This is a little long and roundabout, but I need to give everyone some backstory here. Apologies.

I had my engine diagnosed with sludge back in '09 and had main and rod bearings replaced then. I always have had it in the back of my mind that the engine is still living on borrowed time because of that. It taps pretty constantly (especially under load; coasting down a hill almost never) but until late September it never gave me any other problems. The engine has 175K on it, and it was at 155K when it sludged up (wasn't poor maintenance from ME, but I was at least the 2nd owner).

In September the cam followers on #4 and #6 came off. Had them put back on, it lasted a day, and then another cylinder came off. The mechanic went ahead and replaced them all on the one side.

The day after the 2nd time in the shop I'm commuting to work and my coolant pegged and my oil dropped to the low end of the safe range. Not below the low end, just right at the line that keeps the "Check Gauges" light from dinging. I refilled the coolant and checked the oil level - good level and it was not bad looking. I had the last oil change 2K ago, so it wasn't due yet. Started driving it home watching both gauges like a hawk. About 10 miles the oil press bottomed out. I shut down. Waited about 5 then gave er a quick start, and it came back up to the low limit. Drove it again, about 10 more miles it bottomed out. Did this a couple more times and finally lost patience, and got AAA to tow it home.

Over Thanksgiving, I just let it sit. Today I spun off the oil filter and it was black (not the pretty amber color that was in it last week.) I put a new filter on and added a quart, then started. It went to the low limit again and stayed there.

Drove it carefully about 2 miles to the local Jiffy Lube (yeah, I know, but they are good there, they've done changes for me before) and ordered an oil change. Drove it on some errands, another 5 or 6 miles. Oil pressure still at the low limit, but it was rock steady there.

After the last errand, I got in and restarted it for the trip home. Pressure came up to the middle of the gauge; normal. Now WTF??? Drove it out of the parking lot towards the 65MPH road home, and on the entrance ramp it dropped back to the low limit again. Drove home that way.

OK, so from this long tiresome tale, can anyone tell me what COULD be wrong? I would love it if I DIDN'T have to buy a replacement engine, but I'm so leery of throwing good money after bad. We're going from cold engine to hot engine, from low pressure to normal pressure; I just don't have enough to go on here.

Any opinions are sincerely welcomed!

 

I would look at the oil pump being an issue and who the hell diagnosed sludge? Most every time it is BS. The only time I have ever seen sludge in any auto is when a head gasket has blown.

 

yea sludge is VERY rare in a car engine, i have never seen it, and my 4.7 runs on the low side of the safe range on oil pressure at idle, but moves as you step on the gas up to the dead center, but it never drops, it has always done this, but if yours is intermittently dropping it completely i would agree with MG, check the pump and possibly replace it, make sure the screen on the oil pick up isnt clogged up and that there are no metal shavings in the pan.


and another question, which engine do you have (i may have missed it) and what year is your truck?

 

Sorry - 2002 Durango with a 4.7L. Local mechanic diagnosed sludge. I've been told 'oil pump' by other contributors, and also advised to throw a mechanical gauge on there to rule out a sending unit.

Thanks.

How much of a pain is a pan? Is it a shade tree/jackstand job, or should I go looking for a lift?

 

Pop a valve cover off and take a look you will know immediately that you do not have a sludge issue and definitely go with a mechanical gauge to see if there is truly an issue. IIRC you will need to get a hoist and raise the engine a few inches to have enough clearance to pull the oil pan but from there it should be smooth sailing.

 

So if there's nothing in the valve cover (had it off about three weeks ago) it's a fair indication of what's in the pan? That is a big relief. It's rather clean in there, just a tad of varnish on the non-wear surfaces.

Going to do the mechanical thing asap. Drove it about 10 miles tonight, enough to get it to operating temp, and it was rock-steady in the middle of the range. Whatever was bumping it down appears to have abated.

 

 

A little varnish is normal and nothing to be concerned about and yes by popping a valve cover it gives you a great idea of what is in the pan. Definitely stop taking it to the guy who diagnosed sludge he is trying to make an easy (and illegitimate) buck.

Did you let anyone flush the engine due to the bs diagnosis? If so the flush could have contributed to a lower oil pressure since it thins out oil and you will NOT get all of it out in on a drain and refill.

 

Replace the PCV valve.


The other thing it would have to be is a bad sending unit or bad oil pump or plugged pickup screen. Using Fully Synthetic Oil like Pensoil of Mobil 1 has better detergents and more of them to help keep your engine clean. Stay with one type of lubricant.

This might help?

5.9L loss of oil pressure
5.9L sudden complete loss of oil presure under hot/hauling conditions:
https://dodgeforum.com/forum/1st-gen-...-pressure.html
Testing results:
https://dodgeforum.com/forum/1st-gen-...ml#post1778597

 

I go to one oil change place mostly, since the "sludge" episode. It is a Quaker State Quick Lube 10 minute shop. I take all my cars there regularly now. It's on my way to work. The backup shop is a local Jiffy Lube but I only use that in emergencies. They use Pennzoil in the car.

I want to get another opinion; hijacking my own thread, really; I have heard from multiple folks that synthetic is better if you start out with it, but that it isn't good for this situation. The engine has 175K on it and has run dino oil since day 1 as far as I know. I know I've never put anything but dino in it. Am I wasting money going to synthetic? Am I hurting something?