Mazda 6 Forums banner
1 - 20 of 98 Posts

·
Registered
Joined
·
40 Posts
Discussion Starter · #1 · (Edited)
Good day to all of you,

First time poster from The Netherlands, but been lurking this forum for a while.

I'm having some weird cooling issues with my 2006 Mazda 6 MPS/Mazdaspeed6:

Out of the blue the dash gauge showed overheating but without any of the additional symptoms like steam, pinging, etc. The only thing was that the cap of the coolant reservoir was off.
This was on a 5-10min drive, from cold start.
Stopped the car to make initial observations:

  • No heat from HVAC
  • Rad fans were on
  • Upper rad hose was warm, but not too hot to touch
  • Lower rad hose was cold to the touch
  • Rad itself seemed cold (though couldn't really feel due to fan cowl and spinning fan)
  • Valve cover was warm, but not too hot to touch
  • Coolant reservoir seemed low

Checked telemetries with BT dongle and Torque OBDII app a few times, and every time the temp reading showed max 117 degrees centigrade (242.6 F), but no steam, no CEL, and engine seemed cold enough to touch (temp was measured at cruising speed, both on highway and "city" speeds). Never went higher.

Some other things I found during this "diagnostic"
  • There was some heat coming from HVAC when engine is heating up, and for a short part of the drive, but not 29 degrees C (86 F) as set on HVAC controls.
  • Then, suddenly temp drops, and coolant temp rises (a few degrees every few seconds).
  • Some minor bubbling in coolant reservoir, and a little "smoke", but nothing major
  • No smoke from exhaust
  • No gunk under rad cap, or oil filler cap.
  • Misfire on cyl. #3 on two occasions, rough start which would normalise within 30s, but issue has gone since.

Brought car to my mechanic, and so far the following has been done:
  • Thermostat replaced (first thing that came to mind), temp rating 90 degrees centigrade (± 195 F?), did not fix issue. Temps (normal, ± 90-100 degrees C / 194-212 F) and heat inside car (hot) were fine for a few miles, but then issue came back. Drop in temp HVAC and coolant temp shot up (still using Torque app).
  • Waterpump replaced (according to mechanic the impeller seemed to be very far from the backing plate, as if it was slowly creeping off the shaft). I could see a little wear on the ends of the impeller blades, but to me it looked fine otherwise. Had it replaced, just to be sure. Replacement pump looked the same (OEM parts difficult to get, or $$$/€€€) but replacement impeller was much closer to backing plate, again according to mechanic. Did not see new pump myself.
  • Coolant flushed/replaced (should I use FL22?) during both replacements.

So summarised:
Engine "overheats" (dash gauge, OBDII app), no heat from HVAC, but engine does not seem to be "too hot to touch" (for reference, I always do a ghetto "spit test" first: if it sizzles, engine is too hot to touch. It used to sizzle after a proper drive. With the "overheating" it doesn't do that).
It seems that there is no circulation. Water pump, coolant and thermostat have been replaced by OEM equivalents.

Some things we are considering:
  • Engine Coolant Sensor faulty (during "overheating" many parts of engine are touchable, but does not explain HVAC suddenly turning cold after it seems fine for a short time)
  • Blocked radiator/heater core (is there an easy way to test the heater core?)
  • Faulty new thermostat (but can be checked easily)
  • Still air trapped in system (I will call my guy today to make sure to bleed/burp with front raised).
  • Radiator cap
  • Combination of the above
  • Headgasket/crack in block (but no symptoms pointing that way, other than overheating. No excessive bubbling in coolant reservoir)
  • ...?

As it is, I'm completely stumped what else it could be. Some of the possibilities point to 1 end of the problem (overheating or no heat in car), but do not explain the other.

I've read some things about a plastic t-connector that can fail, but I only seem to find posts referring to the USDM V6 version of this car. Is this even a thing on the 2.3L Turbo?

I don't abuse the motor, I let it warm up properly for longer drives before I push it, and on short drives I don't push at all.
I let it idle for a few minutes before I get out, and make sure not to push it for the last few miles I drive it for that trip to help it cool down.

It seems that this forum isn't as active as it used to be (looking at the timestamps), but perhaps someone knows something somewhere.

I have also searched this forum high and low, and some posts seem to have the same issues, but no solution was posted.
So if anything, I will post mine here if we find it, for others to read.
But for now I could really use some suggestions.

Kind regards,

Sander, The Netherlands
 

·
Super Moderator
Joined
·
18,309 Posts
Welcome to the forum!

Not sure why but I needed to approve this before everyone else could see it. Free bump for your troubles.
 

·
Registered
Joined
·
40 Posts
Discussion Starter · #4 ·
U have broken gasket under cylinder head.

