flucuating engine temperature.....

[79D604SPD]

I have a 1979 chevy K20 with a 400ci engine. I just removed the factory temperature gauge and installed an aftermarket temperature gauge. The factory gauge had C and H and a few marks in between to indicate temperature. The new 2" mechanical gauge has a much larger sweep and has numbers. I have noticed this winter that my engine temperature flucuates quite a bit during and after warm-up. It did it with the old factory electric gauge but is much more noticeable now with the new gauge that has a larger needle sweep and numbers. From a cold start, the engine warms to about 200 degrees then drops to about 160 when the thermostat opens, and then fluctuates back and forth between 170 and 190 for awhile. Eventually the temperature will level off to about 180 after 10 minutes of driving and a steady engine speed. I know some fluctuation is normal because I work at a dealership and have watched vehicles' temperatures vary about 5-10 degrees during driving with a scan tool hooked up. But I have never noticed a temp gauge move this much. Most vehicles warm to 195 and stay there, according to their gauge. What would cause such a wide flucuation?

It has a 180 degree thermostat and 4 core radiator. I put the 180 thermostat in it because I had heard of 400ci engines being notorius for overheating because of the siamesed cylinder walls. But I have had the truck a long time and have never expericenced this. I would really like the engine to run a little hotter than it does. It is an old engine with a lot of blow-by and sludge build-up. Most of my trips are short. Would changing to a 195 thermostat bring my temperature up any? Thanks for any help.
:confused:

[wyldman]

A 195 t-stat will run it a little hotter.It will not hurt to run it at 195.

A colder stat has no effect on overheating temp,just on min operating temp.