I have this stupid coolant leak that I just can't find. There are never any visible drips/puddles underneath the vehicle, but my coolant is constantly dissappearing at a fairly slow rate; like half a quart a week. When I lift the hood, I can smell it. I'm pretty sure that I'm not burning it. Only 12000mi on a professional rebuild - all felpro gaskets - and I don't think it leaked before I had the t-stat replaced. I replaced the t-stat housing gasket thinking that it would solve the problem - but it's still leaking somewhere. It smells like boiled coolant under the hood. I can't smell anything inside the vehicle. I think it's leaking onto the intake, then burning off.

Is there some sort of dye you can put into the coolant to help trace where it's leaking from?

 

Moved

 

Water pump

coming out the weep hole, getting on the back side of the pulley, and getting slung around the engine bay in a mist

 

Also, check your hoses that connect to the heater core. One could have worked it's way loose.

 

Is there such a thing as a pleasing coolant leak?

You might also inspect the hot water valve for the heater. Depending on the type you have, it may be allowing coolant into the intake. Some of the HW valves I've seen on ThirdGens are a completely divorced type, with the vacuum servo enirely separated from the water valve. Some that I've seen on other cars are enclosed and may allow such leakage to the vacuum hose and intake.

Check the transmission fluid, too.

 

Well, I changed the water pump. On the underside of the lower rad hose was dried on coolant residue, so it was definitely leaking from the pump somewhere.

Anyway, after the swap it didn't appear to be leaking anymore, but the other day I notice it was dripping quite a bit in the usual drip location - below the rad on the passenger side. It was VERY cold out that day when it was dripping; -25C and below -30C during the night. I checked the underside of the lower rad hose again, and it was dry. I checked the next morning when I started it up, and there were no leaks. So, I'm thinking this thing only leaks when it's really cold AND the thermostat has opened AND there is system pressure.

Does that sound like a cracked hose? What's the easiest way to test for this?

 

Are you trying to say that you didn't change the lower hose at the same time as the water pump? That means that not only did you work harder than you had to while doing the WP itself; but now you might have to go back and re-visit a bunch of the same work over again.

Easiest way to test for a defective hose is by substitution install a known good one in its place).

It's also possible that your radiator has a crack in one of the tanks, or where a fin goes into the end of the core, or even where the hose nipple goes into the tank.

 

Took me a while to find that my mysterious coolant leak was the water pump

 

Nope didn't change the hose. Rad, upper and lower hose are just over 18 months old, relatively new - rad cap is only a couple of months old, themostat is only 10 months old and has a new housing gasket that's only 6 weeks old.

I can't see any leaking coming from the heater core hoses/connections at all - so, it's gotta be lower hose, or something cracked on the rad, unless the leaking coolant is traversing from the driver side to passenger side.

I would think a cracked rad would leak all of the time though, where as a cracked hose is more likely to leak when it's really cold.

In retrospect, you are right about me being dumb not changing the lower hose while doing the pump - but I would never suspect an GM oem hose to fail after only a year and a half.

I hate taking it to a shop, but maybe I should just take it and get the system pressure tested. Sucks to pay $60/hour to get somebody to fix some you can do in the same amount of time though once you know what the problem is.

 

My radiators only leaked when they got hot. The Camaro radiator was cracked on the front side of the passenger side tank. The Firebird had a hole in one of the coils on the front side, it would shoot out a tiny little stream of coolant when hot, but when it was cold nothing.

 

Makes sense for a cooling system to leak when hot - there's no pressure until it does get hot. What doesn't make sense to me is a system that leaks only when the outside temp is very cold and the system is under pressure (hot). Outside temp -25C it leaks, -15C it doesn't leak.

 

For future reference, the leak was coming from the lower rad hose at the radiator nipple. In super cold weather, the metal nipple contracts more than the rubber hose. The problem often occurs when the gear clamp is overtightened and causes a flat spot on the nipple - or so my mechanic friend tells me anyway.