thats how my 2.7L 1998 is if that helps at all.

 

Does the hot coolant fom the engine enter the radiator throught the top hose and return to the engine through the bottom hose on a 2002 3.4? Or is it the other way around?

Think about it. What if the radiator was a little low? The top hose would become useless to feed the engine. The water pump sucks water in from the bottom of the radiator, pushes it through the block, and out the block to the top of the radiator.

 

You are correct about the direction of flow, but the reason you base it on is flawed! Don't forget the system is PRESSURIZED, and with the water pump pushing fluid from the block UP THRU the radiator, it would still come out the top even if the system was a little low on fluid. The pump doesn't care if there's a bit of air at the top of radiator, it will still push the fluid FROM THE BOTTOM right up and out the top of radiator when the t-stat is open. Think on that a bit and I'm sure you'll be able to understand.

 

Think about it. What if the radiator was a little low? The top hose would become useless to feed the engine. The water pump sucks water in from the bottom of the radiator, pushes it through the block, and out the block to the top of the radiator.

Thanks, I realized that after I posted. The thermostat location threw me for a minute. I was used to it being in the top hose on the other vehicles I have owned, not in the bottom one.

 

I'm reviving this old thread because I just like to understand things. Coolant enters the radiator from the top and flows out the bottom. The thermostat is connected to the lower radiator hose blocking coolant from entering the block until the engine is warmed. Until the thermostat opens, coolant is not moving through the radiator but is still being cooled by air flow through it (especially for you guys up north in the winter). When the thermostat does open, this very cold coolant rushes into the block and it seems like you would see the temperature gauge/needle move down as this cold coolant moves through. Not to mention the thermal shock that you would think would take place. But it doesn't move down. Why not? Because it is moving through so fast or is there something else? (it's a slow day at work this morning )

 

Wow, one of the dumbest posts I've seen.
First, WTH are you looking at when you say the t-stat is on the BOTTOM???? I've NEVER seen a t-stat connected to a lower rad hose. Please give an example. They are ALWAYS (in my experience) connected to TOP radiator hose.
But regardless, a t-stat NEVER opens so quickly as to allow coolant to "RUSH IN". ????? Where are you getting your info from?? A t-stat is a MECHNICAL, SPRING device. This would NEVER change so quickly that the spring would SPRING OPEN. SImply common sense tells you it's a slow gradual process, as the opening of the t-stat is simply caused by the response of the metal spring to the change in fluid temp. The fluid level on the inlet side (regardless of whether that was the top or bottom of block) will obviously change gradually, even if that's only a matter of a couple minutes or even a few seconds. It will change in a gradual manner, and as it does so, the metal spring will gradually respond to that change.

 

I think the thermostat gradually opens as not to shock the system with a temperature difference. I notice it does not take long for my temp guage to be at normal operating temp... within 2 miles... I also always thought the thermostat was at the top of the engine as well... guess not

 

I've seen this happen on the vehicles I drive for work. They're International DT466s.

What the temp gauge sees depends where the temp sensor is located.

My BMW motorcycle has one sensor for the gauge and another for the ECU, in different locations.

 

I've seen this happen on the vehicles I drive for work. They're International DT466s.

What the temp gauge sees depends where the temp sensor is located.

My BMW motorcycle has one sensor for the gauge and another for the ECU, in different locations.

Right.

The thermostat opens only as much as needed to maintain the proper temp. It never goes from fully closed to fully open instanatly.

On the 5vz there are two temp sensors. One in the front of the manifold directly under the passenger side fuel rail for the ECU. There is one on the rear of the manifold right near the heater hose connection for the gauge.

 

Well, also remember that the needle makes up for a big difference, so it always stays at the middle. I remember seeing a writeup a while back, or installing a resistor so that it is a temperature gauge that actually shows temperature, not slowed down so it's in the "general area"

On my old 75 c10 though, you're right, you'll see the neexle bounce up, then shoot down, and slowly rise again.