I'm running out of options with our faultless 2007 petrol Mazda.
History
Bought 2013 50k miles £2400
2015 replaced stuck open thermostat
2019 replaced coolent, had issues purging the system but eventually ok.
6 weeks ago cooling fans stuck on, temp gauge normal.
Whilst waiting for wife outside shop at idle went from hot to cold in cabin, rev engine heat comes back cycle continues, check coolent level all normal?
Replace coolent, no difference but once up to temp fans running no heat from rad(air through rad freezing) replace thermostat run up to temp no change still freezing
Today drove a short distance 5 miles on way home temp rose higher than I've ever seen, once home rad cold, clear bubbling noise but not boiled over once stopped.
I have a new water pump but not fitted, there's is flow through the heater matrix so not sure if it is the pump.
Oil filler fine no white steam from exhaust.
Any suggestions would be really helpful otherwise it's going to be an expensive fix(stealer) add the issue of the wife 500 being in it's accident.

John202020 said:

Bought 2013 50k miles £2400

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At least it doesn't owe you anything.

John202020 said:

Any suggestions would be really helpful

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First thought is thermostat not opening. Sometimes new parts can be faulty.

Not sure how the thermostat works on the Mazda, but if it's the element type you can take out and still run the car, try it with the thermostat removed.

It's hard to imagine how a water pump could stop circulating the water without failing catastrophically, unless a hose has completely collapsed internally, and that's unlikely.

John202020 said:

otherwise it's going to be an expensive fix(stealer)

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You can fix this, John - I have every faith in your abilities. There can't be many things that can stop the coolant from circulating.

Obviously not the case here, but if anyone with similar symptoms is reading this thread in the depths of winter, much the same thing happens if the coolant freezes due to insufficient or ineffective antifreeze.

If rad was not hot, this suggests that either it was empty, or blocked.

Firstly, you need to ensure that the system is full. With it cold, and the cap still on, squeeze each hose. It should be easy to feel if the hose is full or not.
Any fluid loss needs the leak to be found, of course, but the system needs to be full to test properly.

From a cold start, the top hose should get warm as the heat conducts along it, but then get noticeably hot as the thermostat opens. An easy test for thermostat operation.

Then top hose should get hot all the way along, (will take longer in this weather sadly), then the tank of the rad supplied by the top hose should get hot. Without tangling yourself in anything moving, especially the fans, you should be able to feel the passage of the hot coolant across the radiator, until the bottom hose gets warm too.

Same exercise, although quicker should work for the heater. Input hose should get warm quite quickly, followed by the output, soon after. Keep fan off until both hoses are hot. Then operating the fan at high speed should not cause output hose to get cold, only slightly cooler than input.

Hopefully this will help identify whether the heat flow is correct. A blocked radiator may well have cool spots, easier to identify as it warms up. Once fully hot, heat will conduct across it all.

A job for tomorrow morning.

portland_bill said:

If rad was not hot, this suggests that either it was empty, or blocked.

Firstly, you need to ensure that the system is full. With it cold, and the cap still on, squeeze each hose. It should be easy to feel if the hose is full or not.
Any fluid loss needs the leak to be found, of course, but the system needs to be full to test properly.

From a cold start, the top hose should get warm as the heat conducts along it, but then get noticeably hot as the thermostat opens. An easy test for thermostat operation.

Then top hose should get hot all the way along, (will take longer in this weather sadly), then the tank of the rad supplied by the top hose should get hot. Without tangling yourself in anything moving, especially the fans, you should be able to feel the passage of the hot coolant across the radiator, until the bottom hose gets warm too.

Same exercise, although quicker should work for the heater. Input hose should get warm quite quickly, followed by the output, soon after. Keep fan off until both hoses are hot. Then operating the fan at high speed should not cause output hose to get cold, only slightly cooler than input.

Hopefully this will help identify whether the heat flow is correct. A blocked radiator may well have cool spots, easier to identify as it warms up. Once fully hot, heat will conduct across it all.

