Radiator Venting Overboard


Ran the engine for the first duration run to check for proper engine cooling. I have a canton fill can with 16lb radiator cap. With the engine at 190 degrees, I note the overflow tube is releasing anti freeze. The hot side of the radiator is warm to the touch, the return side is very cool. Temp rose slowly and seemed stable at about 192. I haven't added a catch can YET, but wonder why the system is venting overboard at operating temperature.

Thermal expansion, the coolant has to go somewhere as it expands. You probably had the system "overfilled". Once it reached temp. Did it stop venting?

Ian Anderson

Lifetime Supporter
I presume it is just the fluid expanding with temperature.

On the GT40
Fill expansion to top
Get up to temperature and about half a litre comes out.

Leave it at that level and it never goes any lower

Actually it did not start venting until it reached temperature. After it cooled off a bit I looked into the fill can and it is about at the half level point. It leaked about a cup and a half but I shut it down before it stabilized.

If I run without a cap on and bring it to temp, will that prove anything?

Ian Anderson

Lifetime Supporter
I would expect your cup and half may go closer to two cups when at full operating temp and fans cycling on and off.

After that it should not lose any more and that is the level it will run at.

I actually carry a straw in my car, marked at the normal level as a dipstick as my tank is aluminium and seeing the level is thus very difficult.

Your car may also be burping out air bubbles a which normally happens when they first get started.

Oh I would not run without a cap.

Thanks Terry & Ian.

The "dip Stick/straw" is a novel idea.....

Drove to the Summit and picked up a catch can for the overflow. Having the summit within an hour is very expensive...LOL

Terry Oxandale

Skinny Man
Something I did for my LS was to install a Presta valve at a high location, tapped off of the OEM steam tubes on the heads. After coolant maintenance and refill, I would heat cycle the motor a few times, and each time that I shut the motor down (more accurately, shut the water pump off), I would release the coolant system's pressure (typically only an air release), which brings the hot coolant system back down to ambient pressure, thus causing immediate withdrawal from the overflow tank back into the coolant system as the motor starts cooling down. This process reduces the number of cycles by which all the air is finally evacuated out of the coolant system (I initially start with the AirLift refill tool, but that still does not remove all the air). Usually, the third or forth cycle results in some coolant being released out of the valve, which coincides with a quiet water pump (lack of water in the system) again.

Always nice to be able to access something without having to lift off or raise a body panel :).

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