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'87 560SL // Anthracite + Palomino
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Discussion Starter #1
Hi everyone.

Hopefully someone has some insight on this issue...

'87 560SL with 200k miles. Whenever I'm on a downgrade, down hill—say at a stop sign or stop light, the car gets very sluggish, as if "starving" for fuel, and at times, white smoke comes from the exhaust. As soon as I level off, and move again, all is well. Any thoughts on what this might be?

Thanks
 

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1989 560SL
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130 Posts
One possibly is the transmission modulator valve has failed. When the diaphragm ruptures, transmission oil (which burns much more white than blue) gets sucked into the intake on trailing throttle which produces high vacuum in the intake manifold. Then it burns off as you accelerate again.


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'87 560SL // Anthracite + Palomino
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Discussion Starter #6
One possibly is the transmission modulator valve has failed. When the diaphragm ruptures, transmission oil (which burns much more white than blue) gets sucked into the intake on trailing throttle which produces high vacuum in the intake manifold. Then it burns off as you accelerate again.


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Thanks for that. Is there an easy way for me to tell if that's the case?
 

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1989 560SL
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I like to remove the vacuum line from the modulator at the transmission and use a vacuum pump on the spigot and see if it holds vacuum. If it doesn’t, it needs to be replaced.

When you remove the line at the transmission end, if a lot of oil flows out of it, that will also confirm the problem. There should be no oil in the line although sometimes there might be a tiny amount of wetness that accumulates over time from it being connected to the intake manifold.


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'87 560SL // Anthracite + Palomino
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Discussion Starter #8
I like to remove the vacuum line from the modulator at the transmission and use a vacuum pump on the spigot and see if it holds vacuum. If it doesn’t, it needs to be replaced.

When you remove the line at the transmission end, if a lot of oil flows out of it, that will also confirm the problem. There should be no oil in the line although sometimes there might be a tiny amount of wetness that accumulates over time from it being connected to the intake manifold.


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Thanks, but thats WAY above my ability :) was hoping there was another way to tell. Seems I'll have to wait till things calm down and then take it to the shop to diagnose...
 

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560SL '88 Suzuki GS1000E '78
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211 Posts
Hi, you should think about buying somthing like that:
Checking the modulator vacuum line is no rocket sience. And there are plenty of possibilities to use this tool for other diagnostics on your car during the next years.

How is the oil consumtion of your engine?
Martin
 

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'87 560SL // Anthracite + Palomino
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326 Posts
Discussion Starter #10
Hi, you should think about buying somthing like that:
Checking the modulator vacuum line is no rocket sience. And there are plenty of possibilities to use this tool for other diagnostics on your car during the next years.

How is the oil consumtion of your engine?
Martin
Hey thanks, I'll look into this. What exactly is involved in checking this? Do I need to take apart any part of the engine? I'm not confident in my mechanics...Oil seems pretty good, not burning a ton if that's what you mean.

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560SL '88 Suzuki GS1000E '78
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211 Posts
Hi Niko,
Someone will have to do something, otherwise nothing will change. So at least it will be enough if you can explain your mechanic how to proceed.
The easiest way will be to lift the car and connect directly to the modulator actuator which is located at the left side of the transmission. Getting access from the engine bay is not related to remove a lot of parts but it's very uncomfortable.

Here you can see how it looks like at the transmisson, it's not exactly the same as at your car but almost.
The part in the middle is the one. Unplug the rubber hose and connect with the pump to connector at the modulator, apply a vacuum and check, if oil is coming out and/or if the vacuum remains stable.

Regards Martin
 

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'87 560SL // Anthracite + Palomino
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326 Posts
Discussion Starter #12
UPDATE: Hoping this will help with more information. Seems to do this more so, when the gas tank is not so full. I'm on about 1/4 tank now and the smoke was much worse then I'd seen in the past. It did seem to NOT do this, if I put the car in neutral going down the hill and at the stop. But when I put it back in drive and took off, there was a little white smoke...What could this be?

thanks
 

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560SL '88 Suzuki GS1000E '78
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Hi Niko, I don't think that this information will help.
Did you checked the modulator line in the meantime?

My guess is, that your engine at least has aged valveshaft seals. Maybe worn valve guides (long and expensive work). Regarding the mileage it's probably this.
Martin
 

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'87 560SL // Anthracite + Palomino
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Discussion Starter #14
Hi Niko, I don't think that this information will help.
Did you checked the modulator line in the meantime?

My guess is, that your engine at least has aged valveshaft seals. Maybe worn valve guides (long and expensive work). Regarding the mileage it's probably this.
Martin
Thanks Martin...

I've not had a chance to have anything checked yet. I'm hoping there might be a short thats open to have a look soon. I'm a bit scared now. Curious how much the valve guides could cost to have done—do you have any idea? or the seals?

thanks again
 

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560SL '88 Suzuki GS1000E '78
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Hi, the parts are cheap, but the work (to change the guides you need to take off the cylinderheads and other expensive things may follow up) is much. Changing the seals only is not too bad, but nothing for someone who had never worked at such an engine.
But in general it's not a good idea to start the reapair of something without an exact diagnose. You should try to meet an expert in real life.
Martin
 

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'87 560SL // Anthracite + Palomino
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Discussion Starter #16
UPDATE: So I took the car to the Mercedes shop today. He told me that most definitely I'm leaking coolant into the engine, probably the head gasket. He told me it was a major job and probably not worth doing, but rather a new engine if anything—not gonna do that. The auto parts store suggested this, an additive that helps with head gasket leaks. Curious if anyone has any intel on this or similar products.

 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,196 Posts
Before you do that pull the valve covers and make sure the cam oilers are not cracked and seated properly. That stuff will probably seal the head gasket and the heater core and radiator as well.
 

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'87 560SL // Anthracite + Palomino
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Discussion Starter #18
Before you do that pull the valve covers and make sure the cam oilers are not cracked and seated properly. That stuff will probably seal the head gasket and the heater core and radiator as well.
Thanks. He pulled the covers yesterday to check the timing chain which was OK. He didn't say anything about the cam oilers. If it seals the heater core and radiator, what does that mean exactly? (good or bad thing?)

thanks
 

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560SL '88 Suzuki GS1000E '78
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If the theory is, that the engine burns coolant, there must be a notable loss of coolant in the reservoir without findings of coolant underneath the car.
If not, you engine is burning oil - anyway: solving this remains a major job (when changing the valve guides) and at the end, the head-gaskets will be new as well.

The cheap trick (30$) would be to change the valvestem seals only (and by the way the cam oilers) without removing the heads and check/change the modulator actator of the gearbox (where you can suck ATF oil from the tranny if the diaphragm in the actuartor is damaged)!

Cheers Martin
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,196 Posts
Thanks. He pulled the covers yesterday to check the timing chain which was OK. He didn't say anything about the cam oilers. If it seals the heater core and radiator, what does that mean exactly? (good or bad thing?)

thanks
That means he didn't check the cam oilers. When you put the stop leak in it seals the heater core and radiator internal passages and you get no heat and your car overheats. That's a bad thing.
 
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