brother i am in the exact same shoes as you! i have read all the new replies and i am totally convinced that this problem is 100% an over cooling problem. again here in Oklahoma we are in lower temps about 30's to 40's, freezing. same as you. again while my car is level the fans will not cycle unless i hold the rpms at about 4k for about 5 minutes building up enough heat to pass by the fan switch causing it to trip and come on. i think our next step is to find a lower temp thermostat and see if this solves this issue, if not it might be a different rad.

my next question is where can i get a lower temp t-stat that is a good quality. PLEASE LETS KEEP THIS GOING AND GET THIS SOLVED!

 

We had that problem at 80F day, and car was just idleing(so no air blowing towards the rad).

Just low temp thermostat might NOT solve the problem because the bottom hose will NEVER get hot with out flowing some water.

My best bet is drille some small holes on thermostat to allow some water flow, which will warm up the thermostat to open when it water temp gets hot.

This is how we solve the problems on our Time Attack S2k.



I also have 64mm core custom made rad for my turbo S2K which had to do same thing.

 

how small of holes? how many? i dont want to mess anything up any more than it already is. do you have any pictures of the ones you have done? is there any where in particular that is good placement for these holes?

 

A bad thermostat (stuck closed) would cause the upper radiator hose to stay cold and the engine to overheat. Since the upper radiator hose is getting hot then the thermostat is doing it's job correctly. THe lower radiator hose should be cooler than the upper hose since the coolant in the lower hose has been cooled by the radiator. The better the radiator the greater the temperature difference between hoses.

The heater does not get it's heat from the lower hose, it gets it from the engine block so you can have heat and a cold lower hose.

The cooling fans only come on once the engine is well above normal operating temperatures. The car will have to run stationary for a little while to get the fans to come on; any driving or wind through the radiators will keep the cooling fans off.

A lower temperature thermostat will only make your "over cooling" problem worse.

You might be chasing a problem that is not there.

 

the bottom hose is ice cold. not even luke warm. our cooling fans come on at 210 degrees F. when we were going through all of our testing at the shop we thought something was wrong with the fans. this was not the case just that it wasnt getting hot enough at the fan switch to trip it. while driving the car would only come up to 185 and a little less while sitting.

a lower temp t-stat would cause it to open sooner at a lower temp allowing more water flow sooner to the heater core. how would this ass to an over cooling issue? this would be the case if we went up in temp settings

 

This is music to my ears... but like s2kVTAK said, the bottom hose is COLD. There is not even a hint of any warmth to it, and the top of the rad/top rad hose is HOT, as in VERY hot.

This really makes me believe that coolant is not circulating at all, unless the rad is doing such a good job of cooling it off that it's COMPLETELY cooling it to the point where it's not even luke warm

As I said before, I can rest my hand on the bottom of the rad, and it's cold... which would be why the fan switch isn't being triggered

 

My fully functional rad is cold on the bottom and hot on top. Isn't this a downflow radiator where the thermostat opens and flows to the top hose? The thermostat just keeps the fluid in the jacket at a given temperature, any significant temp above that just dumps to the rad (exc for the small flow through the first stage orifice).

 

The bottom hose connects to the thermostat, which would be the intake hose, and the return hose would be the top hose. Hot coolant rises as far as I know, which would mean once the thermostat opens it would push all the coolant from the block into the bottom of the rad, rise through the rad, and then out the top.

Wouldn't this make sense? The fan switch is right by the bottom intake hose... so it would be triggered as soon as the thermostat has opened and the hot coolant has flowed into the rad to be cooled.

Someone please correct me if I'm wrong...

 

I'm also in a similar situation.

My car runs fine around 84-86C degrees usually. If I push it hard then hit traffic or lights the temp can increase to 90C (possibly 92) but the fans kick in at 90 and bring it down into the 80s again.

But ever now and then it will just skyrocket up to about 107 and keep going if I don't shut down the car. I leave it for a while, then drive again and it behaves itself.

Now every time this has happened (3) I have been cruising, good air, low load. And twice I noticed that the temp dropped quite dramatically before the overheat.

I am wondering if the thermostat isn't closing and staying closed. I have a complete new cooling system (rad, hoses, fans, thermostat) but have to do some intercooler replumbing to get it in. I might just do the thermostat and see if that fixes the problem but I am reluctant to drain my cooling system twice.

 

I just did a 20 minute drive in 50 deg weather and my upper radiator hose is too hot to touch and the lower hose is cold. The system is completely stock and the engine maintained operating temperature.

The thermostat is located on the inlet side of the water pump (lower hose) but it does not send coolant to the radiator or heater. When the thermostat is closed the water pump continually circulates the coolant around the engine and through the heater core. Once the engine reaches operating temperature the thermostat opens and the water pump starts to pull in cooled coolant from the lower radiator hose. A lower temperature thermostat will allow the cooled water in the engine earlier thus keeping the engine a lower temperature. If the thermostat was not working then the coolant would continue to flow around the engine until the engine over heated. If your engine is not overheating then the thermostat is working fine.

The fan switch is at the bottom of the radiator and it will not activate until the coolant leaving the radiator gets hot enough. That could take a good while in cold weather especially if the engine is not under a load but very hot weather sitting in traffic the fans will come on quickly.