HI Oil Press & A/C Clutch

[300d4me]

Got two questions for the experts...

I have high pressure on the dash gague during normal opperation. It peaks out the gage. It has been this way since I got the car a few weeks ago (76 300 d)... picked her up for 1k. Is this a common problem with an eazy fix?


Also I have a bad ac clutch bering. Can I use the clutch off of my '79 240d?

Thanks for the help!!

[psfred]

Oil Pressure:

The gauge is supposed to peak out above idle. It's normal.

The gauge is mechanical, so if it stays up when the engine isn't running, it's broken.

Minimum pressure at idle hot is 8 psi, if the gauge does NOT peg quickly as you rev the engine up, you have a problem (probably a big one...). Cold, with a good engine, you may have the gauge peg at idle. On Mobil 1 10W30, my 280SE pegs the gauge cold at fast idle, warm about 20 psi.

The releif valve is set for 4.5 bar, about 65 psi.

If you have 45 psi at idle hot, check idle speed and change the oil, it is always possible that someone put 50 wt oil in it to hide a rod knock or something. If you then get the normal 15-20 psi hot with the gauge pegged above 1100 rpm, listen very carefully for evidence of bad bearing. My brother broke the crank in his 300D because there was some silicone sealant in the #2 main bearing oil gallery, from a crap rebuild, and didn't hear it at first because the engine had VERY thick oil in it. Refused to start the first cold day, and when we put normal weight oil in it, the bearing thumped.

AC clutch will only be exchangeable if both compressors are the York piston type. I'm pretty sure the rotary compressor takes a different clutch. Might be wrong, I've never swapped them.

Peter

[300d4me]

Thanks Peter,
I am pegging my oil press at cold idle so I guess I am all right. I will do the frist oil change this weekend, hope I see the same results.

Both are york so maybe I'll take the clutch off the '79. I have had a hard start problem with her since I took her on a trip to AZ hunting. Had to leave her with a local "shade tree" mechanic who charged me $150 to start her two weeks later. Not to diagnose a problem but just to start her. I let her run the entire weekend I was out there and drove her home. She only started for me twice since then. Hope to get her started in the next few weeks (as it is starting to warm up) and bring her in for a compression test.

[psfred]

Three reasons for hard starts:

Low compression (valves or cylinder walls - if your oil consumption is normal, probably valves)

Very late valve and/or injection timing (stretched chain).

Weak starter. I have this problem on the Volvo, will be putting the new starter in tomorrow to avoid a core charge. Causes the battery to run down faster than normal, as the starter is drawing a fantastic amount of current but not spinning fast enough. Root cause is excessive resistance in the armature, although bad bearings and worn brushes don't help any.

If the mechanic started it on 24 volts, expect a weak starter or bad valves.

A valve adjustment may restore full operation, too.

Peter

[300d4me]

Is there a tell tale way to discover if low compression in a diesel is a valve problem vs a cylinder wear problem... like putting a table spoon of oil in the cylnder to see if compression is restored like a gas 4 stroke?

Don't recall an excessive oil comsumption problem... maybe a quart every 3k.