Hi everyone. I have an 01 4runner that is overheating but only at 3,000 rpm and up. I live in Colorado and heading into the mtns is impossible. This happens at any altitude, if I am staying high in rpm at highway speeds. As far as I can tell it overheats and boils over, but does not burn antifreeze. If I keep it around 2500 rpm I have no issues with keeping freeze where it should be. At first I thought I had too much water in my freeze, but then went through several gallons of pre-mixed freeze to no avail.

It doesn't smoke, but has beeen getting progressively worse MPG lately. I used to be able to clock around 20mpg highway, but am looking at 15 now....

Replaced my radiator last fall with a Koyorad.

T-stat? Head Gasket?

If anyone can give me some advice about where to start checking first that would be great.

Thanks!

 

Check first? I know you said new radiator...but what about the cap?

 

the check engine light on? have you checked your tune up? when was water pump done last? Pull plugs and take a look at coloration and wear pattern. Check compression.

 

Having a similar issue with '03 Prerunner. Runs fine at lower speed and when revving engine in neutral so air flow does not appear to be the issue. At 70 to 75 mph temp gauge begins to deflect high, I have never let it overheat but as this is a step change in the trucks behavior I am pretty concerned.

 

Radiator cap. Problem solved.