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Old 01-25-2017, 07:43 PM
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Join Date: Oct 2015
Location: Dela-where? OH
Posts: 133
500SL may be overheating

Iím looking at buying a Ď91 500SL that's for sale locally. Overall it appears to be in good shape except that it overheats, so the price is low. Before I went to see it, the seller and I discussed her letting me drive it for 15 minutes or so, enough for me to evaluate the car before it got too hot. But when I got to her house, sheíd already started the engine, admitted she got distracted by a phone call, and let the car run 25 minutes. By the time I pulled up, it was already steaming and puking coolant on the driveway. So I couldnít drive the car, only do a static inspection. She claims her mechanic replaced the thermostat and when that didnít fix the problem, he said it was the head gasket. It sounds to me like he was just guessing. I didnít see any signs of coolant intermix when I looked under the oil cap (granted, I didnít check anywhere else). My indy mechanic (MB factory trained) tells me heís never seen a M119 engine that needed head gaskets and said that with this car, heíd be more concerned with other things than the engine.

During my inspection I noticed some damage to the right front air dam and plastic shielding just behind it as if she ran over something so I have a theory that the car isnít really overheating but is losing warm coolant that's trying to flow from the radiator to the overflow tank, due to being physically damaged in that area. Usually when an engine overheats the engine compartment is hot as blazes but this just didn't strike me that way. It was like the car had run for a while and now some coolant was running out. So the seller and I discussed me going back in a couple of days to do an actual test drive. What Iím hoping is that the transmission, A/C, top operation, brakes, etc. will check out and that this will be an easy fix and I can enjoy the car for a year or two before shifting it on to somebody else. I do the majority of my own work and enjoy tinkering. But am I being greedy or unrealistic to think this could be a cheap fix? I hope to get the car for less than $3000.

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Old 01-25-2017, 08:40 PM
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Join Date: Jan 2012
Posts: 7,515
There is always coolant in the radiator so a leak here will occur with a cold or hot engine.

It could be a fan issue ( clutch fan not engaging , pusher electric fan not turning on )

I'd price out a replacement engine ( like from a S class but be sure to verify , it should be $ as some think SL stuff should command more $ )

I'd put $ 1,500 or less on the car as the market is pretty dead for these otherwise great cars and few are going to take a risk on a car that could be $$$ to fix. Hit them with the cost of a replacement engine as they may have damaged it during prior overheating.

Also, with a 91 you will be getting K jet / CIS injection, this is $$ to repair. A car from the mid 90's will have EFI and will generally be more reliable. Don't discount the 6 cylinder SLs, you can buy a better car for less $ and the 6 is enough for general driving and doesn't run out of breath on the highway.
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Old 01-26-2017, 07:33 AM
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Join Date: Aug 2002
Location: Southeastern PA
Posts: 3,077
Various things could cause a coolant leak: cracked upper radiator connection, especially if it is the original radiator; leaking water pump which needs to be replaced; leaking hose connections, etc. If it passes your cursory inspection and you are still interested in buying this 500SL, recommend having a MB-trained tech who is familiar with this vintage MB vehicle perform a PPI (pre-purchase inspection). That way you will know what major repairs are pending.

Fred Hoelzle
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