1990 300SEL Cold Start Problems

[Qrash]

Cold Start Problems 1990 300SEL:

My search attempts did not reveal anything quite like the symptoms I am experiencing. The vehicle has 175,000 miles, just passed PA state emissions with no problem, consumes about a quart of oil per thousand miles (for the last 100,000 miles) and I have recently run several treatments of Techron. I replaced a leaking EHA valve at about 145,000 miles plus new ignition wires, rotor and cap at 160,000. Standard copper-tip spark plugs new.

When the vehicle has sat unused (and cooled) for four or more hours, it takes several attempts to start the vehicle. The problem has worsened over the past month and is exacerbated somewhat on cold mornings (now about 45 deg F). Two or three times in this last month, it has started, idled and run fine while cold, but the intermittent good starts have "gone away." I have tried one of the recommendations (turn ignition on for about five seconds before starting). No change.

Symptoms:
1. First start attempt ... motor kicks over, runs about two seconds and dies.
2. Second start attempt ... same.
3. Third start attempt ... same. For the first three attempts, if I attempt to apply throttle it also dies.
4. Fourth (or sometimes fifth) start attempt ... engine starts and runs as long as sufficient throttle applied and let it warm while holding at about 2000 rpm.
5. If I let the engine warm at 2000 rpm for about 3 - 4 minutes, everything is fine and the car runs and idles perfectly thereafter.
6. If I do not let the engine warm for 3 - 4 minutes and release the throttle, it will buck at about 500rpm ... sometimes dies and sometimes will warm and smooth out to regular idle at 700-800 rpm.

I have located but have not otherwise inspected or tested the cold start valve. Could this be the sole culprit and, if affirmative, is there a way to positively diagnose prior to replacement?

Other considerations / tests / diagnosis? ... Thanks much, Qrash

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[SCOTTFISH]

I have an 89 300se with sort of the same problem. The last time I had this problem I had to have the injectors replaced which if I recall was not a real expensive job. My 300 uses or consumes about a quart to a quart and a half every 800-1000 miles. This seams to be a demon with the inline six's. My MB mechanic the last time did not say anything about the cold start valve, but he may have checked it and just not said anything. I would think that this could be a potential problem. I would have that checked, along with the injectors. I have run Dextron in the tank and even doubled up thinking that if they were extremely dirty, the double dose might do the trick. It improved, but is back. But, when I give a little gas before starting, mine seems to be a little rough starting but will start. I also have a 420sel and it doesn't have any of these problems. I personally think that MB skipped a beat when they came out with the inline 6. I have even had a valve job done and it did not fix the problem. It got worse and I took it back and the MB shop sent it back to the machine shop to have the heads redone and it came back the same as it was before having it done initially. I think the problem is in the heads on that motor as far as oil consumption. Let me know what you find out.

[Cigar Havana]

I had similar symptoms on a 1989 420SEL. I replaced the oxygen sensor and it now starts 1st crank every time, hot or cold.

[hawkpfc2]

You have to have the head gasket replaced with a newer design with more reinforcement I believe. I have put 40,000 miles on mine with new gasket with virtually no oil leak. Itw as not too severe even before, but I considered it to be a consumable.

[TClanton]

Hawk,

Did you have a complete valve job done on a 300SE and cure oil consumption? There may be several of us getting in line for your mechanic.....:p

[hawkpfc2]

timing chain, valve guides, some of the stems, the timing chain actually snapped just prior to me buying the car so the shop fixed it before I bought. only reason I got this deal is my family had used the place for many years. I no longer use them though so that won't help very much. there is still a little oil in the coolant because it was not adequately removed, but the condition has not worsened and there is no evidence of leakage other than a slight slick feeling on the front of the head cover, but my dipstick stays just about near the full mark. I might be using a pint every 3,000 miles which is essentially nil.

I would argue that M103s are more reliable than M104s and M104s have their own leakage problems. Many I6 designs have it (not sure why they seem to have it worse than V6s). M103s are good engines, 300SEs are fairly underpowered but that is why there is 560SEL, S500, and S600 ::snickers::

[TClanton]

We had just the seals replaced on this one, to little effect. The guy who did the seals said the valves looked fine, but my local MB guy is saying you need the whole shebang for it to work. Mind you, this car only has 84K! The seals made sense because they get old and brittle, etc., but it just doesn't make sense that the guides and stems would be bad???

[haasman]

TClanton

Seems surprising to me as well that the guides etc need to be done with so little mileage .... but, it is my experience that the drivers who start and run are the ones with this problem. (I am not suggesting you, by any means).

I practice the start, adjust the seats/mirrors, buckle-up and then go start routine. Probably no more than 60 seconds. Additionally I drive our cars gently until I see the temp gauge start to register heat.

It all comes from seeing what happened to a BMW 2002 engine that belonged to a fellow who wound it out as soon as he could get RPM. The cam, guides and valves were all worn out prematurely. It was actually rather shocking to see this at 45,000 miles. It left an incredible reminder with me to just let the engine get some heat and oil onto the critical components that are not directly pressure fed.

My 2 cents,

Haasman