2005 Duramax Low Coolant Message

[rokbrnc]

I have a 2005 GMC 2500HD with the Duramax engine.

A couple of weeks ago the Low Coolant Level message came on. I looked around the engine compartment for leaks and found that a pinhole had been rubbed through the hose that leads from the overflow tank to the lower radiator hose; the hose had been rubbing against the radiator shroud. I replaced the hose assembly and refilled the cooling system which seemed fine for about 3 days, then the Low Coolant message was displayed again, I filled up the coolant tank again and burped the system with the bleeder screw on the thermostat housing.

Now it seems as if I am receiving the message and having to top off the system about every 200 miles. There is eveidence of coolant in the passenger side wheelwell and it seems as if the system is being over-pressurized since even when it is cold and not driven in a day or two, the system is still pressurized.

I have read some posts about a possible tear in the EGR cooler that could contribute to this, however I am skeptical since the pinhole in the hose was an obvious (physical) sign for the initial coolant loss.

Any ideas?

[DmaxMaverick]

Welcome aboard!

Unless you bleed the system properly, you will have to add small amounts of coolant over time until it bleeds itself. The bleeder screw is only for initial bleeding, and will not bleed the entire system. You still have significant air in the system. Continuing to add coolant as needed makes for a long process, and you'll lose about 1/2 the coolant you put in.

Once the coolant is up to operating temp (stat at or near opening, tranny in P or N, E-brake set), the engine has to be revved up to governor (pedal to the metal) and held there for several seconds, and repeated several times. I've found it works best if the coolant tank cap is removed before it warms up. This will purge the air in the areas not bled via the bleeder. Don't let the coolant tank go dry, or it will suck in more air, and you'll have to start again. The procedure is very specific, but not complicated.

[More Power]

If the coolant is disappearing more than a few hundred miles after replacing the hose and properly bleeding the air from the cooling system, there could be an underlying problem.

A cooling system that is being overpressurized (due to combustion pressure finding its way into the cooling system) can cause a hose to leak where it wouldn't otherwise.

I'd pull the glow plugs (one at a time) after an overhight shutdown, looking for the presense of moisture (coolant). If one of the glow plug tips shows moisture, you'll need to schedule a head gasket replacement on that cylinder bank.

Jim

[Mark Rinker]

Yup - the hose likely rubbed through when expanded due to overpressurization. My bet is you are puking coolant out the overflow tube as one cylinder pumps up your cooling system.

After running the truck up to operating temps, and while idling in P with the parking brake set, observe the small return hose to the bottom of the coolant overflow tank with a strong flashlight. If you see any bubbles rising from the bottom of the tube to the top from the return tube, you have a head gasket problem.

If not, look elsewhere, or perform the glowplug test MP suggested. Dealerships hold white paper outside the glowpug port and crank the truck over with the IP fuse pulled - looking for pink coolant spray...

[More Power]

If the engine had been run for quite some time - while overpressurized - you may need a water pump as well. Those who report cooling system pressure problems usually report changing the water pump as a result. The higher than normal pressures wipe out the water pump seal.

Which brings up another question...... How come the surge tank cap, which is rated at 15-psi, doesn't maintain a pressure low enough to not damage the water pump seal?

Here's something for everyone to do.... When your engine is cold, remove the surge tank cap, and look at the 1/2" diameter valve on the underside. Press on it. If yours is like mine, it'll take a lot of pressure to push it open (the first time). A second push is fairly easy.... I think these pressure relief valves get stuck, which leads to water pump seal failures..... Just a thought.

Jim