Where does thick black sludge come from? Sweet motor though

[rreed]

Just pulled the pan to knock in a new rear main seal while the motor is out. My first concern was when I pulled the drain plug it had a nice wad of thick black sludge on it. Uh-oh.. Knocked the pan off and there is a coat of this thick black sludge in the bottom, just like the skin of chocolate pudding that's been cooked on the stove. It's not a thick layer per se, enough to know it's definitely there, wipes off easily. The oil was pretty darn black, who knows how long it's been in there. But the consistency of it is thick when it wipes off on the rag.

On the good side, this motor has every indication of the 20,400 mi. odometer in the old military ambulance it came out of. Aside from the sludge in the bottom of the pan and around the top of the oil sump, the internals are gorgeous. Beautiful mirror finish (hope it's supposed to be like that) on the cylinder walls w/ very nice, clear cross hatch. It looks brand spanking new inside there. Peering up at the cam looks like it's never been spun. When I did the rear main on my I6 ZJ a while back it had noticeable wear I'd expect to see for a 186K mi. motor. This one has no signs of wear what so ever. It's beautiful inside there, almost makes you want to cry. No shillac like old motors get from old age/lots of use. All metals are still gray/silver. This motor should have a lot of life left in it.

Anyway, just atop the sump and down in the pan there's this layer of sludge like a thin chocolate pudding skin, except it's a very dark/soot black. I checked up under the sump, the screen is clear. No noticeable chunks of metal or anything in the bottom of the pan but I haven't started cleaning yet.

[Ristow]

lack of proper oil change intervals usually.due a couple early oil changes,it'll clean up.

[AMX factor]

I second Ristow on improper oil changes, but the oil is doing it's job...it's cleaning. But sludge also means inferior oil is being used and/or that dirt is getting inside the motor for the oil to get that dirty. Could also be a sign motor got very hot once or twice.

[DanHS]

Do a few oil changes at each 500 or thousand miles with regular oil, then switch to some good detergent oil like Castrol GTX and use that, it'll keep the insides nice and clean. Diesel motor oil has more detergents and some additives lacking from regular gasoline engine oils, I like the Castrol GTX 15w40 diesel motor oil I'm using.

[rreed]

Yeah I'd already planned running a good filter w/ some cheap oil at first, just enough to get the ignition swap/carb redialing/clutch break in/truck shake down done. Just to wash out all the old crap. Will do this probably twice at short intervals just to clean it all out then go w/ my good stuff I normally run.

As far as dirty oil, it had your basic orange Fr*m oil filter on it and I'd say the PO wasn't exactly religious about proper maintenance, but the truck did sit in a field for a long time before somebody came buy and picked it up. Aside from sludge in the pan the internals look good so far.

[Ristow]

use WIX filters,the best by far.

a quart of ATF will help clean the motor internally.works on diesel injectors too i'm told.

[Rogue]

key word is ambulance

why?

probably started occasionally but not gotten good and hot. if you don't get an engine good and hot you cannot rid the oil of condensation and therefore SLUDGE!!! being a military ambulance it probably was well maintained however it was probably also seldom used.

by good and hot I mean at least 10 miles at highway speed.

not having a thermostat or a lower than specified thermostat can also promote sludge.

in the respect of sludge a high mileage engine is better than grandma's sunday church vehicle.

[rreed]

Yeah well it wasn't so bad, a minor coating on the bottom of the oil pan. A little gasoline and a few paper shop towels got it nice and shiney. That I could tell there wasn't anything alarming in it (that I didn't put there) and as mentioned the engine internals look great.

Like most other rare J20 ambulances this one probably saw little service time before it was sold on a used car lot and the next few POs used it for who knows what. Before it was removed it did run like a top, quick start and very smooth idle.

[prayforsurf]

are you sure it wasnt chocolate pudding? heh sorry im jk, guess im hungry for some homemade chocolate pudding.

[Sambo]

sounds to me like someone put some sort of oil additive in!
like slick50 or something to that nature! they usually run thru once and sit in the pan from then on!