My new engine overheats whenever I am at a steady cruising speed, like on the freeway, or when I am in 5th gear @40mph around town. It will start out at 190, then go to 210, then 225, then down to 215 on the freeway. Sometimes when driving around town it will go up to 230 in 5 minutes. If I am running hot and downshift and floor it, my temp will drop. When I race, my engine actualy stays cooler. My radiator is good, I have an electric fan constantly running and it is sucking air through the radiator, coolant is a 60% water-40% anti-freeze mix, 185 thermostat. Answers? Should I replace the water pump with a high flow one?

 

while cruising around with a 180 stat for example all you really need more than likely is an air dam pushing air up into the radiator. my car stays about 190 while cruising.
the engine staying cooler when getting on it more would more than likely factors out a collapsing lower rad. hose.

 

y not try a 160 stat?

 

A 160 t-stat would probably make it worse.

 

If your sensor for the temp gauge is near the headers it will give a reading on the gauge of about 20 degrees hotter. Your ecm may not like the 160 stat as it is programed to open a 195 stat. The best you might do is a 180...tops. You also could have a tiny leak somewhere causing a loss of pressure in the radiator. Try squeezing the top and bottom hoses a few times (with gloves on) to release any air pockets.

 

Having a 185 stat should work fine with the ecm...

 

The ecm has nothing to do with opening the t-stat. But if you do run a 160* t-stat, remember that the fans are still programmed to come on at the higher temps, so without reprogramming the ecm (and changing the secondary temp sensor if so equipped) you wont gain all that much advantage to using the lower temp t-stat.

 

Thats what I meant.... Thanks for correcting me.

 

I would have to ask do you have the Black Plastic air dam mounted on the car. It mounts to the bottom of the Raditor core support. I had this same problem last year and when you are at high way speeds the arestream moves the air straight under the car and also creats a vortex and removes air going to the Raditor. The air dam is what directs high flow air into the raditor for cooling. The problem was gone as soon as I put the air damn on.

Just my .02

 

MTPFI-MAF is right...if you dont have the air dam you need one. They were designed mainly for highway driving. Thats when they cool the rad the best. Also, I am sure the problem is minor. You just have to use process of elimination to find it. Dont replace water pump for nothing unless you really want to upgrade anyway. Too many people here lose patience and start replacing things. Parts cost money. Fluctuating temps within 10 to 20 degrees are normal. If you have an electric fan setup, thats how they work.