72 250 - white smoke from exhaust when started - PeachParts Mercedes-Benz Forum

rgnprof · #1 09-24-2003, 05:37 PM

My '72 250 is blowing a good puff of white smoke when I start the car up. After the initial puff, I don't notice any more smoke. It also seems to get worse the longer I go between oil changes. Last time I changed the oil I used Valvoline's Maxlife (???) 10W-40, and the smoke was much less at start-up.

3 questions : 1) Could it be worn valve stem seals? and, if it is, 2) what is the procedure to replace them - DIY job or not? and 3) what else should I replace "while I'm there"? Thanks.

Ryan

ctaylor738 · #2 09-25-2003, 09:53 AM

Isn't this the classic symptom of a vacuum modulator going bad and allowing a small amount of trans fluid to be sucked into the engine?

Also could be the start of a head gasket leak. If it smells like antifreeeze, that's a bad sign.

rgnprof · #3 09-25-2003, 10:15 AM

When you say a vacuum modulator, are you talking about the AT modulator valve? That's the only part I can find online that's close to what you described?

Ryan

ctaylor738 · #4 09-25-2003, 10:27 AM

That's the one. It takes vacuum off the back of the intake manifold and uses it to help the transmission figure out when to shift.

rgnprof · #5 09-25-2003, 11:42 AM

Thanks Chuck, I know that this smoke is a symptom of that valve going bad, but... why does the problem get worse between oil changes? I just changed the oil last night and the problem is much better today. I am using about a quart of oil every 1000 miles. Thanks.

Mark DiSilvestro · #6 09-25-2003, 01:37 PM

My '60 220S does the same thing, especially with old diluted oil. Big puff of 'white' (actually light blue) smoke at start up. Smells like burning oil, not antifreeze.
Less smoke with new oil. If you suspect Valve seals or trans modulator, how much oil or ATF do you need to add every week? Before condemning the modulator, first disconnect it's vacuum line at the intake manifold and plug the manifold fitting. Start it up and see if it makes a difference. Also disconnect the vacuum line at the modulator to see if any ATF drips out there.
Mines a stick-shift so it's almost certainly valve seals. I just check my oil level more frequently, change it more often and live with it.

Happy Motoring, Mark

rgnprof · #7 09-25-2003, 07:11 PM

OK, where is the vacuum modulator valve - trying to track down hoses from the intake manifold and I'm not sure where the valve is located? Thanks.

Ryan

Mark DiSilvestro · #8 09-25-2003, 08:04 PM

There's a metal vacuum line connected at the rear of the intake manifold. Follow the line down by the dipstick tube at the right side of the transmission and see where it connects to a 1.5 inch cylinder looking thing just above the transmission pan. That's the trans modulator.

Happy Motoring, Mark

rgnprof · #9 10-04-2003, 09:41 PM

I'm not losing any transmission fluid, so I'm thinking that it has to be the valve stem seals or the guides. Can I get by w/o changing out the seals for a while, as long as I keep an eye on the oil and change it frequently? I know the head has been off before, actually I think it's been off twice before - the guy I bought it from fixed a blown head gasket and he's not sure I will be able to surface the head again. So I'm kind of stuck. If I pull the head, I may not be able to put it back on!

Ryan

Mark DiSilvestro · #10 10-04-2003, 11:17 PM

If your oil consumption is not too excessive and it's not fouling plugs, I woudn't lose any sleep over it. Just check your oil level often enough so it doesn't get too low on you.

Happy Motoring, Mark

300SDog · #11 10-05-2003, 01:59 AM

Ryan, knowledgable mechanic can replace valve seals without pulling the cyl. head...... ask around and find somebody who has done it before - using compressed air in cylinders to prevent valves from dropping while setting each cyl. at TDC when replacing seals, thus if valves DO fall into cylinder they can be retreived.

Smart question to ask mechanics when searching for competent valve seal replacement is whether they have spark plug hole adaptor for their air compressor. Then tactfully mention to them that each cylinder should be at TDC during replacement operation.

Previous owner is correct that planing the head can destroy the engine by raising compression beyond tollerances..... however cylinder heads dont need planing at all unless they have warped or severely overheated. Basically, its a load of crap about 'necessity' of planing cylinder heads everytime they are pulled.

rgnprof · #12 10-05-2003, 09:16 AM

Thanks Mark and Diesel, I am not going to worry about it excessively and I may pull the head myself down the road when I have the time to do it. I think I need a new timing chain etc, anyway. Appreciate your help.

Ryan