84 tecate 3 coolant coming out of radiator tube

[Djj624]

So I have an 84 tecate. Motor is fully built and big bored to a 300. She starts right up and runs great but is leaking coolant from the tube coming off of the radiator fill. I figured bad head gasket but tried my sons dirtbike radiator cap and it seemed to fix it. So I got another used original tecate cap but it's still leaks coolant once warned up. Spark plug is dry and doesn't smell. Could this still be a head gasket or are the stock radiator caps junk?

[Red Rider]

Does it start leaking as soon as the bike is started, or only when it gets hot?

[Djj624]

Does it start leaking as soon as the bike is started, or only when it gets hot?

After a couple minutes of running. Maybe like 3 minutes or so.

[Red Rider]

If I remember correctly, the 84-85 Tecates didn't have a coolant recovery tank, and the manual doesn't show one in the cooling system, so it's normal to piss some coolant out, as the coolant heats up & expands, but 3 minutes seems a bit premature, for this to be happening. It's possible that your son's radiator cap is rated for a higher pressure, so it "fixed" your leak. It's also possible, both of your Tecate radiator caps aren't holding the proper pressure. According to the 1984 Tecate manual, your radiator pressure valve should be opening within the following range: 13.5 - 17.8 psi. The manual says to perform a pressure test on your radiator cap, to ensure it is opening within the proper range.

[HondaRidr]

If you fill the radiator all the way to the top, it will dribble a little out as the coolant gets hot and expands a little. After the first ride it shouldn't be leaking out of the overflow anymore unless you get it hot. Its very possible the old radiator caps just are not sealing well. My brother and I have run the tusk caps that have a build in thermometer on our tecates. Work well and very convenient to see the coolant temps.