Strange overheating problem, help needed!
Discussion
This may take a while to read ... but if anyone can shed any light on this problem I'd be grateful ...
Car: '98 113,000 mile Vauxhall Omega 3.0 V6 Estate.
It started occasionally running hot, and 2 or 3 times overheating, in February. The frequency of it running hot increased slowly. It would hold a temperature a couple of degrees higher than normal (say 96) for a while, then back to normal (say 94) for a while, etc. No consistency on type of driving as far as I could tell.
I had the coolant changed (which looked pretty foul), which maybe helped alittle, but temporarily.
It became steadily more frequent in changing temperature. Switching the engine off and back on again very soon lowered the temperature. The dealer diagnosed a faulty sensor and replaced that.
That seemed to help a little, in that the range of varaiation was less - but it still varied, and the "normal" running temeperature soon bagan to creep up again.
So the dealer then diagnosed a faulty thermostat and replaced that (but didn't test the old one
and by the time I asked they'd binned it). That seemed to help a bit, but the warm up cycle was a bit strange - it would warm up to say 96, then cool back down to 93, then back up to a running temp of about 94, and hold it for a while. Then after say half an hour it would creep up a degree or two. In town it would run at about 97.5. This range of temeperatures crept up again, until the overheating light came on twice (once on the way to the dealer for more diagnosis) - which is at 105 degrees incidentally.
The dealer was pretty useless at that point (among other things telling me I needed a new sunroof motor, when in fact (on consulting the manual
) I needed to press the switch for 5 seconds to reset it - diodn't fill me with confidence).
So I took matters into my own hands and (last week) drained the coolant and flushed out as much of the radiator and engine as I could get at, using Holts Speedflush as well. Couldn't flush the main engine section without taking the thermostat out which is a fairly big job on that car.
This seemed to help a lot, it still did the funny thing with the warm up cycle but generally ran at say 94-95. Still not perfect though, and it was a little warmer when driving slowly, cooler at speed. It had never shown this consistency before.
Over the last few days the temperatures have again gradually crept up. Today it ran at about 97 most of the way to work. Again a little cooler at motorway speed - maybe 96 degrees. Up to 98-99 when I stopped, (after perhaps half a mile of town following 12 miles of dual carriageway). The cooling fan didn't run on after I stopped, but when I restarted the car and stopped it again, the fan ran on for a bit. I'm not convinced the fan is coming on properly, but that shouldn't affect it at "over 69mph" anyway should it?
The dealer's mechanic was muttering about a cylinder head gasket, but I doubt that because draining the coolant and replacing it - with and without flushing - seems to have helped it more than once (Four times now - this also when the sensor and thermostat were replaced). Also there's no residual pressure in the system when cold, and there's no loss of coolant.
There's plenty of tension in the auxiliary drive belt that runs the water pump.
When I drained it and refilled, I only managed toget about 7.5 litres out, and it only took about 6 litres back in. It's supposed to be 9.5 litres capacity. However, it was on a bit of a slope - not much level ground nearby - which may have affected that. Also doing a lot of flushing may have retained a bit of water in the system.
Here's my best theory:
The radiator has a significant blockage of crud in it. Flushing cleaned the rest of the radiator etc fairly well but didn't shift the blockage. As it's driven, the crud forming the blockage distributes itself around the system again a bit more, gradually decreasing cooling efficiency. One of the places it distributes itself to is the main cooling fan switch (which I couldn't find when I drained the system), causing it to be erratic. The blockage is also the reason why I wasn't able to get a full load of coolant into or out of the cooling system. Looking in the expansion tank, the fresh coolant is already looking manky - although the expansion tank itself was pretty foul anyway, and I couldn't clean it all.
So that's the story and I'm a little puzzled. If you've read this far - thanks!
If you've any suggestions to make I'd appreciate it as I don't know enough about cooling systems to know whether my theory above might be correct. If it is correct - what do I do about it?
Car: '98 113,000 mile Vauxhall Omega 3.0 V6 Estate.
It started occasionally running hot, and 2 or 3 times overheating, in February. The frequency of it running hot increased slowly. It would hold a temperature a couple of degrees higher than normal (say 96) for a while, then back to normal (say 94) for a while, etc. No consistency on type of driving as far as I could tell.
I had the coolant changed (which looked pretty foul), which maybe helped alittle, but temporarily.
It became steadily more frequent in changing temperature. Switching the engine off and back on again very soon lowered the temperature. The dealer diagnosed a faulty sensor and replaced that.
That seemed to help a little, in that the range of varaiation was less - but it still varied, and the "normal" running temeperature soon bagan to creep up again.
So the dealer then diagnosed a faulty thermostat and replaced that (but didn't test the old one
and by the time I asked they'd binned it). That seemed to help a bit, but the warm up cycle was a bit strange - it would warm up to say 96, then cool back down to 93, then back up to a running temp of about 94, and hold it for a while. Then after say half an hour it would creep up a degree or two. In town it would run at about 97.5. This range of temeperatures crept up again, until the overheating light came on twice (once on the way to the dealer for more diagnosis) - which is at 105 degrees incidentally. The dealer was pretty useless at that point (among other things telling me I needed a new sunroof motor, when in fact (on consulting the manual
) I needed to press the switch for 5 seconds to reset it - diodn't fill me with confidence). So I took matters into my own hands and (last week) drained the coolant and flushed out as much of the radiator and engine as I could get at, using Holts Speedflush as well. Couldn't flush the main engine section without taking the thermostat out which is a fairly big job on that car.
