This started as a low to no oil pressure and valve lash adjusters clacking. I had asked how to get the 2 front pan nuts off on a 99 300m 3.5 engine. This cannot be an isolated issue. In researching this engine, this is a common oil sludge problem.

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After I finally got the oil pan down I found the oil pickup screen almost totally plugged, badly worn rod bearings and a goofy oil cooler set up that dumps oil pressure.

For those who are having similar problems;

First disconnect the battery, jack up the car - place on stands, and drain engine oil. Then:

1- Remove 4 engine mount nuts (underside of engine cradle), jack up engine about 2" each side and place a block under the mounts.
2- Remove the brace/bracket at rear of oil pan to transmission.
3- Unbolt the torsion bar (sway bar) off the cradle and shove it backwards out of the way.
4- Undo the 2 front pan to oil pump nuts and the 4 allen head pan bolts (2 in the oil pump - 2 at the rear in the rear main seal housing)
5- Unscrew the oil cooler return line (right side of oil pan) if equipped.
6- Remove remaining pan bolts - Smack the side of the oil pan to free it from the block - NOT TOO HARD (it's aluminum). Not necessary to remove the dip stick tube from the engine - upper tube bracket is under the AC compressor bracket. Wiggle and jiggle the pan loose with tube in place.
7- Swear at the crusty sludge in the oil pan and in the oil pickup screen
8- Remove oil pickup tube - one bolt and soak for a few days in a degreaser or other decent crap remover - solvent won't do it.
9- Remove the "tray" 8 long bolts which are also main bearing cap bolts. Soak the tray in the same degreaser. Remember that the cut out portion of the tray goes back up to the rear.
10- Remove and inspect at least one rod bearing for wear. Use plastigauge to check for oil clearances. Spec is .001" - .002" with .001" preferred.
11- Main bearings may be OK or not, but your already there. Main bearing caps are 6 bolt - 2 already removed with the "tray", 2 long bolts up into the block, and 2 small bolts (sideways) from outside the engine. Remove one main bearing cap and inspect and plastigauge the bearing. Spec is .0005" - 002" with .0005" preferred. Easiest one to remove for inspection is the very front one - nothing in the way for the 2 side main cap bolts.

If you have to replace the mains, block the engine at oil pump to cradle, unbolt the left side motor mount bracket and the starter. They are in the way of those damn main cap side bolts. You can leave them there flopping around - just move them around as needed.
12- Reassembly is reverse of teardown.

I replaced the mains that were barely worn because I was there anyway and I already bought them. I gauged the old ones and got .003" clearance and then the same clearance with the new ones (standard size). I also replaced the rod bearings the were worn into the copper backing and still got .003" clearance there with the new bearings. The bearing bores were stretched so I cheated. Years ago you could buy tapered shims for bearings to bring them back into spec without having to resize rods or line bore the mains. Those days of tapered shims are long gone. I used .001" brass shim stock to get to .001" - .0015" oil clearance.

Torque for the "fatter" main cap bolts is 15 ftlb then 1/4 turn. The thinner "tray" main cap bolts are 20 ftlb then 1/4 turn. (This seems backwards and makes little sense.) The side bolts (outside the engine) are 20 ftlb - do these up last. The rod cap bolts are 40 ftlb then 1/4 turn - which seems way too much as most rods are 35- 50 tflb. These bolts are NOT stretch torque and can be reused.

The pan gasket is 3 sided - no gasket material at the rear where the pan bolts to the rear main seal housing. Use silicone. I used silicone (gray) to stick the gasket up in place while trying to get the oil pan up and a wee bit on the oil dipstick tube. Remember - align the oil dipstick tube into the oil pan before you bolt it up.

I cleaned the "tray", oil pick up, and all the bolts in a pail of carb cleaner. The oil pan was heavily crudded up and I soaked that in solvent for a day, scraped it out and sprayed with Permatex gasket remover and a brush to loosen the hard to get at crud and de-stain the aluminum. Spray can carb or throttle body cleaner does a nice job too. At this time I can only imagine what the heads look like under the valve covers, but for now I will live with it.

And last I disconnected the "oil cooler". It's a bypass affair that heats the oil in the rad before dumping it back into the oil pan. Seems that this was a lose of oil pressure for no real purpose. I may look into a full flow adapter under the oil filter and a cooler in front of the rad. At least there would be cool oil going back into the oil galleries. I also found an Equus oil gauge - 1 1/2" - and mounted it in the clock hole on the dash. Oil pressure is at 75 lb cold, drops to 20 lb hot idle and runs 50 -60 lb at speed.

I hope this helps someone
P.