rjwittmann92

Hey everyone,

I recently bought a 2011 Z06 with AHP heads and cam already done to it. I've put around 500 miles on the car and have had zero issues with it until recently. I started the car in the morning and during warmup, I noticed the low coolant level light came on in the dash. I parked the car and took another vehicle to work. After work, I checked the coolant level and it was low in the reservoir. I filled the reservoir back up, let the car warm up appropriately and went on a 10 minute drive. When I parked the car, the level had dropped again in the tank. On this drive, I verified that the heat does blow hot when asked to. The coolant temps in the dash are typically around 180-190 depending on moving, etc.

Prior to the low coolant light coming on, I noticed during warmup that the car would reach around 200-205 and then shortly dip down to the 190 range and hold around there within 10 degrees during my entire drive. After adding coolant, this rising and falling behavior did not occur.

Since all of this, I have thoroughly inspected the engine bay for any sort of leaks, which I have found none. I then decided to check the oil cap on the dry sump tank and the cap on the PS valve cover and both had some white milkiness on them. The oil on the dip stick shows none of this and the oil sitting in the head didn't appear to have any of that either. The level in the tank doesn't seem to have gone up either. The car has been sitting and driven on short drives or just moved in and out of the garage recently (also very humid out) and it does seem possible to just be condensation.

As previously mentioned, I have not noticed any changes in how the car runs and drives, no smoke, no obscure noises or anything. I plan on draining the oil tonight after work to see if there is separated water in the oil. The car has never overheated, but aside from a head gasket leak or internal crack, the only other thing I can think of is that there was an air pocket(s) in the cooling system that finally bled and coolant was drawn in from the reservoir. With all of that being said, are there any other things that anyone recommends checking before taking the heads off to look for something more in depth?

Vito.A

I would also pressure check the cooling system. You should be able to borrow or rent a coolant pressure checker form Autozone.
Good luck!

grinder11

I have an LS7 in a C5. Cars are very similar, as I'm sure you know. I was ready to pull my heads 3 or 4 years ago due to a similar problem. It was then that I saw the problem; one of the factory spring hose clamps had evidently lost enough of its spring (20 years old) that when the car would heat sink after a drive, a tiny bit of coolant came out of one of the heater hoses at the water pump. Mine would lose enough coolant that the coolant temp would swing lower than normal (172°), then go a few degrees higher than normal. There was no coolant under the car, none out the exhaust, just like you. Because it evaporates quickly. Whether someone else, or maybe me, had over expanded the spring clamp, and surpassed its elastic limit, or they just got old, IDK. But after replacing with conventional band (hose) clamps, no more temp swings, and it never leaked again. Hope this helps, and needless to say, I no longer trust the factory spring clamps.....

rjwittmann92

Update - I drained the oil and it looks perfectly clean and normal. I watched it drain the entire time and it was consistent and normal looking the entire way. I’m going to do a full oil change and keep driving it to see what happens as far as the coolant is concerned. I’ll also see about renting a pressure tester.

Too-Fast

Had this happen on my 2011Z07 last year, new hose and clamp on lower hose solved it.

subfloor@centurytrans

I've had the same thing happen to me in addition to a small water pump leak that would evaporate almost instantly. The only way I ended up finding it was to get the car up to temp and then run my hand underneath. I didn't find a ton of water but there was enough that it was noticeably damp.

grinder11

There is only one reason GM went to these style clamps, and that is mainly $$$$, as usual. Theres no way a worm style clamp can be installed as quickly as just slipping a spring clamp over the hose(s). Plus it is consistent. If a spring clamp is in place, it's tight. If a more conventional clamp is in place it doesn't necessarily mean it is tight.....

tommyc6z06

Sorry...i'm no engineer, but I disagree with this. Spring clamps distribute pressure evenly around the circumference of the hose, and allow for the expansion contraction caused by changes in temperature. Hose clamps, used in such applications invariably end up over-tightened, and can start cutting into the hoses.
Sure, there are spring type worm-drive hose clamps, and fully lined type clamps to mitigate the teeth cutting into the hoses, but these are designed primarily for higher pressure applications like turbos...not relatively low pressure cooling system applications.

Every time I see a cooling system with hose clamps (ok for garden hoses, and sump pumps), i wonder why the heck the owner didn't just replace his tired old spring type OEM clamps...or at the very least bend them to re-tension them if he's caught out at the moment.

we can agree to disagree on this, but OEMs (not just GM), would not build in a failure point such as this on all their vehicles

Kenny94945

RJ (OP) ... pressure test and report.

That's the first step....I'd pressure test while the motor is cold first, followed with hot if need be.

