Vanishing coolant from reservoir...

Dshow

Registered Member
Original poster
Dec 7, 2011
65
Hi, I have a 2003 TB LT. I was going on a trip a week ago and checked the coolant level in my reservoir. I couldn't see it so I added some DexCool. I went on my trip, a couple hours each way. I checked it when I returned and it might have been slightly lower, but not noticeable, anyway, I topped it off and have been keeping an eye on it.
When I drive there is no noticeable smoke (water vapor) in the exhaust.
I have only driven short trips recently and then the car sits. I check the level every day or two. It is down ~1/2" more every time I check. There is no puddle under the car... Where could this coolant be going (and how can I check for that?)

The easy explanation is a crack in the coolant reservoir (it is ~20 yo plastic) but there is not puddle under the car and I don't notice anything when the engine is hot.

Is there a level sensor on this reservoir so that it will alert me if it ever get's critically low?
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
23,349
Ottawa, ON
Where could this coolant be going (and how can I check for that?)
Not too many places it can go. An ordinary leak somewhere, into the engine either into the combustion chamber or into the oil, or both, and on very rare occasions, into the transmission fluid through the cooler in the radiator. Another possibility is that you have combustion gasses pressurizing the cooling system via a head gasket leak and pushing coolant out of the overflow.

May be worth it to get a coolant UV dye and UV light kit and see if you can spot where it's coming out. Maybe do a compression test on the engine and check the plugs for any anomalies.
 
  • Like
Reactions: djthumper and mrrsm

mrrsm

Lifetime VIP Donor
Oct 22, 2015
6,275
Tampa Bay Area
Are you smelling the Sweet Odor of Poly-Ethylene-Glycol (PEG) anywhere inside of the Cabin? a Pin-Hole leak inside the Heater Core can allow a slow leak to drip down and evaporate along the Fins from residual heat even before it gets the chance to form a puddle anywhere below.

Same thing with Under Hood Heater Hose connections: Check around the Clamps for either Cracked Hoses or at those two weird Black Plastic Hose Fittings at the Firewall that can also become FUBAR. Those complicated items are replaceable using the Dorman Kits unique to each Hose Connection Combo,

Look closely for any leaks at the Heater Hose leading from the Lower Driver's side of the engine block that feeds through an Aluminum Pipe running over the back of the Engine Head to Transmission Bell Housing area and ends in a Rubber Hose attachment. Then Check around where the OTHER Heater Hose exits at the Lower Rear Passenger side of the Block through a Short Steel Pipe.

Also... Examine the Firewall where the Heater Core Hoses can leave tell-tale gravity streaks and traces that don't quite make it to the ground before evaporation makes it all go away under a Hot Hood.

And for GMT360 Owners with V8 Engines... Eric "O" from SMA (South Main Auto) shows us THIS situation as being another possible place to look for "The Vanishing Coolant":


In many cases... looking for any leaks just after shutting down a Hot Motor will NOT work... until the Heat from the 'quiet engine' transfers into the Coolant Water Column.

This can take a few minutes just AFTER shut down to occur. By then... The Radiator and Coolant will have absorbed enough of the residual engine heat and any additional resulting pressure that occurs may provide enough of a 'push' to make the Coolant Leak occur. This may seem counter-intuitive ...but it's behavior in this manner conforms with The Three Laws of Thermodynamics.
 
Last edited:

Dshow

Registered Member
Original poster
Dec 7, 2011
65
Thank you both!
I did smell a faint coolant smell, but I attributed it to topping off the reservoir and spilling. Now I'm beginning to think it may be the heater core, and it's just not cold enough outside yet to make it obvious.

(Until I figure it out, I will do some research here on how to replace a heater core...(if needed) I'm guessing it will be a PITA to get to.)
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
23,349
Ottawa, ON
To replace the heater core, the entire dash has to come out. Not a fun job. I've done it for an evaporator, took a whole day. We do have this thread that shows how to do it without taking the whole HVAC box out:

 
  • Like
Reactions: mrrsm

TollKeeper

Guru
Dec 3, 2011
7,174
Brighton, CO
I did not notice him telling if he had a 4.2 or a 5.3. The 5.3 is known to leak a bit of antifreeze where the connections are at the waterpump going to the heater core. They never leak enough to leave a puddle, but leak enough to leave a whiteish residue at those connections.
 
