Just purchased a 2003, not Z06.

The water temp is around 240/250 at idle, and it wasn't hot today.

Highway temp is around 220.

This seems high, is it correct?

Thanks in advance.

 

Too high.
First thing I would check is your coolant level. Then I would check the upper radiator hose after the car has cooled down to see if it's sucked in, that would indicate a bad radiator cap. Then I would run the car and feel the upper radiator hose to see if it gets hot and coolant is flowing through the thermostat. Then I would check to make sure there is no air in the system. If all those things check out then it might be a bad water pump, but that would be the least likely in my opinion.

 

You should also check to see that there is no debris in front of the radiator - these cars are bottom breathers and they have a tendency to suck up leaves, plastic bags, etc. when traveling down the road.

 

I purchased a 2003 C5 last August. To be on the safe side (on a 10 tear old car), I had the seller change the oil and coolant, and shortly after that I had my dealer change the manual transmission fluid, differential & brake fluids. You made need to have your thermostat replaced.

 

Sorry.

It was around 190 at highway speed, and 240/250 at idle.

About a 50 degree temperature swing.

 

240-250 is still way too high... it should run in the 220s the way it is set up from the factory... 190 while cruising is fine, the reason it drops is because of the increased airflow past the radiator... I would do what everyone has suggested, check coolant level and make sure there are no air pockets in the system, check all the hoses, check for leaks, make sure there isn't any trash clogging the radiator/condenser, etc... you might also go ahead and get a new thermostat and have a tuner change your fan temp settings so it will run cooler

 

The highway temps are good. Idle temps are too high.

Next time the car is up to operating temp, let it idle until the DIC water temp gets to about 226 degrees and see if the electric fan comes on - you can see and hear the fan if the hood is up and you are standing near the radiator. If the fan doesn't come on, then start looking at fan relays and fuses to start debugging the problem.

 

The above is the info you want. Your highway temps are fine so the coolant side of your system is likely good. Check for debris blocking the rad and then check the fans operate at the temps as posted above. Keep the AC off and at 226* both should come on equally running slower so they won't be too noisy. If the temps keep climbing then at 235* they'll kick to a faster speed and really move some air. If it's cooler out probably 75* or cooler, then it should just need low speed to keep cool. My guess is you have a fan issue, possibly you only have one working.

 

My 01 Z06 was doing similar, but worse. It was around 220* on the highway and up to 230* or so in traffic. I had to blow out the AC condenser and the radiator from the backside with compressed air. Now all is good. I blew out a lot of thick road debris, pollen, air blocking type stuff.

I bought this item: http://www.northerntool.com/shop/too...6518_200326518


I cut if off right below the 45 bend and further bent it to 90degrees in my vise so there is maybe less then 1/4 inch after the 90* bend.
(EDIT): This wand also extends to double the length by loosening the fitting and the inner tube pulls out. You can also rotate it so the right angle bend is at the angle you need to get the wand fully down into the areas you need to blow out. Works beautifully!

Then remove your air intake tubing in front of the throttle body and pull the top plastic piece off the radiator. This will get you access with this extended wand to get behind your AC condenser and blow all debris forward.

You can then pull your plastic fans shroud back by hand to just give enough clearance to get this wand behind your radiator to blow out as well.

I then used a toothbrush taped to an extension, to gently brush the front side of both the rad and AC condensor to get all sticky debris off the them, and reblow it again from the backside. After the second reverse blow, everything was pretty clean.

I probably got almost a half gallon of debris junk out of this total.

I then air bled any possible air in the coolant heads area by removing the front throttle body coolant tubing from the front head bleed port bypass tube and let about a full quart of fluid come out. I kept it clean by using an extension tube (36inch) connected to the front bleed port crossover tube outlet, with a rag under the connection, and ran that down to a catch pan for the coolant. After that I just topped off the overflow tank, as that was about 1/4 full only at that point.

Now it runs 195 on the highway and when moving and shoots up to 220 in slow traffic. As soon as I start moving again, right back down to 195 ballpark or so.

