Let me start by saying, I have be experienced coolant seal failure, and know the usual signs. What's been happening with my car recently however has me a bit stumped. For the past couple of weeks or so, I have been loosing coolant. It has differed from my past coolant issues in the following ways;

1. If I start the car cold, with the filler cap off, the coolant level will rise very quickly, all at once, no bubbles. If the cap is on, the coolant will begin to spill from the overflow tank. This is all during warm up. No smoke.

2. The overflowing seems to stop once the car is at operating temp.

3. If coolant light does come on, its only at idle. If the car is revved, the light/buzzer goes off.

4. It never dumps coolant after a drive once car is turned off.

5. Neither the stock temp gauge nor the PFC temp reading ever go above the normal range.

My question is, what are the possible causes considering the symptoms? The car engine was rebuilt about 10,000 miles ago, and has never been overheated.

Thanks in advance for any help.

 

How old are your coolant hoses and caps?

 

1. First things first. Do a compression test

2. You may have an unusually large amount of air in the system. Turn the heat on high and and fan on high. If you have have been loosing coolant you obviously need to check for leaks. You also must realize that as you have been loosing coolant, you must re-burp the system. Use the large funnels that mate to the filler neck to help you diagnose.
Lisle Spill-Free Coolant Funnels 24680 - SummitRacing.com

3. You also may have a blockage somewhere. You haven't introduced any type of aftermarket sealant to the system have you?

 

Go through and make sure each and every coolant hose is sealed well with a nice tight clamp. I've seen something similar, and it was from a 'semi' loose hose clamp which allowed air into the cooling system after shutdown and while slowly cooling off.

 

Thanks for the input guys. As for your questions, The hoses and caps are probably due to be changed, and I have considered that this could be part of the issue. I just couldn't figure out how they could cause the coolant level to rise so rapidly upon start up. No other sealant has been introduced to the system.

I mean its like the only way to keep the coolant from overflowing during warmup is to keep the revs up. As it is, the accelerated warmup is disabled, so the car idles at about 1000 rpm from start up.

 

I had a similar problem a while back with the beeping during startup that went away after the car fully warmed up. Lurked here for a while and turns out I needed to change the radiator cap.

couple months pass by the beeping came back, this time I had to change out the thermostat. (Even if the car was warmed up the "Low Coolant" light and beeeeeEEEeeEEEeeEEEeeep would continue.)

good luck with your car