tag fixed low on the passenger side that says "Pod Base Shop, Pueblo, Colorado, Remanufactured engine". It runs very nice withut a hint of smoke. I changed the oil just because I didn't know what was in it, and put in Rotella 30w. I'll look at the chemistry to see if it's high zinc.

[bmorgil]

Here is an excellent read on high zinc oils. Rotella is a Synthetic I believe. I am not sure if it contains zinc. Early rubbers and seals did not stand up well to modern synthetics. I would recommend a mineral based oil. http://www.sccoa.com/forums/showthread.php?136304-What-oil-brands-offer-the-best-protection-***Good-read***

I am a big fan of synthetics and, I have seen first hand horsepower and durability gains. I would not run a modern engine without them. I do know that many machinists, ring manufacturers and the like, prefer different cylinder wall finishes and even ring material when synthetics are used. One thing is for sure modern synthetic oils are a major contributor to the longevity of today's engines and their fuel economy.

How long it takes the oil to "color" or get dirty, is an excellent indication of ring condition. Compression blow by will quickly color the oil. The oil has the important function of suspending the carbon. The dirtier the oil, the more abrasive it becomes. If the oil stays clean, that is a great indication the rings are sealing fine. A light easy to see through color at 3000 miles is a beautiful thing.

[oldscot3]

No mention of synthetic on the labels, it's labelled "Rotella T, heavy duty motor oil". I bought it at Tractor Suply and use it in my old Ford tractor.

It may have been replaced (somewhat) recently by Rotella T1. The label on that bottle says "heavy duty engine oil for diesels".

[bmorgil]

I am not sure about the Rotella diesel's composition. I do know it is very good diesel oil. We also use it in our tractor and diesel truck. Diesel oils typically have a very high detergent additive content. Diesels are dirty! A lot of fuel and carbon gets by. The extremely high compression is the culprit. I am not sure how well they apply to a gasoline classic. A good question for Shell! T1 is a conventional oil. As long as it has a good zinc content, some good protection for the low oil pressure at idle and can run at high speed it should work. Oils used in diesel engines typically lack the anti-foaming agents found in high speed engine (Gasoline etc) oils. A diesel rarely sees above 3000 rpm. A good conversation to have with Shell's tech line. You may want to consider changing it out to a Gasoline engine oil.

[oldscot3]

yeah, I didn't use the T1 in my jeep, I used the Rotella T. The label says it's good for diesel and gasoline, eighteen wheelers, tractors, heavy equipment,and automobiles. The T1 doesn't mention use in gas engines, so if that's all Tractor Supply has the next time I go in I won't buy that for the jeep, I'll get something else.

The old oil looked pretty clean, but since I didn't know what it was or how long it had been in there, I thought I may as well change it and see if there was any effect on the idle pressure. There wasn't, but now thanks to you guys, I know my engine is operating in a normal condition.