A job for tomorrow morning.

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Thanks Bill,
System is always full
Top hose gets warm is but not scalding
Squeeze either top or bottom hose and level moves in rad filler neck
Even at the point of, switched off, and you could hear boiling bubbles in the top hose the rad remains stone cold
At start up from cold I can hear small air bubbles run through the heater matrix, like a small amount flows round the system round and around, even when the system is hot the heater output isn't what I'd expect set on max heat.
Has had a new thermostat as I suspected that first, not sure if I kept the old stat.
Issue started "out of the blue"

Just a stab in the dark. As you may all know I also "mess about" with VAG "stuff" - mostly Skoda and SEAT - and a while ago we had quite a big problem with waterpump impellers. It was in the earlier days of plastic impellers and what was happening was that they were coming loose on the shaft. So the water pump bearing was undamaged and it wasn't having any effect on the cambelt drivetrain - so actually there was no external sign, no water leak, nothing, that the problem was down to the pump. Also it was somewhat insidious in that some still managed to circulate some water as they were only "slipping" whereas others pretty much stopped rotating entirely when the interference fit between shaft and impeller was destroyed. When that happens there is a very small movement of water still takes place but as it's driven only by the hot water rising in the engine very small amounts of water actually move - sounds a bit like what you've got maybe?

Yours may not be in any way related, but the symptoms do seem to fit? The first time I ran into this I was pulling my hair out trying to figure out what had happened and it was only because a friendly mechanic told me to remove the pump and check it that I became aware this could be a problem. Bit of a pain though if you take the pump out and find nothing wrong with it - and I've done that too!

Good luck
Jock

Hi

Warm water circulating..

Hoses not 'Scalding '

Its sounding like control of circulation


Im guessing access to the thermostat is better than the waterpump.

'Gutting ' the stat should improve flow..

BUT of course it wont improve the SCORCHIO.. factor ( of hoses..)

If you can buy a new stat for sensible money though.. probably worth doing that


@2004 was the era of my colleagues Octavia losing its impellor drive..

Brought on by booting the car past a tractor.. so hard engine acceleration

My friend' old MG recently had issues with system not getting warm, reason being the thermostat fixture had disintegrated - stat not closing. That means lukewarm temperature everywhere, does not sound like what you have.
Rad cold could be stat not opening or only at much higher temp than desired (engine at revs). Wrong spec or malfunction of the new stat?
Water pump not pumping sounds like a probable cause. Japanese cars tend to have those ancillary parts in a quality that never fails, though (my experience). Still worth checking if no other explanation holds up, the symptoms would make sense.

This was happening with the old thermostat(suspect it wasn't faulty) and the brand new one.

John202020 said:

This was happening with the old thermostat(suspect it wasn't faulty) and the brand new one.

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It's starting to look like the water pump needs to be scrutinised. I guess it's possible for the impeller to come loose on its driveshaft.

my neighbour has recently bought a Volvo diesel. Head gasket failed. When the garage dismantled the engine water ways were blocked up with some form of sealant stuff that was probably added by the previous owner in a last ditch effort to produce a 5 minute fix enabling them to px it. I would suggest draining the rad / coolant and checking the volume required to refill it vary carefully. If there is anything similar going on or blockages it would reveal this.

The Panda Nut said:

my neighbour has recently bought a Volvo diesel. Head gasket failed. When the garage dismantled the engine water ways were blocked up with some form of sealant stuff that was probably added by the previous owner in a last ditch effort to produce a 5 minute fix enabling them to px it. I would suggest draining the rad / coolant and checking the volume required to refill it vary carefully. If there is anything similar going on or blockages it would reveal this.

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Owned from new IIRC..

Personally I would dump the coolant anyway..

Any labour required to undo clips.. on various items.. now will save grief if the pump does need attention

The Panda Nut said:

When the garage dismantled the engine water ways were blocked up with some form of sealant stuff that was probably added by the previous owner in a last ditch effort to produce a 5 minute fix enabling them to px it.

