Mk1- Coolant loss / overheating troubles...
Discussion
Hello folks, I would really value some opinions / advice on a cooling system problem I have on a 1994 UK Mk1 1.8 car which I've only owned since March. It has good full service history until a few years ago where I suspect it had stood as a "project" car for a year at least until being returned to use by various owners 2-3 years ago.
Here was the the first symptom: kept noticing expansion tank reservoir filling up resulting in coolant overflowing from out of the overflow breather pipe, mostly when driven the harder end of normal driving. Once cooled the expansion tank would empty out as the radiator sucked back the excess This got to the stage where the radiator itself was taking 1+ litres of water to stay brimmed every few drives. However for months there was no indication of overheating on the temperature gauge itself.
Diagnosis 1: New OEM filler cap
Result: Same problem occurring.
Diagnosis 2: Mazda specialist advised an incorrect thermostat had been fitted so this was replaced, along with a coolant change. They had found it would overheat when left to idle.
Result: Cooling fans coming on correctly, but no change on the expansion tank overflow.
Diagnosis 2: Radiator and/or hose blockage. Had new radiator, two hoses, water pump and coolant change. Coolant had been an awful colour and it was commented that the removed hoses had been very dirty inside with rust/gunk.
Result: Not much change with the expansion tank overflow. When the expansion reservoir is filled to between the middle and upper limits the level rises during even a short drive and seems to overflow a certain amount out. It seems to now settle at the lower limit once everything has cooled and the radiator has sucked back from the expansion tank. However, for the first time today I have had problems with the temperature guagae showing temperature increases. We had driven 100+ miles on mostly B-roads in todays warmish sunshine with no noticeable problems however after about 10-15 mins of dual carriage way cruising at a steady 60mph / 3000 revs I noticed the temp gauge had crept to right of centre, but no further than around 2/3. I stopped and there were signs of a small amount of coolant loss around the expansion tank bulkhead and the tank was almost full to brim, the cooling fan was working correctly. I let it cool for 10-15 mins and carried on at about 50-55mph this seemed to have an positive effect as the temp guage settled back to normal left of centre, experimenting a little this proved it crept back up when higher speed/revs were used and it also crept up on inclines with higher engine load. The furthest it went was around 3/4 towards hot mark.
So here are my thoughts:
Despite new radiator / thermostat / main rad hoses and water pump coolant still not circulating correctly resulting in back pressure forcing coolant up past rad cap into expansion tank, along with overheating at higher prolonged engine revs.
So could it be that the other water hoses / ancillaries are still semi-clogged due to dirty coolant circulating for a long time causing restricted circulation hence the consistent back pressure forcing of water past rad cap into expansion tank. A simple engine block coolant flush with a hose and/or a chemical cleaner would clean out and solve the issue? I don't know if this was done by the garage.
Second option I can think of is could I have excess cooling system pressure from a blown headgasket. I have no usual signs of headgasket failure - no mayo inside oil cap, we did an oil change a month or so ago and there were no signs of water in oil. I have noticed water in the exhaust tip when started from cold but have assumed the usual condensation. However it worries me that the only cause/effect listed in Rod Grainger's workshop manual for coolant lost from expansion tank breather is excess pressure caused by a headgasket failure.
The fact that the rate of coolant loss and the rate of overheating seems to be linked with engine revs sort of supports both ideas I think - high revs equalling high water pump flow causing water to be pumped faster through restricted water channels causing an overflow or high revs equalling more exhaust pressure on blown gasket causing quicker pressure build-up etc.
I hope this post isn't too rambling and I would really value some advice from other Mk1 owners - I'm so frustrated to have spent a fair chunk of money on so many new major cooling system parts and to still have the same problem if not worse! It's a sahme as it is making me fall out with my car, when it is really the only problem it seems to have - it sailed through a recent MOT and in all other areas seems a really good example of one.
I'm thinking a full cooling system flush under pressure to really clear out all the water channels in case they are gunged up and a cylinder compression test are my next two things to get done to get a step closer to finding the problem, is this agreed?
Here was the the first symptom: kept noticing expansion tank reservoir filling up resulting in coolant overflowing from out of the overflow breather pipe, mostly when driven the harder end of normal driving. Once cooled the expansion tank would empty out as the radiator sucked back the excess This got to the stage where the radiator itself was taking 1+ litres of water to stay brimmed every few drives. However for months there was no indication of overheating on the temperature gauge itself.
