Underheating???

I know this will sound weird but I figured I would ask. I have a 91, 4.0, auto. I just changed the radiator to a CFS 3 row, replaced the stat, and cap (195*) but motor very rarely gets to operating temp. it is still reasonably cool up where I live but with new stat I assumed it would get warmer and stay there. Also as I was changing cap I broke then replaced the heater valve (not sure if it matters) and heater works fine. the very day before i changed radiator it was badly overheating due to a small leak in previous radiator. Now I dont use coolant (dont ask) but wonder if by doing so will it help retain heat and hence bring temps back normal? My concern is that I wont be getting the correct fuel consumption given that its not running warm enough. I know some of the normal posters will say " get an aftermarket gauge " but like i said the day before it was working right so while it is a possibility I dont think it is the problem. Thanx in advance for help.

If you do not use "coolant", what exactly do you have in the system? Also, what temperature does it get to?

o-gauge-steamer said:

If you do not use "coolant", what exactly do you have in the system? Also, what temperature does it get to?

Click to expand...

Just water, and a auto safe rust inhibitor (dont know name off the top of my head).

water is coolant... antifreeze is antifreeze

Still should verify. Get an infrared point and shoot thermometer. Point it directly at the thermostat housing on a hot engine. That way, you'll know for sure.

Most 4.0 engines run in the 200-210 farenheit range.

T-Stat controls min temp.

I would bet on a bad thermostat.

t-stat stuck open is my guess

x4 on tstat being the most likely. Use the Stant Superstat only and nothing else

You could also have air in the head that is blocking coolant flow--put your hand on the heater hoses and see if they are hot (you will burn yourself watch out), and that will tell you if coolant is flowing through the engine

If you have a favorite garage you could also go ask them to use their OBDI code reader to pull temperature readings from the computer's temperature sensor (in the thermostat housing) and then compare it to the gauge readings from the gauge sender (at the back of the head) and see if they are close to each other. It's not uncommon for older heeps to have one of them go sour and cause a lot of confusion.