Overheating engine
#11
02-24-2012, 09:43 AM
Thanks for the replies! However I think I will not have the time to redo the work all over again at this point. 
To have it properly machined I would need to have it disassembled from the car, there is a good machine shop in town but they only handle loose engines. Removing engine seems to be a hugemongous job and would requires two persons or a crane? I am also lacking the tools for thread restoration.
As it has been going for almost 200 000 miles it has still done a good job (there are plenty of 626:s around here at the junkyard with only half the mileage). But ofcourse I will keep it alive as long as possible unless cost peaks too much.
Maybe I will consider removing the top once again when summer arrives here, it is not that pleasant to do maintenance in the non-heated garage when it is below zero outside.
The next weeks I will watch for:
- leaks around the cylinder block and monitor oil/coolant level.
- check oil cap for milky fluid (=coolant)
- check cooler cap for oil...
And maybe not run it too hard...
The task now would be to keep engine as cool as possible.
The cooling fan is still an issue, how hot does an engine needs to be for it to start? Remember this was a single speed fan.
When I started it I think the sound was unfamiliar - it might have been off for a long time.
And I still think it's fishy that the coolant is cold behind the thermostat but hot at the other end of the engine, is the coolant circulating the wrong way? And how would the circulation be affected by a non-functioning coolant fan?
To have it properly machined I would need to have it disassembled from the car, there is a good machine shop in town but they only handle loose engines. Removing engine seems to be a hugemongous job and would requires two persons or a crane? I am also lacking the tools for thread restoration.
As it has been going for almost 200 000 miles it has still done a good job (there are plenty of 626:s around here at the junkyard with only half the mileage). But ofcourse I will keep it alive as long as possible unless cost peaks too much.
Maybe I will consider removing the top once again when summer arrives here, it is not that pleasant to do maintenance in the non-heated garage when it is below zero outside.
The next weeks I will watch for:
- leaks around the cylinder block and monitor oil/coolant level.
- check oil cap for milky fluid (=coolant)
- check cooler cap for oil...
And maybe not run it too hard...
The task now would be to keep engine as cool as possible.
The cooling fan is still an issue, how hot does an engine needs to be for it to start? Remember this was a single speed fan.
When I started it I think the sound was unfamiliar - it might have been off for a long time.
And I still think it's fishy that the coolant is cold behind the thermostat but hot at the other end of the engine, is the coolant circulating the wrong way? And how would the circulation be affected by a non-functioning coolant fan?
#12
02-25-2012, 08:52 AM
Cooling system:
There is a mantle around the block and the head. And there is a loop through the radiator and a loop through the heater. I neglect the heater for now.
The thermostat is closed when the engine is cold. The coolant is pumped through the engine's mantel in a closed loop. When the temperature reaches a certain level (about 190 degrees F) the thermostat opens and the coolant also flows through the radiator.
To check the thermostat you idle the engine and take the temperature at the radiator hose that comes out of the thermostat housing. As the engine temperature moves above the thermostat's trigger point the temperature in the radiator hose rises SUDDENLY. If this does not happen you have a problem with the thermostat or a clogged radiator loop.
If the temperature in the radiator hose rises slowly as the engine warms up you can conclude that the thermostat does not close.
I think your thermostat does not open or the radiator loop is clogged. The "other end" gets warm from coolant that tries to go somewhere because the pressure rises in the mantle.
Temperature required to start: the engine should start ant any temperature this planet can throw at you.
You may have a pile of spare parts at your disposal for your next 6. Or you get one of them engines from the pull-a-part.
There is a mantle around the block and the head. And there is a loop through the radiator and a loop through the heater. I neglect the heater for now.
The thermostat is closed when the engine is cold. The coolant is pumped through the engine's mantel in a closed loop. When the temperature reaches a certain level (about 190 degrees F) the thermostat opens and the coolant also flows through the radiator.
To check the thermostat you idle the engine and take the temperature at the radiator hose that comes out of the thermostat housing. As the engine temperature moves above the thermostat's trigger point the temperature in the radiator hose rises SUDDENLY. If this does not happen you have a problem with the thermostat or a clogged radiator loop.
If the temperature in the radiator hose rises slowly as the engine warms up you can conclude that the thermostat does not close.
I think your thermostat does not open or the radiator loop is clogged. The "other end" gets warm from coolant that tries to go somewhere because the pressure rises in the mantle.
Temperature required to start: the engine should start ant any temperature this planet can throw at you.
You may have a pile of spare parts at your disposal for your next 6. Or you get one of them engines from the pull-a-part.
Last edited by tanprotege; 02-25-2012 at 09:32 AM.