Sent from my RMX2170 using Tapatalk
As mentioned, we don't think so. There's no real proof of that: No white smoke from exhaust (not even a little during cold start, save for maybe condensation), and oil is clean.

I do follow the logic: Having hot gases blowing past the gasket into the coolant system could result in 2 scenarios:
  • Hot gases blasting past the temp sensor, resulting in seemingly high engine temps (though this on its own does not explain the sometimes hot, sometimes cold HVAC).
  • The leaked gases could create air pockets, resulting in waterpump functioning incorrectly, meaning bad circulation.

I will, however, ask my mechanic to do a compression test, and check for excessive bubbling in coolant reservoir while revving the engine.
Higher revs should mean more bubbles, especially under boost, no? At the very least the gases should somewhat displace the coolant.
Possibly check for exhaust chemicals in the coolant if they are able to test that.
 

·
Registered
Joined
·
40 Posts
Discussion Starter · #5 · (Edited)
Just had a call, he did a quick flow test for the radiator and to him it seemed to flow a little slow.
He's going to perform a pressurised test now, and see what happens then.
If it turns out to be a (partially) clogged radiator, I hope it can be flushed. Fingers crossed.

EDIT: Unfortunately the radiator flowed just fine.
Next up is flow inside engine block, and compression test of cylinders.
 

·
Registered
2006 Mazdaspeed/MPS 6
Joined
·
48 Posts
If I were you I’d do a pressure test of the coolant system. It’s super easy (if you have the tools) and takes little time. You could have air entering the system due to an old hose or clamp.
 

·
Rally Racer
2004 Mazda 6s Wagon ATX
Joined
·
4,006 Posts
When I read this originally it sounded like the system could not reach pressure because the overflow cap was off. The entire system is pressurized and will overheat if not sealed.

I am in the "trapped air" club here. I have a difficult time purging air from by v6 and it required me to take coolant hoses off. Perhaps rapidly and forcefully squeezing different hoses with the overflow off to help?
Mazda has a fairly detailed purge procedure.
My phone does not tell me which heading this is posted in but I saw 2.3 turbo?

The intermittent nature feels like trapped air.
My temp gauge will do what your does or the opposite where the gauge reads low but the heads super heat if I have trapped air.
A coolant temp switch is pretty cheap and may also be on the way out and worth ruling out.
 

·
Registered
2006 Mazdaspeed/MPS 6
Joined
·
48 Posts
It should be noted that the above procedure did not entirely work for mine. It would start overheating before I could complete it. Frantically pumping 🙄, blowing hard 🥺, through the coolant hoses with my lungs was what helped, with the heater line fully open and hot of course.
I used that once and it worked ok for me. After I rebuilt the engine I didn’t bother :) I did my own version.
 

·
Registered
Joined
·
40 Posts
Discussion Starter · #12 · (Edited)
Thanks all for the replies!

Yeah, other than a blown head gasket, trapped air (either due to bad purging or small leak) seems to be the logical reason for these issues as both the thermostat and waterpump can be ruled out (although the new thermostat could still be faulty, I supplied them a lower temp unit just to make sure, and I've also asked to check the "new" 'stat outside of the car).

That's a lot of details and as such, I'll be similarly stumped! I hope someone else can offer their opinion.
Haha, yeah, I don't want to be that guy who only supplies partial info, resulting in a bunch of unnecessary questions. As a "former car guy" (I'm not as active in the scene anymore), I know I hated it when newbies asked a question regarding their car, only for the more experienced guys having to conduct a full blown "mechanical anamnesis" to figure out the exact problem.

When I read this originally it sounded like the system could not reach pressure because the overflow cap was off. The entire system is pressurized and will overheat if not sealed.

I am in the "trapped air" club here. I have a difficult time purging air from by v6 and it required me to take coolant hoses off. Perhaps rapidly and forcefully squeezing different hoses with the overflow off to help?
Mazda has a fairly detailed purge procedure.
My phone does not tell me which heading this is posted in but I saw 2.3 turbo?

The intermittent nature feels like trapped air.
My temp gauge will do what your does or the opposite where the gauge reads low but the heads super heat if I have trapped air.
A coolant temp switch is pretty cheap and may also be on the way out and worth ruling out.
Correct, MS6. I've indeed asked my guy to replace the temp sensor, I don't know if it will have impact, but it's cheap to replace. Hell, might even be the cause due to leakage. Who knows?
As for the overflow cap; I only had it pop off once, right at the start when these issues began. Or at least then I noticed it.
I think I've read somewhere that the system is self-bleeding (also thought this myself due to the way the overflow tank is set up), but I'll forward the purging sequence to the garage regardless.

jsilva said:
If I were you I’d do a pressure test of the coolant system. It’s super easy (if you have the tools) and takes little time. You could have air entering the system due to an old hose or clamp.
Would any leak not result in the coolant leaking out? We could not find any obvious coolant leaks.


