I am Befuddled:

My '91 300E coolant temp has been running at or just below 80c after ten minutes and more of driving at ambient temp of 60-70f. So I replaced the Tstat thinking this was the problem.

The car still hardly shows anything above 80c. Now I am wondering is it the Tstat or possibly a bad sending unit?

Questions:

-How do I test the sending unit to the temp gauge?
-Is sticking a thermometer into the coolant reservoir a good test of the true engine coolant temperature?

I checked the coolant and it does need more anti-freeze, it only goes down to about +5 degrees. Not a problem though here in N. California.

Any suggestions? Thanks as always.

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'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)