Annoying Overheat issue
Discussion
I am struggling to get to the bottom of an overheat problem in my 2015 Mazda 3 2.2 Diesel (High-ish mileage for age - 71K).
It started when I noticed my cabin heating was pumping out really cold air when I had the heating set high, but then 20 minutes into the journey would suddenly get up to temperature.
A week later the thermal protection kicked in while driving on the motorway and released the throttle (bit like hitting rev limiter), but literally lasted a few seconds before driving as normal. Happened again the next day while in traffic. Madza 3 doesn't have engine temp gauge, just a light when it is cold and another when it is too hot.
No sign of coolant leakage or mixing of coolant/oil.
Normally I would have a poke around myself to see if I can find what's wrong, but I was short on time so took it to my local garage. They kept it for a few days but struggled find find anything at fault. Leak test came up OK so I they think head gasket is OK. All they noticed while running it up to temperature was that it was sometimes cooling down before it got up to the normal running temperature. From this they decided to replace the thermostat which seemed reasonable.
Got the car back yesterday and on my first trip i noticed the cabin heating still runs cold. Today I took a trip up the motorway today and the thermal protection triggered again. This time I had the OBD II plugged in and I could set the engine temp had got to 110C. Higher than it should be, but at least I'm probably not cooking my engine at that temp. Almost immediately the temp dropped back down to about 100C and stayed there for the rest of the journey. Don't really know if that is a normal temp at "above average motorway speeds".
I'm at a bit of a loss to know where to look next. Water pump? Blockage of some sort? I might flush some water through it at the weekend.
I'm reluctant to have the garage throw parts and time at it if there is some more troubleshooting I can do for 'free'.
It started when I noticed my cabin heating was pumping out really cold air when I had the heating set high, but then 20 minutes into the journey would suddenly get up to temperature.
A week later the thermal protection kicked in while driving on the motorway and released the throttle (bit like hitting rev limiter), but literally lasted a few seconds before driving as normal. Happened again the next day while in traffic. Madza 3 doesn't have engine temp gauge, just a light when it is cold and another when it is too hot.
No sign of coolant leakage or mixing of coolant/oil.
Normally I would have a poke around myself to see if I can find what's wrong, but I was short on time so took it to my local garage. They kept it for a few days but struggled find find anything at fault. Leak test came up OK so I they think head gasket is OK. All they noticed while running it up to temperature was that it was sometimes cooling down before it got up to the normal running temperature. From this they decided to replace the thermostat which seemed reasonable.
Got the car back yesterday and on my first trip i noticed the cabin heating still runs cold. Today I took a trip up the motorway today and the thermal protection triggered again. This time I had the OBD II plugged in and I could set the engine temp had got to 110C. Higher than it should be, but at least I'm probably not cooking my engine at that temp. Almost immediately the temp dropped back down to about 100C and stayed there for the rest of the journey. Don't really know if that is a normal temp at "above average motorway speeds".
I'm at a bit of a loss to know where to look next. Water pump? Blockage of some sort? I might flush some water through it at the weekend.
I'm reluctant to have the garage throw parts and time at it if there is some more troubleshooting I can do for 'free'.
Bozwell99 said:
I am struggling to get to the bottom of an overheat problem in my 2015 Mazda 3 2.2 Diesel (High-ish mileage for age - 71K).
It started when I noticed my cabin heating was pumping out really cold air when I had the heating set high, but then 20 minutes into the journey would suddenly get up to temperature.
That is 100% normal behaviour for a diesel, your heating comes from the engine coolant getting hot, diesels are so thermally efficient that the engine doesn't get hot until you are 15 min down the road.It started when I noticed my cabin heating was pumping out really cold air when I had the heating set high, but then 20 minutes into the journey would suddenly get up to temperature.
Some have an electric heater to cover this period, but not all.
Cabin heater going cold is a red flag, because a working heater at least proves that you have some coolant circulating.
I'm not familiar with that engine, but is it possible it has an air lock in the cooling system? Some engines rely on the pump self-bleeding through a vent that flows in the opposite direction when the engine is running, which can lead to a 'catch-22' if the pump pulls the air back in and then stops working.
I'm not familiar with that engine, but is it possible it has an air lock in the cooling system? Some engines rely on the pump self-bleeding through a vent that flows in the opposite direction when the engine is running, which can lead to a 'catch-22' if the pump pulls the air back in and then stops working.
