S420 possible blown head gasket
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94 mazda miata
S420 possible blown head gasket
Hi everyone, new here, looking to pick up a really clean 96ish s420 for dirt cheap. current owner says it wont start, thinks it has a cracked head. the compression numbers are really low on one bank, one cylinder only has 15psi. is it more likely a blown headgasket? New to these kind of cars as ive mostly owned Japanese or american cars. rebuilt a few motors and transmissions so i have a pretty good understanding on how things work on a vehicle. but not sure what this would be. he said it didnt overheat at all but im not sure how likely that is. dont have too much info on the vehiclw other than the interior is perfect and xlose to everything works aside from the motor itself. any insight would be greatly appreciated.
Junior Member
Joined: Aug 2013
Posts: 65
Likes: 8
From: Fallbrook, California, USA
1997 Mercedes S420
1996 S420 compression issues
Hi everyone, new here, looking to pick up a really clean 96ish s420 for dirt cheap. current owner says it wont start, thinks it has a cracked head. the compression numbers are really low on one bank, one cylinder only has 15psi. is it more likely a blown headgasket? New to these kind of cars as ive mostly owned Japanese or american cars. rebuilt a few motors and transmissions so i have a pretty good understanding on how things work on a vehicle. but not sure what this would be. he said it didnt overheat at all but im not sure how likely that is. dont have too much info on the vehiclw other than the interior is perfect and xlose to everything works aside from the motor itself. any insight would be greatly appreciated.
Another thing you might want to consider is that the wiring looms in the 1996 and earlier W140 decayed to the point that they shorted out and became rather useless and unreliable. If the loom has not been replaced in this vehicle and there was any over heating that could become an additional and unforeseen $$$ burden.
All of that aside, the W140s are wonderful vehicles.
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Joined: Apr 2007
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If you can fix it yourself I say go for it. Make sure to have the cylinder head decked and that you clean the block really good with a razor blade before installing the cylinder head to the block. Now would be a good time to a bunch of "while your in there" type things if you plan on keeping it.
Member
Joined: Aug 2016
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From: NEW JERSEY (Union County)
1996 Mercedes-Benz S420
If you can get that car for only $400 to me its a steal,even if you cant do the work yourself and you have to have someone else work on it, in my opinion its really worth it,if you can bring a qualified mechanic who knows about W140's...
Junior Member
Joined: Mar 2016
Posts: 17
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From: NEW JERSEY
1996 Mercedes-Benz S420
1996 S420
The first thing I would consider on the vehicle is the indicated mileage. I have a '97 S420 with 275,000 miles on it and no signs of difficulty at all - it really runs amazingly well. I consider that a result of proper maintenance over the last 20 years.
Another thing you might want to consider is that the wiring looms in the 1996 and earlier W140 decayed to the point that they shorted out and became rather useless and unreliable. If the loom has not been replaced in this vehicle and there was any over heating that could become an additional and unforeseen $$$ burden.
All of that aside, the W140s are wonderful vehicles.
Another thing you might want to consider is that the wiring looms in the 1996 and earlier W140 decayed to the point that they shorted out and became rather useless and unreliable. If the loom has not been replaced in this vehicle and there was any over heating that could become an additional and unforeseen $$$ burden.
All of that aside, the W140s are wonderful vehicles.
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Junior Member
Joined: Aug 2013
Posts: 65
Likes: 8
From: Fallbrook, California, USA
1997 Mercedes S420
I will need to know where you are to know what suggestions to make. By that I mean to ask whether you are in cold climates or tropical climates or something in between.
I am in Southern California at sea level and so am governed by that climate. I should also tell you that Mercedes Benz makes no recommendation as to any type of additives for vehicle fluids. With that said, I use Bestline products which can be found at https://www.bestlineproducts.com/ and elsewhere. I use the engine additive, the transmission and power steering additives and the fuel additives. If it says anything at all the heads have never been off the engine and the fuel injectors are as clean as a whistle. I use 5W40 Euro Spec synthetic oil which I believe comes from Mercedes though I will have to ask my mechanic to be sure. I use a Mercedes Benz oil filter.
The first time you deal with the automatic transmission fluid you might consider having the transmission and all associated parts flushed completely and then replace the transmission fluid and additive as appropriate to your climate. I am not talking about just draining the fluid but instead am talking about pressure flushing the entire system to get everything out. You will be amazed at how differently your transmission responds.
I hope this helps but if there are more questions please feel free to respond. Hopefully others will learn from this as well.
I am in Southern California at sea level and so am governed by that climate. I should also tell you that Mercedes Benz makes no recommendation as to any type of additives for vehicle fluids. With that said, I use Bestline products which can be found at https://www.bestlineproducts.com/ and elsewhere. I use the engine additive, the transmission and power steering additives and the fuel additives. If it says anything at all the heads have never been off the engine and the fuel injectors are as clean as a whistle. I use 5W40 Euro Spec synthetic oil which I believe comes from Mercedes though I will have to ask my mechanic to be sure. I use a Mercedes Benz oil filter.
The first time you deal with the automatic transmission fluid you might consider having the transmission and all associated parts flushed completely and then replace the transmission fluid and additive as appropriate to your climate. I am not talking about just draining the fluid but instead am talking about pressure flushing the entire system to get everything out. You will be amazed at how differently your transmission responds.
I hope this helps but if there are more questions please feel free to respond. Hopefully others will learn from this as well.
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Junior Member
Joined: Mar 2016
Posts: 17
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From: NEW JERSEY
1996 Mercedes-Benz S420
1996 S420 200,400 miles
First of all i really appreciate the detailed feedback,i live in New Jersey about 10 miles south of New York,theres no way i would ever drive it in the snow,but the winters can get pretty cold.Im just trying to do the very best at maintenance on this great car because I want it to last as long as possible,i only had it a week now it drives pretty good,i feel it can drive even better with some work, lil things like the glove compartment wont open,rear windows in need regulators,big back window has a crack,i just ordered one off of ebay for $125,cigarette lighter isnt working,I'll be taking it to a Benz mechanic next week sometime,also the check engine light is on,but theres no sputtering,smoke,hesitation,etc,dont think its anything major...Thanks again i really appreciate it...
Junior Member
Joined: Aug 2013
Posts: 65
Likes: 8
From: Fallbrook, California, USA
1997 Mercedes S420
Living in a cold climate will require a different viscosity oil than what we use here in So California. Your Benz mechanic will be your best guide in that regard.
