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FIX: Coolant Odors/Coolant Loss From Reservoir

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Many members are experiencing coolant loss over time and venting through the reservoir (surge tank) cap. Symptoms include coolant loss and coolant odors both outside and inside the car.

The reservoir vent channel it this plastic piece on the left side of the cap:



If your cap is venting you will see moisture build-up under this channel and/or white and orange deposits. This post only covers issues surrounding coolant loss through this vent channel.

If you are losing coolant vapor through the vent channel the vapor can get into the car through the HVAC intake. This is supposed to be sealed from the engine compartment, but many cars exhibit a gap in the cowl seal right near the coolant reservoir. When coolant vapor exits the tank it is free to pass into the HVAC intake through this gap. Here's a crude cross section diagram of how this happens:



The foam gasket between the cowl cover and cowl tub doesn't seal properly on many cars, allowing coolant vapor into the car. With the hood open you can check your car by shining a flashlight under the cowl near the tank and looking for light through the open grate in the cowl cover. Credit for this information must go to member BlueSkyMontana, who worked extremely patiently with his dealer's service department to figure this out.

I personally had to replace my reservoir since there was a defect in the throat opening. The rough spot in the throat made it impossible for the o-ring in the cap to seal properly. Here's the throat:



And here's the defect as good as I could capture it:





STEP ONE of curing your coolant venting issues will be to inspect the throat of your reservoir and make sure it is smooth and defect free. No o-ring will seal properly to a rough/damaged surface.

Even after replacing my reservoir and cap I was still getting random coolant odors and some slow coolant loss.

At the 2014 Lordstown meet I showed a few people something I was up to. I installed a thicker o-ring in the surge tank cap that dramatically increased the seal between the cap and tank. With this new o-ring I actually ran my surge tank slightly over-filled (coolant level ~1/8" above the cold fill line) and experienced no signs of venting... my tank vent was bone dry.

The problem seems to be with the lower o-ring in the cap taking a compression set (deforming) over time and allowing coolant vapor to escape. In this picture you can see how the round profile of the o-ring can change over time and offer less sealing capacity:



The o-ring on the right is after being removed from the car, the one on the left is the same o-ring fresh out of the package. To be clear, this is the lower o-ring in the reservoir cap, the one at the top of the photo:



Replacing this o-ring with a thicker version works, but replacing it with one made from a superior material also works. The original o-ring is most likely made from Buna-N, a popular material for o-rings, and measures 23mm Inner Diameter and 4.0mm thick.

This o-ring is also 23mm ID x 4.0mm thick but is made from Viton, a slightly stiffer material that resists taking a compression set. This is the o-ring I'm currently using with great success and I recommend as a first try for anyone with venting issues:


Some people have a reservoir that has an extremely loose cap fit, meaning there is very little compression of the cap o-ring as the cap is screwed into place. Here's a video I shot of a brand new '14 LT in my local dealer's showroom:


If you have a very loose cap fit and the 4.0mm Viton o-ring doesn't fix your cap venting (i.e. you still get traces of moisture under the vent channel), you may wish to try a thicker 4.5mm Buna-N o-ring:


This 4.5mm o-ring may be tight to install, so I recommend wiping a little bit of coolant on it before installing the cap for the first time.

I recommend ordering one of each since the Buna-N part is so cheap. In fact, ordering more than one of each is ideal since the shipping cost is likely to exceed the value of the o-rings, and you'll have a spare in case you somehow damage one getting it installed.

Lots of members, many who don't even know who they are, have allowed their coolant levels to drop to a level where they stabilize. As long as this level is safely above the coolant outlet in the bottom of the surge tank this seems to be working OK. The issue here is the reduced pressure in the cooling system will effectively lower the coolant boiling temperature and risk excessive boiling in the hotter parts of the cylinder head and maybe even the turbocharger. Excessive boiling can lead to poor metal temperature control, allowing hot spots to form and increasing the potential for damaging levels of heat cycling of the metal.

This lowered boiling point will be of even greater concern to anyone living at higher altitudes.

The Cruze cooling system should operate properly fully topped up. A reservoir is properly filled when the car is parked on a level surface, the engine is cold, and the coolant level is at the highest rib on the bottom half of the tank. This rib has an arrow pointing to it, indicating it as the cold fill line:



Thanks to @obermd for this photo.

