Mysterious Coolant Leak

[2000YukonXL]

2000 Yukon XL 5.3L, with a mysterious coolant leak. Has been to 4 different shops and checks out fine, pressure checked the system (even over night) and its perfect... Low coolant light comes on after about a 30 min trip, no over heating, front heat works fine, rear heat is ice cold, but not showing any signs of leaking back there either. Maybe I'm looking in the wrong spot?? Been this way for 2 years!! HELP!!!

 

[LinuxMint]

Is it actually leaking, or are you just going off of the light?

 

[2000YukonXL]

Its definitely leaking! Runs the resevoir dry in a short amount of time, maybe 150 miles max on the freeway before you HAVE TO stop and fill it back up, but even when its low, it won't overheat. There's been speculation that it may be the head leaking into the exhaust, but nobody has proved it, and beings that its been 2 years I feel like something would have gone seriously wrong by now...

 

[bkboatnsleds]

Google "Castech Heads" Hope I',m wrong.

 

[04SS99Denali]

sounds like a head gasket issue if there is no visible leak. is it leaving a lake under the truck? do you smell it at all? from the way its leaking you should have a pretty hefty puddle under the truck if its actually leaking

 

[CEN2MENTAL95]

have you found any oil in coolant or coolant in the oil?

 

[2000YukonXL]

Coolant and Oil are not mixing, and other than the fact that it goes empty so fast there is absolutely no sign of the truck leaking. I've checked and rechecked the carpets, hoses and everything else I can find, nothing is wet or appears to be leaking. The only other thing that might be a sign is that when the truck is cold in the mornings, the exhaust steams some for a few minutes then stops, and the rear heat blows ice cold, thats why I was thinking possible rear heat related? Its been 2 years Its getting kinda old!! I'm going to go google those heads.....

 

[bottomline2000]

I have developed the same problem. no source of leak. no puddle under truck, no smoke out tailpipe, no coolant around engine no driveability issues. just missing coolant. I'm thinking I have the castech blues.. heads are stamped 700 I do believe.

 

[2000YukonXL]

Seriously, how long can one drive around with these castech heads spewing coolant into the oil before some serious happens? Something has to give!! We're talkin 40-50,000 miles! I actually took it from WA to SoCal, straight through both ways (except fuel) 2500 miles round trip, I'm baffled! If mine is a Castech head issue, I do have to say they're holding up pretty well lol. I was reading somewhere else from a Google search something about a guy with a similar problem, except he says his was pooling coolant in the intake manifold and blowing it out the exhaust.... I'm thinking that is a plastic or composite intake manifold?? Is it possible that the coolant is going in there? maybe cracked? I dunno, I'm just a chick on a mission

 

[bankswood]

OK I'm going to throw this out . I have a friend with a late 90's Honda. It was using more coolant than gas. Same symptoms as you. No leaks, no coolant in the oil, etc. Finally found out he had a bad 02 sensor. Never threw a code but a new sensor fixed the problem

 

[LinuxMint]

OK I'm going to throw this out . I have a friend with a late 90's Honda. It was using more coolant than gas. Same symptoms as you. No leaks, no coolant in the oil, etc. Finally found out he had a bad 02 sensor. Never threw a code but a new sensor fixed the problem

That's very strange.

 

[Rivieraracing]

When it comes to the rear air blowing cold, it's more than likely the blend door actuator that controls the air temp coming out of the rear air that is bad, doubt it has anything to do with the coolant problem! The actuator is located in the back right of the truck, next to the rear air heater core!!
Does the rear air ever blow out warm or even hot air?

---------- Post added at 07:22 AM ---------- Previous post was at 07:20 AM ----------

Its definitely leaking! Runs the resevoir dry in a short amount of time, maybe 150 miles max on the freeway before you HAVE TO stop and fill it back up, but even when its low, it won't overheat. There's been speculation that it may be the head leaking into the exhaust, but nobody has proved it, and beings that its been 2 years I feel like something would have gone seriously wrong by now...

When you say it runs the resevoir dry, are you saying it goes from full to turning the low coolant light on, or is it completely draining the resevoir? Also, where abouts in Washington are you located?

 

[2000YukonXL]

Rear air works perfect, and the reservoir runs completely dry. I think the only solid answer is to just get in the and start checking things out... At least I know a couple places to look... And I'm in Vancouver,WA

 

[Rivieraracing]

Well I live just east of gresham, if you wanted another set of eyes to check it out, feel free to let me know!! If it's causing the resevoir to go completely dry, you either have a leak or it's burning it soo bad that you should be smelling it out of the exhaust!! That's no good!

 

[ScottyBoy]

Mine had a similar problem. I would have to refill the reservoir about once a week or about every 150-200 miles. I FINALLY found that it was dripping from the weep hole on the water pump. But it was evaporating as soon as it dripped onto the hot engine, that made it extremely difficult to find the leak. Once I replaced the water pump it was fine ever since then.

 

[2000YukonXL]

Now that the water pump has been mentioned, I did hear what sounded like a grinding noise this morning when the reservoir was empty and as soon as I filled it back up, the noise was gone.... Dam, I don't want to just start blindly buying parts and I sure don't want to pay shop prices cuz one could only guess how long it make take a shop to track the leak down, considering they'd be doing it on my dollar

---------- Post added at 08:31 PM ---------- Previous post was at 07:53 PM ----------

And I would definitely be interested in the extra set of eyeballs

 

[ScottyBoy]

Drive it for less than 5 minutes, and then fully inspect it for leaks. That's how I finally found my leak. Once the engine gets hot, it literally evaporated as soon as it dripped out. But taking a drive around the block and then inspecting it, sure enough I saw an actual wet streak running down from the weep hole on the water pump. I was adding coolant about once a week for over 2 months before I finally confirmed 100% that it was dripping from the weep hole in the water pump.

 

[BigAlz71]

Here's my update. 2005 Z71. Had a coolant leak. Reservoir was always slowly draining last 6 mos. took it to local repair shop. Pressure test, all good. Pulled plugs to see if coolant was leaking into the engine, nope. Checked heater core, all good. Car wasn't running "hot", nor was there ever a puddle of coolant under my truck any morning, nor did I smell coolant. Total mystery. I just kept monitoring.
Then, over Christmas, I went skiing. The temp change must have effected it, because now I could see it leaking from the water pump. Best guess is the metal contracted in the cold and cracked a gasket or something.
Repair guy told me that I undoubtedly had a slow leak and the drops would burn off on the hot engine before I could smell it. Excess drops would land in the skid plate.
So, I would check the water pump. Mine lasted 135k miles.

 

[SLCHOE]

Look at the weep hole. If there is any greenish/orangeish crud around it, Your pump has been leaking. Replace it. Same goes for the water pump gasket. Check the perimiter of the water pump for the same residue. This residue is what is left over when the coolant burns off. If there is no residue around the weep hole or water pump gasket, I'd stop looking at the water pump and start looking into whether you have Castech heads or not and/or looking at the or head gaskets.

 

[Mudfrog]

I have to top off my coolant about once a month or so. I've dreaded that it was the heads issue, and my water pump was replaced a few years back. Maybe I'll be lucky and the water pump needs to be replaced again.