HealeyV8 said:
Could be some gunk in the cooling system, probably near the interior radiator, moving around sometimes blocking flow.
You could run some coolant cleaner through the system and drain and refill.
This is likely.You could run some coolant cleaner through the system and drain and refill.
Ideally use an ir thermometer over the cooing circuit hoses and pipes, try and work out where it is and isnt getting hot, especially pipes to and from the heater, and the radiator. Is the water circulating fully? Undo clips on hoses and release te hoses momentarily to check water is flowing as it should.
Main suspects from what I read, are heater rad, or water pump, either of which could be a blockage, or just air.
Have the circuits been disturbed recently, coolant added etc, bled fully?
GreenV8S said:
Cabin heater going cold is a red flag, because a working heater at least proves that you have some coolant circulating.
I'm not familiar with that engine, but is it possible it has an air lock in the cooling system? Some engines rely on the pump self-bleeding through a vent that flows in the opposite direction when the engine is running, which can lead to a 'catch-22' if the pump pulls the air back in and then stops working.
I had previously run the engine with the cap off to try and clear an airlock, and I would have hoped that the garage would have thought of that too.I'm not familiar with that engine, but is it possible it has an air lock in the cooling system? Some engines rely on the pump self-bleeding through a vent that flows in the opposite direction when the engine is running, which can lead to a 'catch-22' if the pump pulls the air back in and then stops working.
On my return journey today with the computer running I noticed that the coolant temp got hot faster than the engine temp (+10C at one point) which seems odd for something that is supposed to be cooling a hot engine.
I think I'm going to work on the theory that there is a blockage and flush it at the weekend. Any value to adding a flushing additive?
OP,
What happens if you set of with a cold engine but don’t put the heater on full? Just set the fan at minimum flow, 18c. Drive it normally, does it start giving warm air after 10-15 minutes?
My old diesel Bora would get properly warm in cold winters for 20 minutes, and in summer gentle driving from cold didn’t get it hot for 15 minutes. Far too efficient!
What happens if you set of with a cold engine but don’t put the heater on full? Just set the fan at minimum flow, 18c. Drive it normally, does it start giving warm air after 10-15 minutes?
My old diesel Bora would get properly warm in cold winters for 20 minutes, and in summer gentle driving from cold didn’t get it hot for 15 minutes. Far too efficient!
Tony1963 said:
OP,
What happens if you set of with a cold engine but don’t put the heater on full? Just set the fan at minimum flow, 18c. Drive it normally, does it start giving warm air after 10-15 minutes?
My old diesel Bora would get properly warm in cold winters for 20 minutes, and in summer gentle driving from cold didn’t get it hot for 15 minutes. Far too efficient!
It worked fine all of the time up until about a month ago. I'm more concerned about the engine overheat protection triggering than the heater to be honest. I only mentioned it as one of the symptoms.What happens if you set of with a cold engine but don’t put the heater on full? Just set the fan at minimum flow, 18c. Drive it normally, does it start giving warm air after 10-15 minutes?
My old diesel Bora would get properly warm in cold winters for 20 minutes, and in summer gentle driving from cold didn’t get it hot for 15 minutes. Far too efficient!
Coilspring said:
This is likely.
Ideally use an ir thermometer over the cooing circuit hoses and pipes, try and work out where it is and isnt getting hot, especially pipes to and from the heater, and the radiator. Is the water circulating fully? Undo clips on hoses and release te hoses momentarily to check water is flowing as it should.
Main suspects from what I read, are heater rad, or water pump, either of which could be a blockage, or just air.
Have the circuits been disturbed recently, coolant added etc, bled fully?
So I got an IR thermometer today. I drove around at 2500 rpm until coolant temp up to 90C (engine was at about 100C) and tested the coolant pipes i could identify:Ideally use an ir thermometer over the cooing circuit hoses and pipes, try and work out where it is and isnt getting hot, especially pipes to and from the heater, and the radiator. Is the water circulating fully? Undo clips on hoses and release te hoses momentarily to check water is flowing as it should.
Main suspects from what I read, are heater rad, or water pump, either of which could be a blockage, or just air.
Have the circuits been disturbed recently, coolant added etc, bled fully?
