So just got my new donor motor dropped in and car runs great. Notice when I put my key in the temp gauge goes up to middle/normal reading, within a couple min its running hot hot, cold air blowing only, new t-stat, checked coolant, still can't get it.... Is there some serious air bubble in the system but Why is the gauge go right up to normal reading on a cold motor, 3 days of trying different things.... Anyone?

Does it actually feel as if its running hot, or just indicate it.

Popped a different cluster in her, sure enough it's the cluster.

Well, that's what I expected. Normally you will feel if its running hot, plus the fact the it "warmed up" so quickly.