  • Like
Reactions: Mike534x

Dshow

Registered Member
Original poster
Dec 7, 2011
65
Thank you both. (I have a 4.2)
The Chevy service manual says I need to drain the AC first...??? Is that true???? (I noticed an access panel in the engine compartment. I don't suppose I could change it that way?
 

Attachments

  • Screenshot 2022-09-20 115620.jpg
    Screenshot 2022-09-20 115620.jpg
    64.7 KB · Views: 5

mrrsm

Lifetime VIP Donor
Oct 22, 2015
6,275
Tampa Bay Area
THIS Trailblazer HVAC -Heater Core R&R Video will painfully Illustrate the INSANE amount of Labor and the headache of having the requisite Mechanical Knowledge of How to DO all of the Detailed Work involved in this Job... and it points out WHY the A/C Freon must be evacuated prior to beginning all of the R&R work:


Look into @Mooseman's Suggestions-Link and try to locate MORE Instructive Videos as to How to perform this Repair. Do NOT Turn a Wrench until you are COMPLETELY prepared with everything entailed here...well before you begin, STARTING with answering THIS Question:

"Are you ABSOLUTELY LEAD-PIPE-CINCH CERTAIN that the Evaporator-Heater Core is Actually Leaking Coolant and is the Actual Cause and Origin of this Problem?"
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
23,349
Ottawa, ON
And be sure it actually is the heater core. They don't leak that often requiring replacement. Telltale sign is coolant in the passenger footwell and coolant smell inside the truck coming from the vents as well as steaming of the windows
 
  • Like
Reactions: mrrsm

budwich

Guru
Jun 16, 2013
1,793
kanata
Thank you both. (I have a 4.2)
The Chevy service manual says I need to drain the AC first...??? Is that true???? (I noticed an access panel in the engine compartment. I don't suppose I could change it that way?
I would look closely at doing some "cutting" before doing any kind of dash removal. Not sure if it is feasible but you never know when "push comes to shove" as in wallet and time.
 

Mike534x

Hobbyist
Apr 9, 2012
805
Out of curiosity, if the heater core does have a "small" leak wouldn't running the heat with the fans on full blast be able to give a passable smell test for anything sweet coming through the vents into the cabin? Or lack of hot air coming from the vents?
 

Joe_67

Registered Member
Aug 9, 2022
56
Central Virginia
I have an '02 Envoy SLT with the 4.2L in it. I've had it for about 3 years and have put like 30K on it. As far as I can tell, the reservoir is just too small. I can fill it to the "full cold" mark and it never stays there. A buddy who owns a couple of GM trucks says they all do it to. (But obviously not "all" - his are early '00 models too). Fill the reservoir to the cold mark - and once it's up to temp there's an excess that goes out the overflow.

I've never verified that 100% visually or in any other way. I just know this - If I fill the reservoir to full cold, it doesn't stay that way. But my radiator NEVER goes low on coolant (and I've certainly not overheated).

So just for a hoot, and before doing anything drastic, try ignoring the marks on the reservoir. Watch the radiator fill level instead. (ONLY CHECK THAT WHILE COOL!! You know, obviously...) See what happens. I'd not be surprised if you have no problem at all - other than an undersized overflow reservoir.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
23,349
Ottawa, ON
I have an '02 Envoy SLT with the 4.2L in it. I've had it for about 3 years and have put like 30K on it. As far as I can tell, the reservoir is just too small. I can fill it to the "full cold" mark and it never stays there. A buddy who owns a couple of GM trucks says they all do it to. (But obviously not "all" - his are early '00 models too). Fill the reservoir to the cold mark - and once it's up to temp there's an excess that goes out the overflow.
I've owned 3 of them, two with the 4.2 and one with the 5.3 and never have I had an issue with losing coolant unless there was a problem. I can't see why a too small reservoir would cause coolant loss. My 07, for the past 5 years, hasn't lost a drop and stays at the full cold mark when cold.

