[SAHE]

Honestly it kind of baffles me that the garage you’re taking to hasn’t already done a coolant system pressure test. It takes less than 5 minutes and will reveal weak points if there are any.

But changing the cap is a good plan. Simple and will either rule that out as the problem or fix the problem.

Personally I wouldn’t put much thought into the head gasket being the issue until you rule out simpler and easier issues to diagnose. But you can get a kit to test for exhaust gases in the coolant system. Here’s a video explaining (there may be better, but it’s the first one I turned up):

It seems to me that if it were the head gasket leaking exhaust gases into a coolant jacket that you wouldn’t hear bubbling after the engine has shut down.

Where are you located SAHE, generally speaking?

I'm in The Netherlands. It's not as common for people here trying to fix their own cars, it's usually hobbyists or car fanatics, and I can do many things myself, but we usually lack things like a place to work, no driveways and such.
If I had a place to do it I'd probably tried these things myself.

As for the pressure test, I did suggest it but they were adamant they had found the issue.
So either the trapped air was the issue but they haven't fixed it thoroughly enough, or it was just a symptom and the problem lies elsewhere.
Though I do agree that a pressure test would be less invasive than changing the thermostat even.

I hope to receive the cap next Friday, so hopefully I have more info then. I'm running out of cheap fixes haha, even though the man hours were somewhat expensive. On the other hand, they charged me less than they actually worked. Hell, they even charged me only half of the coolant used (I double-checked that they did indeed use enough!).

Edit: After checking the video, they guy is talking about steamy bubbles coming from the coolant.
This is similar to what I've seen happening a few times. Smoke or steam in the reservoir, but it could also be just super hot coolant.

I'll see if I can source one of those kits in The Netherlands.

Edit2: Garage did tell me they used some sort of sniffing device that measured (amongst other things) for exhaust gases; they could not find anything unusual.

 

[SAHE]

I posted a message yesterday but it is awaiting approval from a mod (why? Did I use a bad word?).

Something peculiar I noticed this morning, because I had an epiphany:
The bleeding system on the reservoir was not working properly; I tried blowing coolant into the rad by blowing on the breather tube with the rad cap off (so I was sure the rad was topped off, the coolant in the res is all I have at this moment), and I only blew air.
Turns out the pickup tube in the reservoir was above the coolant level (there was a noticeable curvature in the tube). Yes, the coolant was above LOW, and below MAX.
I rotated it a little, and sure enough, I was blowing coolant from the res into the rad. Did not have time to do a purge but will try tonight.
Could this be the reason why I got so much air in the system? That it just drew air when the coolant cooled and shrunk in volume?

 

[Archerfish]

I posted a message yesterday but it is awaiting approval from a mod (why? Did I use a bad word?).


?

I don't think so. I suspect that the site is automatically doing it. I've seen a couple of threads where one of our moderators will approve it to be posted when clearly it is not a Spam.

Speaking of Spam, I haven't seen one lately except in the supermarket.

 

[jsilva]

Turns out the pickup tube in the reservoir was above the coolant level (there was a noticeable curvature in the tube). Yes, the coolant was above LOW, and below MAX.
I rotated it a little, and sure enough, I was blowing coolant from the res into the rad.

The pickup tube should reach down close to the bottom of the reservoir. How long is your pickup tube? Was it somehow bunched up? If it’s not submerged the system would definitely suck in air when it’s cooling down.

 

[SAHE]

The pickup tube should reach down close to the bottom of the reservoir. How long is your pickup tube? Was it somehow bunched up? If it’s not submerged the system would definitely suck in air when it’s cooling down.

I'll measure it later, but it was definitely bending to 1 side (about 45-60 degrees from vertical). It seemed otherwise untampered with (and was stuck enough for me to believe it is the original). I do not know what would've bent it, other than heat cycles.
Previous post is now up, I see.

 

[jsilva]

I'll measure it later, but it was definitely bending to 1 side (about 45-60 degrees from vertical). It seemed otherwise untampered with (and was stuck enough for me to believe it is the original). I do not know what would've bent it, other than heat cycles.
Previous post is now up, I see.

If it was wedged in on the ‘shelf’ of the upper portion of the reservoir and not fully in the lower part, then I could see that as a possible source of air getting into your system.

 

[SAHE]

Well, that was... Surprising.

After repositioning the pickup hose in the reservoir, temps were very stable.

Warmed up car with small errand drive, let it idle to get up to normal temps.

Hot air
Stable temp (highest was about 105C/220F when the rad fan kicked in and temp dropped to 93C/199F).
Turned on the AC and temps dropped even further to 85C/185F (I have a 82C thermostat instead of 90C btw).
I even actually tried to force the temps by revving to 4000rpm, but again it never got THAT hot.

This is a huge improvement over yesterday!

Temp when rad fan had just kicked in (set it to F for your convenience):

Temps after I turned on AC (and fan):

Tomorrow I will take it for a short drive, but damn.

Pickup tube in coolant reservoir. Who thinks of THAT?!

 

[jsilva]

That’s great to hear! Sometimes car issues are ridiculous and frustrating

 

[SAHE]

Alas, it seems that the quick fix did not fix things.

