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FIX: Coolant Odors/Coolant Loss From Reservoir

116416 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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I ordered the 4.5 mm ring before BlueAngel was working with the Viton ring. Here's a few pointers for installing this larger ring.

1. Put the o-ring on and lubricate it with coolant.

2. Carefully install the cap, if it doesn't thread all the way stop. Leave the cap as tight as it is, and leave the car parked for 24hrs. This gives the o-ring time to conform to the bottle.

3. The next day remove, relubricate and install the cap a little further, until it threads all the way.

I initially could not turn the cap all the way. I was about 3/4 of a turn away from complete tightness. Allowing the cap to sit under pressure in the tank for a day allowed the new o-ring to mold to the tank.

The cap now goes all the way on in one attempt, just like a factory cap would. It's that first tightening that can be somewhat over tight. Give it time, don't force it, or you will be replacing the tank!

Works great. I would agree to start with the smaller Viton O-ring, but given the price of shipping of these rings, I didn't want to reorder them again.
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I'm glad I ordered a half a dozen. I did notice that even the BUNA 4.5mm ring takes a visual compression really fast. In three weeks the new o-ring visually looks as flat and smooth as the old cap ring combo.

Nice idea with the tape over the vent to see if it's leaking. I'll put a piece of scotch tape on it for observation. I've had really good luck with Dorman parts. Hopefully 6 rings will provide several years of excellent coolant service. If not, I'll be replacing the tank and cap with the DORMAN before I'll ever go back to ACDelco for this part.

Thanks to both obermd and BlueAngel for this fix. My heat at the heater core is much more of a uniform temperature over time. I always knew the coolant was boiling, but I never realized how bad it was.

I had a Cruze rental in Arizona that was always running the radiator fans even on 40F mornings. I think that car may have vented itself to it's death. I feel sorry for whoever buys it as a used car. What an 0-ring will fix.
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time for my car's first dealership visit since new. :(
I never thought the day would come, where Blue Angel's baby would see the dealership for service! I noticed that the water pumps are now back in the Rockauto catalog for about $50. For a while they were totally missing, and I was thinking due to the extended warranty on the pump, manufacturers wouldn't be selling/stocking a part that most average people may not buy.

I haven't been in either, and I still have a splash shield that hasn't been cut. I really like how it keeps the bottom of the engine compartment so clean.

The trick with the water pump would be supporting the engine. I'm not a fan of a jack on the aluminum oil pan, but Amazon does have a 3 point engine support bar for $60.

Good luck with your first dealer visit.
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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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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.
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.

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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Obermd & Others-

How long is the BUNA o-ring lasting? I think I'm currently leaking again out of the cap, with no other noticeable coolant losses. I think it's about 9 months on the BUNA ring.

I briefly scanned this post again, and I believe Obermd mentioned that he had to order more rings. Maybe it's a temperature thing. It's -2F today, and when I installed the battery tender jr, on the factory battery I noticed the coolant was low.

I have to dig for where I placed those rings, or order others. I don't have Viton to try, but it appears the BUNA ring may have a short lifetime if your in the Midwest Northern tundra temperatures (<0F).
The coolant dropped maybe two ribs based on the markings on the side of the bottle. Final level before filling was level with the top of the lower outlet hose. It took maybe 2-3 cups to fill it back to the molded seal level of the tank.

I the top of the coolant cap above the lower o-ring was wetter than normal. Leading me to believe I'm venting again.

The water pump has had some dry coolant on it over the past year or so, but it would take a mechanic with a lot of patience to actually see it. Since the level stabilized after installing the ring last March I thought the pump was ok. I'm sure there's staining behind the pulley, I can see it with an inspection mirror, but there's not any on the timing cover, or a notable drip, so I think I may have issues asking for replacement.

I'll have to look at it again. I'm a little leery of taking it in for the pump, because I don't want anyone jacking on the oil pan to support the engine.

My 2012 still has the factory splash shield, and no recalls have been completed.

I wish I had a topside engine support and I'd do the water pump myself this spring. Still trying to figure out what to use, vs. a floor jack on the oil pan. I believe this could easily cause an oil leak at the gasket.

Anyway sorry for getting off topic..

It's time to seriously look for the new BUNA rings. I should have put them in the glovebox!
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Welcome to the forum-

I'd get some dexcool and fill it up to just under the weld seam where the tank is welded together.

The next thing I would do is read the threads on the o-ring fix. Which I believe is covered in the seven pages of this tread.

The aftermarket o-ring fix lasts about a year with really cold weather, then a new o-ring is required. There's clearly something going on with the 2012's not sealing between the radiator cap and the coolant tank.

I changed the coolant o-ring again last week and used a little glycerin on the ring, made it screw down much smoother.

Be careful, don't force anything, and make sure you order both o-rings suggested by Blue Angel. I ordered the BUNA ones before the Viton one was discovered, and I don't want to order again.

With the engine hot in a garage out of the wind open the hood and sniff around. The thermostat water pump is on the passenger side. The coolant tank, and the water outlet hose, right to the left of the battery is on the drivers side.

If you can see dried coolant you may have a leak.

The water pump is covered under a special warranty for 10 years 120,000 miles I think..

The water outlet is also covered under powertrain I believe.

But if it's not visually obvious you may find a shop won't give it time to actually fix it, and you'll have a bill for nothing..

Good Luck
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Blue Angel is in Canada, and used the supplier that he listed to deliver. It's a really small package for a few rings, I don't believe he had any extra fees.
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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.
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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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 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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