I built a 400SB for my '71 before I fragged the tranny I noticed that the engine temp. went up and down alot above 40mph. being a 400 I took into account the siamesed cylinders. so I bought an aluminum radiator with two 1" rows in it. I also had my heads drilled for steam holes, I also added a plate to the back of the water pump impeller to increase flow. I have also played with different thermostat temps. My guage is a mechanical one and it was working fine for the 350. i think the thermostat in it now is a 160 degree. The guage will go from 160 to 190 then back down again. it moves slow at first then races up to 190 then does the same down to 160. is this ok for the engine? Oh, and with the other thermostats it did the same temperature spread of about 30 degrees and same reaction. thx for the help in advance.

 

well i know in my car it will jump up high and shoot back down in a few seconds. i have a 180 in my car, ( i have a big block) and as soon as it hits 180 it will dive down to 160. what you may be encountering is that the temp is hot, the thermostat opens. and its just merely the gauge reacting to the temperature change. where do you have the temp sensor? is it in the manifold? heads? radiator? all of these have different effects on where the temp goes. this could just be the gauge reacting. does the temp. climb high or stay low? because that would be more of a problem then the gauge moving around. and in a 400 i would run either a 180 or a 195. 160 may cause overheating on a long trip. jmo.

 

my thermostat is in the stock location on the head. when i put the 190 degree thermostat in the engine would get up too high for my comfort. i know that what im seeing is the opening and closing. the engine stays w/in the 30 degree range regardless of the temp on the thermostat. it just does it at a higher or lower range. i went with the 160 b/c i am running, for pump gas and steel heads, a high compression ratio. my car is only for fun and will never see a long trip or bad weather. is 30 degrees someting to be worried about? or would the rate at which it changes be a cause for concern?

 

i ment the thermostat switch. is that in the head/manifold/ block/? and what kind of fan set up are you running mechanical or electric?