Overflow tank and coolant leak

[Mtf1980 21]

I'm having issues with the overflow tank leaking on a 2014 Chevy Spark. At first, I thought there was a small hole or crack in overflow tank. I noticed coolant on bonded edge of overflow tank and along bottom of tank where the rubber hose meets the tank. I have filled the overflow tank several times. on one of the times of filing tank, witnessed the coolant surging to the top of overflow tank right to the cap. The coolant pretty much came immediately back down. I removed cap and noticed the pressure relief spring in it. So I got to thinking that the overflow tank was still good. Now I'm leading to possibly believe the thermostat might be going bad. Anybody have similar issues?

[Ray Dockrey 97]

Isn't it still under warranty? The thermostat is electronic and quite a unit.

[Mtf1980 21]

No it's not under warranty. Vehicles has 43k on it.

[Retired old Gearhead 201]

When I first read this post I was hesitant to reply in case I was wrong. But I forgot that the Spark has a 5yr powertrain warranty and this is a case where your warranty will really shine for you.

What you have is a head gasket leak/failure (blown head gasket). Let me explain: When the coolant goes down..you have to think of where it goes. If not a tank, hose or water pump leak, then it is going into engine as the engine coolant areas are always full without interruption right up to the tank. If the coolant goes down faster than normal and you have no tank or hose or water pump leak...the coolant is going into the cylinder and being burned (whitish exhaust smoke) and/or the crankcase. This is because it is leaking between the head gasket and the rest of the engine. What gives the blown or slightly leaking gasket away is the sudden surging and overflow you are getting at the reservoir and is cause by combustion gasses leaking into the coolant channels and the pressure forces the coolant back into the coolant reservoir...usually accompanied with bubbling. As the combustion pressure goes down, even for a moment, it will return to a much lower level. If the engine still runs without excessive vibration or sputtering you most likely have what we call a 'gasket friction leak'. This is a gasket that has not fully blown out between cylinders, but a very small leak or tear cause by the Aluminum head on the iron block since they expand and contract constantly at different rates (Aluminum and iron have different expansion/contraction rates) and this constant minor rubbing should not but can result in partial head gasket failure specially if the gasket was not aligned or torqued properly or simply a defective gasket with a weak spot or tear.

First check engine for rough idle/running under load. Second, after running the engine for a minute or more, check the dipstick for 'coffee', pale or whitish colored oil and if the oil seems OK check the filler cap & plate beneath it for similar pale colored oil. Usually when a head gasket goes bad the engine will run much hotter than max spec and the engine temp light would/should come on..but often these idiot lights don't work as they measure temp at the thermostat area which is usually a bit cooler.

If your engine has over heated to a certain point, you may have low end engine damage such as warped components like cyl linings and most certainly the possibility of a warped head and stretched head bolts caused by the slight head warping. Normal procedure is to always replace head bolts (stretched), new head complete assembly (warped), thermostat, all coolant (contaminated) and oil change (contaminated)..and of course the head gasket.

On a complex VVT head and in the case of a warranty job, it may be more cost effective to replace the entire engine due to the excessive labor and margin for error as the factory assembles a complex VVT sensor controlled engine following specific steps and using proprietary tools and gauges made for that specific engine.

By having this done under your 5yr powertrain warranty you will save in excess of $1,500++. Unless you have misused the car by driving with low oil or other obvious stuff, it must be honored under warranty as there are a host of defective gasket, head bolts, incorrect head bolt torque issues that may have caused this.

A good and honest Mechanic will immediately recognize the surging reservoir tank issue as a result of the ignition gasses blow back, only caused by a defective head gasket. If your oil looks good and no white smoke out the tailpipe, a inexperienced or dishonest mechanic may replace the thermostat or other items or re-torque the head bolts and present you with a large bill, only for the problem to return..so indicate to him/her that you suspect a blown head gasket. Also a good idea to give the car a good run on the way to the dealer, assuming it still runs fairly OK as this will make the symptoms easy to quickly duplicate. If the dealership says not covered by warranty (which I highly doubt) contact the GM Customer Support people since the powertrain warrant covers all parts surrounded by oil and the head falls into that category. If they want to only replace the head and gasket, remind them it is standard operating procedure to replace the bolts and all other items I mentioned above.

The only reason for my long and as usual rambling post instead of just saying "blown head gasket" is that you will always fare better armed with some knowledge of functional cause and resolution. Good luck with this and please keep us updated on this interesting issue and how you fare with the dealer.

Edited August 20, 2015 by Retired old Gearhead

[bluer101 241]

Thread locked because of duplicate topic.

Original topic is found here.

http://chevysparkforum.com/topic/3309-overflow-tank-issues/

Edited August 22, 2015 by bluer101