95 E320: Rough idle above 4000RPM - PeachParts Mercedes-Benz Forum

Arthur Dalton · #1 08-09-2006, 01:48 PM

Car has a stored DM code if CE is on..
Te button for retrieve is in front of the battery

EricSilver · #2 08-09-2006, 01:56 PM

Quote:

Originally Posted by Arthur Dalton

Car has a stored DM code if CE is on..
Te button for retrieve is in front of the battery

OK. I will have a look there while changing the oil filter.

EricSilver · #3 08-09-2006, 09:38 PM

Changed oil (Castrol 20W50) and filter (Bosch).

When engine is hot (90C-100C) pressure is now between 0.5 to 1.0 with car in gear, and 1.5 with car in neutral. With engine at approx 83C, pressure is 2.2 in gear and 2.5 in neutral.

The old oil I removed ran very freely and quickly. I suspect it was a lighter, winter weight since it was last changed in March (car was not driven much since then). I also am wondering if lighter oils keep the engine generally cleaner, and if my 20W50 is too heavy....

To be safe, I will have the sender checked this Friday, and perhaps have the service shop change the oil yet again to whatever their standard is, since they have maintained the car in great condition for the past 7 or 8 years. I can live with the low pressure indication if I know there is not a problem.

fastpakr · #4 08-09-2006, 10:42 PM

What is the recommended weight for your engine? 20w50 sounds ridiculously high. I'd have expected something more like 5w30 winter, and 10w30 summer.

EricSilver · #5 08-09-2006, 10:54 PM

Castrol 15W40 has been used for the past 7 years or so. I will be reverting back to that on Friday.

EricSilver · #6 08-09-2006, 11:20 PM

Also, because it has been so hot here (Wash. DC Metro area) this summer, the heavier oil makes good sense.

The 20W50 appears to be causing cavitation, evidenced by the occasionally erratic pressure guage needle, as described in another oil thread. Reverting back to a lighter weight will resolve that (my guage did not do that before).

Since the below-1.0 pressure readings are normal, so long as pressure shoots straight to 3+ on acceleration, I will not worry about it.

fastpakr · #7 08-10-2006, 12:06 AM

You really need to stop worrying about the air temperature and focus on the oil temperature and pressure directly. It's not that hot outside. If you're getting good pressure with the 15w40, then it's counterproductive to go higher. Again, what was the original recommended pressure?

EricSilver · #8 08-11-2006, 11:36 AM

All is fine. It was the filter. Have 15W40 in now, and pressure at 90C+ is 1.2to 1.3 in gear, and 1.8 to 2.0 in neutral.

Quote:

Originally Posted by fastpakr

20w50 sounds ridiculously high. I'd have expected something more like 5w30 winter, and 10w30 summer.

Correct, it was ridiculously high, to the point where all day yesterday I could feel a low, rumbling vibration at idle while the oil needle wiggled. I don't see, or feel, either of those anymore.

Had I used 15-40 on Wednesday, I would have been spared the time and expense of a second oil change today. Some happy news, however, is that the oil change, fluid top-off, basic inspection, etc. cost only $39 at this MB-only shop, so it is no longer practical, or economically sensible, for me to do my own oil changes. (Not that I will miss that.)

fastpakr · #9 08-11-2006, 11:39 AM

Glad to hear you got it sorted out.