Took the car out for a drive in the weekend. All seemed fine, as shown in previous post.
This was a good 15 min drive on highway speeds, and some urban traffic.

Today I went to work (as mentioned before, about 7 miles, 3 traffic lights and about 4 miles of highway), and the issue came back in the last 2 miles.
Coolant warmed up slower than when the issue started (where it would increase about 10 degrees C every minute (can't convert to F, but I would assume about 20-30F)), similarly to the first test drive.
Then I saw it spike back to 117C in the last 2 miles or so.

Parked the car at work, and checked the engine bay:

• Coolant reservoir filled to normal levels for high temp coolant, no bubbling or whatever. No spillage. No smoke in coolant. Did see some black debris! Like, small flakes/specks.
• Both radiator hoses were nice and firm (so the pickup tube fix did to something after all), could not easily squeeze them. To me this tells me that the rad cap is fine. On a side note: How firm is too firm?

Tomorrow she's going back to the garage. Asked them to do both a pressure test on the cooling system and a compression test on the cylinders.
The black debris in the coolant somewhat worries me.

Anyone else have some suggestions? I'm back to square one.

The debris:

 

[jsilva]

Sorry to hear! I think there’s a good chance the pressure test will turn something up. Perhaps the issue you fixed was the main part of the overall issue but something still remains.

I wouldn’t be too concerned about the black specs. You could siphon out the reservoir and clean it out if you wanted. Probably came from the hose.

 

[SAHE]

About a week later, still no fix.

Last thing they changed was the temp sensor, and on top of it they topped of the coolant to the mounting hole.
Car acted pretty well after, but again, after 2 days I'm back to where I started.
Starting to look more and more to a faulty headgasket, where the issue only manifests when the engine is under load/boost (garage mentioned they only performed compression test, and "sniffer test" during idle).
I think the pressure in the cylinders is low enough for the HG not to leak, but at higher RPMs it will exceed the pressure the HG can "take".
On a side note: Would a compression test show any and all HGF? Or just "from a certain severity"?

Contacted another garage, and they're gonna perform some more tests to determine HGF.
I was this close to contact a local dealership, but as the MPS/MS6 is quite rare, I doubt they would be able to immediately pin it down without doing everything my current garage has performed.
Maybe some more "professional" versions of the testing equipment.
It would be more expensive anyway, and my current garage has given me several discounts already (charging half the coolant, and part of the hours).

 

[fedosis]

Won't it be cheaper to inspect head gasket condition and replace it anyway? BTW inspect chain, valve gap and steam seals?

Sent from my RMX2170 using Tapatalk

 

[SAHE]

Won't it be cheaper to inspect head gasket condition and replace it anyway? BTW inspect chain, valve gap and steam seals?

Sent from my RMX2170 using Tapatalk

I'm not sure, I mean, replacing the HG would take more hours than any test they can run, I guess. And that would add up quicker as well.
But at this time I might even consider doing this just to be sure.

Would any of those things have impact on coolant circulation/airleaks?

BTW, I realise you mentioned from the start that it would be the HG. Maybe you will be right in the end

 

[fedosis]

I was looking for any other reason as you. Problem solved after HG replace. Everything, that have or can have impact on engine overheating were checked and replaced.
So it I'm interesting alot in your case.


Hmm, just now think that it is possible to test HGF by applying high pressured air into each cylinder and check for air leaks in radiator. The only thing is powerful compressor and engine warmed up engine due to termal expansion.

 

[jsilva]

So has the garage performed a coolant system pressure test yet? Replacing parts hoping maybe they’re at fault is a waste of time and money. Pressurising the coolant system will reveal weak points. If this hasn’t been done then it really needs to be done.

Replacing the head gasket on this engine is a big job, and many parts should be replaced in the process—timing chain, guides, tensioner, friction washers, head bolts (which are expensive), intake/exhaust/turbo gaskets, etc.—not to mention having specialised timing tools. It is an expensive job. It’s not cheap even if you do the work yourself. I did mine back in Dec 2019 hoping to fix a compression issue, and it was a complete waste of time and money—I didn’t know what I know now.

If they checked properly for exhaust gases in the coolant then you can be pretty confident there isn’t a leak in that direction with the head gasket.

 

[SAHE]

So has the garage performed a coolant system pressure test yet? Replacing parts hoping maybe they’re at fault is a waste of time and money. Pressurising the coolant system will reveal weak points. If this hasn’t been done then it really needs to be done.

Replacing the head gasket on this engine is a big job, and many parts should be replaced in the process—timing chain, guides, tensioner, friction washers, head bolts (which are expensive), intake/exhaust/turbo gaskets, etc.—not to mention having specialised timing tools. It is an expensive job. It’s not cheap even if you do the work yourself. I did mine back in Dec 2019 hoping to fix a compression issue, and it was a complete waste of time and money—I didn’t know what I know now.

If they checked properly for exhaust gases in the coolant then you can be pretty confident there isn’t a leak in that direction with the head gasket.