You're losing it somewhere but unless the tank itself is leaking, which has happened, that ain't it.
 
  • Like
Reactions: mrrsm

Joe_67

Registered Member
Aug 9, 2022
56
Central Virginia
I've owned 3 of them, two with the 4.2 and one with the 5.3 and never have I had an issue with losing coolant unless there was a problem. I can't see why a too small reservoir would cause coolant loss. My 07, for the past 5 years, hasn't lost a drop and stays at the full cold mark when cold.

You're losing it somewhere but unless the tank itself is leaking, which has happened, that ain't it.

Well, then my tank leaks, I guess. But "too small" a reservoir would just mean not big enough to handle the size of the coolant expansion when hot. And they do all have an overflow outlet on the expansion tank, unless they're pressurized. And on the '02 they're not. Can't say about the '07.

I just generally don't go by what's happening in the expansion reservoir as reservoir level, while generally speaking is a thing to go by, isn't the crucial part. The radiator is where the real action is, so I just check that once in a while. All I know is that I've been in it for 3+yrs the reservoir has never stayed full, but the radiator has. (Even if I ignore the reservoir).

But now that it's come up...I'm going to go ahead and figure it out. I'll report back if/when I figure anything out.
 
Last edited:

mrrsm

Lifetime VIP Donor
Oct 22, 2015
6,275
Tampa Bay Area
To follow on with another 'Diagnostic Check List' Item...

If the Vehicle is close to requiring a Change of Spark Plugs... you can use that event as an excuse to poke a 7-9 mm Fiber-Optic Borescope Camera Probe down through each Spark Plug Hole:

et voilà


What you are looking for is the effect of any "Steam Cleaning" that will occur along the Piston Tops as the in-flow of Hot Coolant gets sprayed under pressure into the even HOTTER Cylinder(s) from somewhere around the circumference of a Failed Head Gasket. This action will scour the Baked-On Carbon Deposits, Congealed Oil and Fuel Gas-Gum Residue right off of Top(s) of the Piston Head(s).

Trust when I suggest that if THIS is "The Problem"... you will readily know it If you can see any of the Piston Tops appear Shiny and "Klean as Kleenex". THIS is a sure sign of a Blown Head Gasket (which translates to meaning "An Engine Swap" vs. trying to R&R the Engine Head in the case of having the GM 4.2L LL8 Engine under the Hood).

The added urgency if this turns out to be 'The Problem' is that if enough of the Coolant is NOT being vaporized and it continues passing the Piston Rings down into the Crank Case, getting mixed in with Engine Oil, it can cause the Main Bearings to Corrode and Seize to the Outer Diameter of the Crankshaft Journals.

"Nothing becomes a Dead Engine...Like SPUN MAIN BEARINGS..."

This image below serves as a perfect example of this "Instant Blown Head Gasket Diagnosis". You know as strange as this may sound... I would almost Pray for THIS to be the issue over EVER having to R&R a Dashboard In and Out of any GMT360:

BLOWNHEADGASKET.jpg

Amazon carries a wide selection of Fiber-Optic Probe Cameras to suit your Pocket and your Repair Situation:


An Additional Link to a GMTN Borescope Topic:


If you see NO SIGNS of these Artifacts... Move on to the NEXT Item on The List... :>)
 
Last edited:
  • Like
Reactions: Joe_67 and Mooseman

Mektek

Hobbyist
May 2, 2017
641
FL
I had a pinhole in the heater hose that would only leak with a hot engine. The reservoir was slowly depleting and that's how I got suspicious. When I tried to remove the plastic adapters from the heater core they cracked. I clamped the new hoses directly to the aluminum tube from the core and eliminated the plastic adapters.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
23,349
Ottawa, ON
For using a boroscope to check for a blown head gasket, this video is more on this subject and also features the Depstech dual camera boroscope.


