DDM7

well my problem started when my stock radiator cracked so i bought a used one i know i should of bought a new one but oh well.it overheated on me on the way home and the engine knocked once when i pulled in my drive way i shut the motor off went inside let it cool off and noticed my radiator was leaking then i changed it filled it with water and never put antifreze in it because i wanted to fluch my system well when i started it it ran fine didnt over heat with the radiator cap off idiling i shut it off and it started boiling over. also my overflow tank is cracked at the top and has no cap could that be my problem or is water not enough to cool the motor i need antifreeze?

DDM7

also i filled it back up put the cap back on the radiator and drove like 20 miles and my temp stayed at 210 but when i cut it off i could hear my waterin the radiator boiling

sthon

What does your temp gauge say? Sounds to me like your cooling system isn't holding pressure once the engine is turned off. Once the pressure is lost it lowers the boiling point.

DDM7

it rises up to 210 after about 5 minutes of idiling but nothing over that.

ol"blue

Well water boils at 212 degrees, and when you turn the engine off it's temp will climb from that 210 reading with no coolant going through it. That causes the straight water in it to boil.
Besides this, running straight water is bad for the water pump. It doesn't have any lubricating properties. I know you stated it was only for the short term.

DDM7

well do you think changing my thermostat and puttinjg in anitfreeze cure my problem

dave1123

IMO, listen to ol' Blue. It's called "afterboil" and was quite common with cars that didn't have pressure systems. Just think; water boils at 212 at atmospheric pressure, your thermostat is probably 210, right? Duh. A good pressure system with the proper coolant and pressure cap will not boil until about 260. If you run it without a thermostat, it will not overheat at low speeds, but will at high speeds because the water doesn't spend enough time in the radiator to expell it's heat. Also, if it doesn't get warm enough, the computer system won't go into "open loop" mode and I'll bet set error codes.

When cars didn't have pressure systems, their cooling systems had MASSIVE capacities. After pressure systems, capacities were reduced by 1/2!

Old Retired Fart. Lots to share.

AND, your overflow tank needs to be vented anyway.

ol"blue

You didn't list what year/engine you have, but I'd say the thermostat is a 195 degree model, as are most for the vehicles covered on this forum with fuel injection.

Morat

Antifreeze doesn't make your engine run cooler, it prevents corrosion and stops water freezing in the system when the engine is off and temps fall below 0C.
Straight water is a better coolant than antifreeze because it can carry more heat (higher specific heat capacity) so don't rely on coolant to make your engine run cooler. Sounds nuts, I know.
in your position I'd check for leaks, and replace the rad cap (its cheap).
Then come back and tell us if there was any change. Don't leave straight water in your engine too long or your cooling system will get bunged up with rust, but if you're going to do a proper flush with a flush product, that won't ever hurt so do that before getting antifreeze in there.

dave1123

Actually an antifreeze/water mix is a "compound" fluid similar to leaded solder in that different ratios change it's melting temperature. Antifreeze compound ratio changes it's boiling temperature as much as pressure does. A 50/50 mixture of antifreeze and water has been found to be the best for raising the coolant's boiling temp the most without reducing the cooling capacity of the water component's ability to carry away heat and still provide adequate freeze protection.