They told me that they did pressurise the coolant system and that it did not give any negative result.
They also told me they did a compression test. Which also did not showed any negative result.
They have performed some sort of gas-sniffer test and that they could not find any exhaust fumes anywhere, including the reservoir. I know that there are kits to use on the coolant itself, but I can't really dictate what a professional garage should do.
However, they did the last one at idle.

My thoughts would be that, in order to have a result for HGF (in terms of leakage into cooling system), the pressure in the cylinder should be higher than that in the coolant system, and high enough for the HG to fail. In my mind it could be possible that there's a minuscule crack in the HG that results in a failure/leak only under higher revs/boost, but nothing during idle/low revs).
So maybe they need to perform the test under load?
Additionally: What if the crack in the HG is so tiny, that even a compression test (which would normally be done by removing the sparkplugs, cutting fuel, and using the starter motor to crank the engine) will not show a negative result?

As for the costs for a HG job: Yes, I am aware that things can get expensive.
However, other than going straight to a dealer, I have very limited options to get OEM parts.
Local (read: Dutch) shops only offer aftermarket material. I am aware that OEM is always better than aftermarket, but as it is, the only source I can find is onlinemazdaparts.com (and some other US based companies). Other than that, it's brands like Febi Bilstein, or even more obscure ones like Ajusa (the only brand that even lists the head bolts with the "correct" OEM part number).

(EDIT: Dealers in The Netherlands generally don't sell parts directly to consumers)

If I go with the non-Mazda brands, I can get a full gasket kit, a timing kit (chain, guides, spanner/tensioner) and the aforementioned bolts for about € 350,-. And I should receive it before the end of the week.

For reference:

Complete pakkingsset, motor voor MAZDA 6 Sedan (GG) bouwjaar 2002.06-2007.08 | Winparts.nl - Cilinderkop pakking

Complete pakkingsset, motor 50286000 Ajusa ! Snelste levering in gehele BeNeLux

www.winparts.nl

Kettingset distributie 170105 FEBI voor o.a. MAZDA | Winparts.nl - Distributieketting

Kettingset distributie 170105 FEBI 170105 Febi ! Snelste levering in gehele BeNeLux

www.winparts.nl

Cilinderkopbout set voor o.a. MAZDA | Winparts.nl - Cilinderkopbout

Cilinderkopbout set 81042400 Ajusa ! Snelste levering in gehele BeNeLux

www.winparts.nl

If I will go through onlinemazdaparts.com, the amount would be $ 522, but I would have no idea when they would arrive, and also I will have to pay extra taxes, importduties, etc.
Plus, the material needs to be mounted.

I am aware that I should not "preemptively" address the HG, but at this point I have no reason to believe my garage hasn't done everything they can do to diagnose the problem.

As mentioned:the last time it held up pretty well, albeit for 2 days (whereas before it would not last an hour).
But air/gas enters the system somewhere. And it does not appear to do so under idle/low revs.

I will ask the local Mazda dealer for input, though.

 

[jsilva]

Ok, I must have missed that they pressure tested the coolant system.

After you repositioned the reservoir rubber tube have you noticed the coolant level going down at all? Is the coolant up to the radiator neck after a longer drive and cool down?

It’s possible the rubber pickup tube in the reservoir has a crack or hole. Perhaps you could disconnect that tube and blow hard into it with one end blocked. Perhaps even inspect all of those parts—the tube from the radiator neck to the reservoir, the plastic reservoir top, etc.

Personally I’d suggest you wait to order parts for the head gasket until you have definitive reason to think it’s that. You definitely don’t want to do that repair on a guess (unless you’re doing the work yourself, and you’ll need more parts than you linked to).

 

[SAHE]

When I repositioned the tube, I did saw a big improvement. It would no longer suck in air that way, when it was cooling down, but the coolant itself (even though I had a collapsed radiator hose right after). Yet, after that it would still "overheat".

I will double check all tubing in the reservoir in a minute. However, this would still not explain why the car behaved for a few days (I even drove some distance on the highway).

BTW, I've asked the local Mazda dealer for a second opinion (it's 1,5 miles from here), I hope to get a quote for diagnosis tomorrow.

 

[jsilva]

My thought was that you made the issue better by repositioning the tube. Perhaps if there is still a small leak via a crack in the tubing or the plastic that the issue would show up again but would simply take longer to show up.

 

[SAHE]

Yeah, it was better as it did not immediately sucked in air when it cooled down enough for the coolant to reduce in volume.
But it was not the cause of the problem. The upper rad hose is just empty after a short drive.

If I need to go somewhere close-by I just transfer some of the coolant in the reservoir back to the radiator (by removing the cap, and blowing into the breather tube of the res), and I need to lift the middle part of the upper hose to make sure the coolant flows back into the rest of the system (there's a small bend that sits ever so slightly lower than the rad and engine connection, by raising it up the coolant flows back into the engine).
It's difficult to explain, but when I do that, the system holds out a little longer.

The tubes are fine, btw, the only (small) leak is between the breather tube and the plastic nub it's fixed to (but that should not matter as it is in contact with the outside air anyways).
The rad cap opens with a slight release of pressure as well (not sure if positive or negative) when cold.