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1999 SL600 | 2001 SL500 (sold)
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Discussion Starter · #1 ·
So I’ve noticed coolant dripping onto the ground right below the right side of the underbody plastic oil pan shield. Always happens when the car is parked and the puddles vary from small to medium sized. I looked down into the engine bay on the right side and can see coolant all on top of the plastic oil pan shield. Near the banjo? Bolt on the top right corner of the radiator I’ve noticed very very minor wetness.

when driving like I normally do, the coolant light comes on and off BUT the car doesn’t overheat and stays in normal range. When I check coolant every day I see I only lose a little bit below the max line. I’ve been adding distilled water. All the hoses I can see to and from the expansion tank and the radiator appear to be perfectly fine. Is this a water pump leak? Pics attached, thanks.
Automotive tire Tread Grey Bottle Road surface
Automotive parking light Automotive lighting Automotive tire Hood Motor vehicle
Vehicle Automotive tire Hood Car Tire
Automotive tire Wood Road surface Asphalt Cloud
 

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1998 Red SL500, 2002 Black SL500, 2014 Black E550 Cabriolet
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You are adding distilled water often..there you have it....coolant leak.
Water pump leak....would be colored....greenish..blue....orange...depending on what coolant was used...but you're diluting it by adding water...so...
Coolant warning light comes on...issue.
Engine running at high rpm's....warning light coming on would be depending on how much fluid is in the system.
You didn't provide the mileage or last time the pump was replaced....or as mentioned above... cracked radiator.
Pressure testing will give you the answer....
 

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600 coupe, one of the very first built
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The wet spot is on the black plastic of the radiator, can NOT be from the water pump. If it were the pump, the trace would be on the front cover/block

Automotive tire Hood Automotive lighting Tire Automotive design


FATHERTIME and RESTO SL are 100% right that the radiator is done.
 

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1999 SL600 | 2001 SL500 (sold)
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Discussion Starter · #6 ·
You are adding distilled water often..there you have it....coolant leak.
Water pump leak....would be colored....greenish..blue....orange...depending on what coolant was used...but you're diluting it by adding water...so...
Coolant warning light comes on...issue.
Engine running at high rpm's....warning light coming on would be depending on how much fluid is in the system.
You didn't provide the mileage or last time the pump was replaced....or as mentioned above... cracked radiator.
Pressure testing will give you the answer....
Current mileage is 84,000. Pump replaced probably never I have no idea
 

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1999 SL600 | 2001 SL500 (sold)
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Discussion Starter · #7 ·
The wet spot is on the black plastic of the radiator, can NOT be from the water pump. If it were the pump, the trace would be on the front cover/block

View attachment 2711855

FATHERTIME and RESTO SL are 100% right that the radiator is done.
I believe it. It's strange though how coolant leaking from the radiator made its way to the top of the oil pan shield and it's also sprayed all over the suspension piece as pictured in my 3rd photo. Every time I park coolant pooled up there then leaks down the right side of said plastic shielding instead of right below the radiator..

Id imagine coolant blowing back would be obliterated by the fan blade..
 

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94 SL320 98 SL500 99 SL600
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I"m on my third radiator in my 99 SL600 78k One more thing I put an aluminum radiator in my 98 SL500 and I really think I could put the same one in the SL600. So next one I lose I'm gonna try it.
 

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2009 CL63 AMG / 2013 GL550 / 1994 SL320
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Not sure if the M120 has the same one, but I had a water pump leak on an M104 (similar in some ways; it's like half of the M120 🙂)

Here's what a failed water pump looked like - you can get a mirror around behind it and there's a common place (weeping hole) where it can leak

Here's what mine looked like when I replaced it:

Wherever the leak is, once you find it and fix it...you gotta get proper coolant added in there 🙂 You can corrode parts in the coolant system if you don't use the right stuff and then you'll have a nasty problem. You can either use the concentrate (part# Q-1-03-0004) and dilute to 50/50 with distilled water or just buy 50/50 (something like Prestone - European vehicles (Teal))
 

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1999 SL600 | 2001 SL500 (sold)
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Discussion Starter · #10 ·
I"m on my third radiator in my 99 SL600 78k One more thing I put an aluminum radiator in my 98 SL500 and I really think I could put the same one in the SL600. So next one I lose I'm gonna try it.
I think someone has done it on here but they had to do a very small modification. I really wish there was an aluminum radiator for sl600. Maybe you can get into contact with CSF and see if they can take your radiator to study it for potential production. They're in Rancho Cucamonga.

