Time for an update.

I've flushed and burped the system the best I could with the funnel in the radiator neck (that included heating it up, cranking the heat all the way up and keeping the revs at 3k rpm for a bit to get more coolant flow to push the air around) the coolant levels are stable, there is still very miniscule bubbling from the reservoir and air in the top portion of the radiator itself but there is no loss of coolant and hot/cold level fluctuations are like in a textbook, even after hour of stop and go traffic with 27C outside. So maybe the general design of top-down flow radiator is to blame (as next gen SSS has the filler neck that's like 10cm long)

The splashing from the overflow issue has been resolved by making a makeshift grommet, that I've been missing, on the reservoir neck with some tape and adding a silicone tube to the vent port so If it spills it'll be instantly visible and in more manageable place (not the air filter, around battery tray or headlight)

Let's hope that during the next event the coolant level won't raise as rapidly as they did the last time.

I'm attaching the photo of the reservoir with my makeshift solution.

 

Has the thermostat been replaced at all? These definitely need a bleed hole in them, and it has to be at the top to allow air to bleed. Water flow is via heater core to Thermostat wax pellet so if heater core blocked or air trapped behind thermostat it won't open, and level fluctuations can ensue. Heater core is always in circuit you're only moving the blend door with the controls.
If its getting air into the system its coming from somewhere. Prime candidates are head gasket ( probably not as the combustion gas check is negative) or more likely a water pump seal or something thats porous under vacuum but seals when engine heats and cooling system comes up to pressure. Silly thought, have you replaced the line from radiator cap to expansion tank? If that's sucking air and water from the reserve bottle in when it cools down that could explain a lot. Even check the hose in, and cap on the bottle for cracks

 

Yes, I've replaced the thermostat about 3 months ago, I've done it according to manual, after checking if it opens (temperatures and lift). I've replaced the line from radiator to overflow and checked the tank itself. I've checked the temp sensor with multimeter and there are no abnormalities in temperatures. (that rules out the thermostat itself), the heating works as intented, no fluctuations up/downhill or in turns.
It's a bizzare issue, and I'm going to try to come up with some kind of test to see from where it might be pulling air without leaking coolant when it's at 1.1bar... I will change the fittings on the line to the expansion tank and keep observing how it all behaves, before I'll start throwing all possible parts at the problem... Worst case scenario I'll find out what happened next year when I'm going to do some major overhaul of the whole car for the next season.
Thanks for your insight!

 

I'm also betting its sucking air in when its cooling down and sealing under pressure. Where its doing that is the big question. Obvious culprits are rad cap, and expansion tank components. Ill be interested in knowing what you find.

 

I've just came home after a track event (160km drive to even get there) and the issue persists. I've changed the fittings to an expansion tank and tested it and the line the best I could. It's safe to say they've been ruled out as a culprits. That means I'll have to wait a bit to get the answers till I'll get some things done around my engine. As mentioned already there seems to be a ''perfect'' amount of air in the system and the whole thing is in equalibrium as it is. I'll definitely change the rubber radiator hoses and their fittings as the hoses are a little too soft for my liking. (they seem fine otherwise).
Just a loose thought: I've compared the radiators of zc32s and zc31s, the newer swift has a lot taller neck where the rad cap is supposed to go (more than ideal for that potential air pocket ).
If I'll manage to find the culprit/fix or anything useful, I'll update this thread.

 

small update: the temperatures dropped to about -10C here and the issue with some portion of air being stuck in top of radiator (about 200ml) persists. the heating works like a charm (blowing 48 on right side and 41C at the left side at highest setting), No other related issues other than overflowing if I try to force coolant back to radiator and top up the reservoir. There is some kind of pressure when I remove the rad cap, I doubt that throwing third OEM rad cap would improve anything and the expansion tank and its line are good and not cracked/collapsed. After I finish the body work I'll try to find and install an aftermarket expansion tank (maybe in different location, somewhere higher)

 

I've replaced the radiator, checked the coolant lines to reservoir and flushed the system and changed the radiator cap. The cooling has improved, when running the pressure in the system is a tad higher. Coolant on stable level near the full mark, it goes up about a centimeter or two when hot.
Bubbling at a rate of about 0.5 to 1 bubbles per second that's independent of rpm, after warming up and the air pocket on top of radiator till persist. I've decided to ignore it for some time and look for other symptoms and that's all that happens. Maybe the heater core warms up a bit slow but gets hot nonetheless.

Running temps: 89-93 when warmed up, no creeping in traffic. It naturally goes up when I slow down from spirited drive and drops a bit when I suddenly get more air flow/pump rpms. It gets hot when I turn the car off. Coolant expands and contracts, there is vacuum when it's cold

In a few words: It behaves normally other than the bubbles/air pocket. I'd expect higher temps from headgasket leak.

