2003 4.8L Consuming Coolant

thamilto · June 21, 2014

My 2003 Z71 Sportside with approx 107K miles has started to consume about a Qt of coolant every 6 months. Other than that, it runs fine. The coolant is not puddling under the engine so it appears to be an internal leak.

Is it time to have the upper intake seal(s) replaced? I hope to get another 5 years of use out of the truck.

The engine has very light mods: K&N filter and Borla cat-back exhaust. I've kept the engine/trans/diff serviced regularly.

gmtech4 · June 21, 2014

look for staining around water pump weap hole and mounting points ,,,,also inspect everywhere else for staining before assuming anything

my 2 cents

thamilto · June 21, 2014

look for staining around water pump weap hole and mounting points ,,,,also inspect everywhere else for staining before assuming anything

my 2 cents

With the orange coolant, do I look for orange stains? Like I mentioned, it doesn't have any puddles underneath that would indicate an external leak.

txab · June 21, 2014

Intake has no water flowing through it. As Gov said look for signs of leakage around the WP. Gaskets are quite common to leak on these. Check all hose connections for signs of leaks. Check heater core. Evaporated coolant will usually leave signs, a crusty, flaky, somewhat white-ish material. Not always though. Check all external possibilities first. You can buy and add dye to the coolant to help in tracing the leak

thamilto · June 21, 2014

ok. Took a flashlight to the front of the engine and did not see any leaking hose connections as well as gaskets on top of water pump. Will check underneath next.

gapost · June 23, 2014

I'm surprised no one said it could be a bad Castech head. If it were me (I've had several on GMT800's), I would pull the valve covers and see if you see chocolate pudding inside. It's not that hard to pull the covers and it will tell you for sure if you have a bad head.

Mikeee · June 23, 2014

The 5.3 had coolant leak thru the head into the crankcase. Don't know if the 4.8 have the same problem.

txab · June 23, 2014

I'm surprised no one said it could be a bad Castech head. If it were me (I've had several on GMT800's), I would pull the valve covers and see if you see chocolate pudding inside. It's not that hard to pull the covers and it will tell you for sure if you have a bad head.

Until he clears all the external possibilities no need to mention it. BTW, it's more like butterscotch pudding, because it's not dark in color.

I still suspect WP gaskets or WP

Snow White · June 23, 2014

if' you're using a qt of fluid every 6 months and it's from a "leak" you're going to see it unless it only leaks while it's running.

head gasket.... pull a couple of plugs and look at them.

thamilto · June 23, 2014

Wouldn't the dipstick also show glycol in the oil? Dipstick just looks like oil, no glycol or unusual appearance.

Also, if I had glycol in the oil and have consumed the coolant since mid-2013, wouldn't the engine/bearings have seized by now?

thamilto · June 23, 2014

I replaced spark plugs last summer at 103K about time I added the first bit of coolant. Will inspect them and advise.

Snow White · June 24, 2014

if it's leaking into the cylinder, it won't show up in the oil because you're burning it off. However, if it's leaking into an oil valley then yes, you'd see water/oil on valve cover etc.

gapost · June 24, 2014

On one of my vehicles, with dexcool, it formed black sludge in the oil pan. My daughter was driving it and it kept loosing coolant. Finally realized the problem when opened oil drain plug and nothing came out. Sludge had blocked up the hole. It was about an inch thick in the pan and almost up to the oil pickup. This was my first gmt800 with bad heads and I got refurbished heads and they went bad after two years. Really, it's not that hard to pull the valve covers and you will know for sure if it's a head problem. Just don't over-torque the valve cover bolts when putting back on. They are like 105 in/lbs.

thamilto · June 25, 2014

I inspected the spark plugs removed last summer. Nearly every plug has a light brown/orange stain that rings the white insulator near spark plug tip (near the gap). About .10-.20" wide. Other than that, the plugs look ready to replace after 103K miles of use. From what I can find, a light brown ring is indicative of normal burn of unleaded fuels. I run 87-octane with 10% ethanol.

I am going to focus on radiator, hoses and water pump mounting points with closer inspection from underside of truck. Then, if no indication of leaking/stains, I'll take it into the shop I use for my repairs for estimation.

thamilto · June 25, 2014

Took a closer look at the front drive belts after suggestions to look for brown staining on the belts. There appear to be three ribbed belts that drive accessories of the crankshaft. The third, inner belt that is nearest the engine on the crank pully has a dirty brown 'stripe' on its outer surface... as if something has been staining it for thousands of miles. The radiator was flushed, filled and the serpentine belt replaced back in early spring 2011. If they did not detect the issue on that service, tt could have started sometime after since I embarked on a long move to the Central US in May 2011. Prior to that, I did not drive my truck heavily from 2007-2011.

I suspect that it is a water pump seal or the water pump itself. I will investigate what it will take to service myself vs. have my shop perform the service.