FWIW the seephole, under the water pump as mentioned, visually could be a step in tandem with the above.

Good hunting.

dlandsvz28

Agree totally.

IMO as a precaution - might be a good idea to replace the hose as well - with early C6's approaching almost 20 years old (2005, 2006 ...)

grinder11

Nothing succeeds like success. I stand by my post. If GM worried about failure points, the LS7 would've been discontinued or redesigned by 2009. All ANY of the OEMs care about, besides making and saving money, is getting the vehicle reliable enough so there’s no issues before the warranty expires. Then, as we LS7 owners are painfully aware, you're on your own! Also, please explain how a worm style clamp doesn't clamp evenly. I have NEVER had any leaks using worm style band clamps that were sufficiently tightened in over 50 years of experience.......

rjwittmann92

I’ve got a pressure tester on the coolant reservoir and it is holding 20psi with zero drop at all for the last 30 minutes.

After doing an oil change, I’ve driven the car for a couple of hours and in some 85 degree drop and go traffic. There has still been zero smoke or anything, and the reservoir level has only slightly dropped since last topping it off. There has been no overheating and it holds around 198-200 in stop and go traffic in 85 degree weather.

I think for now I’m going to keep and eye on it and see if there was maybe just some air in the system that has been working its way out.

Too-Fast

When I had the problem the leak did not show for over an hour, half hour is not enough if the leak is very small.

rjwittmann92

I’ve still got the tester on the tank so I’ll take a good look at everything to see if I can find any sort of leak.

grinder11

On a slow oozing leak like this, pressure testing may not work. Because the engine hasn't heat sinked. The only way to replicate it would be to install the tester, and bring the engine up to approx 200°F., and up the pressure to 20lbs while at 200°-220°F. But then you'd have to trust the pressure tester to not fail. Kind of chancy. Also, if you buy traditional hose clamps DO NOT WORRY about the clamps "eating" (there's a Hell of an exaggeration!!) into the rubber. In over a half century of using these I've NEVER had any leaks, whether the clamp "ate" into the hose, or not. As for expansion? Rubber is compressible, and will self adapt. Again, like EVERYTHING today, the GM spring clamps are made down to a price, not up to a quality level, just like the LS7 heads. They are also for faster install on the production Iine. BTW.....I am still waiting for someone to please explain how a traditional hose clamp doesn't tighten just as evenly around the perimeter of the hose as the spring clamp......

tommyc6z06

No matter how old I am, or how much I think I know, I'm always prepared to change my mind.
ive learned the hardway about this 🍻
https://ca.jbtools.com/blog/worm-gea...-best-for-you/

dlandsvz28

My hunch is that the installer never added enough coolant from the get-go since you lost than much coolant in just 500 miles. Total system capacity is 12.5 quarts. IMO, if you find that the installer did not properly bleed and fill the cooling system, then I would perform a do-over and flush with the correct mixture including distilled water. Who knows if the previous owner(s) ever flushed and refilled with new coolant. Your car is 13 years old.

The steam vents are another likely source for a slow leak if the o-rings were not replaced and/or torqued to spec during the R&R.

Been there done that when the installer reinstalled the same steam vent o-rings on my TSP 370 in my 98 Z28 Camaro (holy cow - the o-rings were 20 years old). Since the coolant burned off so quickly with little telltale signs from coolant leak, it took awhile to visually diagnose the issue.

Observe by starting the engine and visually look for the leak (s) while it reaches normal operating temps as the thermostat opens. Mast states that it takes about five to 10 minutes for an LS thermostat to fully open once the coolant in the block reaches the stamped temp of the thermostat. Temps will rise at first until the T-stat fully opens then temps will drop as engine coolant mixes with the radiator coolant and then finally stabilizes.

grinder11

I hear you. Nobody knows it all or is above making mistakes, as the author of that article did. I lost interest when he said "tightening the screw results in a larger diameter, and loosening it results in a smaller diameter." Uh, no. But I don't know everything either. What I do know is I've experienced a failed spring clamp, and never had a failed worm gear clamp. Which resulted in me chasing the same problem as the OP. Which is why I posted my info. Just trying to help him run it down.....

tommyc6z06

yep...here's the result of having to keep tightening a worm gear clamp as it can't expand and contract with temperature swings (don't recall if this was a heater hose or turbo water cooling hose). Anyway, like you, just trying to help the OP and for sure, a tired leaking spring clamp is also a possibility.

double06

I have found on the spring clamps that have some age you need to relocate them back to their original position when reassembly. They kind of make a specific dent in the hose on the outside and the inside.