Alternator replaced, now gauges work right

About a month ago I noticed the 81SD was getting harder to start on some mornings. Just didn't seem to have any battery power on some days. Checked the battery voltage while running and it was at 13.2 v. Getting low. I figured the alt was giving out.
Didn't have the time to replace it right then, and with a diesel running in daylight who needs a full charge anyway?
This last weekend I checked it again and there was no output left. Voltage across the battery dropped when it was running. I had been charging the battery most nights anyway. So I got the replacement bolted in and now running at 14.7 volts.
First thing I noted was the temp gauge began to stay pegged at 85c. It had been taking excursions up to 95-100. Now it stays right at 85 all the time. The oil pressure has improved at idle now. Sits at just under 2 bar, before it would bounce along at 1.3-2.0.
Now I may be nuts, but do you think the old diesel has improved? Or could this be something else going on here?

[84300DT]

did you replace the entire alternator or just the voltage regulator?

Has a used alt from my parts car and bolted that in.

[JamesStein]

Perhaps your old Alt was binding up, causing the water pump to turn slower than it should.

Just replaced voltage regulator after suffering identical symptoms. Swap-out took ten minutes (including putting car on jack stand). Battery charged right up. Thanks doubleyew. What a gem - 24 year old German diesel. Go figure. (9 year old Ford = pos).

I am thinking it will be a good idea to replace the voltage reg on the old alt, just to keep a good one in inventory.

[Lycoming-8]

That sounds like a good plan, but you might want to get the whole alternator / regulator package tested once you have replaced the regulator. That way you would be fairly sure that you have a good spare when the need for it arises.