What weight oil? (93-4.0-134K)

Got a 93 with 4.0 and 134K on the ticker. Im running 10W30, as I have in everything else. But Im thinking its time to change grades. What weight oil do you suggest I run, and why please?

Ive got a little blowby problem, and some a little smoke after its sit in park for a while.

Im getting ready to Seafoam the crank (1/2 bottle) for about 3 daze then change the oil, so Im looking for advice before I do this.

Many thanks,
Andrew

Why do you think its time to change grades? 10W30 should do it for you.

Good question Helix.. I was thinking with the milage it was time for a little thicker, but Im open to suggestions. Also, I was under the impression with the blowby, a thicker oil would help with the pressure. Im not sure about these two specific details, is why Im asking.

Andrew

I would not bother with thicker oil unless there's a significant drop in pressure. As long as the oil stays in the bearings long enough to cushion them, it is thick enough, and the faster it flows, the better it cools the bearing surfaces. If 10w-30 works for you I'd stick with it.

For the blowby, don't forget to check the little vacuum tube for the crankcase vent for cracked rubber at the joints, and also for constriction by sludge. It's pretty critical, and even a little impediment to flow will mess up your venting. For example, part of the blowby problem in the original 4.0's was solved simply by replacing the original tube that had sharp 90 degree elbows with one that had curved elbows (it made a big difference on my 87).

134k isnt that much at all on the 4.0. I'm still running 10W-30 at 180. That and matt hit the nail right on the head about the blowby.

I have an 87 w/200k+++ on it and I run kendall semi synthetic 5/30 w/tons of oil pressure.... idles @ over 40lb.@ 205*

What is your oil pressure? The oil pressure will indicate wear, and keeping a good oil pressure will be your gauge for what viscousity oil pressure to use.

If you get signficantly lower oil pressure across the board in all conditions, then I would bump up to a higher viscousity oil that gives you the same or close to the same pressure as before.

If you still close to original oil pressure, or the engine still makes good oil pressure, then keep doing what your doing with the same oil.

Since I mentioned the little blowby problem, I guess I should have also mentioned the following.

Ive replaced the rear vac hose that goes from the intake manifold to the valve cover, and also the 1/4 turn lock adapter that is in the rear also. (The old hose was partially obstructed, and the adapter was caked up inside and at the bottom).

Before, my oil pressure was always over 80.

After the new parts, my pressure is at about 40 cold. Once warm (210 deg), it at 40 idle and between 40 and 60 running in the city. HOWEVER, just over 2K RPM on the interstate the needle pegs again just over 80, but not as far as it used to. SO, Im under the impression I still have some high crank pressure going.

Im hoping some Seafoam in the crank will help free up more sludge and maybe reduce what remaining pressure problem Im having.

Thanks again...
Andrew

Ttt??

I have found that 10W40 Mobile 1 is the best for high Kms oil change intervals also go to 4000 kms instead of 3000

I have found that with higher mileage engines (100K plus) that anything that is semi-synthetic or full synthetic makes thigns run a little smoother. If you are looking to transition to a full synthetic, I recommend cycling through 2 oil changes of Quaker State 4x4 Semi-synthetic blend. It's good for the abuse wheeling puts on an engine, especially with the 4.0L. I currently run Royal Purple, but Mobil 1 or Lucas are two great alternatives. It might not give you extra horsepower, but having a smoother, more efficient engine is good insurance when it comes down to having to push your Jeep that extra bit to get out of squirrely wheelin' incidents.

Just my 2 cents.:compwork:

MyJeepXJ said:

Since I mentioned the little blowby problem, I guess I should have also mentioned the following.

Ive replaced the rear vac hose that goes from the intake manifold to the valve cover, and also the 1/4 turn lock adapter that is in the rear also. (The old hose was partially obstructed, and the adapter was caked up inside and at the bottom).

Before, my oil pressure was always over 80.

After the new parts, my pressure is at about 40 cold. Once warm (210 deg), it at 40 idle and between 40 and 60 running in the city. HOWEVER, just over 2K RPM on the interstate the needle pegs again just over 80, but not as far as it used to. SO, Im under the impression I still have some high crank pressure going.

Im hoping some Seafoam in the crank will help free up more sludge and maybe reduce what remaining pressure problem Im having.

Thanks again...
Andrew

Click to expand...

It kinda sounds like a stuck pump bypass valve, or a bad sender/guage.
80+ is kinda high for oil pressure, even cold.
You might want to sub the electric guage with a mechanical just to see what is really going on.

If you think it is PCV related, just unscrew the oil cap and take a reading at, say, 2-2.5K in the driveway and see if makes a difference. My bet is it won't.

I wouldn't add anything which moves deposits around the engine. Murphy's law generally indicates that messing with things which work is not a good idea.

Piston ring blowby and high crankcase pressures won't give you a high oil pressure. The high oil pressure readings usually occur only for two reasons:

1. Faulty gauge sending unit.
2. Oil filter bypass valve or oil pump bypass valve stuck closed.

Common things being common, I'd go for the sending unit being faulty. Verify the oil pressures with a mechanical gauge and you'll know where the problem lies.
Normal oil pressure is minimum 13psi at 600rpm idle and minimum 37psi above 1600rpm using 10W-30 oil. If your oil pressures (after verification) are above those minimum levels, there's no reason to go for a higher viscosity oil. If the oil pressures are marginal, try 15W-40 and then 20W-50 as required. If you reach 20W-50 and oil pressures are still marginal or low, it's time for an engine rebuild.

Dr. Dyno said:

Piston ring blowby and high crankcase pressures won't give you a high oil pressure. The high oil pressure readings usually occur only for two reasons:

1. Faulty gauge sending unit.
2. Oil filter bypass valve or oil pump bypass valve stuck closed.

Common things being common, I'd go for the sending unit being faulty. Verify the oil pressures with a mechanical gauge and you'll know where the problem lies.
Normal oil pressure is minimum 13psi at 600rpm idle and minimum 37psi above 1600rpm using 10W-30 oil. If your oil pressures (after verification) are above those minimum levels, there's no reason to go for a higher viscosity oil. If the oil pressures are marginal, try 15W-40 and then 20W-50 as required. If you reach 20W-50 and oil pressures are still marginal or low, it's time for an engine rebuild.

Click to expand...

how can you tell just by looking at the oil pressure that you need an engine rebuild? i would think that there would be other telling factors than just low oil pressure?

If the oil pressure is less than 13psi at idle and less than 37psi above 1600rpm when using the thickest engine oil available (20W-50), it's likely the main/rod bearings are excessively worn and/or the oil pump is worn. Either way, you need to drop the oil pan and investigate. Bearing clearances should be measured with Plastigage and if they're more than 0.0025", the bearings should be replaced.
Low oil pressure is the first warning sign of impending main/rod bearing failure. The engine may otherwise run great and not be making any funny noises so you might not have any other sign that the bearings are on the way out. If you wait until the oil pressure is zero at idle or until you hear a bottom end knock, the engine's already toast and will need a full rebuild. Neglect the bottom end knock for long and you could find a piston/rod getting thrown out from the side of the block with a nice pool of oil on the road. Not a pretty sight!
Excessive piston ring blowby will not only cause high crankcase pressures (leading to oil-soaked air filter, oil coming out of dipstick tube, leaking gaskets/seals) but it'll also result in high oil consumption and blue smoke appearing from the exhaust. The time to rebore the cylinders and install new pistons/rings will depend on how much oil consumption, performance loss, and hydrocarbon emissions you (or or local smog testing station) are prepared to put up with, and how much blue smoke your Jeep will be allowed to belch out before you get pulled over by the cops.