Coolant leak from reservoir tank cap

I'd try a new cap first. If the pressure goes over 15 pounds it should vent through the side cap, not the top.

 

The rubber 0/ring on cap is cracked or broken, put a new factory cap not a china made copy on it.

 

loosen it some where it dont build pressure. see if it still comes out.

 

Just start with replacing the cap, the actually where out.

 

my second truck never did. i bought a pretty purple freightliner from select trucks once. paid cash. truck never made it past 6 months. come to find out cap had just 1 o ring on it to keep pressure from building. i put new cap on it. truck used 2 gallons a day of coolant.

 

Don't want to be the bearer of bad news but, you could have other issues. Take cap off (carefull if it's hot )and start up , look in with light and see if it's got bubbles , if you got Constant bubbling it could be bad to worse, bad= air compressor , worse= head gasket, devastating = cracked head. Don't forget about ,expansion if you filled too much, as it warms the water will expand in volume % wise to temp, hopefully your just over filled.

 

But in that case it should still be venting out of the side cap, not out of the top cap.