In case you or anyone else is so inclined, this is the one I bought from Amazon.ca


And for US members, there are quite a few choices:


I would recommend the one with a screen as the wireless ones are a bit of a PITA to use.

If you do buy one, please use one of the links above so the site can get a little kickback.
 
  • Like
Reactions: mrrsm and Redbeard

TequilaWarrior

Active Member
Dec 5, 2011
497
Central Pennsylvania
I have an '02 Envoy SLT with the 4.2L in it. I've had it for about 3 years and have put like 30K on it. As far as I can tell, the reservoir is just too small. I can fill it to the "full cold" mark and it never stays there. A buddy who owns a couple of GM trucks says they all do it to. (But obviously not "all" - his are early '00 models too). Fill the reservoir to the cold mark - and once it's up to temp there's an excess that goes out the overflow.

I've never verified that 100% visually or in any other way. I just know this - If I fill the reservoir to full cold, it doesn't stay that way. But my radiator NEVER goes low on coolant (and I've certainly not overheated).

So just for a hoot, and before doing anything drastic, try ignoring the marks on the reservoir. Watch the radiator fill level instead. (ONLY CHECK THAT WHILE COOL!! You know, obviously...) See what happens. I'd not be surprised if you have no problem at all - other than an undersized overflow reservoir.
This is the exact same experience I have... I've gone to ignoring the reservoir (more or less) and check the rad when I think about it. I've never had a low level in the rad.
 

Dshow

Registered Member
Original poster
Dec 7, 2011
65
Thank you all... I'm not doing anything until I figure out where the coolant is going. The engine is not overheating so right now, it's just a 'keep and eye on it'. In the winter months, that will tell me if I have a heater core issue.

I read somewhere that the reservoir has a low level sensor? Is that true? If that's the case, I don't see any issue with driving until that goes off and if it does, just refill the tank.

I've got some rusty power steering lines that I see as a potentially bigger issue I'd like to address first...
 

TollKeeper

Guru
Dec 3, 2011
7,174
Brighton, CO
Neither of my V8's have a low level sensor..
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
23,349
Ottawa, ON
Never saw one in any of mine, including the "high-end" '06 Saab and LTZ '02 TB EXT. They did have an oil level sensor for the '02 4.2 but they deleted that in '03+.
 

budwich

Guru
Jun 16, 2013
1,793
kanata
Thank you all... I'm not doing anything until I figure out where the coolant is going. The engine is not overheating so right now, it's just a 'keep and eye on it'. In the winter months, that will tell me if I have a heater core issue.

I read somewhere that the reservoir has a low level sensor? Is that true? If that's the case, I don't see any issue with driving until that goes off and if it does, just refill the tank.

I've got some rusty power steering lines that I see as a potentially bigger issue I'd like to address first...
tape a paper bag to the overflow outlet.... IF you are losing fluid because of the "small tank thought", your bag will either be wet or gone depending on how big a "blow" happens. Go from the result. You might be surprised. :smile:
 

Dshow

Registered Member
Original poster
Dec 7, 2011
65
OMG!!!!! I just watched the video on the heater core replacement...

Please, don't be the heater core. Please, don't be the heater core....
 
  • Sad
Reactions: mrrsm

mrrsm

Lifetime VIP Donor
Oct 22, 2015
6,275
Tampa Bay Area
Forgot to mention one of The Most Simple and Effective Diagnostic Tools around when it comes to isolating Fluid Leaks of ANY Kind:

Large Sections of Cardboard

The Bigger...The Better ...and in the case of having to Park the Vehicle on any unprotected, uneven (Highly Absorbent) surfaces outside of having any Nice, Level and Open Concrete Garage Floor, make some "Notches" at the perimeter around the Front Tire Contact Surface Areas so that the Wind cannot get underneath, catch it and move that Large Cardboard Section around ..."Uber-Nacht".

