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A vacuum leak on our 1988 420 sel..Rough idle..rubber..rings

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Had a vacuum leak on...
Had a vacuum leak on our 1988 420 sel. Rough idle when cold. Replaced the rubber rings as well. Had it off and back on multiple times, still is not fixed. Ran a straight edge on both the intake and the heads, no warpage noted. Used new gaskets each time. The last time we developed a coolant leak into the ehaust. Cannot seem to get this thing sealed up. Please HELP. Thanks Joe
Submitted: 8 years ago.Category: Mercedes
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Answered in 14 minutes by:
8/9/2009
Mercedes Mechanic: Marty, Mercedes Technician replied 8 years ago
Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 54,156
Experience: Bosch Certified Master Tech. Over 35 years experience.
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Hi Joe, are you certain that your manifold is the problem and is not sealing? Have the cylinder heads been taken off the car?

 

Marty

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Customer reply replied 8 years ago
There was absolutely no coolant leak when we started . The car was perfect except for a vacuum leak under the upper intake. When I put carb cleaner near the front or rear of the upper intake the engine smoothed out. So we replaced the intake and the rings. Somewhere we have a coolant leak, it is coming out the exaust. The coolant system builds no pressure after it has been running for at least an hour. I let it run that long thinking maybe it just need to burn out the coolant spilled during the change. It does not steam at all when the engine is cold, but as soon as it warms up we are sucking coolant from somewhere. Thanks for your time Joe
Mercedes Mechanic: Marty, Mercedes Technician replied 8 years ago

Ok, if the heads were not removed prior to this problem I would suspect that possibly either the wrong intake manifold gaskets were used or they were put on backwards. There are a couple of different gaskets available. If the heads were removed and resurfaced then you may have a problem with the mating surfaces lining up. Either way it looks like it will have to come apart again. Let me know what you find.

 

Marty

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Customer reply replied 8 years ago

We purchased the gaskets from mercedes. We put the side with the red sealant that comes on the gasket down towards the cylinder head just like the mercedes service manager told us to do. There was actually a picture on the gasket package to show which way to put them on. I just can't figure what could be leaking. I don't know what removing them again is going to do until I know where The leak is coming from

Mercedes Mechanic: Marty, Mercedes Technician replied 8 years ago
When you say it's leaking out the exhaust I assume you mean the tailpipe? Is there any leakage at the engine?
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Customer reply replied 8 years ago
If you mean visibly around the intake no it is bone dry. That is whst I meant, it is leaking out the tail pipe. Thanks Joe
Mercedes Mechanic: Marty, Mercedes Technician replied 8 years ago
Are you sure it's coolant? If it were coolant it would be billowing white smoke. Can you pressurize the cooling system?
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Customer reply replied 8 years ago
That is the next step, I have a pressure testure But I need a different attachment for this car. It is definetly coolant. It steams bad and stinks really bad of anti freeze when the car warms up. Thanks Joe.
Mercedes Mechanic: Marty, Mercedes Technician replied 8 years ago
Ok, it's going to have to be one of your end cylinders (1,4,5,8). The only thing I can imagine is that the gaskets are incorrect or one got damaged during assembly. I'd pressurize the cooling system and remove the plugs. Let it sit under pressure and then crank the motor and see which cylinders spray water out. Make sure you disconnect the single green wire from the ignition module first so you disable the ignition.
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Customer reply replied 8 years ago
Do you think I should run the motor to get it warm, because it only leaks when the car is warm? If you are right and the gasket is not sealing at the spots you think, Do you think I should put sealant on the next set I install? With all the comunicating We are doing I will pay you one way or the other this afternoon. I am going to my shop after church to work on this car. I don't want to have to pay again later to communicate with you about this situtation if I need to ask you something. Thanks Joe
Mercedes Mechanic: Marty, Mercedes Technician replied 8 years ago

When you originally removed the intake did you drain the coolant? Is it possible that coolant ran ino the cylinders and simply needs to burn off or have you given it enough time for that to happen already? If you're burning coolant you should be able to look at the plugs and see which cylinder it is or look at the top of the pistons. I'd also expect a misfire. You shouldn't need sealant on the gaskets. Just inspect your surfaces really well. It shouldn't matter much hot or cold when you pressurize the system. Let me know what you find.

 

Marty

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Customer reply replied 8 years ago
I will definetly let you know what I find. Now we did not drain the system prior to changing the gaskets. I have let the car run for about an hour. There is no steaming until the car is warm. That is why I figured there was a leak. I find it hard to beleive that there is still coolant laying in the cylinders/exaust system. I so wish that was the case. The car runs perfect though with just still the rough idle we started with. If we give the car some gas it smooths right out. This whole thing is puzzling and I don't understand why the coolant system is not building pressure?
Mercedes Mechanic: Marty, Mercedes Technician replied 8 years ago

A coolant leak from the intake manifold into an intake port would not necessarily build up pressure in the cooling system. I would take the car for a good test drive and watch the temperature and see if the smoking diminishes before you get too deep into it. It can take awhile to burn coolant out of the exhaust system. Keep me posted.

 

Marty

Marty
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Customer reply replied 8 years ago
I have been away from my computer for a week or so. Sorry for the delay. We did just that and you were right, we just needed to take the car out and run it. There wasn't a leak after all. Once again sorry for the delay. Thanks again Joe.
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