#13
02-26-2012, 05:06 AM
I ran the car in idle mode and tried to feel the temperature at the thermostat. Sure enough it seems to work, after running a while the cool side of the radiator suddenly turned very hot (easier to fel the difference here than on the hose connections). It do not open up very early...
Now to the thing, actually it seems like the sensor I have replaced before is the "Temperature gauge sending unit" (has green plastic contact). Closer inspection shows another sensor "Engine coolant temperature sensor (PCM)" closer to the front of the engine (has black plastic contact).
The picture in Haynes manual is not very clear here, the arrows pointing out the sensors are off with 1 cm...
Measured the resistance on ECT sensor and got a very high value. The plastic contact is black but visually (wihtout removing it) it seems to be the same kind of sensor as the Temp gauge sending unit? Atleast the contact pins are the same.
Now to the thing, actually it seems like the sensor I have replaced before is the "Temperature gauge sending unit" (has green plastic contact). Closer inspection shows another sensor "Engine coolant temperature sensor (PCM)" closer to the front of the engine (has black plastic contact).
The picture in Haynes manual is not very clear here, the arrows pointing out the sensors are off with 1 cm...
Measured the resistance on ECT sensor and got a very high value. The plastic contact is black but visually (wihtout removing it) it seems to be the same kind of sensor as the Temp gauge sending unit? Atleast the contact pins are the same.
#14
02-26-2012, 10:15 PM
Ferret, they do different things. The temperature gauge sensor is for the in dash gauge only, it does not have to be very responsive. The ECT sensor is delivering data to the ECU and it has to be very responsive and accurate.
I don't know how this is in your car, but in some cars the fan get switched by the ECU, in others it gets switched by a separate temperature switch at the radiator.
Maybe someone who knows your car better than I can chime in.
I don't know how this is in your car, but in some cars the fan get switched by the ECU, in others it gets switched by a separate temperature switch at the radiator.
Maybe someone who knows your car better than I can chime in.
#15
02-28-2012, 01:56 PM
Fan working!
This has been a really long thread, with two main problems. Overheating engine and coolant fan which refused to work.
To summarize:
1. Engine overheated and coolant leaked from timing belt side of engine.
Either this was caused by:
- cylinder head bolts which had not been tighenet enough.
or
-overheating due to cooling problem (problem started on a really cold day, blockage in the coolant system?)
2. Coolant fan did not seem to work at all.
Actions:
Top was removed and some cleaning task took place. The following parts were replaced to improve engine cooling and ignition:
- cylinder head gasket
- camshaft gasket (sits behind the camshaft wheel)
- water pump + gasket
- thermostat + gasket
- radiator
- distributor cap and rotor
- ignition wires and spark plugs
- primary oxygene sensor below the exhaust manifold
- Fan control sensor
- coolant and oil
- adjusted ignition timing
I kept the original KA30 fan control relay and only cleaned the "Engine coolant temperature sensor" (ECT) located close to the fan control sensor.
The result:
- No visible leak so far, oil / coolant look like they should.
- Finally the fan is running!
It only seems to start if I run the car in idle long enough and it then only runs briefly. Outside temperature is +5 C so it might only run when really needed...
I believe that cleaning the ECT sensor got the fan going, I just removed deposits on the metallic tap. Unfortunatly I have not found a replacement ECT sensor which I would have preferred, it might still be off specifications. According to Haynes the PCM will control the coolant fan relay given the information from the ECT sensor. I also straighened out a really sharp bend which had been made on the connecting wires.
The other replacement actions were probably not completely "wasted" as the radiator was not 100% OK and this must have affected cooling.
A non-running cooling fan seems to be a common problem for Mazda 626? Might be worth to write a good sticky thread on how to troubleshoot this...
Drove the car to the annual condition check here in Sweden, it passed!
That the temperature looks higher than before the problems started is probably because the reading is more accurate now, or that the replacement thermostat is of inferior quality. It had not opened after I had been driving for 30 miles on a 50 mph road, rubber hose completely cool close to thermostat housing but the left hand side (fan side) of the radiator was hot...
Do I have an:
- extremely good cooling even without radiator flow?
or
- bad coolant circulation (but I replaced the water pump?!?)?
or
- inferior quality of the new thermostat I installed?
I guess the problem is that the thermostat opens too late, the temperature at the opposite side of the engine exceeds +82 C for sure. I will try to find a different brand thermostat and replace it once again.
Looking at the coolant sensors there were maybe 0.1 or 0.2 mmm with deposits (brownish, which sits quite hard to the metal). Maybe this prevents a good heat transfer from the metal to the coolant, could be from using tap water when mixing coolant?
This time I used distilled water for a 50/50 mix coolant mix.
Might be a side track but... Any way small deposits like that could cause coolant fluid circulation problem? Dissolve this by plugging up the thermostat housing and fill engine with citric acid + water from the opposite end? Or something else someone has tried?