I'll keep suspecting the headgasket and will get it checked when I'll be doing stuff to the engine.

 

I would not suspect the head gasket, but suspicious about the pump..

Have you ever pressure tested the system or even applied a vacuum when cold ?

 

I've checked it only through the coolant flow, spinning by hand and visual inspections for wear and leaks. Couldn't take it out myself because of the frickin weather and stuck bolts as I can't get my big ass impact in there, I've applied significant force through the breaker bar but it was getting scary and don't want to break the bolt and get the car grounded, because I'm forced to using it as a daily for some time. I might need to take it to a mechanic but I have major trust issues and it's double hard for me. I have the new pump lying somewhere tho...

I'll inspect it and try to get some vacuum on the system, maybe even make an appointment... thanks for the insight, it was definitely heart lifting to hear it's something so ordinary. it's bizzare that it only occurs when it's fully warmed up.

 

I've been defeated. After changing the water pump and bleeding the system etc. The issue remains, same intensity, although the coolant is cleaner.
The old pump had a little bit of offset on a wheel and a bit of surface corrosion on an impeller but in general there was nothing that would qualify it for a replacement other than me chasing a ghost. Bubbling continues.
I haven't been able to determine anything from applying a vacuum with a giant syringe for injecting oil into transmission etc as it wasn't see-through and sealing well enough.
I might try bridging the heater core inlet and outlet hoses so it's not in the system anymore.
As there is less and less parts left to check I'll be saving up for a rebuild and a crane so I can pull the engine and do it myself as the mechanic did a shoddy work for a great sum of money with the pump/belts.

The car is finally back to being weekend project so that's some good news.
Thank you all for the input. I'll be updating this thread when I'll find something really worth the read.

 

Nice to know I'm not the only one struggling with this issue Puzzling to say the least

 

haha same, I hope that my case study has been at least a bit helpful/reassuring.
I have two questions tho: How long have you been having this issue? Do you have any additional symptoms?

 

New piece of evidence/clue:
I've burped the system again, with the front lifted about 10 cm. burping as burping, some single bubbles from time to time, the level fluctuates as they move to the rad neck and drops when they go away.
this is a video of the car running with no rad cap (the rad fan has already started/ stopped 2 times) :

No bubbles/ completelly filled, It's been full and stable for atleast 2 minutes before the recording.

this is a video where magic happens, not more than 3 minutes after I've sealed the topped up system with OEM new rad cap. first: a bit of positive pressure when I removed the cap, coolant's been spilled. I've been filling it with the coolant from reservoir to make it more visible during the video but the coolant is literally swirling like crazy and the ''foam'' forming. as you can see there is also more steam than before but it's been present since the moment it got hot and smells just like coolant.

it's repeatable each time. I've been mistaken there is a little of positive pressure even when cold/no pressure 50/50. coolant temp is 90-95 deegres (drops slowly when revved), no detectable leaks external nor internal, everything else with the car (not counting the positive fuel trims, loose rattling exhaust and burnt out interior bulb) is ok. I swear to god it makes no sense. I'd expect a bit of boil-over when the pressure in the system drops when I remove the rad cap but all of the pieces do not line up at all.

 

That looks like a blown head gasket. What else can pump air into the system?

 

That looks like a blown head gasket. What else can pump air into the system?

<SNIP>
It seems like the headgasket is to blame but:

-I've repeatedly took 2 different tests for exhaust gasses in coolant, one chemical and other electronic with a probe at service station. Both negative.
<SNIP>
I would appreciate some feedback, observations of your cars or loose ideas, as I'm starting to believe I'm just severely schizophrenic 🥴

 

You can have a blown head gasket without combustion gases present.
Have you done a hot compression test? Got one cylinder thats down compared to the rest??
Does the water stop bubbling if you remove the oil filler cap? If crank case is pressurising and its blowing between the oil return galleries and the water jacket.....
I've seen head gaskets blow or leak due to warpage and act like one way valves.

 

I'll check what has been suggested and start diagnosing specifically for a blown headgasket/warpage because it looks really bad...
What's puzzling tho is that it doesn't act like that unless the cooling system is starting to build up pressure. I haven't caught that before because it never does that or misbehaves in general when the rad cap is off. That is really weird as leak technically would be bigger when there is no counter-pressure from the cooling system. The oil pressure is great, no abnormalities, there is blowby but not enough to move the oil cap when placed on the inlet.
I have a lot on my plate right now and funds are a little limited but I will keep updating this thread. At least the revelation with crazy behaviour when the rad cap is removed when pressurizing vs no rad cap at all might help others in diagnosis.

 

Heat equals movement in mating surfaces. Closed system plus heat equals a consequential increase in pressure as the liquid can't expand, and the ability to hold more compressed gas in suspension. Think of it like a soda bottle. Cold and it doesn't hiss much when you unscrew the cap. Heat it up then try.
I am personally suspicious of a not so much blown, but imperfectly sealing head gasket, or God forbid, a crack somewhere.

