Hello everyone. I've been struggling with cooling issues on my 1996 C4 LT1 for quite some time. I have been scouring these forums, doing my due diligence before reaching out for assistance. I understand these cars run hot but I don't think what I'm experiencing is in the realm of normal.

The Story:
I've had this wonderful Vette for about two years now. I bought it at around 103,000 and I've put ~8000 miles on it since. I've typically done well by only driving it when the temperatures aren't above 85F. When I drive my C4, I'm pretty paranoid about my coolant temperature so I always have the digital cluster set to display coolant temp. I recently got a new job and it's about a 15-20 mile drive. I've been daily driving the C4 as it gets better gas mileage than my truck.

I'm in the Midwest and today it reached about ~92F. There was some stop and go traffic on the highway. Went anywhere from 10mph-35mph for about 15 minutes before it cleared up. Even then, it was only hovering around 210F. Once we got back up to 60mph, it started dropping per usual. I've noticed that as long as I'm going highway speed, the car is adequately cool. As a baseline, when it's 60F-75F, I've seen my coolant temps on the highway however between 165F-190F. Seems like it does fine on the highway!

Idle is a completely different story...

I stopped at my local fast food drive thru for some food but they were moving slower than usual. Outside temps are still~91F. My temp was at around 208F when I ordered my food and by the time I picked it up (10 minutes later), my coolant and oil temperatures were at 244F. I have confirmed that both of my radiator fans were working prior to this event. As I've said before, I'm pretty paranoid about my coolant temps and I've tried some of the basic tests that were mentioned in past posts with fellow owners dealing with high coolant temps (waiting until 228 to see if the Primary kicks on, turning on the AC to ensure the secondary spins, etc).

The Primary fan came on at 228F. Once the fan kicked on, I started seeing my coolant temperatures bouncing back and forth for a little bit but the temps still slowly climbed to 238F and then the secondary kicked on. Even with both fans spinning, it still crept up to 244F. I got my food from the window, started driving away and then I decided to turn on my heater to help drop the temperatures a little bit. I set it to the highest temperature possible (I have the auto climate system) which is 90F and I started feeling the heat come through the vents. After about 5 seconds, I noticed steam coming through the passenger side of the hood. I immediately knew something happened with the cooling system.

Thankfully, my house is only 2 streets away from the fast food place so I limped it home and shut it off immediately. I found that it was the heater core hose that has the one-way valve (please correct me if I'm wrong). Seems like it was under immense pressure and it exploded. I already ordered a replacement from Corvette Central, and I also ordered new radiator hoses while I was at it, as they were pretty squishy.


Video:

Final Thoughts:
I don't know if the thermostat is bad but I'll find out once I get the replacement hoses in. I saw something about a possible heater core flush but that doesn't explain what is causing my C4 to overheat at idle with both radiator fans engaged without the AC or Heater turned on.
No debris or leaves were in the usual places in the radiator or AC condenser.
I verified there was coolant in the overflow tank before and after the hose exploding. I noticed about two months ago that the overflow tank was below the cold line so I filled it back up to the proper level.
Replaced the radiator cap on the black expansion tank.
Possible water pump issue?

Does anyone have any recommendations on what else I should be looking for? Apologies for the wall but wanted to provide as much info as possible. Thank you very much in advance.

 

You hit.the correct things and yes in slow traffic they do climb but this what I found, don't be up the *** of the car in front. Give a little extra space sucking all the hot air from the car in front will drive my car over the top and I live in Florida so heat can be an issue.

You might want to take the hoses off of the radiator and look at the inner cores, for all you know Previous owner may have poured many bottles of stop leak in and you now have a cinder block for a radiator. Also make sure your coolant is properly mixed.

 

I had a similar issue with my LT4 C4 immediately after buying it. I sympathize with you on this! It is frustrating. The car ran way hotter than I had expected and at one point the coolant in the over flow was boiling. Instead of continually trying to root cause each component in the cooling system I went nuts and am replacing everything. Flowkooler ater pump, Dewitts radiator, thermostat, all rad and heater hose - and eventually fan reprogramming.

Hoping you get to the root cause of this and can enjoy the car.

 

Will do. I'm going to be tackling the job today since my replacement hoses came in. I will update the thread with my findings once complete.

 

Everything has been working as expected. The new hoses have been holding well. I think I have found out why my C4 has cooling issues. The previous owner replaced the stock radiator with an aftermarket one. However, the aftermarket fans that came with the radiator are absolutely junk. They barely cover any surface area and there was no shroud around it either. I'm going to save my money up for a Dewitt single + fans.

It explains why the C4 did fine on the highway but not in idle/slower speed situations. The fans were barely doing anything, which is why the coolant temps wouldn't drop below 238 even with both fans on. Thanks everyone.

 

try a 160 degree thermostat as well as a fan switch at a lower temp
Try Lingenfelter or Summit.