1993 w124 cold start oil pressure
 

hey there - I left my 1993 300CE sitting for about a week while driving the e320 around. During this time is was sitting in a garage, but I did not start it (8 days). The temp for the week has been around 45F (8C) or so.

So Sunday rolls around and I want to give it a start, drive around, just to make sure everything is working, etc.

The engine started immediately as usual. What was unusual was that the engine was extremely rough, shaking and loud (basically, sounded like there was no oil). I knew the oil was at the right level and there wasn't any oil on the ground. After about 2 - 3 mins of rough, knocking idling, it gradually calmed down and basically toned down to the regular silky smoothness.

So my guess is that it had something to do with the engine sitting for a week and all the oil draining to the bottom. However, I've never had a car start like this after sitting for just a week - usually the starts are pretty normal.

Car is running fine now and in light of this, I'll go back to driving it more regularly (every couple of days). But wanted to ask members on the board what the cause could be?? Many thanks.

Edit: I did a search before posting but found one post with similar symptoms from a 190E mechanic but no replies. Hoping to have better luck!

What weight oil is in it ?

right now it's 5w30, and i change it every 2500 miles or so. should i be switching to a different oil now that its colder? how does the oil impact the cold start problem i had? thanks

I don't like 30 weight oils. Personally, I would go with 0W-40.

But still, your motor's reaction is awfully bad for sitting for just a week. I'd be more inclined to think there might be some other minor problem going on. Idle air valve maybe?

hmm... thanks for confirming my suspicion that such a rough start isn't right. but what does the idle air valve do? wondering what impact it would have?


Alternatively I'm thinking that there must be some part that either builds up oil pressure when the engine is started or something that maintains a minimum level of oil pressure if the engine is off (sorry I might be way off here). Could there be something wrong with one of these? E.g. the oil pressure is not building up quick enough?

Your lifters leaked down and it took a while for them to build up oil again. You could replace the lifters or just not do that again.

Still not normal ..I let my 3.2 sit for 5 months..and when it fired up, it was smooth. What was the indicated oil pressure? Cold should read 3 bars + within a few revolutions (like maybe 1 -2 seconds) , and drop down as low as 1.5 while hot after a hard run while sitting at idle..say 750 rpm's.

If your oil pressure is good..I would suspect something else.

Normal cold starts the oil pressure does get right up to 3 pretty quick, and yes, once warm and at idle, oil pressure remains around 2 / 2.2.

When I started it that time, I can't remember specifically what the oil pressure read but the needle did go up and when the engine was finally stable, oil pressure was at its norm of about 3 for a cold idle.

I also have the m104 - so do you still suspect it is oil pressure or something else?

is that because the lifters should normally retain a certain amount of oil when the engine is off? if mine are not doing that can they be cleaned / relubricated / or something or is replacement a given? How big of a job is this?

Also, after that incident, I started listening really closely to my car on a cold start and on a cold start you can hear the faintest of a similar knocking sound. But this is super faint, you'd have to open the hood and really get your ear down close to the engine to hear it.

Could also be electrical...

...I've had mine sit for a couple of days and it did just that when starting, while other times it sat a month for a major repair, and started up smoothly as if it had been run a day ago.

Check the harness, and coil packs, as well as the resistor caps that sit on the plugs...

thanks for the suggestion, but i'm not sure i follow.

i guess first i'd ask what should i be checking for regarding the electrical components? my wiring harness was replaced in 2005.

second, if it is electrical, curious to know the rationale? (don't take that the wrong way i'm pretty clueless about this stuff but can understand the rationale if its explained! :D)

did you trace the starting issue in your case to an electrical problem? if so what was it? i'm not sure i want to repeat test the scenario by letting it sit idle for several days and then checking if it starts the same way. It doesn't sound too healthy for the engine.

Typically, mechanical problems are systematic...i.e., once something mechanical has an issue, the symptoms are consistent.

Electricals, other than a totally failed component, usually lend themselves to sporatic symptoms.

As far as my case, I had a complete top-end rebuild a couple of years ago, so I believe I have attacked the major mechanicals. Now I am trying to diagnose the electrical gremlins that cause my ills right now...including the rough idle after sitting for periods.

Unfortunately, I am still not certain of the culprit...but I'll post if a solution emerges while this thread is still alive...

i'm scheduling a service with my trusty mechanic sometime next week and will bring this up with him at that time and see if he can suggest anything that makes sense.

would like to get any other input though of thoughts / ideas? i'm almost tempted to let me car sit idle again for a while and see if it comes up again but maybe will only let it sit for a few days this time. If it is mechanical internal leaking then the engine should still do the same but on a much smaller scale, so long as all the oil hasn't leaked.