I changed thermostats in my 350 this winter while i had the motor out. The old thermostat i took out was a 160*, i replaced it with a 180*. With the 160* degree thermostat my car would run about 180*. I had it out the other day for a cruise and it seems to be running hotter with the new 180* thermostat. Seemed to wanna run around 190-195* This concerns me a bit as it was only 55 degrees outside. Is there any reason why changing to the 180* thermostat would cause my car to run hotter.

it could very well be that your guage is off a bit. Seems too close of a coincidence that a 20 degree thernostart change would cause a near 20 degree temp change.

Shoot the thermostat housing with a temp gun and see what the gun reads.

Should be pretty close to the thermostat. Also, look for a min 20*F differential between the radiator inlet tank and outlet tank. Measure at the tank wall next to the hose nipples. This will show if radiator is doing its job or not.

Well, sounds logical to me if your 160 was producing 180 readings that a step up to a 180 would produce 200 on the reading.

First, where are you sensing the temperature???? Is this an intake or head sensing unit? Head sensing usually will be higher due to exhaust port tainting or esp if you have aftermarket heads and/or headers.

I think you are fine actually and when summer comes the temperature gauge will live right where you are now. The thermostat is doing it's job and cycling where you want it. If you suspect the thermostat or want to use the best, the "balanced" and/or high flow thermostats from Mr. Gasket are the most accurate, highest flowing design and won't fail in the shut position. About $10 from Summit Racing. Try a MRG 4364 part number.

a quick easy guage test would be to put a meat thermometer in the rad cap hole and compare readings (make sure you got a cool engine when you take the cap off, and let it warm till the thermostat opens before checking any readings.)

It is a head sensing unit. Had it out again today and its pretty much running 190*, about 10 degrees hotter than before. As long as it stays there when the warmer temps come along its fine.

Head sensing temperature devices can become heat tainted from usually headers (cast manifolds remove more heat) and/or aftermarket head use (the media and distance can be different for the sensor). So, not a biggy.

I would suffice to say that summer will not make a difference to any great extent...maybe on those real hot days and/or super long traffic lines etc. But, even 225 on the head reading is not something to get reeeeal excited about as long as you are containing your coolant.

Use at least a 12lb cap (even tho it's on the suction side of the crossflow) with the appropriate overflow and high flow water pump to assure plenty of "friendly" pressure to keep the coolants vapor point up too!

Thanks for all the great info. Based on the responses i guess im not to concerned about it at this point. Will keep an eye on it as warmer weather rolls in and go from there. Thanks again.