If I have any further trouble this summer, Ill try the reverse blow with a water wand, as I hear that may work even better then air.

 

^^

I took compressed air and blew (from the inside/fan side towards the front) all of the debris from between the radiator fins and it cooled my temps down about 8 degrees. I was suprised at how much stuff actually came out.

Good luck

 

A platic shopping bag was blocking the bottom half of my radiator and it only ran hot at an idle or stop and go.

 

if all else fails post 12..Drain the coolant from the heads

http://forums.corvetteforum.com/c5-t...erheating.html

 

235* idleing is about all you should see EVER. The fans run when the AC is on and should keep things cooler a bit longer.

BUT....remember that our C5's are "bottom breathers" and rely on the fans for air moving across the radiator when at rest. The first fan speed operates about 225* and then the second at just over 230*. For me, that is WAY too late.

I see mid 220's in stopped traffic, but quickly back to 190* when moving for some distance.

Best part, there is a "limp home" mode built into the CPU if in the event it gets too hot.

Watch your temps, but don't stress over it if you know all systems are up and running well.

Good luck.

 

not sure why folks just don't replace their cooling systems at 10 years.

new water pump-thermostat, hoses, radiator, problem solved

scaling, debris, seen too many people spend countless hours trying to figure out a really simple problem

i would first verify the fans working, once that is confirmed change out the cooling system

if you shop smart all the parts can be had off amazon with a total shipped cost of $500 for the entire cooling system short of the plastic tank. add $65ish for one of those if you need it

 

fuse doesn't have an expected running life

cooling system is a consumable

it's not throwing parts, it's standard maintenance.....which most car owners neglect

the c5 sucks a lot of debris into the radiator and it's a major bear to try and get it out. a good air gun will get 30-40%. a new ac delco radiator is under 200 shipped via amazon

and you can pound sand about the touching your car comment. why you would suggest someone who does actually maintain their cars not touch your shows a lot about what you do with YOUR car

your ignorance just irritates me which is why i'm being a bit brash. there is no standard test to check for cooling system heat transfer in a radiator. you can't see scaling and you can't see reduced heat transfer. i still have my ASE cooling system test book on the shelf behind me and there are specific tests for specific reasons but the c4 and c5 are two cars that need time interval radiator replacement if you want to stay running in the cooler end of the range. something like a jeep cherokee may go 20 years on the OEM radiator if the coolant PH is correct. totally different design

standard tests like a radiator pressure test and fan check are a given. if you have an issue there you crawl it to the source. most the time you don't and the radiator is the problem

 

03 Z06 was getting hot today. I dont have much time in the car, but noticed that the temps were much higher than I have seen before. It was sitting at idle for a long time today during a smog check. On the freeway coolant temps were 190f, and it would climb steadily to the 230f region once stopped. I checked fan operation and they run when the AC is on (and the temps drop quickly) but they do not start at the 226f mark as they should. There is also nearly 1/4 of the surface area of the radiator blocked with leaf garbage. I have no started deep troubleshooting yet to solve the issue.

 

when are the fans coming on with ac off if you just have the car parked idling?

 

They are not. The fuses are OK so im wondering if it is a relay or possibly something deeper. Like the ECU is not reading the coolant temp and then not firing off the fans.

 

Clean that crap that you say is blocking it and you should be gtg. 235 is when the second fan comes on or 236. I know 8vette7 has the fan operating temp from the manual. So do I if you search my user name. You are chasing nothing your car is running exactly as it should with factory setting. If you want cooler temps get a 160 thermostat and have your fans reprogrammed. I'm posting from my phone if you can't find the post I'm talking about when I jump on a PC ill paste it up here. You are chasing nothing.unless its still going past that like your first post said.

 

you found your first problem

cleaning the radiator is a great idea and all

but fans not coming on when the engine is at 235 is a big deal

start troubleshooting.

fan relays are cheap

part number is D7065c

all of $4.16 ea at rock auto. if i remember right there are 3 of these for the cooling fans right there by the battery