I have a 1994 S420 with a couple of symptoms that point to a coolant leak into the intake.

1) all 8 plugs have a white deposit on the center wire

2) there is a puff of white smoke from the tail pipe when starting the car in the morning

3) I use about 1 cup of coolant every 2-4 weeks

Since all 8 plugs are identical in color, I assume that the leak must be on the intake side (not just a head gasket) but I don't know enough about this model to know where to look (coolant line on a throttlebody/idle air controller etc ?).

Does anyone have any suggestions? The car doesn't use oil and the plugs are white, not black. A mechanic suggested a leaking fuel injector but again I would have expected to see a delta between plugs if that was the case.

Thanks.

 

was it like a lime deposit?

a cup every 2-4 weeks is not that much to worry about.

as you can see, the cooling system goes directly to the a/c heating from the engine block. it doesn't go through anywhere else. nothing in the intake manifold body which could create common problem, much more on the intake system.

the only way is from the cyl head gasket... but all together at the same time is something else.

to confirm, use cylinder bore scope to see if the piston head is white clean too.

 

All plugs have a white powdery/flakey deposit. The plugs only have about 3000 miles on them and I would expect a tan color if the A/F mixture was correct. I haven't scoped each cylinder but I have looked into each plug opening and each cylinder looks black/normal. The concern is not the amount of fluid loss but what could be causing the burst of white smoke coming from the exhaust during cold start up.

PS the smoke seems worse if I park the car with the front pointed downhill.

 

sleepwalker,

How does MB handle thottle body icing? Isn't there some sort of throttle body warmer on this car that uses the engine coolant?

 

i have been working on these older versions 8 years ago lugnut, but i haven't encountered icing on the throttle body yet.
one of the reason also i am joining the forum is that i could also learn from you and other real time user.
so how do they eliminate such problems?
during the time i was doing those engines, i was in the north where the temperature goes down to -10 for two months. i usually give the right clearance to the baffle plate (not less than 4mm) to maintain continous flow of air.
am not sure if the US version got a heating element on it.
i will check my resources.

 

On all my other cars I have a coolant line that runs to the throttlebody, hence my original question. It would seem strange not to have some sort of cold start heater on the 420.

 

It seems like you'd have constant problems with the idle if you adjusted the plate to address icing, if that's what you're saying.

 

I'd remove the throttle body and check it for cracks if you can see a small hose going to and from it. Hopefully you can remove it without doing a major engine breakdown.

 

so it means that USA version really got this throttle valve pre-heating system. it must have been eliminated on later models i searched the workshop information system but i cannot find the model that have it.

although i can now recall seeing one of them years ago, i still can't understand its full function.
if the throttle valve got icy stuck, the coolant cannot help much because the coolant itself is also cold at that moment, and cannot give heat since the engine cannot run (throttle valve is stuck). so it must be using the coolant preheater but this is only available on cars with auxialliary heating system.
so this could explain why your 420 don't have it hennesystealth? in this case, that was not the cause....hmmmnnnnn.

you got 3 vacuum lines going to the throttle valve from the thermo switch. these thermo switch is mounted on cooling system line. it's quite impossible for it to break from inside and the coolant is being sucked by the throttle valve, but just check for any sign.

 

Icing isn't a problem during starting. It's when the ambient air temp is cold and the car is travelling at highway speeds and the engine is revved and sucking in air at a relatively high rate. All this can lower the air temp below the ambient air temp to the point of freezing. It doesn't have to be in Antartica in the winter either. Sorry for not using actual specs for air temp, speed, RPM, and air volume, but I don't know what they are.

It may be that the engine design alone lends itself to effectively de-icing the throttle body. Not good news, though, if you want your engine to run most efficiently with the coldest air it can get. Maybe the throttle body design resists icing. Maybe I'll win the lottery.