Fluctuating Temperature
Thread Starter
6th Gear
Joined: Sep 2019
Posts: 6
Likes: 0
From: Botkins, Oh.
Fluctuating Temperature
I recently purchased this '87 C4 and had to change heater core, Fun Fun.. Then I replaced thermostat. I still have a lot of temperature fluctuation. 80 degree weather and 45mph engine temp. remains around 190 plus or minus 5 degrees. Then make a couple traffic stops and temp. raises to maybe 200 to 205. Get in town with ambient temp. at 80 and engine temp. goes up to around 213. Then at ambient temp around 80, sitting still temp goes up to around 222 degrees and then I hear radiator fan comes on and RPM raises to around 1200. Temp drops to around 212 and fan shuts off. RPM stays the same, Temp. goes up to around 222 again and fan comes on again and
temp will drop again and keeps repeating this cycle. IS THIS NORMAL???
temp will drop again and keeps repeating this cycle. IS THIS NORMAL???
Last edited by piscestoo; Sep 12, 2019 at 11:04 PM. Reason: Add a couple remarks.
Drifting
Joined: Feb 2006
Posts: 1,423
Likes: 96
From: Magnolia Tx
As far as the temperature goes its 100% normal. The fan doesn't come on till about 228* or so. Temp will go that high if you're in idling along, then drop down to the thermostat setting when you're moving along. The RPM increase is odd. It should idle in gear about 650 i think.(mines a manual so i'm not sure about automatics). I know 1200 rpms is too high if the tach is accurate.
Thread Starter
6th Gear
Joined: Sep 2019
Posts: 6
Likes: 0
From: Botkins, Oh.
Thanks for that info, Benny. Honestly we are thinking the IA valve is not working correctly all the time. I just want to mention that I live in a small farm community here in West-Central Ohio and I am thinking there are only 2 Vette owners here in town. Therefor, not many to chat with. As I have mentioned, my 1st was back in '65 and now in 2019.. LOL.. Long time in ;between. The RPM's definitely increase when the fan comes on. Otherwise there are times when the RPM's will increase to a variable amount and yet, most of the time after warmup 600 to 700 is where it seems to hold.
Drifting
Joined: Feb 2006
Posts: 1,423
Likes: 96
From: Magnolia Tx
Check the car thoroughly for vacuum leaks before you replace the IAC or adjust the idle stop screw. The IAC valve can cause issues. Look close where the throttle crank arm meets the throttle body at idle. There is an adjustment screw that sets the minimum air for idle. The factory put a little plug over the screw head but If the plug is gone, someone has probably adjusted on it. IF it has been adjusted, there is a procedure to set it, don't just "set it by ear". Welcome aboard & keep us posted.