Pipe into top of radiator = 60C
Pipe out of bottom = 50C
Pipe into heating matrix = 30C
Pipe out of heating matrix = 27C
Not sure where else I should be pointing it but these results suggest to me that water is flowing around the system.
I spent some time watching what was going on under the bonnet with the temp at 90C. There was a movement in the liquid in the coolant tank, and the fan was switching on and off as I would expect.
I didn't unclip any pipes as I didn't have any extra coolant to hand to top up.
I decided not to flush the engine today until I had a chance to speak with the garage to see if they had done it. It occurred to me that they would have drained the coolant while changing the thermostat.
CP12 said:
Heater matrix is blocked up with crap and needs flushing out!
I flushed just the matrix yesterday. Nothing nasty came out of it and it hasn't made a lot of difference on my drive this morning.I think I may have been taking the temps from the matrix hoses wrong before however when I realised that the temperature was a lot cooler on the bends. Taking the temp now on the straight bits they are now only 10C lower than main radiator pipes.
I did 80 miles of motorway driving this morning with the OBD II plugged in. The temps were fine for most of the journey until all of a sudden they went up rapidly and triggered the overheat protection again, before coming down again seconds later. This is what confuses me about my problem. How does it come and go in such a short period of time?
Bozwell99 said:
CP12 said:
Heater matrix is blocked up with crap and needs flushing out!
I flushed just the matrix yesterday. Nothing nasty came out of it and it hasn't made a lot of difference on my drive this morning.I think I may have been taking the temps from the matrix hoses wrong before however when I realised that the temperature was a lot cooler on the bends. Taking the temp now on the straight bits they are now only 10C lower than main radiator pipes.
I did 80 miles of motorway driving this morning with the OBD II plugged in. The temps were fine for most of the journey until all of a sudden they went up rapidly and triggered the overheat protection again, before coming down again seconds later. This is what confuses me about my problem. How does it come and go in such a short period of time?
Poster above me says airlock and I agree that is the next step.
Look at the procedure for bleeding your engine cold, and then start the engine with fan on low and continue to bleed.
CP12 said:
If the new temps are 10 lower than main radiator then I agree that's probably not the problem.
Poster above me says airlock and I agree that is the next step.
Look at the procedure for bleeding your engine cold, and then start the engine with fan on low and continue to bleed.
Mazda 3 is supposed to self bleed, but I went through the process anyway yesterday after flushing the heater matrix. I would have thought the garage would have done after replacing the thermostat as well.Poster above me says airlock and I agree that is the next step.
Look at the procedure for bleeding your engine cold, and then start the engine with fan on low and continue to bleed.
All I seem to be doing is ruling things out without finding any new ideas on what the cause could be. Really frustrating!
I'm not familiar with that particular engine, but here are a few thoughts which might help.
i) When you are experiencing cold air coming into the cabin, is this ever *after* the engine has fully warmed up? If yes, this argues that there is a lack of coolant in the colling system, with the interior heat exchanger radiator running dry. Solution - add coolant and bleed system.
ii) Have you checked if there are combustion gases in the coolant? I'm wondering if there is a minor head gasket failure which is allowing combustion products into the cooling system under larger throttle openings, which might account for the rapid overheating and subsequent quick return to normal.
iii) Have you checked the water pump and has the car been run on an appropriate mix of antifreeze and water? If run on water only, the water pump (and potentially the cooling passages too) might have suffered through corrosion and be failing or blocked.
I have to emphasise that these are generic guesses but may hopefully be of some assistance.
i) When you are experiencing cold air coming into the cabin, is this ever *after* the engine has fully warmed up? If yes, this argues that there is a lack of coolant in the colling system, with the interior heat exchanger radiator running dry. Solution - add coolant and bleed system.
ii) Have you checked if there are combustion gases in the coolant? I'm wondering if there is a minor head gasket failure which is allowing combustion products into the cooling system under larger throttle openings, which might account for the rapid overheating and subsequent quick return to normal.
iii) Have you checked the water pump and has the car been run on an appropriate mix of antifreeze and water? If run on water only, the water pump (and potentially the cooling passages too) might have suffered through corrosion and be failing or blocked.
I have to emphasise that these are generic guesses but may hopefully be of some assistance.
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