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Here's the thing; John's owned this for quite awhile, and it's only recently started to have a spectacular cooling issue. It seems to me that rules out something a previous owner may have done, and John is far too sensible to pour that kind of thing into the cooling system.

jrkitching said:

Here's the thing; John's owned this for quite awhile, and it's only recently started to have a spectacular cooling issue. It seems to me that rules out something a previous owner may have done, and John is far too sensible to pour that kind of thing into the cooling system.

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I understand your points. Being cooling there are few things that can cause it. You just don't know whats been done on the past though. It has just occurred to me however that there may be something extraneous in the system. It could be as daft as something that shouldn't have ever been in there in the first place like a piece of PVC that has now moved and blocked something. A broken gasket / coolant bottle label for example. Something that could flap back and fore. Had a single grain of polystyrene in my central heating system a few years back and boy did that cause me some pain before I stripped all the rads out and eventually found this thing. It was big enough to pass the valves only in one direction so sometimes would have a cold radiator, but not always the same one...

I had a Citroen BX a number of years ago that had misbehaving suspension, It did all sorts of peculiar things that "it can't do that sir". That turned out to be paint flaking off the reservoir blocking valves and orifices. It eventually took 4 months back at the factory for them to identify this and fix it.

I would still suggest checking the actual capacity with the expected might be worth it. Also suggest can you get some clear hose and put some into the system somewhere so you can actually see the liquid flow. Drop the coolant, fill with clean water and add a little dye then run it up and see what the flow is like.

Just a bit of sideways thinking.

Certainly no suggestion of a thinking mechanic having added any 'stuff' himself!

Adding to what jock said further up, I’ve seen the fins of plastic water pump impellers break off or wear right down, this means that at idle they don’t really shift any water but when running normally or rev’d they will push enough water around to keep the engine cool or push water into the heater core

I did have problems with a big air lock on my Grande punto stopping the water flow through the heater core but there was still coolant moving through the radiator and the pipes were getting warm normally

We bought the car at 50k and six years old, was previously a Mobility car with its first owner, the second had the same surname so think it was a relative that owned it so has pretty much comprehensive history up to the point we bought it, have to say its be a typical perfect example of Jap engineering and a bargain.
Not sure if its relevant, once fully drained, removing the thermostat, about a litre or so(maybe more) of coolant comes out, the stat is on the side of the block near the water pump fairly high up the engine side.

The chief suspect for me would be the water pump, since a cold radiator means that either it is blocked (but you replaced the coolant and presumably would have noticed anything odd, like bits of rust, gunge or green slime falling out of it) or the coolant is not being circulated quickly enough.

The coolant in the radiator is cold because it's being cooled and not replaced with new (hot) coolant.
The heater is cold until you rev it some more because it too runs out of hot coolant (mimicking what's happening in the radiator).
The overheating at random is again, the hot water in the block not being pushed into the radiator, so that cool coolant can take its place.
You'll get all of these is the pump is being turned, but the impeller blades aren't spinning at the same speed.

New pump will sort it... but that may mean a new cam-belt and tensioners, depending on how Mazda does it.
I wouldn't use it too much in case the pump spindle decides it's had enough and seizes or collapses, which would melt or throw off the cam-belt.


Ralf S.

Thanks Ralf not driven it as I'm aware of how critical the issue is, water pump is aux belt driven cam is chain driven don't have a chance until thur to look at it(work) by which time our hire car 're accident of wife's car will have gone back, the coolent that has come out has been pristine bar the odd black flecks which could easily be rubber?

Handy that the pump is driven by the aux' belt.. it means you could still drive it a mile or so, if you really had to.. since the coolant will be just warming up by the time you turn it off again.

The flecks could be pieces of neoprene O-rings from the water pump shaft seal (in which case it'll start leaking soon) or just bits of gasket than fell into the coolant channels the last time someone changed a rocker cover or something. I quite often find "bits" in the coolant.. as long as they're small and soft, it's probably not conclusive.


Ralf S.