I have a slow leak somewhere, I have to top off about once a week. Takes about a quart of coolant, but I cannot find the leak. I can smell coolant sometimes under hard acceleration and sometimes while idling for a while at a light. I have looked everywhere and cannot find a leak, the passenger floorboard is dry, no coolant on the ground. Only think I can think of is a blown head gasket, but there is no smoke from the exhaust and the leak is not constant, meaning I can drive it for a day and coolant level stays the same.
This happens more often than you would expect. There is probably a puncture in a hose that only leaks when the system is up to pressure....so you are probably driving. Then sometimes the leak squirts coolant directly at something hot like an exhaust pipe...so there is no evidence. Pretty clever. Try laying out newspaper where you are going to park the car and put it on there nice and hot.
I have a radiator pressure tester. Looks like a small bicycle pump and dozens of radiator cap fittings. Lets you put the 12lbs into the cooling system even when it is cold. Much less dangerous way to find a leak that only occurs under pressure. I have seen it where a cylinder head leaked coolant into a cylinder ONLY when under the pressure of highway speed. The amount was so small there was no smoke. There was also a van I worked on where the head gasket again only leaked at highway load and displaced the coolant - We used a test kit that had colour changing liquid to find exhaust gases are in the coolant. Hope yours is just a pipe somewhere.
I had a mystery coolant leak that couldn't be pinned down as there was no coolant on the floor or car. I was losing coolant as vapor via the front radiator hoses and possibly a bad radiator tank. The only reason I found it was I pulled over one night on a test drive to check stuff and saw the vapor due to the headlights, it wasn't visible during the day. Replaced the coolant hoses and the radiator and I'm no longer losing coolant.
Originally posted by randy86:corrections Most cars have a switchvalve to bypass flow to the heater when not needed and it is NOT on the heater core (geez) and I expected the fiero to have one too.
Some cars have heater bypass valves. Fiero and Most vehicles Never had this. Some cars Need the heater core hot even to run AC w/o evaporator freezing etc.
Even with a bypass valve the bad heater core will still leak coolant because often the core is still under pressure. Very common a valve Diverting Flow is Not = core sees No Pressure. Making a bypass killing Pressure to the core when bad would cost more to make.
The only way to bypass on most vehicles w/ bad core is remove both hoses and use tube to connect the ends. Example:
This keeps both ends same size as heater core. Solder blobs keeps hoses on even if clamps get a bit loose and to make just get less heat and flux to prevent flow. I made it 20+ years ago and posted before but can't find old img so just cleaned it for today pic to show easier.
Can use anything in a hurry but hose barbs etc have their own problems.