SL55/63/65/R230 AMG: SL55 Overheating at Idle w/AC on
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2003 SL55
SL55 Overheating at Idle w/AC on
Exactly as the title says, 2003 SL55 overheats when idling, 80 deg ambient temp, with AC on. Recently had the coolant temp sensor and coolant housing replaced by Mercedes, they also flushed the coolant 3 times apparently, which was very expensive, only for the problem to persist. There are no leaks, the tubing looks good, and yet, the car continues to overheat. So much so, my water pump was spraying coolant out of the cap, which occurs to relieve pressure from the water system. The exterior hood and forward side panels of the car become very hot. When I run my diagnostic scan, I no longer receieve the P202C - 008 code for the coolant temp sensor, and I dont receive any others. Anyone else encountered this issue before?
As a side note: Mercedes recoded my car’s computer and now I have my headlights on 24/7 and can’t turn them off, and i have a fuel reserve warning indicator turn on now with 4.5 gallons still in the tank. Wtf?
As a side note: Mercedes recoded my car’s computer and now I have my headlights on 24/7 and can’t turn them off, and i have a fuel reserve warning indicator turn on now with 4.5 gallons still in the tank. Wtf?
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SL55AMG, GL450, SLK, S550, Maserati Coupe
Cooling system is radiator, water pump, thermostat, hoses. DO NOT allow the engine to overheat!!!! I would personally start with a new thermostat and new coolant, if that didn't fix it, a new water pump maybe? Radiator could have blockage. Really good to have an indy shop near you where they know these cars and are capable, and honest. Dealers will rob you blind, break it more and steal everything that isn't bolted down.
Maybe there is a more logical approach to solve your problem, but at 90K miles my water pump was toast. And if replacing a water pump it is a no-brainer to also get a new thermostat at the same time. Don't buy cheap parts at a local auto parts store!! FCPeuro is online and they guarantee all parts they sell for life.
Maybe there is a more logical approach to solve your problem, but at 90K miles my water pump was toast. And if replacing a water pump it is a no-brainer to also get a new thermostat at the same time. Don't buy cheap parts at a local auto parts store!! FCPeuro is online and they guarantee all parts they sell for life.
Thread Starter
Junior Member
Joined: May 2024
Posts: 15
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2003 SL55
Cooling system is radiator, water pump, thermostat, hoses. DO NOT allow the engine to overheat!!!! I would personally start with a new thermostat and new coolant, if that didn't fix it, a new water pump maybe? Radiator could have blockage. Really good to have an indy shop near you where they know these cars and are capable, and honest. Dealers will rob you blind, break it more and steal everything that isn't bolted down.
Maybe there is a more logical approach to solve your problem, but at 90K miles my water pump was toast. And if replacing a water pump it is a no-brainer to also get a new thermostat at the same time. Don't buy cheap parts at a local auto parts store!! FCPeuro is online and they guarantee all parts they sell for life.
Maybe there is a more logical approach to solve your problem, but at 90K miles my water pump was toast. And if replacing a water pump it is a no-brainer to also get a new thermostat at the same time. Don't buy cheap parts at a local auto parts store!! FCPeuro is online and they guarantee all parts they sell for life.
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From: My house
SL55AMG, GL450, SLK, S550, Maserati Coupe
Seems odd a Benz dealer would flush the coolant three times. Maybe it is time for a new radiator. When I first got my SL600, I had the notion that a radiator might become impossible to get, so I bought one and years later it's still in my garage, new in the box. I paid over $400 for it, and today you can get one on RockAuto for under $200. Any time the belts are off the engine it is good to check the water pump pulley, bearings for smoothness, any gravel feel replace it. The bearings could still be good while the impeller can be bad. For these cooling system it is really important to use good parts, obviously. I got a brand new Bosch water pump, not remanufactured, etc., for mine, the exact one it wad born with... the car is very happy.
Thread Starter
Junior Member
Joined: May 2024
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2003 SL55
Seems odd a Benz dealer would flush the coolant three times. Maybe it is time for a new radiator. When I first got my SL600, I had the notion that a radiator might become impossible to get, so I bought one and years later it's still in my garage, new in the box. I paid over $400 for it, and today you can get one on RockAuto for under $200. Any time the belts are off the engine it is good to check the water pump pulley, bearings for smoothness, any gravel feel replace it. The bearings could still be good while the impeller can be bad. For these cooling system it is really important to use good parts, obviously. I got a brand new Bosch water pump, not remanufactured, etc., for mine, the exact one it wad born with... the car is very happy.
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Joined: Sep 2019
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From: My house
SL55AMG, GL450, SLK, S550, Maserati Coupe
I hope you are not taking it back to the same Benz dealership. If they flushed the coolant three times, why did they do this? Certainly good to rinse the system but they'd only do this if there's a definite problem, and to hand the car back to you and have it still overheating shows they are stupid or incompetent. I would no longer trust them and need to find a local independent shop that knows these cars and has honest owners. That dealer should KNOW that it will not overheat before taking your money and giving you the keys! If it's still overheating after getting a new thermostat and new coolant, I would replace the radiator cap first, those can go bad and they are very cheap, may be unlikely that this is the cause, but anything's possible... then replace the radiator and buy the best quality one you can find, not the cheapest one. If STILL overheating I would replace the water pump, and if you get to that point, only use a genuine Mercedes/Bosch water pump that is brand new, not "rebuilt or re-manufactured. You'd want one just like what the car was "born" with, and once you go through all this, your cooling system should be golden for at least a couple of years, probably longer. No messing around, this is a very special engine and you cannot allow it to overheat. Dealerships are Stealerships!
If you do replace the radiator, be sure to get a new cap for the cooling reservoir at the same time.
If you do replace the radiator, be sure to get a new cap for the cooling reservoir at the same time.
Last edited by tonylinc; Jul 7, 2024 at 12:26 PM.
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95 SL600
It may have had mixed coolant at some time, which can lead to a silicated radiator. I have experienced this before, the tubes were blocked with a radiator that had been replaced a few years prior. The 2 coolants didn’t like each other and started the clogging.
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2003 SL55
Originally Posted by tonylinc;[url=tel:8997759
8997759[/url]]I hope you are not taking it back to the same Benz dealership. If they flushed the coolant three times, why did they do this? Certainly good to rinse the system but they'd only do this if there's a definite problem, and to hand the car back to you and have it still overheating shows they are stupid or incompetent. I would no longer trust them and need to find a local independent shop that knows these cars and has honest owners. That dealer should KNOW that it will not overheat before taking your money and giving you the keys! If it's still overheating after getting a new thermostat and new coolant, I would replace the radiator cap first, those can go bad and they are very cheap, may be unlikely that this is the cause, but anything's possible... then replace the radiator and buy the best quality one you can find, not the cheapest one. If STILL overheating I would replace the water pump, and if you get to that point, only use a genuine Mercedes/Bosch water pump that is brand new, not "rebuilt or re-manufactured. You'd want one just like what the car was "born" with, and once you go through all this, your cooling system should be golden for at least a couple of years, probably longer. No messing around, this is a very special engine and you cannot allow it to overheat. Dealerships are Stealerships!
If you do replace the radiator, be sure to get a new cap for the cooling reservoir at the same time.
If you do replace the radiator, be sure to get a new cap for the cooling reservoir at the same time.
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From: My house
SL55AMG, GL450, SLK, S550, Maserati Coupe
That's great news, these cooling systems lose some of their cooling ability to some degree, if not pressurized. The cap is one of the cheapest parts on the car!! Keep an eye on the temps for a few weeks just in case.
