Coolant leak - cant find it

[20streetrod06]

I have a coolant leak... somewhere. i have tried looking for it with the naked eye with a warm engine, cant find it. I have hooked up a pressure test kit, and pumped it up to 15 psi, let it sit for an hour or hour and a half, and it only dropped to ~14 psi. felt everywhere imaginable, and never found a drop. but once or twice a month the odometer will say low coolant. and sure enough, the tank is low. checking it on my own periodically, I've never caught the level dropping.

any ideas on where to look for my missing coolant?

 

[EXT4ME]

I used my pressure tester and pumped up my system to 15 PSI.

I found my mystery coolant leak to be coming from a tiny hairline crack in the driver's side head between the two center head bolts.

The leak was very small and would only appear after a good period of time while the system was under pressure.

While the engine was operating, that coolant leak was draining down into the engine crankcase and mixing with the engine oil and was getting pumped all throughout the engine.

And no, the engine oil in my crankcase never turned "milky" like we have all been told to look for.

The oil turned jet black and thin.

There was some milky looking snot goo inside the valve covers when I took them off.

Since this problem was present for about a year and a half before I finally found it, I feel there is too much possible internal damage to bearings, lifters and the cam for me to trust the engine, so I have parked the truck until I can replace the engine.

Below is a picture of what the inside of my valve cover looked like when I first pulled it off of the engine.



And here is the black gelatinous goo that was formed by the coolant mixing with the engine oil inside the crankcase.





That black goo also settles in the bottom of the oil filter and clogs the filter media.



I finally found the cracked head after I had found and fixed a few tiny coolant leaks at hose connects and such.

I would pump up the system and the pressure would drop off ever so slowly.

Finally, I took off the valve covers and found the leak..

Look closely and you can see where the coolant is beginning to pool in the depression around the head bolt.



The longer you let it sit, the more coolant appeared.

 

[2004Slickside]

I have a coolant leak... somewhere. i have tried looking for it with the naked eye with a warm engine, cant find it. I have hooked up a pressure test kit, and pumped it up to 15 psi, let it sit for an hour or hour and a half, and it only dropped to ~14 psi. felt everywhere imaginable, and never found a drop. but once or twice a month the odometer will say low coolant. and sure enough, the tank is low. checking it on my own periodically, I've never caught the level dropping.

any ideas on where to look for my missing coolant?

There is a dye that you put into coolant (and oil) that fluoresces bright yellow under a black light. This was a standard way of checking for oil and coolant leaks at GM dealerships. Might help find yours if leak is external. You can buy the dye from GM parts dept (and other sources too I imagine). Get a black light from the grocery store (not nearly as bright but it will work). You do have to watch the source of the leak to catch it before it gets spread and turns everything yellow, but this can be a very effective way of diagnosis if you are watching things carefully.

 

[EXT4ME]

Amazon has the dye and I got my UV flashlight at Harbor Freight.

Good tips, here.

 

[ygmn]

Have pressure cap tested... might be old and weak and relieving too low a pressure which will allow slow coolant steam out your system.

 

[Raekal]

My mystery leak was apparently at the fittings going into the firewall for the heater core. I never saw any leaks or drips. I could smell it from time to time but that's it. Local shops called me crazy and thought it was just the pressure relief for the system. But then the coolant consumption noticeably increased as we went into winter and the dealer found it (presumably with dye) coming from the back of the heater core. Which, thankfully didn't require them to get to the core to fix.

Which, depending on your climate and hvac control unit might be pretty similar. Having a digital hvac unit like mine i think disconnects you a bit from making that connection of "turning the heat on" to "im having this issue a lot more often".

Just another thing to check on. Hopefully you can get it nailed down. Mystery coolant leaks are the worst. At least you can fit a bottle of antifreeze in the saddlebags.

 

[20streetrod06]

My mystery leak was apparently at the fittings going into the firewall for the heater core. I never saw any leaks or drips. I could smell it from time to time but that's it. Local shops called me crazy and thought it was just the pressure relief for the system. But then the coolant consumption noticeably increased as we went into winter and the dealer found it (presumably with dye) coming from the back of the heater core. Which, thankfully didn't require them to get to the core to fix.

Which, depending on your climate and hvac control unit might be pretty similar. Having a digital hvac unit like mine i think disconnects you a bit from making that connection of "turning the heat on" to "im having this issue a lot more often".

Just another thing to check on. Hopefully you can get it nailed down. Mystery coolant leaks are the worst. At least you can fit a bottle of antifreeze in the saddlebags.

it never leaked from there during the pressure test, but i will try to remember to check those connections out real well with the motor warm after my drive home today.

 

[MS03 2500]

Castech Head

 

[BainMan]

My mystery leak was apparently at the fittings going into the firewall for the heater core.

If I'm thinking of the same part that leaked for you, Dorman makes an upgrade! It's metal instead of plastic. I've had this bookmarked since the plastic part left a forum member stranded on the side of the road, but I haven't been proactive enough to make the swap myself yet...

Check this out: https://www.amazon.com/Dorman-Coolant-Connector/dp/B07RK3JYZN/

 

[Raekal]

it never leaked from there during the pressure test, but i will try to remember to check those connections out real well with the motor warm after my drive home today.

Yeah, i'm pretty sure these were the fittings. Wish i would have looked around before having them replaced. xD

 

[2SmokinBarrels]

Mine has a little seapage from there. first noticed the stain it was making on the injector below. Think I might flush the core and get them fittings.