I'm a very novice C3 owner. I had my 75 out on a drive and after about 30 minutes of driving the driver behind me pulled up and let me know I was leaking coolant. I looked down at the temp gauge and it was also climbing into the red. I pulled over, opened the hood and noticed immediately that the radiator cap wasn't properly secured and that was the source of the coolant coming out (I had previously had a fluid flush and they must not have gotten the cap totally on). When I got the car home I had no idea how much coolant was lost from the radiator (I assume it was a decent amount). The reservoir is still reading like it doesn't need coolant to be added. I added about a quart to the radiator, started the engine and let it run for about 4 minutes to see what the temp would do which after about 4 minutes of idling kept climbing to about 200 on its way higher, before I turned it off.

Is the problem of temperature just not having enough coolant in the radiator to start, after the coolant loss? Should I just keep filling up the radiator (how much) or trust that it will pull from the reservoir and give me a better idea of levels? And should a proper amount of coolant (when I get it there) keep the temp down, unless there are other things going on, such as a bad pump or thermostat potentially. Really appreciate the help and insight

 

Before I went down the road of the thermostat etc etc I would make sure there are no air bubbles in the system. You obviously lost a good amount of coolant and these cars are very particular about refilling them since the radiator is so low. Do a search and read all you can about burping the system. A very technical term but a good first thing for you to learn. Actually the first thing you should have learned is never go back to the place where you got the flush. Welcome to the club.

 

The radiator needs to be full, full. To the very tippy top. Absolutely no air in there whatsoever! Run engine with the car up on ramps, front end high. Get ALL the air out. Cap it up just as the thermostat opens. Leave it up on stands or parked on a hill. Let it cool overnight. Top up the overflow tank. Should be about 1/3 full when cold. Then try again.

 

wait for it to cool completely, fill it with the correct coolant. Check your oil for coolant, it should still look like oil and not have any white foam or goo on the valve cover cap or the dip stick. you can run it with the radiator cap off and wait for the thermostat to open, you should see the coolant start to circulate, the level should drop a bit, shut off the car and refill the radiator and put the cap on , then add water is needed to the reservoir. At this point the coolant is hot but not at the boiling point so you will be fine. If you are afraid you will get burned leave the cap on tight and drive it until you get up to 200 and then bring it home and let it cool and refill as needed

If it doesnt circulate well then your thermostat is sticking and should be replaced.

 

Woody123,

Use a 50 / 50 mix, with front end on ramps. Let it idle . . . . . . . . . . . .a long time, Rad Cap off.
Do not rev it or the waterpump will pitch everything on the floor.

Never use "tap-water". Too much crap that the cast iron does not need.

I like to leave a couple inches of space below the filler neck to allow anything that wants to leave the Rad, room to leave.
That is how you burp them.
Note the flow of coolant at idle. Lots of bubbles surfacing, going by the filler neck.
Only top-off the Rad when you are 100% sure it's done burping.
Never put the Rad Cap on until its ready to drive.

The overflow / Rez will replenish the Rad only after a complete cool-down. The Rez does not push coolant uphill to the Rad, but rather the Rad syphons (vacuum) coolant out of the Rez tank.

Consider adding a bottle of Red Line Water Wetter to your Rad. That stuff really works in lowering temps.

 

I've always refilled from cold with 50/50 mix as others have mention. I start the car with cap off. If it draws down or is low from a leak add till a few inches below. Run with cap off until thermostat opens. You should see level drop and flow inside radiator. I slowly fill up and let run making sure all air is burped out. Maybe 5 to 10 minutes after thermostat opened. Put cap on before turning off motor.

After this is done take of and watch temp gauge. If you have high temps after the car could be missing foam gaskets sealing shroud to radiator. Air flow through radiator is critical on these cars.