Having an issue with my 1995 C280 overheating. Typically runs in the range of 80-90C and recently, although the weather has not been above 80F, the car has been moving towards 105-110, up to 115C when its idling in traffic, or even parked with the air conditioning on. Took it to the dealer and they replaced the fan as well as the thermostat.. and the problem continues to exist. Can someone help diagnose what this might be?

if your system is full of water[coolant]if your fan clutch is good and if your aux fans are working the problem is shrunken aluminum tubes in radiator.it needs replacing. david poole e.p. dallas tx.

If everything else checks out OK, you may just need a new radiator. I once had a car that, despite good H2O pump, hoses, correct coolant mixture, etc. it always ran a little hot. It used to be very stressful watching the temp needle in stop-and-go traffic with the A/C on as the car was always on the verge of overheating. At one point the radiator sprung a leak and I had to replace it. From that point on, the car always ran on the cool side, even on a 90 degree day with A/C on high, parked and idling for an hour.

Before discarding the old radiator, I took a good look at it. The fins were loaded with bugs, though not too bad. There was some corrosion, but with the exception of the area that leaked, again it looked pretty good. Inside there was lots of grit, probably from the PO not flushing coolant as often as needed (if ever). I'm guessing all of the above just combined to reduce thermal efficiency significantly enough. Bugs cut down airflow, corrosion and grit inside might have cut down H2O flow through a few of the tubes, at least enough to make a difference.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

First check is aux fans.
Pull connector off blue sensor at thermo housing and see if fan comes on to High speed.. if not, check fuse on top of High Fan relay behind fuse box.
If it does come on , then check resistance of aux fan sensor.
Low fan is checked by jumping high pressure switch at reciever/drier ..if low fan does not come on when sw. is jumpered , check fuse on top of Low Fan relay.. if blown, replace 15 A with 25, as this is a Benz up-grade.
If it does come on w/jumper, then the high pressure sw is not working or the a/c system does not have enough refrigerant to get high side to cut-in pressure spec for fan .
Report findings.

I picked up the car for the fourth time from Mercedes service after they took it to have the radiator cleaned, replaced the radiator cap (and had done the fan clutch as well as the themostat).. they tell me the aux fan is working. 10 minutes after leaving as I am sitting in traffic the car goes back to 110C. I was in disbelief.. I even called the radiator shop that Mercedes took the car to- he verified they cleaned the system and there was no build-up on the radiator afterwards- did not recommend replacing as they could see no blockage. The car is back at Mercedes as the service manager wanted to have "another look at it".. I see no point as they can't seem to fix it but curious as to how to get this taken care of. Any ideas?

Have them look for signs of head gasket failure. It was common on the M104 and will cause the overheating you mention.

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'96 C280 (gone)
'97 C36
'05 C230k

I will have them take a look at the head gasket although at this point I don't think I would trust their opinion as they haven't been able to accurately diagnose the problem and gave me the car back three times telling me its fine.

Take it to an independant for the diagnosis of this. The dealership would love another shot-in-the-dark repair try at this point. It's a relatively easy diagnosis, involving coolant testing, oil testing and coolant pressure leakdown testing. You can look for evidence at the back of the engine on the exhaust side. Is there traces of oil at the head/block joint?

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'96 C280 (gone)
'97 C36
'05 C230k

That is my plan. The dealership has it but they know I am not going to pay for another item, which is why they replaced the radiator cap and had the radiator cleaned without any charge. At this point I know they don't want to ever see the car again.

In answer to your question- there is no traces of oil and the head/block joint. The area was actually checked over last year by an independent who I instructed to check it over as Mercedes told me I had a head gasket leak... turned out there was no leak (or none that he could find). Supposing I had this issue, would the car only overheat when I am in idle and then return to normal temps when driving faster?

It's quite possible with a minor leak. I had that with an old BMW 733 I owned over 20 years ago. I finally figured it out when it got so bad that the coolant system wouldn't pressurize. At that point it was all leaking into the engine. Before that, everything tested fine (pressure-wise, nobody did the oil and coolant tests), but the temperature ran up and down.

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'96 C280 (gone)
'97 C36
'05 C230k

Thanks Benzfan.. when I get it back from the dealer (eventually they will give up), I will take it to an independent and have it checked. Hoping its an aux fan or radiator issue at this time but still have no clue.

C220, 1995
I have similar case, it always over heat during idle/ traffic, it reach 100C+, with A/C on. On Freeway it run o.k 80-85 C.
I notice Aux fan is just running 5 second and off.
Flush new MB coolant done, New Water pump.
How to fix this ?
Please advise, thanks.

I have a 86 300e that had all of these symptoms. It turned out that the radiator core tubes were plugging up. These tubes are very narrow and they have an aluminum strip running down the middle acting as a turbulator. Its purpose is to cause the water flow to be turbulent which makes it loose heat more quickly. You cannot even stick a round toothpick through these tubes when they are clean. They are very very narrow. You cannot even see through them when they are clean. As they plug up the flow is reduced and you effectively have a smaller radiator. These radiators cannot be cleaned or rodded out. I tried to have that done. Nobody would do it for the reasons previously mentioned. If the tube is blocked, no cleaner will cure it. If you want to confirm that water flow is reduced or non-existant just put your hand on the radiator and feel for cooler areas while the engine is running. This is where there is low or no water flowing from plugged tubes. The radiator should be equally hot over the entire surface. If its not - its plugged. I know this is almost impossible to do but I did it and then I disected the radiator and confirmed that it had about 1/2 of the tubes were blocked.

An almost 100% guarenteed solution is to replace the radiator and the fan clutch. If everything else is Ok that should fix it.

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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k

I'm having the same overheating issue I bought the car 4 days ago off Craigslist from a guy who seemed honest. I told him I bought the car simply to drive back and forth from Arizona to Las Vegas and it needed to be very reliable. I chose this car because I had a 97 E420 and the car it was the most reliable car I ever owned plus I loved it for the same reasons you all do. I drove the car around for 2 days no problems then Thursday morning drove to vegas ran perfect till I came back this morning and got stuck in traffic on the hover dam check point. then again back in town during rush hour and construction. The info here seems very helpful I'm taking it to a shop tomorrow and now know what to expect. My question is How much should these different things cost? Replacement of thermostat fans head gasket replacement etc. Thx again for your help

My gauge is always on 80 or 81 no matter what I do. When I turn on the A/C it slowly creeps up to 85. I get nervous so I turn it of and the temp drops back to 80. Would a coolant flush help? I am going in for an Oil Change today at Grease Monkey and they do these. Will Grease Monkey be able to check my transmission level since it is not like other cars when checking tranny fluid?

How will I know when I need my breaks checked?

Dumb questions but I am a female and I just bought this car a year ago and drive it maybe 4 times a week for 10 miles. I put synthetic oil in when I bought the car for 2,000 with 164.000 miles.