Hi,
My 87 560 SL heats up when the weather is hot. I have replaced the radiator and the thermostat to no avail. When heat gauge gets to 90C the all the other gauges go crazy and the turn signals won't work either. When it cools off everything works fine again. Is this an unusual problem? or what? It is very anoying that I can only drive in cool weather.

90 cel is the correct operating range, although the fact that all your other guages go goofy when it gets hot is something really strange. Perhaps your car is trying to tell you something? ha ha. I would recomend checking the grounds, there are bunches of brown wires gathered up and grounded to the chassis in several places, loosen and tighten to refresh the ground, next if you have not already replace every fuse, those type of fuses are tricky and cause irregularities in contacts and even burn out without any visible evidence. Then I would check the temp sensor sending unit, make sure it is not creating a flat ground to the IC (instrument cluster) the temp sensor signals temp by level of resistance and if it is goofing up it can likely cause other errors as well, when it hits that temp it may go to registering no resistance and freak out your IC. Give those a try and report back. Good luck! If you need help identifying the Temp sensor let me know.
Brian

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Brian W. Heitman

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What I meant by "goofy" is that all the gauges at the same time flip to the high end of their range; the temp. gauge, the gas gauge, etc. and the turn signal indicators don't flash, the light just stays on steady. I thank you for the information and will have the ground wires checked out. In Western Oregon the weather is quite cool and until we get a day that is about 82 degrees all of this is not a problem. Before I replaced the radiator the car was definetly overheating but now I am not sure whether it is or not.

Thank you again for your reply.
Hazie.