So I have a mysterious coolant leak, I fill up the radiator and every few seconds a bubble of air comes up. I let it set overnight and added a cup or 2 of antifreeze, if I drive it I have to add a little more than that, so I take it to the shop thinking I have a heater core leaking, so I get a call today saying they did a pressure test cold and after it warmed up, it held pressure for over 30 minutes both times. They even pumped it up to 22lbs, still no leak. Yes it does smoke a little when starting up but once warmed up it's fine. Can't figure out what's happening, EGR leak perhaps? But again the system held pressure for 30 minutes, I'm stumped, can't figure this out. Would appreciate any advice or recommendations of what to look for.

 

Check your water pump weep hole. Look for a greenish stain around it. You may need a mirror to do this as it's cramped in there. You might even grab the radiator fan and see if it will wiggle. If your water pump is starting to fail, it will leak a little while the engine is running. It will get worse. If you do have a water pump going out, if you have 100,000 or more miles on the engine, go ahead and put a timing chain set in the engine while you're at it. You have 75-80% of the work done already. Why do some of the work twice?

If you're wondering why you don't see a puddle, the fan is blowing it around while the engine is running.

 

Aside from the obvious bad news stuff like head gaskets, the timing cover gasket loves to leak coolant at the two passages where coolant travels.

I couldn't tell ya why exactly, but sometimes pressure testing shows nothing. Also a water pump weep may only show when running. Radiator side tank leaks can be REALLY fickle and only leak under certain conditions.

If all that isn't it, then you're likely burning it out of the tail pipe. You could test for combustion gases in the radiator.

 

When the radiator is full and the reservoir tank is to the proper level how long does it take before you have to fill it again? Have a look around the motor, water pump, water neck, hoses etc for any signs of a leak. Antifreeze has a distinct smell when it's being burned so see if you have a "sweet" smell coming out of the tail pipe.

 

The steel tube/thermostat housing could be leaking. If it or isn't the water pump, I would replace the tube, thermostat, and waterpump. New hoses, especially the short one behind the water pump.

 

I had a leak under the alt/a/c comp bracket, that would drip down onto the top of the timing cover, and then get boiled off from there.... You couldn't see it, and nothing ever hit the ground, but, I was losing coolant, and could NOT find where it was going..... I was working on something else when I discovered that.

 

You can get a glimpse of that area if you look on the side of the motor past the alternator. A bore scope comes in handy if you have one.

 

If the problem persists, get a UV dye kit. Black light and safety glasses. Be SURE you use the yellow safety glasses. Add the dye for cooling systems and drive it a bit. Then use your light to look for dye streaks. I have tracked many a leak down this way and found some really hidden leaks that way.