G203 overheating coolant lose need help..!

Hey everyone so recently I was sitting in traffic and knowticed steam coming out of my bonnet. Didn’t think it was mine till I looked at the temp gauge​:anguished::open_mouth: pulled over had no water in my radiator. And knowticed only 1 of my thermos were working so I’ve been checking daily my water levels some days it needs nothing some day it needs a little bit. Maybe 300-400ml a week took my thermostat out and flushed the cooling also tested it. It shuts off really slowly my heaters are warm not cold also the other day I filled my radiator up and made sure the overflow bottle was full got home and it was way passed full and the radiator was empty I have also check the oil cap it’s not milky also checked the radiator with the cap off no bubbles. The mechanic at work told me this is normal that water will go from the radiator into the over flow but if I leave it it overheats and their is no water in the radiator when I check …?

replace your radiator cap. its not sucking coolant back in as it needs it. its something cheap to try. :slight_smile:

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Moved to question and answers section


Only one fan will cut in the other is for aircon and only runs when it is on. Sounds like a leak somewhere or bad cap like evil said.

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+1 for rad cap.
Check all your coolant lines (there are many on the HC-E) and the two-prong outlet at the back of the motor too. They are made of steel and corrode to the point of failure. [Item No. 85 below]

Section_23052017_1516.pdf (131.5 KB)

Basically, eliminate points where air could enter the system. Let us know if you need more help.

Hey everyone so I replaced the radiator cap and it’s stoped the overflow issue, thought it stoped the overheating though it was all running perfect till one day I was racing off the lights or 3 sets of lights😂. And the revs got to 4-5k and then after the third set of lights the temp gauge went up all the way to h, since then I have flushed the radiator completely their doesn’t seem to be a block plenty of water coming from the bottom outlet. Since then it hasn’t overheated but I haven’t drove it like that again any advice on this the water doesn’t bubble or foam in the radiator or overflow it only happens when it’s revved it also did happen a while ago when I was sitting in traffic before I replaced the cap

Might be worth checking the thermostat.

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I put the thermostat into boil water it opened very slowly I chucked it into ice water and it closed slowly. From the videos I’ve seen it snaps shut

Yes it opened when thrown into boiling water. But it should open before the water boils. I check mine on the stove by heating the water and monitoring the temp with a thermometer noting at what temp it opens.

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I was always told to test a thermostat

Place thermostat in luke warm water and heat slowly on stove top, at a specific degrees (designed for that specific thermostat) it should open.

I then have been advised that you shut off heating and add cold water to the hot water, not dunk it in cold water instantly as it can damage the unit.

Following instructions of a mechanic, he said making a new thermostat instantly hot and cold is likely to damage it and does not simulate what happens in a car.


I always test new ones using FrAsErTaG’s method and a mercury thermometer