how can you tell if your engine is running too hot if you don't have a temp guage?
What the most likely symptom/solutions?

If you have a fairly good threshhold for heat, you can get a good idea on the engine temp by holding the dipstick.
At normal running temp you can touch the
dipstick briefly without undue pain, but when over heating even a breif touch will be too hot. Its one of those things that you have to get some experience with.
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If you are getting petrol vapour lock - this could indicate too hot.

The one piece of advice I can give is invest in a temp gauge, Some are more accurate than others. I have a vdo gauge with a dipstick sender as this is immersed in the oil showing a fairly accurate temp.
Found my beetle was running hot in the hot Brissy summers so popped the decklid open and it runs upto 20 deg/f cooler.Close it up again when it cools of to prevent other problems.