I would also like to point out that I still had coolant odors under the hood after getting my reservoir and cap figured out. I had to replace the small steam hose that connects the reservoir to the water outlet on the cylinder head. This is covered in more detail in CruzeEcoBlueTopaz's thread here:


I hope this thread helps some people rid their cars of coolant odors. Remember also that the Cruze water pump is a popular source of leaks and is now covered under an extended 10yr warranty.

Good luck, and leave your feedback if you try a new o-ring for your reservoir cap. :)
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I ordered the N70 o-ring (4.5mm) and it seems to have stopped the problem where coolant was boiling and vapor was escaping.
Tank appears to be holding pressure and I have not had to add coolant since. FYI, tank is a Dorman part.
This is proof that this is a design flaw and not a general manufacturing issue. Management's assumption that an o-ring can hold pressure in all scenarios is what destroyed the Challenger in 1986.
 

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cufarmer-

Does a standard cap fit the dorman tank, or do they have their own cap design? I believe there tanks are sold with the cap, and with some of their products they redesign the cap as well.

I've been going through 1 ring every year. If I ever have to replace the tank, I'm thinking Dorman for this, vs. taking another shot with OEM.
 

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I had the severe bubbling coolant in the reservoir after the engine was turned off (temperature gauge and all else were fine during running). I discovered that my reservoir throat had a burr (distortion) that made anyone (i.e. my GM mechanic today) think that the cap was at its bottom of travel/tightening. NOT SO. Turning the cap past this false stop gave me 3 more turns before the O-ring was engaged and sealed -- BUBBLING COOLANT PROBLEM GONE!! Caution - never remove the cap when the coolant is hot. Thanks all for focusing me onto the reservoir cap and throat.
 

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I got my 14 6MT with 20k miles back from the dealer yesterday, I think this is the third visit for coolant loss. Last time, it was the water pump and I got the burning coolant smell.

This time they had it hooked up to pressure three or four different times over nights and weekends, after driving and while cold, and could not get it to leak.

Based on this thread and the fact the cap is where the pressure was connected, I suggested they replace the cap and we'll see what that brings to the party. He did mention that the parts department has been going though a lot of caps (or maybe cap O rings), and he did not know that previously.

We have a 6 hour drive ahead of us this weekend so that will give it a chance to show me if the cap fixed it. I'll check the coolant reservoir surface tomorrow where the cap seals for defects before we take off.

I asked them what was next if this didn't solve it and they thought head gasket failed in a spot where the oil and coolant couldn't mix. Apparently, the converter burns hot enough that any traces of coolant in the cylinders is burned off before it reaches the end of the tailpipe. Not sure how many HG failures people have seen but hopefully we won't get to that point.
 

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I got my 14 6MT with 20k miles back from the dealer yesterday, I think this is the third visit for coolant loss. Last time, it was the water pump and I got the burning coolant smell.

This time they had it hooked up to pressure three or four different times over nights and weekends, after driving and while cold, and could not get it to leak.

Based on this thread and the fact the cap is where the pressure was connected, I suggested they replace the cap and we'll see what that brings to the party. He did mention that the parts department has been going though a lot of caps (or maybe cap O rings), and he did not know that previously.

We have a 6 hour drive ahead of us this weekend so that will give it a chance to show me if the cap fixed it. I'll check the coolant reservoir surface tomorrow where the cap seals for defects before we take off.

I asked them what was next if this didn't solve it and they thought head gasket failed in a spot where the oil and coolant couldn't mix. Apparently, the converter burns hot enough that any traces of coolant in the cylinders is burned off before it reaches the end of the tailpipe. Not sure how many HG failures people have seen but hopefully we won't get to that point.
GM has a coolant dye that dries where ever there's a leak. This is how I figured out it was my cap/tank seal.
 

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We drove the car around 8 hours on a road trip this weekend after the cap was replaced and the level remained the same. I didn't have time to inspect the surface finish where the cap O ring seals.

That was a lot more drive time than it usually took to show up before, considering my wife drives maybe 3 miles each way to work. So I'm hopeful the O ring just hardened up and that was behind the problem. if so, I can round up a viton O ring somewhere and it may last longer than the standard NBR.
 

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GM has a coolant dye that dries where ever there's a leak. This is how I figured out it was my cap/tank seal.
I'll keep that in mind if I have more problems. It wasn't suggested by the service guy yet, which is a bit concerning.
 

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I'll keep that in mind if I have more problems. It wasn't suggested by the service guy yet, which is a bit concerning.
He may not be aware of it.
 