 

I've done another coolant test and the result came out ''not obviously positive'', instead of yellow (works as intended on exhaust itself) the test fluid turns only slightly slightly less blue. At this point I guess there is no other possible culprit that wouldn't require removing the head.
I've asked for quotes in my area and they were trying to rip me off or didn't want to bother. So I guess I'll be doing it myself whether I want to or not, as selling the car is not in consideration. I've known I'll be pulling the engine at some point anyway, not this soon, but this year heh. It's unbelievable the gasket is holding so incredibly well considering the problem I'm facing, no problems with oil, good temperatures and running 8,4s to 100 and pulling as fast as the gearbox allows for so long...

Is there enough space to do the timing chain and possibly some welding (in case I break the timing cover bolts) semi-comfortably with the engine still in the bay? (any tips in general regarding dealing with the timing cover are needed and welcome )
do the Camshafts from M15A/M13A fit? I can get them for cheap and need a blueprint (regarding mounting/ distances) for a guy to make me custom ones to avoid waiting for the ones from my engine. I have the exact profile of the ones I want to have machined.

 

Cams are machine matched to the head for journals and afaik only the M16 cams fit. Never successful fitting a new cam in a second hand head, I wouldn't try unless its a fix to get an engine going.

If you have test solution going lighter after passing gas thru it, thats a positive test. Yellow is a " yep, its definitely blown" and a large " don't drive the car" flag.

 

Didn't expect it to be this bad, I can also see cyl 1 and 4 are running lean as the spark plugs have been replaced some time ago also they have more carbon deposits as seen on the pistons. no visible hairline cracks and the cylinder walls look good. What worries me is that the breach is on the block side. Will be checking for warpage in a moment. I'm not a mechanic and I'm not sure how much is it blown, I've never had detonation issues. Is it done literally most of the way around the chambers? there is also wear (the black material wiped off) between the layers on cyl1, I don't see one obvious path between the jacket and the chamber so could it be just old age deterioration?

 

Changing the head gasket resolved the issue, car runs better than ever (thanks to some shiny new parts ) . I'm gonna write a quick summary for anyone who might have a similar issue, forums, and people giving answers to even simple questions have been really helpful in my adventures with cars or literally everything else, thank you all, internet people

Observed issue:
Coolant not returning to radiator, coolant level in the radiator gets stable around where upper rad hose connects to the radiator, when hot: slow but steady bubbling in the overflow tank, kind of rusty bits or residue on the top of radiator/in the overflow. NO BUBBLING WHEN WARMING UP WITH NO RAD CAP. no positive results from any tests or other worrying signs

what it was: age related head gasket deterioration on the block side/between the layers of steel as seen on the photos above.

how it was finally confirmed: after letting the car warm up with open radiator, then radiator cap has been installed till the system started building a little bit of pressure, rad cap removed carefully and instantly the chemical head gasket leak test has been conducted. (the specific bubbling and swirling was also finally visible, then and only under this procedure)

give the thread a read to see the whole process and everything what this issue wasn't and how I've been testing and eliminating other components.

as an ending words: the block and head were perfectly straight, measured compression was even/quite normal, I doubt leakdown test would confirm the head gasket leak because of the very specific prerequisites that had to be met to make the car behave not-normally.
Since I was already there I've cleaned and inspected everything I could access, I've installed new exhaust manifold and ported/polished the head, working on this engine was pure pleasure, can't wait to do it again

 

Thanks, I have similar issue with coolant bubbling over in expansion tank (suspect exhaust gas leaking out) when at track days. Resolved to change the head gasket. Hope it fixes it like you did!

 

Confirming after I changed head gasket the over heating issue - coolant bubbling out of expansion reservoir - while under load is gone.

Engine head was badly warped but it was machined back to spec.

 

Simplistic, you are my hero!
Thank you very much!
I have exactle same sympthoms on M16A engine on Suzuki SX4 (Fiat Sedici branded 4x4)
I also made tests for combustion gases in coolant and color was slightly changed But thought it was not positive.
Now, thanks to your work I will go and replace head gasket.
Best regards, from Sofia, Bulgaria.

 

ANY change in colour is considered a positive test.

 

Having same situation, I decided first to try with K-Seal.
I found this https://www.kseal.com/uk/faqs Looks like suitable for my case.
If I succeed I will report here.

 

Having same situation, I decided first to try with K-Seal.
I found this FAQs - Frequently Asked Questions - K-Seal® Looks like suitable for my case.
If I succeed I will report here.

Thats only a stop gap solution, not a permanent repair, and quite often blocks the heater core as well. Ok if you're patching it to sell it i suppose