so my cooling system works perfect in town and sitting still.. fans are perfect, air dam in place, but when i get out on the highway doing like 70mph on a 90-100 degree day turning about 2500rpm she hits 240degrees.. im baffled as to why.. ive read through hundreds of posts about this subject.. have a 18- stat 180 secondary fan switch, fan shroud is good, fans turning the right way.. the only thing im unclear of is the on/off specifics of the fans when driving above 30 or is it 40mph theyre i believe supposed to shut off.. but i havent seen a straight forward answer.. next step is a high flow water pump i guess?

 

2500 rpms at 70 mph sounds high. But try flushing your block and rad. If the coolant isnt circulating good, its a going to get hot while driving highway speeds.

 

or you have no thermostat, easy to check so do that first. in town and stop and go your not turning as many RPM for extended time, so the coolent is pumped slowly, and has time to cool in the radiator. on the highway, the coolant is being pumped fast because a thermostat isn't regulating it, and its going through the radiator so fast that it doesn't have time to cool, so the car gets too hot

 

has 3.73's in it, it may be at 2500 at 80.. has a 180 stat works perfect, coolant is like 4 weeks old, and is good stuff not cheap.. the coolant not having time to cool sounds legit and is something that i could use help on

 

check to see if your radiator is plugged. take off your bottom radiator hose(when engine is cold) hold your hand over the bottom outlet and fill with water. remove your hand and your radiator should drain instantly, if it doesnt it is plugged or if it only drains a little it is most likely plugged.

 

Have you taken the radiator cap off, let the engine heat up intil the thermostat opens, and checked the water level, AFTER the thermostat is open?

I thought mine was full too, but it turned out the radiator WASN'T full. The thermostat wasn't fully open, so it just LOOKED full. Had to let it circulate good to get the air pockets out. And every time I added cold water, the thermostat would close up more, even if not fully closed, it slowed the circulation of the water, trapping air pockets.

 

yeah i had the rad pressure flushed about a year and a half ago.. and drained it from the bottom hose about a month ago.. drained fast as hell.. and i used an air evacuator to put a vacuum on the cooling system then ran it hot to be sure.. shes air free.. keep the ideas comin tho guys i dont mean to have answers to em all haha

 

[quote=dippo6;3789715]yeah i had the rad pressure flushed about a year and a half ago..
But did you flush the block?

 

well the block was only put in the car under 2 years ago.. it was a rebuild done at an engine shop.. so i would assume they used the big hot tank u can see in the back to clean it.. i would hope.. but this makes me think about doing it myself.. they by the way are the ones who flushed the rad for me..

 

The old trick is to pull in at home, pop the hood, & run water with garden hose for 30 sec. on the sides by the fan. Then you know the water is pumping. The temp will not get too cold if the thermostat is closing at cold temps. This may also push built up dirt out of the fins in radiator. Also after a long trip, the trans temp increases. The cooler is in front of the radiator. Try to touch the hose or side - it should be 20 degrees cooler then a hot radiator.

 

check ur upper and lower hoses to, they could be soft and tightening up under higher rpms