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FIX: Coolant Odors/Coolant Loss From Reservoir

116303 Views 117 Replies 39 Participants Last post by  Blasirl
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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You don't need to worry about bleeding the cooling system unless you think you have air in it. Just taking the cap off and replacing it is fine, no worries there.

As far as the high coolant level, I wouldn't worry about it. If you see signs of venting and the fluid is too high, that's probably why. The system should loose a little water over time from that steam and the level should drop. If the level is correct and it's still venting, that's when you know something's still not right.
carbon, it hasn't been into the dealer yet! If I could get my hands on a $50 water pump I would probably do the job myself. Chances of that happening are pretty slim for me up here in Canader, where the dealerships LOVE to charge for parts.

My car has to go in for a recall notice (air bag coil), so I might have to bite the bullet and just get the pump done at the same time. Drat.
"We have received your order and wanted to confirm you know the V4.00X023 O-ring is backordered. We will e-mail when we have the expected date that they are due in from the factory. If you would like to upgrade to expedited shipping call or e-mail us. "

Blue Angel looks like you increased sales of their o-ring :) looks like it is backordered.
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Blue Angel looks like you increased sales of their o-ring :) looks like it is backordered.
Time to call them up and collect my commission! :D
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Doing some technical googling, I found another potential source for you.

Viton O-ring 23 x 4mm Price for 5 pcs - Orings and More

I haven't ordered from them, so please check everything out before ordering. It looks like they only sell packages of 5 rings for $6.30, but will ship them for $2.75. However, it looks like the 4.5 mm x23 BUNA ring is not there. If I recall from googling earlier this year the 4.5 mm cross sectional area is a bit harder to find.

I also remember seeing amazon carry rings. "Viton O-Ring 23mm x 4 mm" you'll have to look there.

I believe here's the product on Amazon. Amazon specifies rings by OD. If the cross section is 4 mm and ID is 23 mm. OD is 31 mm right? Appears to be that way reading the posting info. Package size varies here all the way up to 100 rings per package. The link is for 5 rings for $8.20. Probably not the best price per ring, unless you buy the 25 pack, but that's a lot.

Blue Angels original seller still gives you the advantage of buying a bunch of different sizes and materials to try to solve the issue. If they restock the Viton, I would probably order from them, unless I was doing an amazon order for other items.

The problem is finding the 4.5mm x 23 mm Buna ring. I couldn't find it on Amazon. That cross section has to be an odd ball.
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My 2 Cents on this issue, it may help others troubleshoot. Thanks to the posters on this thread for helping me self troubleshoot this.

I have a 2011 Cruze 1LT RS 1.4 Auto

I ordered the O-Ring as well before they sold out and also ordered a new surge tank, cap and various hoses online from gm parts direct for $60 as I was about to dive into this myself, see my story below.

I previously had the dealer do the water pump about 3 weeks ago under the service advisory as I was losing coolant pretty consistently. I must have bought 2 gallons of 50/50 mix over 3 months.

Anyway I got it back and it was ok for about a week then started leaking again but this time it was different. I couldn't see anything obvious but the surge tank was venting and the coolant was now boiling where it didnt really do that before, I was mostly losing coolant from the water pump dripping. This new symptom was also causing coolant to hit the engine and cause steam to emanate from under the hood and also you can smell it in the cabin now.

I put the new O-Ring on which sealed much better and checked the rim/lip and it was smooth on the tank. The engine did appear to warm up faster and blow hotter air from the HVAC. After this I noticed I was still losing coolant and now more rapidly. I finally found the culprit.

The Water Outlet has a small hole in the elbow which I couldn't see before, now it was very easily spotted due to it bubbling and steam coming out. I am thinking now the system is pressurized better it made the hole more visible. I noticed the coolant is bubbling from the joint and leaking onto the engine. I don't know if this is caused by the dealer putting pressure on it during the water pump replacement or if there was a smaller hole that grew over time.
Tire Automotive tire Auto part Automotive wheel system Wheel

Auto part Engine Fuel line Vehicle Automotive engine part

Again it leaked from the pump before and the engine was clean to now leaking from somewhere higher and leaving Dexcool stains over the top driver side of the engine.

