97rebuiltZ28

To start off, 3 weeks ago I bought another 97 Camaro Z28 from a friend of mine that was totaled 5 years ago for running into a ditch and damaging the front end and passenger front quarter panel. The car still runs and drives and has been started and ran often over the past several years. I drove the car home(about 2 miles).

The car starts up excellently and runs smooth but my question is this: After running for just 2-3 minutes the temp gauge in the car is already at 210. If I wait even just another minute or two it will start hitting the red line, so I of course kill it before that point. The radiator is full of coolant. (The car has a new radiator that my friend installed, he also never ran it longer than a couple of minutes ) The really weird part of this is that after those 3 minutes of running I can plug in my computer and the pcm temperature will be like 90-100 which is similar to my other Z28’s temp after just a few minutes of idling. No codes, everything seems to be put together fine, and no leaks that I’ve found.

As you can imagine, I don’t want to drive it or let it run very long with the gauge acting up. Is it a faulty gauge or do y’all think coolant is not getting into the heads?

Chimera96

LT1/4 motors are reverse cooling so the cooling system needs to be bleed after installing a new radiator. You will overheat quick otherwise

If you did bleed the system, your thermostat may be stuck closed

97rebuiltZ28

Thanks for the reply. I am not sure if he bled the system. I’ll look up the steps on shoebox and try that.

I have one question though, correct me if I’m wrong. I was under the impression that, since it is reverse flow all of the coolant went to the heads first and then the thermostat opened at 180 degrees to allow the coolant to recirculate through the radiator to stay cool. Am I wrong? That’s why I don’t understand why the heads are getting hot since the coolant should be hitting the heads first.

Chimera96

T stat opens up "circulation"....be it heads or block first...until any T stat opens there is no circulation

Try bleeding first

You should feel the radiator hose get firmer and get hot when the T stat opens

If you have scan ability that would show coolant temp also.....to compare against what dash gauge is showing

97rebuiltZ28

In my first post I was saying that I plugged my scanner in and the pcm temp would be like 100 degrees when the gauge showed 210+. That’s why I’m scared to let it run for long enough to get it circulated. Is the gauge wrong? I never ran into anything like this in my other Camaro when I engine swapped it.

Injuneer

Test both temp sensors and the wiring.

Courtesy of Shoebox:

4th Gen LT1 F-body Tech Articles

If you have an air bubble in the driver side head, it’s going to affect the gauge coolant temp sensor in the head. Is the steam pipe that runs behind and connects to the heads and vents air and steam into the radiator still in place?

97rebuiltZ28

I will check them. I’m pretty sure the steam pipe is still there since it was wrecked while being a daily driver and he didn’t touch anything in the engine other than replacing the damaged radiator as far as I know.

Chimera96

The gauge temp sensor is on the head. The PCM temp sensor is on the front of water pump.

without "circulation" the temp sensor on head would read higher since no coolant is circulating until T stat opens

as noted check wiring ad sensors per shbox site

My best guess is you have air in cooling system if radiator was replaced and cooling system was not bleed

or the T stat is sticking closed

bleed system first and see if problem persists. If so pull T stat. You can put it in a pan of water and boil it to see if it opens. Stock T stat should open completely at 180-185 degrees. You would need to re-bleed the system again if you do replace T stat

93z28maro

Great info I have the same kind of issue on my 93z. Takes longer though about 20 min in stop and go traffic when the temp goes up. But then when i drive it goes down. Guy I bought it from put a new radiator in it as well.

97rebuiltZ28

LT1 engines run pretty hot, especially when idling, or in stop and go traffic. Whenever I’m cruising in my other Z28 it runs about 190 but if I am in stop and go traffic or let it idle it’ll get up above 220. The LT1’s fans are programmed to turn on low at 226 degrees and high at 235 degrees. Also if you have A/C and you have it turned on fans automatically come on. I usually have my AC on and that will keep the temperature pretty low.

RUDEDOG

Your scanner probably reads in Celsius so you need to convert.

97rebuiltZ28

My scanner reads in Fahrenheit. No worries though, here in the next couple of weeks I’m going to get it all sorted out and I’ll check back in with the solution.

97rebuiltZ28

It’s been a couple of weeks now, and I finally got a chance to work on it a little. It turns out that the main culprit of the problem was the thermostat sticking closed. When I took off the radiator hose connecting to the thermostat housing the hose didn’t have one drop of coolant and had some rust in it. Also there was some surface rust on the thermostat and it was overall in bad condition. I replaced the thermostat and ran the car until it opened up and temps didn’t go to red this time. I didn’t have much time today so
I’ll recheck everything next time I’m out there to make sure everything else is in order.

Chimera96

Good news. Assume you bleed system again after T stat install

Also after the car cools down it is not uncommon for the reservoir tank to drop some so top that off to fill line if needed