Hey guys and gals. So here's my story. I came home Friday night from work, and I noticed a hissing sound coming from under the hood. I pop the hood, and notice that my coolant reservoir tank is steaming. I look under the car to see if there are any leaks, but there aren't any. So I wait an hour....

I pop open the radiator cap and notice there is NO COOLANT. At this point I'm worried, dreading that I fubar'd my engine. I checked the oil dipstick to make sure that there wasn't a milky substance, because from what I've heard it would mean that there was water in the engine. Thankfully that wasn't the case; the dipstick came out with nothing but oil on it. I decide to top the radiator and reservoir tank with coolant.

So I start the engine and thankfully there is no leaks.....yet. I decide to drive the car around the block and pop the hood again. I then notice that there was a few drops of coolant leaking out from the radiator cap.

So my question is this: is the oem radiator cap known to become faulty, or is there an underlying problem that I should know about? I'm a bit worried to drive the car around (thankfully I have a beater car to lug around in the meantime). I want to nip whatever problem there is in the bud before it gets potentially worse. Any help is appreciated. Thanks.

 

Possibly a small leak in the head gasket. Not leaking water in the oil but leaking pressure from the combustion into the cooling system causing it to build pressure in the cooling system resulting in a overfull/flowing reservoir and it possibly leaking from the radiator cap as well.

 

Update: I think im just paranoid. The small leaks MAY have been from when I opened the cap and put it back on, causing some of the coolant to drip without me even wiping it. I test drove the car around the block again, pop the hood, and still no signs of leaks or loss of coolant from anywhere. Will report back soon.

 

Paranoia may save your engine if overheating is the issue. There should not be any hissing or steam escaping from your cooling system if everything is working properly. Keep an eye on your temperature gauge, and refer to this graphic (Stock Display) for the temperature ranges associated with each bar:


Photo courtesy of Bob's Modifry ECT page.


I experienced a similar issue last summer and followed a long winding road to discovering the true causes of the issue. It turns out I had a faulty OEM radiator cap, pinhole leak in OEM radiator fill neck, cracked coolant reservoir cap, and failing radiator fan. Whenever the radiator fan was working, there were no observable issues. However, whenever it was not working heat and pressure would build and and cause coolant to seep out of the system from the cracks and holes. The seepage eventually allowed air into the system and the overheating would worsen. Refilling and burping the system did not cure the problem long term, so eventually I replaced the leaky caps (radiator and reservoir), radiator, lower radiator hose and thermostat. Only after all this did I discover the failing radiator fan. I found the problem by monitoring the temp (with a scan tool) in the driveway and noticed the fan did not always turn on around 205F. I then tested motor by connecting it directly to a 12v source and found that it only spun up about 60% of the time. When I gave the fan a whack with a screwdriver handle/rubber mallet, the fan would then start spinning so I knew the brushes were likely well worn after ~10 years of service.

Good luck!