This seemed to help a lot, it still did the funny thing with the warm up cycle but generally ran at say 94-95. Still not perfect though, and it was a little warmer when driving slowly, cooler at speed. It had never shown this consistency before.
Over the last few days the temperatures have again gradually crept up. Today it ran at about 97 most of the way to work. Again a little cooler at motorway speed - maybe 96 degrees. Up to 98-99 when I stopped, (after perhaps half a mile of town following 12 miles of dual carriageway). The cooling fan didn't run on after I stopped, but when I restarted the car and stopped it again, the fan ran on for a bit. I'm not convinced the fan is coming on properly, but that shouldn't affect it at "over 69mph" anyway should it?
The dealer's mechanic was muttering about a cylinder head gasket, but I doubt that because draining the coolant and replacing it - with and without flushing - seems to have helped it more than once (Four times now - this also when the sensor and thermostat were replaced). Also there's no residual pressure in the system when cold, and there's no loss of coolant.
There's plenty of tension in the auxiliary drive belt that runs the water pump.
When I drained it and refilled, I only managed toget about 7.5 litres out, and it only took about 6 litres back in. It's supposed to be 9.5 litres capacity. However, it was on a bit of a slope - not much level ground nearby - which may have affected that. Also doing a lot of flushing may have retained a bit of water in the system.
Here's my best theory:
The radiator has a significant blockage of crud in it. Flushing cleaned the rest of the radiator etc fairly well but didn't shift the blockage. As it's driven, the crud forming the blockage distributes itself around the system again a bit more, gradually decreasing cooling efficiency. One of the places it distributes itself to is the main cooling fan switch (which I couldn't find when I drained the system), causing it to be erratic. The blockage is also the reason why I wasn't able to get a full load of coolant into or out of the cooling system. Looking in the expansion tank, the fresh coolant is already looking manky - although the expansion tank itself was pretty foul anyway, and I couldn't clean it all.
So that's the story and I'm a little puzzled. If you've read this far - thanks!
If you've any suggestions to make I'd appreciate it as I don't know enough about cooling systems to know whether my theory above might be correct. If it is correct - what do I do about it?
Hmm, I'll inspect the radiator more closely! But the fact that the situation has been temporarily improved by flushing/replacing coolant suggests that the problem's not external corrosion/damage etc.
Would taking the radiator out to reverse flush it get a better result than what I did, which was use the oulet hose turned upside down so that the open end was higher than the top of the radiator, then run water in through there until it ran clear out of the top hose opening?
Would taking the radiator out to reverse flush it get a better result than what I did, which was use the oulet hose turned upside down so that the open end was higher than the top of the radiator, then run water in through there until it ran clear out of the top hose opening?
Latest installment: I tried switching the engine off when it hit 100 deg on the way home today, and immediately back on - in the space of 5 seconds or so the temperature fell by 4 or 5 degrees. This is unlikely in reality so I concluded that the gauge must be faulty ... but if it were a gauge fault, flushign the radiator wouldn't have made an improvement - would it?
Could something be fooling the gauge, rather than the gauge itself being faulty? Something which may have been temporarily helped by flushing out the system?
Could something be fooling the gauge, rather than the gauge itself being faulty? Something which may have been temporarily helped by flushing out the system?
That sounds like a good plan Peter.
How would I get the thermometer into the hose while the engine's running?
Is it possible to get some kind of pressure retaining plate with a valve in it and drill through?
Do you mean literally a "cooking" thermometer or a "cooking" as in "bog-ordinary for a car"?
Any ideas where I'd get one from?
How would I get the thermometer into the hose while the engine's running?
Is it possible to get some kind of pressure retaining plate with a valve in it and drill through?
Do you mean literally a "cooking" thermometer or a "cooking" as in "bog-ordinary for a car"?
Any ideas where I'd get one from?
Ah, now I did wonder about oil on the fan belt, that's interesting. Another symptom is that the power steering - driven off the same belt - is possibly, maybe, I might be imagining it, faintly heavier than it was.
How did you confirm that? Was it much oil? There's none obvious but a lot of the belt is hidden. Oil's not that easy to clean off completely and solvents may not react well with rubber - how did you clean it?
My multimeter doesn't measure temperature. Not that easy to get the probe in anyway 'cos it's a pressurised system - stick in a probe through something and the coolant will spray out the hole.
How did you confirm that? Was it much oil? There's none obvious but a lot of the belt is hidden. Oil's not that easy to clean off completely and solvents may not react well with rubber - how did you clean it?
My multimeter doesn't measure temperature. Not that easy to get the probe in anyway 'cos it's a pressurised system - stick in a probe through something and the coolant will spray out the hole.
Hmm, I think this is an avenue that needs investigated. It also looks as though the belt self-adjuster is up against its stops, although it's not that easy to see or feel. The dealer mechanic reckoned there was enough tension in the belt but I'm not convinced any more about that bloke.
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