Please help a newb...coolant loss

**jarretts70** · 03-07-2011, 12:02 PM

I've got a 2003 GMC 6.0l daily driver. I beat on it daily, and it has been a super dependable truck. But it has developed a problem I haven't been able to figure out. It's going thru coolant at an alarming rate, like a gallon every couple of weeks. It's not leaking it (at least when it's parked), there is no foam in the oil, and no white smoke when driving that would indicate coolant is getting into the cylinders. I've got lots of experience with old school GM engines - small blocks, big blocks, Pontiacs - but I've never worked on a LS series engine, never even changed my own oil. Does this engine have any sort of history of loosing coolant like this? Note that its got lots of miles on it, and like I said, I beat on it pretty hard...

**Knight** · 03-07-2011, 12:06 PM

Have you tried letting it run while searching for the leak? Make sure to check it after the t-stat has opened too. It sounds like a leak with the conditions you are describing.

***SMWS6TA*** · 03-07-2011, 12:14 PM

Like knight said you need to run it to find the leak. Water Pumps have a weep hole that is by design to leak so the pump will not seize. When you say alarming rate, by how much?

**pajeff02** · 03-07-2011, 12:36 PM

Pull your dipstick -- does the oil on the end look normal or does it have a "milky" appearance?

**jarretts70** · 03-07-2011, 01:11 PM

It's going thru coolant at about 1 gallon every two weeks. I average about 500 miles every week. The oil looks fine, not milky. I've let it run while parked in my garage a couple times, and have never seen a leak

I'm worried that I've got a head gasket issue and that coolant is getting into the cylinders and being burned. I've run ito that problem on other engines, but there was always a bit of white smoke in the exhaust. On this truck, there is none, or at least none that I've noticed. Do high mileage LS engines have any sort of history with head gaskets?

**bills98ta** · 03-07-2011, 01:18 PM

Maybe do a cylinder compression test & put air to each cylinder to see if your radiator bubbles, With the radiator cap off. Might be a head gasket, and the water is going out the exhaust.

**KMdef9** · 03-07-2011, 01:22 PM

Originally Posted by pajeff02

Pull your dipstick -- does the oil on the end look normal or does it have a "milky" appearance?

Originally Posted by bills98ta

Maybe do a cylinder compression test & put air to each cylinder to see if your radiator bubbles, With the radiator cap off. Might be a head gasket, and the water is going out the exhaust.

This is what I am thinking as well. Check the dipstick and even the oil fill cap for a milky liquid/residue.

I wouldn't say it's and LS thing as much as it's a GM thing as far as head gaskets go. Had to do with the original OEM coolant.

**pajeff02** · 03-07-2011, 04:23 PM

You can also pull your plugs and compare them. Coolant will sometimes leave speckled deposits, more so with green than the others though. Also, coolant will have the effect of washing the combustion chamber -- a real clean plug compared to other normal looking plugs could be indicative of coolant infiltrating the cylinder. I would pressure test the cooling system -- you may be able to rent a pressure tester from Autozone if you do not have access to one. Do not pump it up to more than 15-16 lbs if you do test it.

**Cutlass** · 03-08-2011, 03:37 AM

Check it over very carefully for external leaks from the waterpump, hoses, radiator, etc. If it dry then I suspect you have a slow head gasket leak into the combustion camber. It'll be hard to prove a small leak, so you'll have to eliminate other things first.

**jarretts70** · 03-08-2011, 05:52 AM

That's some good advice,thanks. I'll start by comparing the plugs. It never occured to me that a plug(s) would be cleaner than the rest of them if coolant was getting into the cylinder, but it makes sense. I should change the plugs anyway, they probably have about 100K on them anyway - did I mention I tend to beat on my work vehicle?...

**JayTA98** · 03-08-2011, 06:09 AM

Have you replace the radiator cap with a new one?

**blue02Z** · 03-08-2011, 08:19 AM

Originally Posted by Cutlass

Check it over very carefully for external leaks from the waterpump, hoses, radiator, etc. If it dry then I suspect you have a slow head gasket leak into the combustion camber. It'll be hard to prove a small leak, so you'll have to eliminate other things first.

this.

those engines are notorious for water pump leaks. crawl up under there and look at the wire harness going right in front of the oil pan. if it has coolant on it then its the water pump. also you say you do alot of driving so maybe it is blowing back on the engine and that is why you dont see the drips

**35th-ANV-SS** · 03-08-2011, 09:23 AM

Agreed. Sounds like internal leaking.

If it is a head gasket leak, be sure to check both the block and head for flatness before replacing the head gasket.

**allbaugh_04** · 03-08-2011, 10:43 AM

Check the plugs and let us know.

**nickracer** · 03-09-2011, 06:10 AM

run it cold with the radiator cap off. If you are leaking coolant into a cylinder you should see bubbles in the radiator. If you see air bubbling in the rad then do what Bills98ta said, put air pressure to each cylinder thru the spark plug hole to verify source.

**0rion** · 03-09-2011, 06:57 AM

Originally Posted by jarretts70

I've got a 2003 GMC 6.0l daily driver. I beat on it daily, and it has been a super dependable truck. But it has developed a problem I haven't been able to figure out. It's going thru coolant at an alarming rate, like a gallon every couple of weeks. It's not leaking it (at least when it's parked), there is no foam in the oil, and no white smoke when driving that would indicate coolant is getting into the cylinders. I've got lots of experience with old school GM engines - small blocks, big blocks, Pontiacs - but I've never worked on a LS series engine, never even changed my own oil. Does this engine have any sort of history of loosing coolant like this? Note that its got lots of miles on it, and like I said, I beat on it pretty hard...

you basically ruled out every possiblity in this post so that tells me one thing.....you've overlooked it.

Park it on a few sheets of cardboard overnight first and see if you're dripping it. Make sure it's enough cardboard to go from the front bumper all the way back to the tranny. If you're not dripping then look under and around the engine really good to make sure it's not blowing back and getting burned off by the exhaust manifolds or something. Normally you'd be able to smell it if it's doing that.
I would then pressurize the system and check for leaks that way. That's a substantial amount of coolant to be losing so if it were going into the cylinders or oil you'd definitely know it I think.

Does your passenger side carpet get wet? Could your heater core be leaking?