Tech Question for My Geo Metro! - Boiling Coolant in Overflow

[opponheimer]

Car doesn't overheat, doesn't smoke, plugs are clean and dont smell of antifreeze.

After driving the car and in hot weather, ill stop. Open the engine bay and i'll hear collant boiling in the overflow.

From past experiences I've heard that this could be one or a combo of the following:


Bad Radiator cap - already replaced
Bad Headgasket
Bad Thermostat
Bad Waterpump
But the one kicker is, after the car is warmed, and overflow is already boiling, when I try and start the car, coolant will try and spray out the overflow and purge all over the ground. The car will also not start either. It doesn't smoke in the process though.

When the car cools down almost half the coolant is gone and i refill and it starts fine.


Please help :)

[Phlip]

For what it's worth, I had a similar issue with my 240, but instead of shooting it all back in the overflow, it would blow a hose... I replaced the hose, waterpump, thermo, radiator and cap, and bled the system thoroughly 5 times.
Guess what? It still did it, but has not since I replaced the head gasket.

[burnsauto]

when you refilled the system...did you bleed it out? if you have enough air in the coolant system, you'll have problems like this.

[Phlip]

^^^ Good point, my answer is provided you HAVE thoroughly bled the system (with the heat on, don't forget).

[opponheimer]

Hey guys I just did a little test, i opened the radiator and topped it off, started the car and let it ran for 10 mins with the radiator fan unplugged.. i left the rad cap off and the coolant level never once dropped down and the coolant didn't flow at all.. The top coolant hose from the thermostat to the radiator was cold, while the bottom block coolant hose was extremely hot.

Am i to assume this is the thermostat? Should I be worried that I have damaged the engine if it has been ran like this for over a hundred miles in intense heat of the day?

[Somnambulist]

Like they said above. I would guess you have air in your coolant system. Have you tried flushing the system properly, refilling with new coolant, and bleeding the system again?

[opponheimer]

Like they said above. I would guess you have air in your coolant system. Have you tried flushing the system properly, refilling with new coolant, and bleeding the system again?

I don't have air in the system, and thats not what they said. I'm leaning towards thermostat.

[NismoS13Chuki]

throw in the new thermostat and see where that puts you

[lazierhobo]

clip the thermostat, gives you proper flow so you dont have problems reaching operating temp, and you never have to worry about it getting stuck.

had the same sort of problem in a subaru. replaced everything in the cooling system, bled the system with snap-on vacuum bleeder still even the new thermostat kept getting jammed....took the thermo out and clipped it....6 months later still running strong. worth a shot, its the zero cost fix if it does happen to be the thermostat which it kinda sounds like from what you have said.

[opponheimer]

what do you mean by clip the thermostat?

[lazierhobo]

cut out the center section with the heat activated valve. this way there is always a inch wide hole in the middle that water can flow through.

the only purpose of a thermostat is to make your car heat up faster so that you can have cabin heat. also if its cold out you want the engine to heat up, but its summer out and the thermostat is doing nothing but probably causing you a lot of problems.