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1991 500sl overheating

6K views 15 replies 9 participants last post by  tusabes 
#1 ·
Hi guys, having issues with 1991 500sl. Mileage is 56000. Bought it from someone, car starts overheating after about 40 minutes. Took it to mechanic, he changed fan clutch, thermostat, was test running and radiator cracked, put new original radiator, same problem. And hoses have high pressure i can tell. Checked cylinder pressure. 180 to 185 which he says is normal. Hoses are too tight seems to me. No idea what it could be. Dead end. Could it be bad engine even with normal pressure?
 
#4 ·
If your cylinder head gasket has gone, you would probably also get oil and combustion products in the coolant system and emulsified oil around expansion filler and inside expansion tank. Are there any milky oily deposits in the top of the expansion tank? Did your mechanic do a sniffer test? M119 is a strong engine and unlikely to be 'bad'.

Another reason for pressurised radiator top hose is a PARTIALLY BLOCKED RADIATOR.

Check out this thread: -

http://www.benzworld.org/forums/r129-sl-class/2475825-hot-running-v8-conundrum-11.html

Alan67 had a similar problem. His mechanic replaced the radiator in an attempt to cure an overheating problem, but unfortunately he did not flush the cooling system first. He also used antifreeze which was not compatible with the antifreeze already in the system, which led to a reaction between the two antifreezes (IAT and OAT), which caused the coolant to gel, creating a partial blockage in the brand new radiator.

At the end of Alan67's thread is a video of him testing the new rad, confirming it was blocked. He flushed the system and replaced the radiator again, which cured the overheating.

This tale is a credit to Alan's tenacity and sense of altruism. He documented everything step by step and followed it through to the end, so that the rest of us at Benzworld could benefit from his experience.

Alan67, if you're out there, you deserve a reward and I take my hat off to you. :thumbsup:

Benzworld working at its best!

Hope this helps :)
 
#12 · (Edited)
...Another reason for pressurised radiator top hose is a PARTIALLY BLOCKED RADIATOR.

Check out this thread: -

http://www.benzworld.org/forums/r129-sl-class/2475825-hot-running-v8-conundrum-11.html

Alan67 had a similar problem. His mechanic replaced the radiator in an attempt to cure an overheating problem, but unfortunately he did not flush the cooling system first. He also used antifreeze which was not compatible with the antifreeze already in the system, which led to a reaction between the two antifreezes (IAT and OAT), which caused the coolant to gel, creating a partial blockage in the brand new radiator.

At the end of Alan67's thread is a video of him testing the new rad, confirming it was blocked. He flushed the system and replaced the radiator again, which cured the overheating.

This tale is a credit to Alan's tenacity and sense of altruism. He documented everything step by step and followed it through to the end, so that the rest of us at Benzworld could benefit from his experience.

Alan67, if you're out there, you deserve a reward and I take my hat off to you. <img src="http://www.benzworld.org/forums/images/smilies/thumbsup.gif" border="0" alt="" title="thumbsup" class="inlineimg" />

Benzworld working at its best!

Hope this helps <img src="http://www.benzworld.org/forums/images/smilies/smile.gif" border="0" alt="" title="Smile" class="inlineimg" />
Hi Rob.

Just came across this thread. What an ordeal that was back then eh, but I actually look back on it now as a good memory. It became part of my journey with my R129, and strengthened the bond that I now have with my car.

Anyway, I just wanted to say thank you for your kind words above, and I do apologise for not having seen your post earlier.
Life had rather got in the way of visiting dear old Benzworld, but that will hopefully no longer be the case. Life is good again ?
 
#5 ·
Thank you for info! Also, which coolant is the best for this car. Obviously, dealership will have a good one, but if I just buy it at autozone? Also, I live in phoenix arizona, it is 115 degrees outside now, i'm sure that makes things worse as well.
 
#8 ·
Also, I live in phoenix arizona, it is 115 degrees outside now, i'm sure that makes things worse as well.
Perhaps the radiator alone is insufficient to keep the engine at temperature in that extreme heat. I would check to see that the auxiliary electric fans mounted in front of the radiator have switched on.
 
#11 · (Edited)
Hi Sasha377

I am the 'Alan67' mentioned above by Robm.UK and having gone through what you are experiencing, I certainly feel for you!
As far as I can see, the coolant hoses themselves have not been mentioned. I replaced all of mine during the course of trying to get to the bottom of the hot running that I was experiencing. The hoses can collapse internally, with no visual external clues. This can cause a 'flap' to form inside of the hose, which restricts the flow rate of the coolant, leading to raised coolant temperatures. Cheap fix, and it might just cure your problem if indeed you have not already done so. All the best.
 
#13 ·
Well, i guess it's game over. Cylinders 2,3,6,7 all show evidence of consumption of coolant. There is very little carbon build up and there is a tanish residue on the tops of the pistons. Thats what other mechanic said, his shop specializes on these models. It is upsetting but I guess I will rebuild heads or just sell it cheap as is. Didn't decide what to do yet. Anyways, thank you all for your posts! What you thinks its worth as is or with rebuilt engine? 1991 500sl, ice blue metallic, 56000 miles, 18inch amg chrome monoblocks, upgraded music system, very clean car overall.
 
#14 ·
If mileage is correct then at 56 000 miles there shouldn't be much carbon in the heads. Only one test you or your mechanic have not done and that is the sniffer test of CO in the coolant.

Still, hard hoses is a definite sign of leaking heads or extreme over heating due to corroded and blocked coolant channel ways.
 
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