Those 85c warnings are so near the boiling point that it's not just "warming". When you get capacitors really hot they fail. We knew that, before you mentioned it.

Michael,

I want to focuse, that an electrolytic capacitor is not only prone to get damaged, when temperature rises up to +85°, but that also rather slight increase of temperature will drastically decrease reliability.

In the '90 'Roederstein' fabricated an electrolytic capacitor series called 'EL'. This was a standard electrolytic capacitor widely used in all sorts of applications. I found it even in professional ones.
Sevice life of this capacitor was specified to 30,000 hours at <=40°C and 1,000 hours at 85°C. This specification seems quite acceptable, if application is powered 8 hours a day. An 'EL' type capacitor seeing only room temperature would need about 10 years to reach its service life end.

But situation looks totally different, when your application is powered 24 hours a day and if ambient temperature increases: As a rule of thumb, service life decreases by a factor of 4, when increasing ambient temperature by 20K. So, when your 'EL' type capacitor is powered 24 hours a day seeing an ambient temperature of 60°C, then end of service life is reached after about 300 days!! Not to mention, how situation looks like, if more than only one such capacitor would be used under this condition...

If you take a todays high quality cap, like 'ERF' series from 'Frolyt', on the other hand, situation looks much better: Service life is specified to 200,000 hours at 40°C, 10,000 hours at +85°C and 2,500 hours at +105°C. In the same application, where the 'EL' type would reach end of service life after 300 days, an 'ERF' type would reach end of service life after nearly 6 years!

If in an application very many electrolytic capacitors are used, at temperatures near +40°C and slightly above, using types being specified for a max ambient temperature of only +85°C would be a heavy misconstruction! This +85°C specification would be acceptable for all other sorts of components, like chips, resistors, ceramic capacitors, etc. but for an electrolytic capacitor this only means, that +85°C should never be applied to it, otherwise you could even SEE the cap failing...

If one wants to use electrolytic capacitors in an application, it's a must to check according datasheet, in order to get information about service life specification.

One should never use 'no name' electrolytics!!! I have noticed, that many todays mail-order houses do offer +105°C types to quite acceptable prices. If in an application high reliability is needed, then just take these +105°C types standardly!

Kai