Hey guys,

My 03 Z is overheating.

I jumped in the car, 50 degrees outside 2 days ago. The car jumped from a normal 190-210 to 260 and overheated. I shut it down, got out of the car, and all looked ok.

So first, I don't know a lot about these cars, it's my first vette. I do know they have dual fans. I warmed the car up after I let it sit for a few hours. The temp jumped to 230 in a few minutes. So, I turned on the AC max with heat, and it brought the temp back down to around 205. On the highway, the car runs a perfect 190 with no AC on.

So, is one of my fans out? I went by the Chevy Parts place, talked to a guy named Mark at Davis Chevy in the service station. He immediately told me that one fan was out and needed to be replaced without looking at it. 310 bucks for parts and labor.

However, I'm curious if there is a sensor or thermostat that could be the problem. The car will jump from 230 to 190 in 20-30 seconds just by driving at a higher speed and turning the AC(second fan) on. I just don't see the coolant temp dropping 40 degrees in 20 seconds regardless of airflow or the fan on. I don't want to get hosed by replacing the whole fan if something else is wrong.

Any suggestions or test are welcomed, and I will report back to you guys with what the car does. I have to run the AC in traffic to keep the coolant at 200-215. Thanks

Mark

 

Do some more diagnosing first. I would recommend NOT letting Davis Chevrolet anywhere near your car. Serious.

Possibilities could easily include a faulty/failing ECT sensor (driver's side cylinder head behind/under alternator), debris blocking airflow through radiator (leaves, plastic bags), low coolant level, erratic and/or failing thermostat, faulty radiator cooling fan, faulty radiator (expansion tank) pressure cap, or any combination thereof.

I would focus on airflow and sensor first, provided coolant level is confirmed as OK. Especially if this problem just occurred "out of the blue" so-to-speak and is not something that has been building over time.

P.S. Amazing how "Mark" can make such an accurate "driveway diagnosis".

 

LOL, I ran over a plastic bag 2 weeks ago, posted about it here, and it smelled for 8 days, even over a 300 mile road trip like burning plastic.

Problem is, I don't have any tools, they are all my river house, and my only car experience is 2v mustangs. I am not a gearhead and only learned by working on my 3 2v 4.6 mustangs. I don't know where to start on any of this stuff. I would love to go by England Green but don't want to be treated like "the little guy". Do you know anybody here in the Houston area that is educated and can give me a fair diagnoses on my car without having to wait 1 month to get in and ripping me off on undo parts and labor?

 

There are several choices that I have heard over the last few years, including Corvettes of Houston (I've had a couple small things done there) and there is another business out in the NW area whose name escapes for the moment.

BTW, even though this is probably not something severe, give Jason or Stephen at EG a call, and even if they are unable to help you themselves, they are stand-up guys and could point you in the right direction to someone who can.

If you don't get more responses here in the next couple days, post up over in the Southwest section too.

 

On the C5 both fans are turned on and off at the same time. There are relays that control the speed of the fans. Here is the description of how they operate and are controlled.

Cooling Fan Control
The engine cooling fan system consists of two electrical cooling fans and three fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage and ignition 1 voltage from the underhood electrical center. The ground path is provided at G102.
During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the cooling fan 1 relay coil, closes the relay contacts, and supplies battery positive voltage through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan 3 relay and the right cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the PCM supplies the ground path for the cooling fan 1 relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the cooling fan 2 relay and the cooling fan 3 relay through the high speed cooling fan relay control circuit. This energizes the cooling fan 3 relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the cooling fan 2 relay coil is energized closing the relay contacts and provides battery positive voltage on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.
The low speed cooling fan is commanded on when the coolant temperature reaches 108°C (226°F). It is turned off if the coolant temperature lowers to 104°C (219°F). The high speed cooling fan is commanded on when the coolant temperature reaches 113°C (235°F). It is turned off if the coolant temperature lowers to 108°C (226°F). When the A/C is on and the coolant temperature reaches 85°C (185°F), the low speed cooling fan will be turned on at vehicle speeds less than 56 kPh (35 mph).

As you can see 230 degrees is nothing to be concerned about. However, you say you saw 260. Given the temp drops to 190 when on the highway it seems there may be a problem with a fan relay or fuse at one of the settings. Check to see if the fans are running at low speed. Since they are in a serial circuit for low speed operation anything that interrupts that circuit will keep both fans from running. During high speed operation one or the other fans could operate since they are configured in a parallel circuit and don't depend on each other. Here is the schematic:

Bill

 

Good tip Bill, and that brings to mind yet another possible source: cooling fan relay(s).

 

Bill, Lonestar, and all others, thanks for the help!


Lonestar, thanks for advising me not to bite the dust and fork over the cash to the stealership.

I took a look at the car myself, just low on coolant. It was full 2000 miles ago, but I ran over a bag and figured it could have messed up a fan. Turns out the fans are fine. I feel like a retard.


Looks like the car just has a small coolant leak that I can't find. I will probably call England Green and see what they will charge me to find the leak. I hear they are stand up guys.

Thanks again.

Mark

 

just lay on the gournd and look up under the front bumper into the radiator compartment. I bet there is a lot crap and melted plastic bags, maybe a miata or two stuck up there.

Clean the ac condenser and radiator out with a high pressure air hose, or medium pressure water hose.

 

Or a simple, quick, cooling system pressure check can find it. Takes about 5-10 minutes.

 

Just lift the hood and take the cover off the fuse box in the engine compartment. Look at the drawing under the cover and locate the two big fan fuses. The bad fan will have the fuse blown if it sucked up a bag which is common.

You can try replacing the fuse but the new one will blow once it kicks on if the fan motor is ruined and the fuses are something like $3. Don't think you can clean the fan motor up and try it again, it will just blow another fuse...been there, done that.

New fan is something like $70 at a dealer. Shouldn't take more than one hour to install by someone who's been there before. GM probably has the job time as 2 hours, that's how they really screw you at the dealerships.

Good luck...

 

Fan? Fuses?

 

yep, just open your engine bay fuse box and look. One large fuse for each fan motor.

 

So how's the fan relays and/or fuses going to fix the fans he says are fine and find the leak he said he has?

 

Maybe one of the relays is leaking coolant.......DUH