Remember to FIRST Top Off ALL of the Fluids (Engine Oil, Transmission Fluid, Engine Coolant, Windshield Washer Fluid, Power Steering Fluid, etc.) Then, thoroughly Warm up the Vehicle, allowing the Engine AND Transmission Temperatures to come up to nominal levels.

Then Park and Shut Down the Motor and Slip the "Tell Tale Leak Catcher" Firmly in Place. Afterwards...Walk Away... or just like NOT being able to 'Wait for a Baking Cake and Cookies to get "DONE!", you will NEVER Catch The Leaks... unless you leave the SUV-Truck to remain "IN SITU" for at least a few hours. (NO Peeking!)

YMMV... But it is often surprising what CAN be found using this Basic Leak Detection Technique; even from just doing this as an Irregular or Monthly Exercise in figuring out ..."Why DOES My Transfer Case keep making SO Much Noise...?" :>)
 
Last edited:
  • Love
Reactions: Redbeard

Redbeard

Guru
Jan 26, 2013
3,238
Just a suggestion for the cardboard: Check out a Lowes or Home Depot or local Appliance store to find a large box so that the wheels can easily hold it in place. The large piece of cardboard I am now using came from the air conditioner replacement I had done last year and the large size works great. I also makes working under a vehicle much more comfortable.
 

rcfowler64

Newbie
Feb 14, 2022
2
SC Pennsylvania
I had something similar (02 Envoy, 4.2 L). Main culprit was a leaking water pump. I could smell coolant in the engine bay but no drips on the floor or wet spots that I could find. Turns out the water pump was slowly leaking out the weep hole just enough to drain the system slowly over time - about a quart every couple of weeks. Had shop replace water pump to fix that. However recently I was having the same symptoms. Had the shop reinspect the water pump - it is OK. While working on other front end items, I just happened to touch under the small coolant hose that goes from the top of the radiator over to the overflow tank. I found that the small coolant hose was dripping at the radiator connection. There was no hose clamp on this hose so I figured it must have loosened up over time (20 years) and would drip out slowly when under pressure - when the radiator cap opened up. I put a hose clamp on that hose at the radiator and no leaks since that time.
 
  • Like
Reactions: Dshow and Joe_67

Dshow

Registered Member
Original poster
Dec 7, 2011
65
I thought I had mentioned previously that I found a couple of drips on the driveway. From underneath the car, I could see the radiator was leaking. I added a can of Stop Leak to the radiator and was going to keep my eye on it...
Well... today I went to check my coolant level. This is what I found:
1664394400425.pngLooks like replacing my radiator just moved up on my priority list...
I like the card board idea... my driveway may thank you.

A couple of general questions:
- Any particular brand people recommend? Alot of brands I have never heard of. The GM brand is about 2x as expensive...
- Does the fan have to come off to remove the fan shroud?
- I need to also do my power steering lines at some point (they have not failed though...) Should I tackle these together or can I do the power steering lines later and without removing the fan shroud?

Thanks!
 

Blckshdw

Likes lights and stuff
Moderator
Nov 20, 2011
10,360
Tampa Bay Area, FL
I had something similar happen to my radiator. Upper tank got a hairline crack in the top, coolant sprayed everywhere once it got up to temp. I ended up going with this aftermarket radiator since it has a drain on it. Have had it for 3 years now, and no problems.


Since it was 2019 when I did mine, I'm pretty sure (but not 100%) the fan has to come off, to get the shroud out, but I wanted maximum space when I was working on it.
 

Joe_67

Registered Member
Aug 9, 2022
56
Central Virginia
It obviously didn't help much anyway, but I'd avoid stop leaks in general, particularly in cooling systems. I'm not saying that they can't help as a band-aid sometimes. But their job is to clog stuff. Those radiator passages are really small.

As for a radiator brand, others might have different ideas and I welcome those - but a radiator is just a radiator. Not a complex electrical item or something. And even if you buy one branded "AC Delco" or something it probably comes off the same line as many of the alternative brands. For things like that, I have a local parts store (meaning not some big box chain). They've been around a long time, know what they're doing and don't sell junk. So see if you can find a place like that to source parts.

