Losing coolant but find no leaks

[cheapie408]

I have a 2003 5.3l Z71, I only used my truck to tow a boat, it seems every several hundred miles I'd get a low coolant message. I'm not able to visually see any coolant leak. The oil is clean and not milky so it doesn't seem to be the head. I did a radiator pressure test and it doesn't appear to be losing pressure for the past 10 minutes. I still have the pressure tester on the system as we speak. I'm going to leave it for awhile and see how it goes. 

 

Any suggestion on where/how else to check? 

[richard wysong]

Castech heads?

[CamGTP]

If no leaks on the hoses or the radiator and nothing is in the oil, it's likely eating the coolant through the head or the head gasket.

[txab]

Check water pump and wp gaskets. They can leak and not really be noticed

 

 

[richard wysong]

agreed, it's a difficult area to see, sometimes using your nose can help or stick your hand down there and see if it's wet

[EightTrackHits]

I had a similar issue recently and looked at quite a few things.

 

The initial trouble was a visible leak, but I inadvertently installed a cracked head during the repair and had coolant disappearing with no visible leak found or loss of pressure during a pressure check. 

 

Coolant was leaking into the head under the valve covers and being dissipated throughout the engine as sludge through the PCV system.  since the coolant was being suspended throughout the engine, the oil level was not rising in a direct correlation with the coolant loss.  It would steam out the pipe on startup, but after warming up that would stop.  Take a look at the underside of your oil cap and tell us if it looks discolored.

 

The initial few posts are not related to your problem, but later the thread gets into something very similar.  Hopefully your issue is one of the things txab mentioned.  Good news is, I fixed it and still drive it.  I will follow your thread and try and answer any questions that I can.

 

You can read my full thread here: 

 

 

[newdude]

I'd be looking to see if you have Castech heads.  If you can find the external head identifier # and its a 706, time to pull the rocker covers and looking for coolant.  

[KARNUT]

I was losing coolant since I got my 02 Avalanche almost three years ago. Last year I got the oil change at the dealership while getting inspected. They said the oil was clumpy at the beginning coming out. Never saw water on the stick, on the ground or steam out the pipe. So I stopped at auto zone got bars leak. Stoped the water loss so far. Next oil change I’ll do it. I’m not really concerned that much. My plans when my brother in law retires and builds his shop. I’ll help him with his 69 firebird restoration. Then spice the Avalanche a little. I want to lower it. If the engine becomes a problem, nothing goes back stock. I may even consider one of those new GM 4 cylinder engines. That would be cool and different.

Edited October 25, 2022 by KARNUT

[It's Tim]

20 hours ago, cheapie408 said:

 so it doesn't seem to be the head.

Slimy goo inside the exhaust pipe?

[eric85davis]

Will a bad hose clamp cause your coolant to disappear 

[eric85davis]

Also I just changed my water pump on my 06 Silverado 5.3L

[richard wysong]

Welcome to the Forum!  A common leak is the spring clamps rust out and lose their tension, they were never designed to be reused once released but most folks do anyway. Any sign of coolant getting into the oil? pull the oil cap and see if its got white goo on it