Hey all, 2004 C5 Z06 here...

I'm having a really weird issue. I developed a small coolant leak after my last track day, so I replaced the water pump and tried a 160 thermostat. It was running too cool - like 170's on the highway. I had plans to upgrade my radiator for track use, so I recently bought an Engineered Cooling Products (ECP) radiator.

I installed the radiator and replaced the 160 thermostat with a new 180. I thought everything was all good temp wise, but when I road tested it, I couldn't get a half mile away without the temps skyrocketing to 230. The higher the revs go, the hotter it gets.. and fast. It slowly comes back down if I let it ide.

I figured maybe I had a bum thermostat, so I drained the coolant, swapped to the stock (known good) 187 thermostat. Completed the fill procedure, let it cool down, topped it off, and took the car out. The same thing happened. Temps skyrocket when driving the car and they slowly come down if I let it idle.

I double checked my sanity by confirming there was no blockage of the radiator core, all the lines were hooked up correctly, and everything was good. I tried blowing out the heater core into a gallon jug. A bit of coolant came flying out, but absolutely no debris. (The heater also was blowing plenty hot when running the car during my coolant fill process, so I didn't really suspect anything was wrong with that)

I figured the only thing that could be bad was my brand new Gates water pump? A little weird considering I know it was working before, but I guess nothing is impossible. I drained the coolant today, pulled everything apart, and pulled out the water pump. The new water pump has the bolt on cover on the back, so I took off the cover and confirmed the impeller spins with the pulley. Nothing appeared to be wrong with it.

So now I feel crazy, I boiled some water and confirmed all three of the thermostats I had were opening properly at their respective temperatures. I looped a rubber hose on the two radiator barbs and then I blew through the upper radiator hose with my mouth and I couldn't feel any obstruction, just a little coolant gurgling from the lower radiator hose that probably hadn't drained from it.

You should also know that with it idling in the garage, I have tried manually activating my "Fan 2" via HP Tuners and it didn't really seem to have an effect on lowering the temps at around the 205 Degree range. I seem to recall my stock radiator even being able to bring the temps down at a reasonable rate if the fans were running at full speed....

Is there anything else I can test here? At this time I went ahead and requested an exchange for the water pump from Amazon.. the new one will be here on the 13th. Should I be pointing the finger at the radiator at this point? It seems like such a simple device....

 

https://www.corvetteforum.com/forums...nt-system.html

Try the above link. I think you need to "burp" your system as you have trapped air.

 

This is the procedure I've been using 😩.

Im waiting for the new pump to arrive and I'll try again and update.

 

i always drill a couple of small holes in the stat…..really helps with trapped air

 

I agree. OP: Get the front end as high as you can, whether it's on jackstands, or on a knoll in the yard, or whatever you have. IIRC, you should leave the cap off the expansion tank, and add the 50-50 mix while someone varies the rpms from idle to 2,500-3,000. Hope this helps....

 

I have always done that, too. My definition of small is 3/32"-1/8".

 

Why do you think you need a new pump? Was it leaking? Was the car overheating? Pumps are very rarely replaced because they arent moving a sufficient volume of coolant. It's usually because they get old and leak....

 

PARTS CANNON! Try burping it several times between cooling and heating cycles. What ratio mixture are you using? Are you sure something didnt get sucked up in the front shroud intake?

BC.

 

I'm not familiar with ECP radiators. But I find it hard to believe a new, different radiator would cause an overheat.....IF the cooling system was burped properly. I doubt very seriously it's the water pump, unless the impeller shaft somehow broke internally. That would be as rare as Unicorn teeth. I agree with others, you must have air trapped in the system somewhere. Bill is right about the parts cannon. Before you buy anything more, install the pump, burp the system, and see what happens ....

 

I got it all back together with an LS1 one piece thermostat to go with the water pump and when I filled the system this time I cracked the passenger steam port on the head and waited till fluid came out. I proceeded with the mentioned fill procedure and all seems well now. It was probably air in the system which is weird to me, but whatever.

By the way hardly "parts cannon," all I ended up buying what a $13 thermostat that matched up better to the new LS1 size water pump. Thanks for the help folks. Ready to race again