I called GM to find out if this is covered under the powertrain warranty since my bumper to bumper was up 2 years ago. The lady on the phone while nice was not sure, I found the wording on the website regarding the cooling system unclear as it stated "and/or outlet" . They through in a free hour of troubleshooting on my file if I bring it into service since the last time I brought my car in the dealer made me agree to a diagnostic charge of $129 an hour when I brought it in under the service advisory. They wound up covering it with no charge and I did wind up spending $500 with them on 2 tires, pads and rotors which I knew I needed anyway.

Anyway I am awaiting a call back from the dealer to schedule this, I found the part for $20 online (55565334 ) but if I can get this covered I might as well since I don't want Dexcool all over my driveway when swapping this part out and risk them using it against me if I have future claims on the powertrain.

In the end I think there are a multitude of issues with the cooling system design on the early Cruze's, from the water pump to the surge tank sealing to the various parts in between.

Also my AC hasn't worked in 2 years also but that is another story for another thread...
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FYI on the stock status of the o-rings.

Your sales order #58873 is attached.

The O-rings are expected in by 3-12-2015 from the factory. The warehouse will check them in and ship the order out complete ASAP.

Thank you for your business - we appreciate it very much.
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Your first picture is zoomed in so far I can't specifically tell where it's leaking. Some members have reported leaks on the hose from the water outlet to the top of the coolant reservoir. This is the coolant bleed hose. I believe that's what GM calls it.

Isn't 55565334 a completely molded plastic piece? So the plastic is actually cracked and leaking?

Make sure you check the coolant sensor that goes into 55565334. It appears that the sensors may be a press fit with an o-ring and clip, vs. a traditional threaded fitting. There's a seller on flea-bay that is selling 55565334 and it shows a lot of pictures, and apparently it comes with the electrical coolant sensor in it. It's that picture that made me realize that connections may not be traditional threaded, and rather may be a press fit with more o-rings.
Hi Carbon, the part is the water return that I zoomed in, theres 4 Outlets after it leaves the block, 1 goes straight up and back to the surge tank, the other 2 go two the front to various places and the 3rd heads to the back, I cant remember exactly. 55565334 is a complete mold but you can see the crack in the crease of the elbow in mine. It started so small and underneath is the hot engine / exchaust manifold I believe so when it leaks on there it creates steam and the smell of burning coolant. I should be receiving the part tomorrow so I will dive in and see what kind of sensors are connected.
While I haven't lookd physically at the car, I can't figure out the connection that heads out the back. The ones in the front are the water coolant from the oil cooler, connection to the top radiator, and air bleed back to the tank.

The connection that heads to the back must maybe go to the throttle body? I suspect that's heated, you can't see that connection all that well. or maybe somehow it's tied into the heater core hose at the firewall?

It's the heater core outlet to the coolant system.

Now my mind is thinking. I'll have to take a look tonight.

Good luck with the repair.
Could the connection heading to the back of the engine actually be going to the cabin heater core?
The connection that heads to the back must maybe go to the throttle body? I suspect that's heated, you can't see that connection all that well. or maybe somehow it's tied into the heater core hose at the firewall?
The rear output of the water outlet goes straight to the heater core, the throttle bodies on these cars are not heated.
Yes the one going straight back was going to the heater core. I replaced the water outlet over the weekend, it wasn't that bad just a lot of hoses to connect 3 torx bolts and a sensor which looks like a temperature probe possible on the inside. The new water outlet came with the sensor pre-installed and the gasket. Of course whatever coolant was in the hoses leaked out onto the engine, I had a pan under to catch as much as possible. So far no leaks or smells.

Hand Optical instrument
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Yes the one going straight back was going to the heater core. I replaced the water outlet over the weekend, it wasn't that bad just a lot of hoses to connect 3 torx bolts and a sensor which looks like a temperature probe possible on the inside. The new water outlet came with the sensor pre-installed and the gasket. Of course whatever coolant was in the hoses leaked out onto the engine, I had a pan under to catch as much as possible. So far no leaks or smells.

