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Old 04-26-2002, 03:03 AM
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Join Date: Mar 2002
Location: Fort Lauderdale, Florida
Posts: 15
Unhappy Problems after Head Work on S420

Hi all,
Briefly, car [1995 S-420, 88k] overheated - suspected closed thermostat. Had heads done, new thermostat and new head gaskets.
Car idles very roughly, worse when warm. Temperature is normal on highway and in town. Also appears to run ok at increased revs or normal driving speeds. No apparent stumbling or vibration.
The oil pressure is around the "3" mark when cold, and during normal driving drops to 2 - 2.5. However, when stopped and idling the pressure falls below "1". This could just be due to the grade of oil used [I'm checking to see what was used], or something more serious.
My mechanic suspects the idle problem to be related to the O-2 sensors, and wants to replace them next. He's checked for vacuum leaks, etc.

Would appreciate any thoughts on possible causes of idle problem, or if something was missed during the engine work.
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Old 04-26-2002, 08:10 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
Iwould have the compression checked! The valve work on this engine is very critical.
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Old 04-26-2002, 01:16 PM
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Join Date: Jan 2002
Posts: 352
Overheated to what temp. I have a 99 s420, I'm getting scared.
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Old 04-29-2002, 12:58 AM
Registered User
Join Date: Mar 2002
Location: Fort Lauderdale, Florida
Posts: 15
I'm not sure what temp it went to and for how long.
I was on the expressway for about 30 mins, going at about 90, and, on exiting and stopping, noticed that the gauge was in the red. There was no coolant loss, but the engine was idling rough.

It's the first time I've had something like this happen where apparently the coolant flow was obstructed by a clogged/closed thermostat. I'm examining the thermostat to verify our suspicions.

Also, will have them check the compression as suggested.

How many miles do you have on your '99 ?
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Old 05-31-2002, 04:59 PM
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Join Date: Jan 2002
Posts: 352
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