To be continued...
- Thermostat, replace with different brand
- Possible to cleanup deposits in engine block with it in place?
- What the h*ck does the "Fan control sensor" do if the ECT sensor controls the KA30 Fan relay?
To summarize:
1. Engine overheated and coolant leaked from timing belt side of engine.
Either this was caused by:
- cylinder head bolts which had not been tighenet enough.
or
-overheating due to cooling problem (problem started on a really cold day, blockage in the coolant system?)
2. Coolant fan did not seem to work at all.
Actions:
Top was removed and some cleaning task took place. The following parts were replaced to improve engine cooling and ignition:
- cylinder head gasket
- camshaft gasket (sits behind the camshaft wheel)
- water pump + gasket
- thermostat + gasket
- radiator
- distributor cap and rotor
- ignition wires and spark plugs
- primary oxygene sensor below the exhaust manifold
- Fan control sensor
- coolant and oil
- adjusted ignition timing
I kept the original KA30 fan control relay and only cleaned the "Engine coolant temperature sensor" (ECT) located close to the fan control sensor.
The result:
- No visible leak so far, oil / coolant look like they should.
- Finally the fan is running!
It only seems to start if I run the car in idle long enough and it then only runs briefly. Outside temperature is +5 C so it might only run when really needed...
I believe that cleaning the ECT sensor got the fan going, I just removed deposits on the metallic tap. Unfortunatly I have not found a replacement ECT sensor which I would have preferred, it might still be off specifications. According to Haynes the PCM will control the coolant fan relay given the information from the ECT sensor. I also straighened out a really sharp bend which had been made on the connecting wires.
The other replacement actions were probably not completely "wasted" as the radiator was not 100% OK and this must have affected cooling.
A non-running cooling fan seems to be a common problem for Mazda 626? Might be worth to write a good sticky thread on how to troubleshoot this...
Drove the car to the annual condition check here in Sweden, it passed!
That the temperature looks higher than before the problems started is probably because the reading is more accurate now, or that the replacement thermostat is of inferior quality. It had not opened after I had been driving for 30 miles on a 50 mph road, rubber hose completely cool close to thermostat housing but the left hand side (fan side) of the radiator was hot...
Do I have an:
- extremely good cooling even without radiator flow?
or
- bad coolant circulation (but I replaced the water pump?!?)?
or
- inferior quality of the new thermostat I installed?
I guess the problem is that the thermostat opens too late, the temperature at the opposite side of the engine exceeds +82 C for sure. I will try to find a different brand thermostat and replace it once again.
Looking at the coolant sensors there were maybe 0.1 or 0.2 mmm with deposits (brownish, which sits quite hard to the metal). Maybe this prevents a good heat transfer from the metal to the coolant, could be from using tap water when mixing coolant?
This time I used distilled water for a 50/50 mix coolant mix.
Might be a side track but... Any way small deposits like that could cause coolant fluid circulation problem? Dissolve this by plugging up the thermostat housing and fill engine with citric acid + water from the opposite end? Or something else someone has tried?
To be continued...
- Thermostat, replace with different brand
- Possible to cleanup deposits in engine block with it in place?
- What the h*ck does the "Fan control sensor" do if the ECT sensor controls the KA30 Fan relay?
#16
02-28-2012, 05:49 PM
SKOL!
Thermostat: You can test it by putting it into boiling water and letting it cool. Take the water temperature when it closes. Compare to specs.
Has there ever been any radiator leak stop added to the coolant? This stuff could deposit itself on the ECT sensor and the temp sending unit and mess up the readings. In fact a distant family member of mine lost an engine due to overheating because of that. When in doubt give it a thorough coolant system flush and put fresh coolant in. I would be cautious about using acids. I would use copious amounts of water. Look up some Youtubes on that. If you do it clean the whole system including radiator and heater core.
Fan control sensor: It may set the fan speed. It may just be one of those peculiar translations from Japanese to English, just like EGR Boost Sensor. What exactly gets boosted there? Nothing.
Thermostat: You can test it by putting it into boiling water and letting it cool. Take the water temperature when it closes. Compare to specs.
Has there ever been any radiator leak stop added to the coolant? This stuff could deposit itself on the ECT sensor and the temp sending unit and mess up the readings. In fact a distant family member of mine lost an engine due to overheating because of that. When in doubt give it a thorough coolant system flush and put fresh coolant in. I would be cautious about using acids. I would use copious amounts of water. Look up some Youtubes on that. If you do it clean the whole system including radiator and heater core.
Fan control sensor: It may set the fan speed. It may just be one of those peculiar translations from Japanese to English, just like EGR Boost Sensor. What exactly gets boosted there? Nothing.
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