Thermostat

[alf1096]

I bought the truck about 1 month ago. When it started getting cooler here I noticed that the engine would not heat up so I ordered a new therm housing and stat. I put both of them on and the truck now heats up to about 200 and the the temp gauge goes from 200 to 240 in about 3 sec and then the truck cools down from 240 to 190 in about 5 sec. I thought that may be I got a bad therm so I changed it again with another new one. It still does it but not a often with the new one. Has anyone else had this problem if so what is the fix. And will the spike to 240 for a few seconds hurt the engine any help will be great.


thanks