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I have 95 subaru, 170K miles.  I'm losing a small amount of coolant.  Preliminarily, maybe 8 oz/ week.  There are no hose leaks.  I've looked carefully at each and every one.  No green stains.  No drips.  No smell in the car.


My question:  Is it possible to have a leak in the middle radiator and have it evaporate so that there is no drips?  I guess I'll be going over the radiator with a magnifying glass.


Yes, I know that it could be going into the cylinder.  No there is no white smoke, but maybe it could be.

Edited by mikec03
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pressure test could help here - even clean under the hood and use UV dye in the coolant, pressure it up, then search with the UV light and yellow glasses. Parts store can loan that stuff out.



not impossible, but very unlikely the coolant is going into a cylinder.


these cars sometimes need to get their noses up to burp out air.


how old is the radiator cap?


try putting a coupla small zipties to act as clamps on the overflow hose at its radiator neck nipple connection.


does the overflow bottle's level change? which direction?

Edited by 1 Lucky Texan
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It is possible to have a leak in the middle of the radiator core that evaporates before it drops. More likely to happen where the plastic end tanks are crimped onto the core. You'd smell coolant, though. 


As texan said, not likely you have an internally leaking headgasket with no other symptoms. However, it's pretty easy to tell if you're burning coolant. Pull your spark plugs out and look at them, coolant steam cleans the plugs so if one is significantly cleaner than the others, that cylinder may be burning coolant. 

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The radiator necks for the hoses can be problematic. They are plastic, and can crack with age or over-tightening. It might take full pressure to drip a small amount out, which might not be seen.


Pinholes in hoses (radiator, heater, etc.) can open at high pressure, spray a very fine stream/mist which might or might not actually hit anything i.e. lower hose sprays a stream that hits the ground, then immediately close once pressure drops. In this case, you'll most likely still smell it, or you'll end up with steam rolling up from under the hood.


Heater cores (speaking in general) or their connections can sometimes leak, which will end up being inside the car and might get wicked up in the carpet or padding. This can cause windows to fog up excessively and you'll most likely smell it in the car.

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 Agree that  there could be an internal coolant  leak via a tired headgasket into a combustion chamber and coolant consumed out the exhaust.  Had an EA82 that did this.

Agree,  Fluorescent dye in coolant and use of a fluorescent light will confirm this (on exhaust tail pipe) -   or if the leak is elsewhere.

Recently another member on this forum had this similar issue with a Forester XT  confirmed with fluorescent dye use / light.




If there are leaks with radiator etc  there should be some evidence of  coolant colouring  in the location of the leak despite it  being evaporated.


Head gasket failure can happen with older cars also particularly if they haven't had a good history of regular oil/filter  and coolant changes

Edited by subnz
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I found it!


I borrowed the pressure system from advanced auto.  I finally found the leak on the 5" long hose just above the thermostat.  It's the heater return I think.  Anyway, the hose failed at the clamp.  It's 22 years old so it's about time for it to fail.  It was only putting out a  drop/min at high pressure.  The drops were running down the black hose and not leaving any kind of green residue that I could  see.  I also put in the dye and used the UV light which spotted it quickly, but the most important thing was the high pressure for 15 minutes to get it to leak a noticeable amount.


Thanks for all the help.  I didn't know about the pressure system

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