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I've found that using a little glycerin on the o-ring goes a long way to getting these "buna replacement rings" to fit without having to stress the cap when screwing it back on.

I'm still using the larger Buna ones mentioned in this thread. After lubing the gasket before screwing it down I've now gone 18-20 months without replacing this seal.

The solution works for me, but for some reason I've gone through seals. About one every 12 months or so.

I'm not sure if this weird problem ever got fixed with latter GEN1 Cruzes. You don't see as much action with these threads as you did when the issue was more prevalent.
 
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This thread looks like it may help solve my coolant loss reappearance. I had sooo many issues with coolant loss, fluid odours in the car, heat loss, etc, etc. Had water pump and heater core replaced while still under warranty, and they put some tape/tar on the drainage tube of the overflow tank. I'm now having coolant boiling in the overflow tank, coolant loss and car overheating, but not regularly. Frustrating when I can't seem to replicate a cooling event to my mechanic.

I have thought about replacing both the tank and cap, which now seems to be likely culprit.

Anyone ordered these items in Canada? Really don't want to be ad with the ridiculous cross border shipping we now face
 

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Rockauto does ship to Canada competitively. The O-rings we were ordering for the coolant reservoir cap were from a company out of ID If I recall correctly.

The oring store.com or something like that.

Also make sure that with the engine cold, and off you remove the white bleeder valve on the passenger side coolant tank near the top. When doing this have the coolant bottle full greater than the plastic welded seam. You'll see fluid pulled in.

You may have a venting problem.
 

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185K on a cruze diesel and I just started to smell some coolant smell after driving from the engine compartment. I'm going to try these fixes to see if it will mend the problem. Thank you.
 

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So the wife drove Chicago to Indy - solo - for the first time ever in our 2015 1LT 1.4L Cruze (bought new, currently 35,3xx I think) and sends me this text message:
282994


Just what I wanted to see when I'm at home with the kids, 180 miles away. Luckily we have relatives nearby, and there was easy access to some coolant for the ride home. She made it home safely, and refilled the coolant shortly thereafter. After leaving Indy, the needle never made it past halfway, but upon inspection, I saw there was coolant apparently leaking from the not-quite-accessible water pump, and had gotten on the accessory belt etc., not to mention a fair amount on the garage floor. My '99 Tacoma has not has such issues (knock on wood) so it has taken over family transport duties.

I'm not exactly clear on the warranty status from what I've read here and elsewhere, as we are past our 3/36 bumper to bumper, but still under the 5/60 powertrain warranty. Plus I've read about the extended 10/150 warranty for certain year water pumps. I called a local Chevy dealer who of course not only hadn't heard of Cruze water pump issues but also said there was no special coverage either. No, I won't be taking the car there. It will likely be going back to the dealer of purchase, but they don't have any time open until next Monday.
 

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HELP PLEASE!!!
I have a 2016 Cruze Limited LT with 118,300+ HW miles. I just got the water pump (I think) and thermostat replaced at the dealer, oh and the purge valve. It was running like a dream. I got my oil changed and of course, they bring up more work that needs to be done (that wasn't mentioned previously). One service, in particular, was the coolant reservoir needs to be replaced (but no rush, his words), that was a week ago. I just drove 50+ miles home from work, stopped to get gas and BOOM, WHITE SMOKE BILLOWING FROM MY HOOD. I immediately pull over and pop the hood, COOLANT EVERYWHERE! I have no clue what happened, or what to do now except take it back to the dealer.
 

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This is a great thread in identifying a problem and seeing the solutions to help fix it. Too bad my daughter's Cruze has the issue. Long story short, I:

a. Replaced the O-ring on the cap (saw yellowish crust on the cap)
b. Didn't see a decrease in the reservoir's fluid level after getting the Cruze up to operating speed
c. Didn't notice any leaks

So after my test run, the reservoir's level didn't change. I thought it would be less but, maybe I didn't run it long enough to make that difference. Anyways, after the test run and looking at the engine I noticed the sound where it seems like air and fluid are exchanging places.This lasted for over 3 or 4 minutes after turning the car off. I have a video that I can post, but, this site won't allow links in first posts. However, my phone was placed between the fan and engine and more toward the driver's side. I can only assume that I need to bleed off the air in the cooling system and will do so. But, could this sound be coming from any other areas/systems in my engine bay and/or is this sound normal?

Thanks in advance.
 
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