2004 Avalanche consumes coolant

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Irish Jake

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My 04 Avalanche Z71 5.3L consumes a gallon or more of coolant each week. I've looked every where for signs of leaks - found nothing. Pressure tested radiator - held perfectly. No signs of steam from tailpipe. All hoses/connections tight and dry. Replaced remote reservoir cap with brand new from Chev dealer. No check engine light or codes. Runs strong. No skipping or sputtering.

Anyone have any ideas??
 
if your vehicle has a separate radiator cap did you pressure test it, you only comment on the reservoir tank? Have a shop do a hydrocarbon test of the the coolant to see if you have a blown internal gasket.
 
My truck doesn't have a cap on the radiator. Only on the remote reservoir. At wits end with this thing.. It consumes A LOT of coolant. I'm under the impression I'd see steam from the exhaust if a head gasket was the problem.. No? I would also think it would be running poorly or throwing codes based on the amount of coolant I'm replacing. Nothing in the oil either.
 
well it can only leak or burn, how long did you pressure test the system? look into the cost of the hydrocarbon test. A gallon per week is a hugh amount, cannt see how something like that wouldnt show up on one of those two tests. Did you check the NHTSA for service bulletins/recalls covering your vehicle's problem?
 
The pressure test was 20 minutes - didn't lose any.. I understand the whole "leak or burn" thing, and assume it's burning, just can't understand how if it doesn't run poorly or throw a code - or show up in oil... Had another (older) Chevy truck that ran awful when head gasket let go..

Been hoping there might be something else to newer/electronic Chevys that I wasn't aware of.

Hydrocarbon test scheduled for next week. Am unfamiliar with "NHTSA" etc but will ask my mechanic when I go. Thank you for the replies - I really appreciate.
 
this is the link for the service bulletins, there is also a section for recalls. Your mechanic may use a service such as Alldata which has more detailed information on the contents of the bulletins.

http://www-odi.nhtsa.dot.gov/tsbs/
 
Great thank you! I've got one more question...

First/cold start the engine always sounds like it's full of marbles. It starts well, quickly etc.. Oil pressure comes right up.. but.. it just sounds like everything inside is loose somehow. Once it's warmed up, it's absolutely fine. Quiet and smooth. Is this somehow normal? The noise is substantial, like some kind of rod slap...
 
what viscosity oil are you using 5w30? If 5w30 I would try 10w30 next oil change.
 
Yes.. I do use 5w30 - mostly because it says that right on the oil fill cap.. I don't really know the difference, other than one of them being a bit "thinner" I suppose? I just wonder about deviating from factory recommendation for the engine?? You seem very knowledgeable so please don't take my question the wrong way.. I'm trying to learn as I go.
 
I had same issue. Came to conclusion it was burning it on the intake stroke. We replaced the motor as it was a high mileage situation and I wanted to keep my paid off truck for as long as possible. We did the motor swap from 190k to a nice 54k motor. When we pulled the heads off, it was the #3 cylinder. The piston was crystallized per say and the plug was toast.

Have you pulled your plugs to compare all 8? Should give you an idea which cylinder is causing the issue.
 
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