Again, thanks for the replies, I'll keep you posted.

EDIT: Would removing the temp sensor help with bleeding the air? I know it sits fairly high on the block, and as long as the coolant isn't too hot, maybe it can be used to aid in bleeding?
 

·
Registered
2006 Mazdaspeed/MPS 6
Joined
·
48 Posts
Would any leak not result in the coolant leaking out? We could not find any obvious coolant leaks.
An issue with a hose or clamp wouldn’t necessarily show up as a leak. Another car I have would suck in air either at startup or when it cooled down (I forget which now…) and there was otherwise no leak. It had sudden periodic spikes of the temperature gauge which were due to air bubbles. That car is self bleeding as well, but that doesn’t mean it instantly purges any air.

If you haven’t done a pressure test, that will reveal any weak points in your cooling system.
 

·
Registered
Joined
·
40 Posts
Discussion Starter · #14 ·
Thanks for your input guys.
Latest verdict is insufficient purging of air after thermostat replacement (thermostat was probably the main issue). They spent 2 hours purging the air from the block before no bubbling could be heard in the radiator/coolant system, after I forwarded them the procedure above.

Hopefully this will fix the issue, I will let you guys know tomorrow.

@jsilva: I keep reading your name as "Silvia", but that's due my Nissan background xD.
 

·
Registered
Joined
·
40 Posts
Discussion Starter · #15 ·
Driving home (<5 miles) driving normal speed (not pushing, max 50mph), I had the issue again.
However, the issue was much more intermittent than before.

I saw temps quickly creep up until they stabilised at normal temps, but then it crept up again and heater turned cold.
Then, when nearly home, it again stabilised somewhat. At home I noticed quite a bit of coolant had spilled out of the breather hose of the overflow tank.
Let it idle a while and did some short 2500rpm runs (not 5 min as this was for testing purposes only). Temp was around 108 degrees C (226F). Heater blew warm, then hot (to a point where I said "ouch").

There was still definitely a lot of air in the system, quite a bit of bubbles in the tank, and I could feel it in the upper hose.

Did some squeezing of both hoses which, after some coolant came out of the breather, made significant improvement to both heater and coolant temp (93C/200F).

But then the upper hose collapsed on me. After some wiggling it was ok again. I'm going to order a new rad cap just in case.

I'm gonna check coolant levels tomorrow again, and test the cooling over the course of a dew days.

If I see no improvement, I will return to the shop and have it pressure tested (I never got around to asking it because they were convinced they found the problem).
 

·
Registered
Joined
·
40 Posts
Discussion Starter · #16 · (Edited)
Whelp, I just found this:


Can someone confirm pressure rating is about 19psi?

Edit: Nevermind, it says so on the cap I currently have.

The coolant level is much lower now.
Also, this looks empty-ish, no?

242920
 

Attachments

·
Registered
Joined
·
40 Posts
Discussion Starter · #18 · (Edited)
Man, I have had same issue and complete all the way step-by-step before realize that it is head gasket issue.

Sent from my RMX2170 using Tapatalk
You mentioned this in your first post, yeah. But then I would expect the bubbling to be present all the time, no? Not just when the coolant is hot.

Also, if there IS an issue with the HG, wouldn't the coolant immediately expel from the breather hose? As the gas trapped in the coolant system would first fill the highest cavities, replacing and forcing out whatever coolant there is between the gas and the only open connection (rad cap if it is off, or breather tube when rad cap is replaced).

EDIT: Tested again just now, temp got up to previously mentioned high temps again. Both rad hoses very hard, could barely squeeze, no coolant spilling, no bubbles. Heater scorching hot.

Turned car off, and heard more bubbles as it cooled. Either rad cap is leaking, I have another air leak, or HG.
If rad cap replacement does not work, I'm taking her back for pressure and compression test.

Sidenote: As someone who has never seen a failed headgasket in person, how thick should the smoke from exhaust be in that case? Like, Steamboat Willy thick, or breath in cold temperatures thin (so basically condensation)? I have a bit of the latter but it hasn't concerned me until now.
 

·
Registered
Joined
·
11 Posts
At early stage of HG lamination high pressure needed to leakage of hot gases from cylinder to coolant, it is the only one way leak. This is how i can imaging this.


Sent from my RMX2170 using Tapatalk
 

·
Registered
2006 Mazdaspeed/MPS 6
Joined
·
48 Posts
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?
 
1 - 20 of 98 Posts
Top