Yes the DexCool could have clogged your radiator but there is no way to tell.
It is also possible that your water pump impeller is not pushing enough coolant at higher engine speeds to cool the engine.
If you are not loosing coolant than it is not a bad head gasket.
To completely flush out all the the DexCool youi will need to drain the system, fill with plain water, run the engine with the heater on for 15 min, shut it off and cool for 15 min, drain, refill...repeat this procedure until nothing but clean water comes back out.
You need to run the heater while doing this to make sure it all comes out of it as well.
This type of overheating is very hard to track down, a new radiator is big $$ and a water pump is cheap but you dont want to throw parts at it.
Start with a complete cooling system flush and go from there.

 

I still have the original over heating problem, and here is what I have done so far in trying to correct the problem: new radiator, new water pump, new thermostat, new serpentine belt, new top & bottom radiator hoses.

Again, I can find no leaks or coolant residue on engine anywhere, no coolant in the engine oil, and no coolant smell at the exhaust. The heater operates very well, and when the temperature gage shows high temp, the coolant is boiling in the expansion tank - ready to boil over if I would keep the engine running.

Any ideas?

 

Send me your number, I'll call you and quit driving it in the mean time before you toast that engine.

 

PM sent with number - call anytime! Thanks much Mike.

 

argghhh mine is doing the same thing and I have replaced everything but cannot get to the source of the problem. Mechanic says it can't be the headgasket because I am not losing coolant, oil level doesn't change, compression test is good, and he did some chem test and it way negative. What do I do? I here a chirp in the engine and need something to drive before the snow flies.

 

PM sent but for benefit of all I have yet to check condenser fan operation on mine, nor have I done the cooling system pressure check. I'll post back after that ...

 

this might sound pretty dumb, but did you check the fuse for the cooling fans?
i started to overheat about a month ago and it was just a blown fuse.

 

my cooling fan works. Any one know a shopp[ in Rochester NY that can work on Rovers?

 

I'm in Burt NY about an hour away from you if you can get it here we can take a look at it. A chirp in the engine sounds like a bad pulley or a bad belt or water pump but it sounds like you took care of the water pump already.

 

Make sure your belt is routed right. Make sure the thermostat is connected properly. The perpendicular pipe needs to go the the upper radiator hose, the one that is at an angle goes to the water pump. If everything is hooked up right feel your lower radiator hose. It should be cold. If the lower hose is cold and the upper hose is hot, the only thing that would cause that would be the thermostat.