Hey Guys,

I've done my fair share of searching but wanted to make a specific post. Here's what's going on. The last week or so my car has randomly been spiking up to the point in temp where the temp gauge is pegged @ 260 and the DIC reads temps at 270. Every time I was about to pull over and it would go back down to normal temp. I have not been driving it, had to yesterday though, and sure enough she his 271 on the freeway and did NOT go back down. Went into reduced power mode and I was able to get her off the freeway quickly, park it, and got it towed back home.

I just got done replacing the thermostat AND checking the fans. Both are working (turned on AC to double check both were on and to see what temps would be IDLING with BOTH on). Sure enough she got up to 237 and just stuck there IDLING. Somethign is not right. Does this mean the thermostat I Just replaced was probably not bad? Seems like it!

I'm not sure where to go from here. Fans work, thermostat replaced..I need to check for debris on the radiator.

Any advice here would be appreciated. I had all day tomorrow to diagnose it and check it out.

Thanks,
Zach

 

Check to make sure you didnt pick up a plastic bag or something on the radiator. It can happen very easily!

 

That would affect it just idling in terms of temp?

 

Both

take a high pressure air hose and blow all the sand, dirt, straws and dead miatas you find in your radiator and ac condenser. makes a world of difference in engine temps

 

my 04 z06 is overheating . First noticed it at the autocross after a hard run it was sitting at about 250 . Another vette owner told me to turn on the ac so i did and the fans kicked on after about 2-3 minutes it was down to 220 and holding . Not so great not getting better now i notice this 220 is the norm in city driving hwy she gets down to about 190 and hold which is much better . I'd love to know a resolve for this myself .

 

i'll check the above mentioned tamorro and check back in on this tread

 

Pull the air filter assembly and radiator shroud off. If I was doing it over I would try to get my hands on a pressure washer. Air and water hose still left some bugs behind but it stays on 212 now. Mine never got as high as yours though. It made it to about 235 and I couldn't stand to watch so I pulled rad and flushed everythying then went back with new coolant.


Afterwards I put a piece of 1/4" hardware cloth over the bottom openings.


Got my first indication this was working yesterday. Pulled up in front of the garage and when the fans shut off a pile of leaves fell down under the front of the car.

 

Ok, the engine temperature is not going to drop 60 degrees that fast. Are you sure the coolant is really reaching that temperature? Perhaps you have an indication problem.....

 

Lot's of overheating C5s...

 

Are you sure you don't have air in the system. My buddy changed out his coolant, topped it all off, everything appeared good. We started out on a long trip and suddenly the temp was way into the upper 200's. We went and got some water, topped up the overfill tank while idling and squeezing the hoses and all is now normal.

 

Check your antifreeze level....it should not be filled to the top. There is a cold level mark on the front of the tank to show the proper level.

 

Do you remove the radiator shroud(s) to do this?

 

yes I did and jack the car up.

I also bought a baby bottle brush and put a wire coat hanger wire on the end of the brush handle.

Ran the bush up and down between the radiator and AC condenser. man did the crap come out.

Also the high pressure air hose with a long thin tube wand. That blew even more crap out.

you guys would be suppressed how much dirt, sand grass and just garbage gets sucked up there.

I also have a screen now. It prevents large things but not dirt and sand from getting at the radiator

 

If you want to leave the radiator in the car then pull the fans and the front shroud. A pressure washer should be the ideal tool to blow all the crap out but I didn't have one. I was pulling my radiator to flush anyways. Make sure you tape off any hoses and the throttle body.

I'm thinking of trying some window screen over the hardware cloth. It might be to restrictive though.

 

whoah whoah whoah... easy with the pressure washer idea. those cooling fins that direct the air over the exchanging tubes in a uniform fashion are very thin and bend extremely easily. ill put money on it, that if you take a pressure washer do it youll lay some over. i just pulled the 4 10mm head screws off the top of the rad. and dug out some by hand, and used compressed air GENTLY to get the remaining crap out. i dno wher ethe guy had been driving but htere where leaves, red dirt, and animal hair just totally packed in the top 6" of the radiator on a 10K mile car.

 

Your description sounds like normal operation to me. When the temp got down to 219 the fans cut off as they are supposed to do.

Bill

 

Also make sure that front middle piece of cowling didn't get broken off. If it's missing and air isn't getting deflected up you will overheat as well....

 

the pressure washer is too strong. Even a garden hose is can be too strong

that is why the air hose.

the screen I use is 1/4" x 1/4" chicken wire not window screen. Window screen is too flexible and will get clogged up with grass too.

have to get use to cleaning out the radiator and ac condenser once a year at a min.

Bill brings up a good point.

What are your operating temps?

coolant needs to be between 200 and 220*F any colder and it will not boil off crap. Forget 160* t-stats, those dont allow your engine to get up over 200 which you need. IIRC most LSx engines provided the most HP at 205-210* F coolant and oil temps Significantly less HP for coolant Under 180* and over 230*

Oil temp at least 180* but 250-260* for track days / racing is A GOOD THING


Coolant I use water and 2 bottles of water wetter. No coolant. I am far enough south that it seldom freezes here and I do have some heat in my garage. Plus by vette is a tack car. Wife's vette and pickup are normal coolant.

Several years ago I cleaned out the radiator and ac condenser then did a three day track event.

when I got back I clean out the radiator and condenser again

The pic below is from three days of hard driving ( floor was clean prior )



Now take several years of NEVER cleaning out the radiator and condenser

 

Wow I didn't know my thread was still going. Anyway..this is where I'm at right now.

I am going to be picking up the car from the bodyshop Wednesday. I went by today and we pressure tested the system and it was holding consistently (I believe 19PSI). So up to this point:

Thermostat has been replaced
BOTH fans are working
System is holding pressure
Got some leaves/junk out of the ac condenser/radiator. I wouldn't say it was a ton but there was definitely some junk in there.

Tomorrow they are going to flush/refill the system and bleed it. I guess I need to wait and see how this affects it and go from there.

I don't think it's the water pump but that is a possibility right? I've read that it's rare for them to fail and that if mine HAD failed it would have overheated much faster than it did when I changed out the thermostat. The car actually didn't overheat that time but I just let it idle and warm up. It took a good 5min but it DID get up to 238 and was holding there.

One other thing. My middle piece of the cowling was in fact missing for two days I believe. I know this will affect cooling and will not allow it to get the correct airflow.....but the car got up to 238 while just idling so this leads me once again to think it's something else.

Any advice here would be greatly appreciated. Is it possible from the light impact from my rear ending somebody @ 5MPH could form a bubble somehow in the system?

 

ADDITION: I just went back to the top and I did not describe what I did before all of this started to happen. I rear ended a car (DOH!) and this overheating issue arose within a day or so afterward. I was only going about 5-8MPH @ the time of the accident and was able to get on the brakes so I did not hit the vehicle in front of me with "full force". The bodyshop found no damage to the cooling lines/hoses etc. What could have happened from rear-ending somebody that would lead me to this issue? There is no obvious psychical damage to anything whatsoever in relation to the cooling system.