The easiest way to get the fan/shroud out, as far as I know, is all at once - fan and shroud come out at the same time.

I can't answer intelligently about the PS lines. Haven't yet had to mess with them.
 
  • Like
Reactions: Dshow

TequilaWarrior

Active Member
Dec 5, 2011
497
Central Pennsylvania
Real experts will be along soon but....
Removing fan and shroud together should be the goal... it's not that complicated. Once the cooling system is drained the rest shouldn't be overly difficult. Pay attention when removing the fan - make sure you're turning the nut in the right direction! If I'm not mistaken, the shroud/fan lifts as an assembly straight UP (make sure you get all fasteners for the shroud!). Also, be very aware of your fan's pig tail. If you're replacing the radiator, STRONGLY consider replacing all the hoses that connect to it... you may not ever get this good a chance to do so. Removing the water pump is straightforward but installing it you need to be careful not to overtorque the bolts. Check/doublecheck the specs. That block is soft aluminum, you don't want to pull the bolt threads out of it. You may also want to consider the thermostat and temperature sender since you have the cooling system drained - but that requires removing other "stuff". Again, you may never get this good a chance to do so.

As for your power steering lines.... I don't believe they are affected by the radiator. You SHOULD be able to do them entirely separately from the radiator without having to touch the cooling system in any way. I will say, if you're doing PS lines, consider replacing the entire cooler... if the lines are shot it probably is too. Them PS lines are a real PITA to change, though.
 

Dshow

Registered Member
Original poster
Dec 7, 2011
65
Thanks all...
I'm taking this opportunity to flush the system. I've bought new Dexcool to replace it with. It looks pretty straight forward, I've replace my fan clutch before.

If I recall, the trans cooler hoses are held to the radiator with clips that I need to use a pick to get off? Is that correct?
 

TequilaWarrior

Active Member
Dec 5, 2011
497
Central Pennsylvania
Thanks all...
I'm taking this opportunity to flush the system. I've bought new Dexcool to replace it with. It looks pretty straight forward, I've replace my fan clutch before.

If I recall, the trans cooler hoses are held to the radiator with clips that I need to use a pick to get off? Is that correct?
That is correct... there should also be a little plastic "cover" that slides over the recess that the clip inserts into. You should have to pull the cover back and then you should be able to remove the clip with a pick. I used a hook shaped pick to do mine. Be careful though... they are "springy" and will go flying if you're not careful.
 

djthumper

Administrator
Nov 20, 2011
14,946
North Las Vegas
Stop Leak = Clog Radiator

He didn't mention where he was located and how the "temp gauge" was reading. people always overlook the radiator cap as a potential issue.
 
  • Like
Reactions: Mooseman

Dshow

Registered Member
Original poster
Dec 7, 2011
65
Spent yesterday changing my radiator. Not an easy job, but pretty straight forward. While I was in there, changed my lower radiator hose and noticed some cracks in my serpentine belt, so I changed that as well.

I got a TYC brand radiator on Amazon. Not the cheapest or most expensive (OEM), but had good reviews on Amazon.
1664715066429.png
I'm impressed with the initial quality. Was packaged very well and had all the pieces for the trans cooler quick disconnect. Time will tell if I'm still impressed a year from now......
While I was topping off the overflow tank, I noticed some coolant hitting the ground, so there may be a crack in that plastic as well... (They're pretty inexpensive and it looks like an easy replacement so I ordered one...)
 

Forum Statistics

Threads
22,402
Posts
625,815
Members
17,029
Latest member
Bama Bill

Staff Online

Members Online

About Us

  • Our community has been around for many years and pride ourselves on offering unbiased, critical discussion among people of all different backgrounds. We are working every day to make sure our community is one of the best.

User Menu

Secure Browsing

GMTNation.com uses SSL to secure all traffic between our server and your browsing device. All browsing and transactions within are secured by Sectigo SSL with high-strength encryption.