My evo 8 is starting to over heat after cruising at about 2.5-3k RPM in fifth gear after about three miles. It goes right back to normal running temperature if I just pull over and idle for about a minute. Heater, ac, and radiator fan works fine, and so far I've only had this problem in fifth gear. It only starts to over heat in other gears after doing like four or five pulls to redline. Has anyone had this before?

 

Change the thermostat, make sure both fans are turning on.

 

Those are basic things to start with

 

flow test your radiator

 

sticky thermostat, check for air in the system, make sure the fan kicks on.

 

Also check coolant lines for pin hole leaks.

 

Thanks guys I appreciate it!

 

highly doubt a pin hole leak would cause this problem and only in one gear. Any overheating I've ever encountered on my vehicles in relation to a radiator or coolant hose leak occurred at idle and temp would go down once the car moved and got air across the radiator. As mentioned it's probably a fan or thermostat issue or something else mechanical like that. Hell, my radiator has a tiny leak in it right now and some coolant was working its way past my thermostat housing after beating on the car and the temp gauge didn't move one hair and it was more than a pinhole leak.

 

Check the basic and cheapest items first there's also a bleeder valve you can get air out of the system if there's any.

 

Is your coolant in the res vanishing? If your radiator has a leak that you cant see with your eyes and your fluids drop enough system could get air in it and cause it not to flow. Fix what you know is broke for sure first to start your process of elimination. New radiator, and while that's off re place your tsat and any hoses that need replacing. If any do, replace all of them as not to create a weak link. Don't forget to check water pump for moisture. Now what's left. Temp sensor. You can use a Lazer temp thermometer to see if it actually reading true. I know sometimes the actual temp gauge craps out. Check both fan cycles. Check for exposed wiring. After your system visually checks out do a pressure test on it. If it drops more quickly than it should, and or still loosing coolant. Do a leak down test. Could be pinhole in head gasket getting ready to completely fail. Which could have been caused by your leaky radiator that could have possibly caused improper cooling, causing hot temps, causing slightest head movement, causing water to find it way. Just be thorough with your inspection and elimination process. If I remember correctly the only other way to loose coolant is a broken turbo housing and something with the idle speed control servo on the Throttle body, the o ring. Hopefully it's a minor electrical. But wire chasing is also a pain.

 

Make sure your radiator and both radiator hoses are filled with coolant. And double check your coolant reservoir hose to make sure there isn't a clog. I've had this problem in my old eclipse.

 

So I replaced the thermostat, topped off the coolant, and bled the system today. It idles just fine, and the temperature doesn't rise. Only now the temp gauge drops after I drive it around. I took it on the highway and the needle went down really close to the c. I figured it had to be a faulty gauge, but I pulled over to check things out just in case, and the car was idling pretty high just like it would on a cold start. This thing has me so confused! ��

 

Get an IR thermometer and see what it registers when you aim it at the Tstat housing. Something isn't jiving here. It's acting like your sending unit is bad. How long did you drive it after you did the stat? Long enough to get to operating temperature?

 

After I installed the thermostat I let the car idle until it got to operating temperature. Then I let it idle for like five more minutes checking if the heater, ac, fans etc all worked. Everything was working fine, and the temp was staying just below the middle of the gauge, where it normally is. I drove it around my neighborhood a little bit, shifting at around 2.5k rpms the whole time. The temperature was still staying the same so I started bringing it into boost a little bit, and that's when the temperature gauge started dropping. The more I got on it the more the gauge would drop, and when I stop and idle it goes back to the normal operating temperature.

 

What is the ambient air temp where you are located? If its really cold outside, once you get moving at a good rate of speed, the cold air will drop the temps in the radiator. Put a piece of cardboard in front of the rad to block airflow and see if it still drops.