Oil filter change vs oil change

Dave_J said
Any known 'SLUDGE' engine needs a few mods to keep the oil from gunking up the valvetrain. Somehow the oil gets trapped up in the heads and valley due to piss poor engineering. Those you MUST change the oil at 2,500 or so but that only helps a fraction.

All Jeep 4.0L run hot due to piss poor designing. The radiator is too small for one. The head traps air in the rear of the head and you must lift the rear end up high enough to get that air to 'BURP' out. The coolant overflow system was designed in a Kindergarten class. And if you do the 4.2's crank swap for a stroker 4.5/4.6/4.7/5.0 Liter that heat is even worse. You should add an oil cooler with its own fan and thermo switch.

The 5.2 and 5.9 Magnum's oil pumps SUCK, no pun intended. The bypass valve sticks open when real hot and as you are doing 70 MPH, the idiot light comes on and the crank is eating bearings. Does not matter what type oil you use. Drop the oil pan and put a Melling HV pump in. Where the type of oil matters is sludging in the heads and lifter valley. Hot oil gets trapped and bakes. After replacing the crap oil pump, add an exterior oil cooler.

Good to know, when I rebuild my 4.0 it'll be stock stroke but I may turbocharge it (with forged pistons and beefed rods). I did always feel like the radiator on my XJ Cherokee was a bit small for an all-iron 4.0L straight-6 designed in the 1960s. I overheated it many times while offroading until I installed an aux electric cooling fan; apparently since mine was a manual trans with no A/C it only got the engine-driven cooling fan from the factory which only pulls on half the radiator core. Might have some design flaws but the thing is so damn bulletproof it can take being overheated and run with dog-piss in the oil sump lol. Mine started having weird oil pressure issues likely due to me revving it to 4500 RPM on a regular basis, pretty sure the con rod big ends got ovaled and the bearings are bad. But that Jeep got totaled from being rear-ended a few months ago so the engine is now in storage.

On the subject of the cooling system, the heater also sucked lol. Might be because with no A/C it didn't have an air-recirc function so it was always pulling in outside air but that thing wouldn't put out heat worth a damn basically until the thermostat was opening. And I did a lot of maintenance and small mods to the cooling system to increase flow (took out heater control valve and replaced with higher-flowing brass ball valve, added Water Wetter to coolant). Got it working better but still sucked compared to my other vehicles.

Back on the subject of oil, I am curious about doing an oil analysis on my vehicles. Would be nice to confirm with actual data that I can extend my oil change intervals past 3k miles. And same as @YY1 I run Valvoline full synthetic in all my engines (Duster has a roller cam so it gets the 5W-40 Euro-spec MST stuff), good price and IMO better than Mobil 1. Supposedly Pennzoil is a lot better than it used to be but I don't feel a need to switch when the Valvoline FS has been serving me well for over a decade.