Been trouble shooting my system for some time.

It's generally in adequate shape. Temp sits at 82C 95% of the time.
On hot days however (hot days defined as anything above 30C/ 85F), highway runs above 65mph will bring me up to around 100C. If I'm running AC, 105C. This goes for extended grades during average temps as well.

Before anyone posts a form letter, I've been through all of the usual steps.
Thermostat is working as intended, water pump is new, hoses are firm, citrus flushed (not much came out), 50/50 coolant mix with G-05, new rad cap, and so on. No visible coolant leaks.

The only thing left is the radiator. But before I ready the parts cannon, I'd like to make sure everything else has been ruled out.

Many have suggested using an IR thermometer to check for cold spots.
With the condenser on the front and a spinning fan on the back, I haven't found this very practical. I'm sure it's also possible to a have a marginal radiator with no "dead spots" per se, but rather a systemic under-performance due to age. I am running the original Behr/MBZ rad...

A buddy suggested testing for a slight pressure leak –one small enough to leak air, but not coolant. I'm considering doing this, but would like to make sure I'm not wasting my time. This got me thinking that the system is already pressurized after a drive, though it's not possible for me to know how much, without a gauge. By hand, the top hose is nice and firm.

* Is there a rule of thumb for how long it should stay this way?

* If I do perform a pressure test (I've a power bleeder I can attach to the radiator via auto zone loaner program) is ear enough to find the leak?

* Am I missing anything here?



-

__________________
1981 240D 4sp manual. Ivory White.