Car in sig loses 1 quart of coolant and no more in about 1 hour of driving...

here are the FACTS:

Ebay aluminum radiator
New cap
New thermostat
Coolant jug was filled on bench and held water over night with no leaks
No water in oil
No oil in water
No combustion in cooling system (chemical block test)
Coolant jug is empty all the time after the system loses the quart
NO external coolant leaks of any kind
No coolant burning in exhaust
Car does not overheat
Compression test = fine
Leakdown test= fine

Just to clarify, if I fill the system to the proper amount, and check it again after an hour of run time or 3000 miles the radiator will be exactly a quart low, and with empty coolant jug. It loses a quart and only a quart, no more, and no less, and is accurate pretty much to the drop! I am completely stumped, I have no effing clue what to do next. Any ideas? Thanks in advance!

 

Is the coolant jug you're referring to the overflow reservoir? Are you overfilling it? If you drive around with the climate control set to cold, do you still lose the same amount?

 

I had a similar problem, but mine was leaking coolant intermittently from the drain plung under the radiator, when overtighten it, the rubber gasket stretched and would start leaking, but not all the time, this is weird I hope you can find some help if this didn't help you.

 

Could it be leaking (only while driven) onto something hot and evaporating, since you don't see it dripping anywhere while it's parked? It could be somewhere towards the top of the system, which would explain it only letting out a quart and stopping.

 

For sure not overfilling, no change with climate control settings...

Thanks, no drain plug to speak of, this particular radiator you have to pull the lower hose off to drain it.

I have idled it to operating temp and thoroughly inspected everything while the car was running and found no leaks, is there another place in the system other than the top third of the radiator itself that could leak to only allow a quart out?

 

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if there are no leaks, and your heater core is not busted, you say no fluids are getting mixed...i would say blown head gasket leaking into the cylinder while hot. did you do the leakdown test when the engine was at operating temp or close to it?

 

Did the leakdown test cold and hot, also performed a chemical coolant block test (looks for combustion properties in the coolant) which was negative... also if there was a leak into a cylinder, why would it leak only a quart and stop?

 

ARP suggests re-torquing your head bolts after 1000 miles... DO IT...

 

Same sort of thing was happening to me and I couldn't figure it out. It wasn't leaking visibly at all, etc. But the reservoir would be empty or close to it after a day or two of commute.

It ended up being a pinhole leak in the heater hose that runs from the head to the firewall. It wouldn't leak at idle when cold or hot, so I figured it must be leaking when I'm driving and spraying a fine mist onto the block and transmission casing. Must have been fine enough to evaporate almost instantly as no traces of coolant, which are easily identifiable if its a larger leak, were visible. At that point I had checked all the other hoses for leaks and when I took the heater hose off I could see a teeny-tiny pinhole leak on the underside of the hose that is not visible when it's installed and you're looking directly at it. It was about 3 inches from where the hose attached to the port on the cylinder head.

Replaced and no issues since.

Hope you're problem gets worked out.

 

LOL thanks for the input, but my last post was the solution!

 

Gotcha...