my mud toy a 94 2door 4.0 35's not street legal.=as fast as i go is 30mph . question is im changing the water pump and thermo. do i need a thermostait or not

for 3 bucks? why not.

thermostats are there to prevent overcooling, not overheating.

im pretty sure the thermostat prevents overcooling AND overheating... the thermostat is the module that regulates the cars temperature without it your car will over heat in a matter of mins

Wait what!?!? I have had small blocks most all my life with out a t stat and I never had a heating issue. With out a t stat and an Efan I ran at norm temp all day could idle for hours with out an issue. With out a t stat it takes longer to warm up. But if you have adequate fans and radiator you shouldn't over eat

not all motors need it... the 4.0 is designed to run on a thermostat to regulate temp... i mean if you want take it out just but it will over heat mine went about 6 months ago and it was smokin up real good... spend like 5 bucks at autozone and it ran perfect

You are wrong.
Your thermostat must have been stuck closed because having no thermostat is like an open one. It allows for coolant to flow through freely all the time.

x2

you will be just fine without a t-stat just dont plan on having heat if its cold out

http://www.ehow.com/facts_5076347_car-thermostat.html

good luck not overheating... believe me i tried this IT DOES NOT WORK!

ya I'm going to disagree, something else was wrong withs yours because with out a t-stat, your coolant is free flowing, the t-stat stays closed so that the coolant in the engine heats up quick to operating temp them opens to keep it at that temp by flowing. with out that t-stat, its going to take longer to heat up because the coolant is going to be constantly flowing through the radiator cooling what little heat it obtained from the engine.

from your link:
Prevents Engine Overheating
"A thermostat also keeps an engine from overheating by opening and allowing heated engine coolant to flow into the radiator, which cools the engine coolant, thus reducing engine operating temperature"

thats exactly like having no T-stat.............

again that link says and shows that the main purpose of a t-stat is for the prevention of under heating

if yours went out 6 months ago, its most likely that yours went out by staying shut, some t-stat fail and stay open while others fails and stay closed.

I read many years ago in Hot Rod magazines, that one purpose of running a thermostat is to slow, or regulate the coolant from traveling too fast through the radiator to allow the coolant/radiator enough time to work properly.
When I first got my XJ, I changed all the fluids, and installed a new thermostat.

I would say run it. its cheap to run it and whats the worst that happens your engine runs like its designed to?

This. Without the thermostat the coolant will move too fast through the system and will not absorb the heat from the engine or rid the heat through the radiator. Do you cook bacon in the pan for a minute, or leave it there until it is fully cooked? Same thing applies.