View attachment 138226
I had the sensor leaking and the dealer just replaced the sensor. I wish they gave me a new water outlet under the power train warranty. Is the new one you bought plastic and is it a different design than the old one? I think this thing should be metal.
To add to this thread, I was having the coolant venting issues as described in the OP. After discussing the issue with Blue Angel, I've been using the 4.5mm Buna-N o-ring since September 2014. I have not experienced any noticeable coolant loss since installing the new thicker o-ring. I haven't checked to see how well it is resisting compression set, but as long as it stays properly sealed I am happy. Great job on the write up!
Since burping my system and filling it up to a little over the the full cold mark and not replacing any rings on my cap I am not seeing any coolant loss. I do have a question I do see a little white residue at end of the vent on the side of the reservoir tank. Is that normal? I am not losing any coolant and don't have any coolant smell. Since I am not losing coolant I am almost afraid to touch anything and replace the o-ring. I am thinking if I start to lose any coolant though I will replace an o-ring ( I bought a few and have them ready to go lol) but I am leaning towards leaving well enough alone.
I would just clean the vent (it pops off the side of the reservoir) and then monitor for any signs of venting. The vent isn't a functional sealing component so you won't be disturbing the delicate balance of your cooling system. :)
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I had the sensor leaking and the dealer just replaced the sensor. I wish they gave me a new water outlet under the power train warranty. Is the new one you bought plastic and is it a different design than the old one? I think this thing should be metal.
Funny my Wife said the same thing, she didnt understand how a little piece of plastic is connected between a metal engine and rubber hoses. It appears to be the same as the old one, it had a Made in Germany sticker on it. I was told the part number I had originally was replaced with a newer part number and I would receive the updated part. Perhaps a new vendor makes it? I know the hoses I ordered were made in some East European country and I think the Surge Tank was produced in Bulgaria, the surge tank appeared to be slightly different, better built.

So far No Leaks, knock on wood.

To summarize, the Water Pump was replaced, surge tank, cap, water outlet, overflow hose from outlet to surge tank, Had the new O-ring at first but didnt put one on the replacement cap since it appears to click now so I figured i would see how that goes.

Spent around $130 for everything from various sources, eBay gm dealer, GMpartsdirect.CO (not .com, they suck), the Oring store provided in this thread.

FYI the Water Outlet was backordered from the major online dealers with no ETA at the time, luckily I found a Buick dealer on ebay that had one in stock and sent it priority mail (restored my faith in some dealers).
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I wonder if there's a high demand on the water outlets due to leaks?

Regarding the revised part number, it's likely if the part number changed then something functional changed with the part. If early parts were failing that could be why. Do you happen to have the two part numbers handy? The current part number listed through Cultrag is 55565334:

55565334 | WATER OUTLET | 2012 Chevrolet Cruze

For $21 it includes the coolant temp sensor, seems to be a decent value.

A while back I was commenting about a thread about the air bleed hose leaking. In researching that thread I noticed there were two separate part numbers for the water outlet. If I recall from some pictures online from an E-Bay seller of the old part, the connection from the water outlet to the air bleed is different.

In your link it's around the plastic piece at the top of the page. From the air bleed connection to the water outlet.

I've never had this apart, and I know you have. Is this a hose connector with flow going through it, or is it some type of float check valve that lifts up to burp air, but remains seated to prevent coolant flow back to the tank?

I could be wrong, but with my engine running it doesn't seem like there's liquid flow in this line back to the coolant bottle.

There's a lot going on at the water outlet, and I'm not sure that I've figured out the flow path of coolant with thermostat open & thermostat closed.

Thermostat closed just doesn't go to radiator, but always flows through heater core, but not air bleed, or at least it doesn't look like there's flow in the bottle.
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carbon, the connection is just an open hose connection. There's a small circular feature on the reservoir where the hose connects. If you watch it closely, every now and then a few small air bubbles will get trapped in it and spin around, indicating the flow into the reservoir.

It is my understanding that the flow through that line is actually quite high. Someone (obermd I think) posted when they had dye added to the cooling system, they saw it circulate back through the tank shortly after being added.
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