Oil Pressure

Shatteredglass · #21 05-23-2008, 08:52 AM

Wow what a great board alot of knowledge here i will get me some stp and 30wt or 40wt oil and put in it and see how she does what wt would you recommend in the Indian winters?

RRich · #22 05-23-2008, 09:41 AM

I'm not sure what an Indian winter is - we only have Mexican summers. We range from 120 degrees in the summer down to 0 once or twice in the winter.
I keep 30 or 40 in all my vehicles.

If it was to go below 0 much, I'd go a little thinner. The only time ambient temperatures affect it are during a cold start when the oil might be sluggish to get flowing.
That's where the STP comes in, it's coating stays there. Just try to wipe it off your hands without soap or solvent - you'll know what I mean.

But - when using STP it's important to change the oil regularly - when it get old and polluted with unburned gas and water, it forms a plastic-like substance. Not a problem if you change it once in a while.

Jim_Lou · #23 05-25-2008, 10:25 AM

FYI the pressure relief valve in my stock '78 258 is set at 60 PSI. Cold idle pressure is around 20, while hot idle drops down to 10, or less if I turn the idle speed down. So if the gauge read 20 PSI low at all times it would behave exactly as the one in question here.

I don't know how likely that is, but being electrical I can think of several things that might affect it; the voltage regulators, either in the alternator or the one in the speedometer, high-resistance connections, faulty sending unit, faulty gauge, or poor grounds (as unlikely as THAT may be in an old Jeep

)

Shatteredglass · #24 05-26-2008, 08:42 AM

Well i drove it for about 30 mins the other day and at start up the pressure is about 2 to 30 after about 25 mins it started dropping below the 10 mark and had a little ticking at idle not much thou once i reved it up the ticking would go away so i think i will try 6 quarts of some 30 wt and see if that helps before replacing the pump? Sound like the right thing to do ? have a great week all

Jim_Lou · #25 05-26-2008, 10:47 AM

I think I'd just drain it, drop the pan and replace the pump. There's almost no doubt that you have a pressure problem. A heavier oil might bring the pressure up a little, but the underlying problem will remain. After you find out that it's still there you'll be throwing away six quarts of new oil when you take the next step.

On the other hand, there's a very skinny chance that it is just an oil problem, so it's a long-odds gamble of $20 and a half hour's work against maybe $100 and three hours work. Doesn't really matter much.

GeeAea · #26 05-27-2008, 12:27 AM

I'd use a 15w-40 for one oil change. See if the condition, which will be reduced, returns or moves toward the same state near the end of your oil change interval. It would point to thinning due to fuel dilution. The 15w-40 mixed fleet oils are shear stable ..so that typically leaves fuel dilution.

You could be suffering from all kinds of worn stuff, but if someone abused or neglected it, the last place I'd look for issues is the bearings. I'd expect blow-by due to long spans of being idle (102k over 23 years isn't full time usage) where the internals on the open valve cylinders rusted from moisture ingress. Since you report no such anomalies, I could see internal pump leakage, but that should also follow the general wear pattern of the engine. You may have a varnished or scored oil pump relief valve. You may try something like Auto-Rx to clean stuff up internally (web search).

Shatteredglass · #27 05-27-2008, 10:36 AM

Well i might give that a shot and see what happens like said above if have to i will replace the oil pump and get her back so she can run for a while

GeeAea · #28 05-27-2008, 12:54 PM

NAPA carries a high volume oil pump for the 4.0. I got mine from Qualcast. It's not a sure fit in every 4.0 however. My buddy threw one in a Cherokee that had hot idle pressure issues, and he had to hammer the pan just a tad to get the pan back on. YMMV

OlllllllOCJ · #29 05-28-2008, 09:14 PM

Quote:

Originally Posted by Shatteredglass

Well i might give that a shot and see what happens like said above if have to i will replace the oil pump and get her back so she can run for a while

Try the easy stuff like different oil first to see what happens.

I had a little tick a few years ago on my 1985 258... Kept getting worse but became obvious that it was the timing chain so it didn't worry me much. When I got around to it I changed the timing chain and the oil pump (to a high volume pump) at the same time. Well worth doing both if you are planning one or the other since you have to loosen or remove the oil pan to get to the timing chain. Today there's no ticking and the oil pressure stays between 20 and 40 psi no matter what.

As a bonus you get to use the 4.0L (one piece) Oil Pan gasket and stop all of that dripping.

Dale

Shatteredglass · #30 05-29-2008, 02:31 PM

i will have to try this thanks a bunch all