White smoke at startup

[GM]

Hi all,
I feel like I’m tempting fate with this post, but here goes. My car runs beautifully – starts right up, idles smooth at about 750-800, all fluids (oil, trans, coolant) spot on -- everything great! Except…when I start it up there is a puff of white smoke from the exhaust. Just at startup, not while I’m driving (that I can see).

Recent activity: the temp gauge started to register lower than my usual 180 running temp until the next time I drove it, when it didn’t register any temp at all. I replaced the thermostat (79⁰) and sent the gauge and probe to PA Speedo for repair/calibration, reinstalled and now temp registers fine, if not a little lower than 180.

I’ve started wondering if I’m running too rich. Might that cause the smoke at startup? I’m wondering if I’m running beautifully at the potential expense of washing the cylinder walls with fuel, and causing premature unnecessary damage. However, after doing too much reading on various subjects from this august group, including diving into the CSV and WRD, I was struck by a comment by Benz Dr from a few years ago: “If you can't accept a small amount of wrongness about your car, you will never really enjoy it.”

Believe me, I’ve taken that to heart and don’t want to push my luck here, but might there be a simple explanation for the smoke – and not to worry about it? Or is it worth checking out some things to identify its source? Given the great luck I’ve had so far, I’m hesitant to start monkeying with the engine and mess everything up. Like I said, I don’t want to tempt fate, and hope this post doesn't jinx me. 

Thanks

[mrfatboy]

The quick and easy question is what type/grade of oil are using?  I have seen a 280sl switch to mobile one and exhibit the same smoke issue. Switched to conventional and no more smoke.

[GM]

My mechanic (same as Kampala's) discouraged use of synthetics and I think he used Castrol GTX 20-50. When I got the car 10 months ago (relocated from Florida to Los Angeles) before I started using it he completely went through and did everything so I would have a baseline that I knew was good to start. Now it's on me, unless I get nervous - hence the post!
But now that I think about it, the PO had the car only 3 years, changed the oil regularly, but had no service records (I have all the service records from 1991-2016). If the previous owner used synthetic and then I changed to traditional, could that transition cause it? Thanks

[doitwright]

White smoke from the exhaust can be a coolant leak into the combustion chamber. Usually caused by a bad head gasket or crack in the engine block. I hope neither of these is the cause in your case.

[GM]

Thanks - me too.
From the history I have on the car it has been driven about 12,000 miles in 29 years.
In 2003 (5,000 miles ago) the engine was partially rebuilt by a reputable Mercedes shop in Atlanta, with an new short block because of an oil leak that seized a piston. The two valves for cylinder #1 were replaced. Other than that nothing has been done. Sounds like it might be time to pop off the head?

[Pawel66]

Is your car automatic? I have read in many posts that white smoke in exhaust can be the modulator diaphragm issue.

[Peter]

White smoke from the exhaust can be a coolant leak into the combustion chamber. Usually caused by a bad head gasket or crack in the engine block. I hope neither of these is the cause in your case.

Additionally, leaking valve stem sealings.
The leak is very small and when the car is parked the remainder oil near the valve stems is leaking in the combustion chamber.

^Peter

[stickandrudderman]

Burning excess fuel gives black smoke.
Burning engine oil gives blue smoke.
Burning transmission oil gives white smoke.
Burning coolant gives white steam whch people often describe as "smoke". Steam is much lighter than the white smoke you'll get from burning transmission fluid and in any case that (burning transmission fluid) will not happen only on start up and will be exacerbated by heavy throttle application.

[MikeSimon]

I am with Peter. Valve stem oil leak. Slow leak when parked, only smokes when starting up. Leaking head gasket would show other symptoms too. How does tranny oil get into the engine?

[GM]

Thanks for all your (expected) excellent responses, gentlemen.
Yes, Pawel, it's an automatic.
The trans fluid level is spot on, but I don't drive a lot, so it might take a while to show up in fluid level.
The smoke is smoke, not steam.
I too read about the trans diaphragm, but in my gut I suspect the valve stems too.
How urgent is this repair? What are the damaging effects?

[Peter]

I too read about the trans diaphragm, but in my gut I suspect the valve stems too.
How urgent is this repair? What are the damaging effects?

my experience is that this repair is not urgent, but it is getting worse and worse until you are ashamed to start the car.

^Peter

[stickandrudderman]

How does tranny oil get into the engine?

Via a failed modulator diaphragm.

[Jonny B]

Yes, the shame factor will do it. That happened to me. It finally got the better of me, and I had the head redone. We also had the FI pump rebuilt. This was a credit card melter if there ever was one! Thought not quite as bad as the whole engine.

[GM]

You guys are awesome.
Based on https://www.sl113.org/forums/index.php?topic=24197.0 and https://www.sl113.org/forums/index.php?topic=13766.msg93527#msg93527 I've decided to try the easiest and lowest cost approach first - replacing the transmission modulator diaphragm.
Do I need a lift to do this, or can I jack up the car on one side?
Thanks

[GM]

From all I've read it seems like the modulator diaphragm replacement is a relatively easy fix, but there aren't any instructions in the Tech Manual. I read Joe's post here - https://www.sl113.org/forums/index.php?topic=13766.msg93527#msg93527 - but I'm a novice here, so imagine I'm 16 with my first car (well, it's not that bad, but you get the idea).
I need help with some basics:
- does this procedure need a lift, or can I use either ramps or a single jack on the side of the car?
- is there a basic diagram of the underside of the transmission, showing the parts, like mounting plate, etc? Once I see what it looks like, with a little wrenching, I can do it.
Otherwise, if it needs a lift, I'll have to take it to my mechanic.
As a bonus, if I can do it, I'll post the procedure to the Tech Manual when I'm done!
Thanks, all.

[Peter]

I never did this repair, but is does not look too complicated.
I question if you have to remove the mounting plate underneath the transmission.
If you have to remove the transmission mounting plate then you need a bridge.
Looking to the picture this is not necessary.
If you jack up the car please use axle supports, otherwise it is much to dangerous/risky. You would not be the first to be squashed by a car!

The replacement of the diaphragm looks is straight forward.

[GM]

Most excellent, Peter! Thank you - it's exactly what I need.

[doitwright]

Have you determined if the modulator diaphragm was the cause of the white smoke?

I just watched this video on brake booster rebuild. At the very end of the video he explains that if the rubber seal around the brake booster plunger rod fails it can allow brake fluid to get sucked into the intake manifold resulting in white smoke.

https://youtu.be/h6wf1WuGc1k

[GM]

I haven’t got to the diaphragm replacement yet - stay tuned. Thanks for the brake booster tip!

[Camhi]

Were you having smoke like the picture below?