if your gauge needle starts at cold and comes up to operating temps, it sounds like temps are fine, i wouldnt worry myself digging further into those points.

with a solid rear axle, i'm not sure the alignment guys would bother looking at your rear wheels, yet alone spin them for resistance. its an easy thing to check yourself.

if you aren't losing oil, i'd personally be looking more into the catalytic converter and o2 sensors as landyacht pointed out.

 

If it ends up being #3. Fan Clutch is defective. DO NOT get the HD clutch. It will make the MPG even worse! The regular fan clutch spins just fine and easy without robbing engine Hp and adding more friction like the HD one does.

 

What did you refill the rear differential with???

Chrysler has a TSB 03-02-98 to use a fully synthetic 75W90 to increase fleet MPG for our vans. http://dodgeram.info/tsb/1998/03-02-98.htm
If you went with a 80W90 or heavier, that would make the MPG worse.

Redline Synthetic 75W90 with the friction modifier was developed and designed for these rear diffs.

If the Lucas went in the rear diff "without" the friction modifier, then yes, your MPG will tank as the rear keeps slipping causing more engine fuel to burn while in stop and go traffic.

I'm also not so clear why you had replaced the distributor. On your model year, it's computer controlled. There is no hard shaft mechanical to the engine. Moving it forward or back means nothing on the timing. Just the hall-effect sensor reports the revs/sec to the PCM (computer). The PCM controls the timing of the engine.

 

Perhaps you meant SEVERE duty, rather than HEAVY duty? More info on differences as linked by blackvan.

Anyway, seems the temps are fine...

 

Lucas Oil stabilizer is well marketed junk.

It has zero additives, not antiwear, no extreme pressure additives, no anti friction additives, no detergents, nothing.

It Dilutes the additives in the motor oil you put it into.
It can cause the oil to go all foamy.

It is so thick that it makes the motor oil too thick, which causes more drag in the engine.

It is a last ditch effort to raise oil pressure on severely worn engines by used car salesmen.

It should NOT be used in a differential either.

If you want better motor oil, buy better oil. If you have leaking gaskets, then a high mileage oil might help swell the gaskets.

Gear oil requires all sorts of additives that Lucas Oil stabilizer is completely Devoid of.

Avoid this junk.

 

Rear Diff- got 75W90 / The lucas I mentioned went into the engine not the RD. Distributor was replaced 6 months prior to this work as I mentioned. it was simply old and corroded looking inside; i was changing the wires and plugs anyways. I understand the timing isn't set using it. Sorry if I made it seem otherwise. thanks for your input.

 

i didnt end up using lucas until about 2 months after i changed the oil when I noticed very slight leaking. The MPGs were already low. using Lucas didnt seem to make the fuel consumption much worse if at all but it did stop the leaks and I haven't had to add ant oil since. 3 months now. not disputing your disdain for the product. my experiences are certinaly not the be all end all test for this stuff. Just seems to be doing what I was told it would do.

the oil hasn't been foamy and looks okay to me. i hope it's not doing anything bad to the engine. this summer i will be replacing the manifold gaskets (plenum?) and maybe even the engine block gaskets and wont need oil supplements for a very long time after... I hope. - Ill have a shop with all the tools in the world where i can spread out for a few weeks and really go at this engine.

oh and i DIDN'T put Lucas in the Differential~

 

Lucas will cause some motor oils to get foamy when pumped through the oil pump. This would only be evident on the dipstick with engine running.

While Lucas 'might' not do any harm, it certainly is doing no good, unless the engine is so worn that 20w-50 was not allowing enough oil pressure.

 

There is a standard duty, heavy duty and severe duty.

The 3.9L would benefit using the standard duty.

I went with the heavy duty for my 5.2L/318cid Magnum engine. I should have went with the standard duty instead. The engine temps tend to stay cool even in hot southern weather down here. Many of the Jeeps with the 5.2L have the standard duty fan clutch too.

 

Hi guys - Sorry if this is splitting the thread (Im sure this will be a quick answer or easy link I just havent found yet) but I just bought the actron 9580a scanner tool... Also are there any accessible charts the states what the outputs and reading SHOULD be or should I just try to find the info for each thing? ... I wanna do a full diagnostic on this thing over the next few months.

update - just changed the downstream o2 sensor but it's too early to tell if it had any effect. - I have the feeling my Cat is bad; may have melted it back when my engine was running hot from the toasted thermostat.- gonna do a back-pressure test tomorrow.