Camarokid95

I have a 95 Camaro z28 and normally the car runs about 225 around town (about 10-15 miles an hour) or so the gauge reads. It was really hot yesterday (91 degrees and muggy) and I drove the car to my local Oreilly's. I went in and asked about a part and walked back out to the car and started it and within 30 seconds noticed that my temp gauge was around 240 and almost to the redline area of the gauge, i quickly shut the car off and later noticed that a little antifreeze had boiled out of the reservoir tank. I waited and the car cooled and i drove the car home, coolant level was still at the full hot mark. I also was able to hear the boiling of the coolant by the radiator while the car was cooling down after i got it home and you could hear it boiling by the radiator and this was only at 225 degrees or so on the temp gauge, is this anything to worry about?? I dont like the car running so hot, i believe the radiator cap is not factory, its aftermarket, should I change it??

Injuneer

The cap should hold 18psi. Have it tested.

Camarokid95

Thanks man, I think i may just go to my gm dealer and grab a new cap. Could the cap be the reason for the boiling antifreeze due to little or no pressure??

C. Joyner

I'm having the same issue...have replaced cracked water pump, thermostat (twice) and hoses, and still having overheating issues. I had the same boiling episode after in stop and go traffic and got it home in the garage. Would it really be because of a bad cap? Any other suggestions on the overheating? I've had my 97 Z-28 for 14 years and never have had a cooling problem. It all started when the low coolant light kept going on and off. Thanks!

Camarokid95

I havent had a low coolant light issue yet, just the car getting hott (around 240) after i shut it off at 225 degrees.

8cylinders>4

yes a bad cap could easily cause your boiling issue, as you know im sure water boils at 212 degrees at sea level, at 18 psi its more like 270 degrees

if your running around at 225 degrees (which is normal in traffic) then boiling your coolant causing hot spots and steam pockets is a guarantee if you dont have a radiator cap that hold the correct pressure, replace it, they're cheap.

As far as the temp increasing after you shut the car off, its completely normal, even when you shut your car off your coolant doesn't stop absorbing heat from the (hotter) combustion chambers/heads... your dash coolant temp sensor is screwed right into the head, it will read higher when coolant flow stops and its still absorbing heat.

Camarokid95

I went to my local GM dealer and got a radiator cap ordered for 14 bucks, i'll put it on and see if it makes a difference. Also, my car has been sitting for the last 2 days and when i took the cap off i realized the coolant was up to right under the cap, is that normal?? In my 97 V6 when i took the cap off I couldnt even see any coolant.

moparman

Yes, the coolant level should be visible and almost to the bottom of the cap.

Injuneer

That's the purpose of the reservoir setup. When the coolant heats up and expands the pressure relieves through the cap, with the coolant flowing into the reservoir. As the coolant cools down and contracts, it creates a vacuum in the radiator, which pulls coolant out of the reservoir, back into the radiator, to keep the level right up to the very top. Without that type system, you would end up with air in the radiator.

Sabin SS

Do you have a 50/50 mixture?

Camarokid95

I think so, i can smell antifreeze on the dipstick.

tgoble

I have a 95 Camaro 3.4 V6. Been thru an overheat problem earlier this year. What a pain! We troubleshoot every possible electrical item on our car and nothing turned up bad. We replaced the Thermostat, both temp sensors that trip the Fan and provide info to the Dash Gauge. My car has one Fan. We tested the fan, the fan motor all good. We shorted the circuit and it tripped the fan on. So nothing in the fan circuitry was faulty. This lead to one thing possibly remaining... The ECM computer mounted on the passenger side on the firewall.

Things you can check.

- Do you have enough anti-freeze
- Do you have air pockets in your system. Have it flushed and re-filled if its been a while.
- Do you fans cut on at around 220? (not certain what the fan cut on temp is for Z28's)
- Do your fans cut on when the AC is turned on?
- Do you fans cut on/off at all?
- Check/replace the thermostat
- Check/replace the radiator cap - you did that already.
- How old is your water pump, it could be faulty or I've read the fins go bad over time getting eaten up by the anti-freeze.
- Can you or mechanic short the fan circuit to see if the fans come on? If they do, check/validate your temp sensors
- If those are good and the fan does kick on when shorted, then you see where I am going with this... If all things check out and you can't seem to find the problem, it's probably your ECM computer.

I can't obviously guarantee this is your problem, but it's worth checking these items out.

I researched this issue online for about a month during our problem and found that the fan circuit going bad in these computers is the #1 problem with them over time.

I picked up a spare ECM at a salvage yard for $50, installed it but it was also bad. Go figure. So I did more research and found a guy in sells them on Ebay and warrantees them for 1 yr (I believe). He will program them to your VIN also with the latest updates that were available.

When the 2nd ECM computer arrived, we installed it and BAM!!! Problem solved. The fan started working again! No problems since!

See SpareECM Link to find your specific model ECM:
http://myworld.ebay.com/ebaymotors/s...id=p4340.l2559

If you don't see your ECM type online, call the guy. I did and ordered mine over the phone.

Hope this helps as I did not have the luck of finding this much info in one posting, so I wanted to offer it to you instead of searching for a month like I did. :-)

Best of luck!

tgoble

P.S. One more thing to check that I can think of.

- Check your fan relay(s) depending if you have 1 or 2 fans. The are in your fuse box under the hood. Swap or replace them to see if they are bad. I think they are $10-15 each at an auto parts store. See your owners or a Haynes or Chiltons manual.