Or maybe there are people out somewhere who can fabricate. I definitely don't wanna buy a new plastic junk radiator for $400+
 

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97 SL500
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Radiator end tank leak. Hence the spray pattern. Its not a big leak and takes the system to build quite a bit of pressure for it to happen.
However, Even though its small, I would not wait. I'd get it swapped sooner than later as it will undoubtedly let go at the worst possible time.
As my pops always told me, its easier to proactively fix problems at home (or before you actually need to) than on the side of the road. Id try to find an all metal construction replacement for reasonable price. If not, a solid brand replacement will do fine. No need to go all nutso on this.
 

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Discussion Starter · #12 ·
Just watched an interesting video where a guy has an aluminum radiator for his SL600. It appears its a 500 aluminum radiator, and all that needs to be done to make it work is replacing the trans cooler line with one for an SL500. He too claims to lost radiators fairly quickly. V12 engine bay heat probably a factor

Link:

Gonna look for the part number for this line and embark on this replacement journey
 

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97 SL500
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Just watched an interesting video where a guy has an aluminum radiator for his SL600. It appears its a 500 aluminum radiator, and all that needs to be done to make it work is replacing the trans cooler line with one for an SL500. He too claims to lost radiators fairly quickly. V12 engine bay heat probably a factor

Link:

Gonna look for the part number for this line and embark on this replacement journey
Id get the dimensions and see if you can get a universal piece to fit in there. Shouldnt be too difficult. Probably easier than trying to find out what that dude used in a random video. There is nothing special about a radiator.
 

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Just decided to check the place I been buying radiators for my cars over the last few years to see if they had a MBZ application.... turns out they do. Might be worth a shot.
1800radiator.com
They will deliver to your door in a day or two most times. And it seems they have an all aluminum construction for the 500s but not the 600. Same demensions though. So maybe 600 has an integrated cooler line that the 500 doesnt have.
 

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1998 Red SL500, 2002 Black SL500, 2014 Black E550 Cabriolet
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Yiks!
Just pressure test the system and you'll have your answer....
 

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Discussion Starter · #16 · (Edited)
For anyone wondering what the part number is for the SL500 trans cooler line needed to use an SL500 aluminum radiator in an SL600 its:
0199978482 ***


Going to have my mechanic confirm the radiator leakage then if it’s 100% the radiator I’ll take the SL500 aluminum radiator route and report back
 

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If you are going to replace one, why not replace both -- age takes its toll. For an SL500, the second cooler line is 019-997-85-82
 

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Discussion Starter · #18 ·
If you are going to replace one, why not replace both -- age takes its toll. For an SL500, the second cooler line is 019-997-85-82
Just replacing the one cooler line because according to the video I linked above, it's needed to fit an SL500 radiator into and SL600. Will deal with other hoses later down the road
 

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So I’ve noticed coolant dripping onto the ground right below the right side of the underbody plastic oil pan shield. Always happens when the car is parked and the puddles vary from small to medium sized. I looked down into the engine bay on the right side and can see coolant all on top of the plastic oil pan shield. Near the banjo? Bolt on the top right corner of the radiator I’ve noticed very very minor wetness.

when driving like I normally do, the coolant light comes on and off BUT the car doesn’t overheat and stays in normal range. When I check coolant every day I see I only lose a little bit below the max line. I’ve been adding distilled water. All the hoses I can see to and from the expansion tank and the radiator appear to be perfectly fine. Is this a water pump leak? Pics attached, thanks. View attachment 2711829 View attachment 2711830 View attachment 2711831 View attachment 2711832
On my sl500, do not know about the 600..On the passenger side tank I had a 3/4 nipple with a rubber cap and hose clamp, it leaked exactly same as yours.dealer couldn't find it. Rubber was weak and cracky from hight temp moral so temps..I put my finger on it one day and it was wet..dealer didn't have 3/4 inch rubber cap.wsnted to sell me new radiator..went to auto zone bought assortment cap put on, refilled radiator, and topped off after thermostat open..never s leak again 6 months now..worth a look..maybe yours has rubber cap or not..$3:50 cent fix.
 

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Discussion Starter · #20 ·
On my sl500, do not know about the 600..On the passenger side tank I had a 3/4 nipple with a rubber cap and hose clamp, it leaked exactly same as yours.dealer couldn't find it. Rubber was weak and cracky from hight temp moral so temps..I put my finger on it one day and it was wet..dealer didn't have 3/4 inch rubber cap.wsnted to sell me new radiator..went to auto zone bought assortment cap put on, refilled radiator, and topped off after thermostat open..never s leak again 6 months now..worth a look..maybe yours has rubber cap or not..$3:50 cent fix.
im actually starting to think the leak is at the back of the engine or below it because the actual concerning leak involes coolant pooling up on the plastic underbody shield and spilling over onto the ground
 
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