Diagnosis 1: New OEM filler cap
Result: Same problem occurring.
Diagnosis 2: Mazda specialist advised an incorrect thermostat had been fitted so this was replaced, along with a coolant change. They had found it would overheat when left to idle.
Result: Cooling fans coming on correctly, but no change on the expansion tank overflow.
Diagnosis 2: Radiator and/or hose blockage. Had new radiator, two hoses, water pump and coolant change. Coolant had been an awful colour and it was commented that the removed hoses had been very dirty inside with rust/gunk.
Result: Not much change with the expansion tank overflow. When the expansion reservoir is filled to between the middle and upper limits the level rises during even a short drive and seems to overflow a certain amount out. It seems to now settle at the lower limit once everything has cooled and the radiator has sucked back from the expansion tank. However, for the first time today I have had problems with the temperature guagae showing temperature increases. We had driven 100+ miles on mostly B-roads in todays warmish sunshine with no noticeable problems however after about 10-15 mins of dual carriage way cruising at a steady 60mph / 3000 revs I noticed the temp gauge had crept to right of centre, but no further than around 2/3. I stopped and there were signs of a small amount of coolant loss around the expansion tank bulkhead and the tank was almost full to brim, the cooling fan was working correctly. I let it cool for 10-15 mins and carried on at about 50-55mph this seemed to have an positive effect as the temp guage settled back to normal left of centre, experimenting a little this proved it crept back up when higher speed/revs were used and it also crept up on inclines with higher engine load. The furthest it went was around 3/4 towards hot mark.
So here are my thoughts:
Despite new radiator / thermostat / main rad hoses and water pump coolant still not circulating correctly resulting in back pressure forcing coolant up past rad cap into expansion tank, along with overheating at higher prolonged engine revs.
So could it be that the other water hoses / ancillaries are still semi-clogged due to dirty coolant circulating for a long time causing restricted circulation hence the consistent back pressure forcing of water past rad cap into expansion tank. A simple engine block coolant flush with a hose and/or a chemical cleaner would clean out and solve the issue? I don't know if this was done by the garage.
Second option I can think of is could I have excess cooling system pressure from a blown headgasket. I have no usual signs of headgasket failure - no mayo inside oil cap, we did an oil change a month or so ago and there were no signs of water in oil. I have noticed water in the exhaust tip when started from cold but have assumed the usual condensation. However it worries me that the only cause/effect listed in Rod Grainger's workshop manual for coolant lost from expansion tank breather is excess pressure caused by a headgasket failure.
The fact that the rate of coolant loss and the rate of overheating seems to be linked with engine revs sort of supports both ideas I think - high revs equalling high water pump flow causing water to be pumped faster through restricted water channels causing an overflow or high revs equalling more exhaust pressure on blown gasket causing quicker pressure build-up etc.
I hope this post isn't too rambling and I would really value some advice from other Mk1 owners - I'm so frustrated to have spent a fair chunk of money on so many new major cooling system parts and to still have the same problem if not worse! It's a sahme as it is making me fall out with my car, when it is really the only problem it seems to have - it sailed through a recent MOT and in all other areas seems a really good example of one.
I'm thinking a full cooling system flush under pressure to really clear out all the water channels in case they are gunged up and a cylinder compression test are my next two things to get done to get a step closer to finding the problem, is this agreed?
Well I have rigged up a hosepipe and flushed things as best I can - first question is how do you flush through the engine block with a hose. Surely the thermostat needs to be open to complete the circuit? All I got was a lot of backwash when I tried...
I have also put some Holts Flush cleaner in the system and run it for 50 miles or so which I will flush out again on sunday and replace with antifreeze.
I really can't tell if things are better. The temp gauge started to climb for a few seconds on my first dual carriageway run but then suddenly dropped to a normal level and didn't move from that at all after that. When driving relaxed and cruising at 60 it all seems to behave itself with the expansion tank and rad levels settling where I filled them. When driving a little harder and cruising at 70-75 I still seem to get a large amount of water collect in the expansion tank when checking at the end of the journey, which will then be empty when checking it again when cooler.
I have also put some Holts Flush cleaner in the system and run it for 50 miles or so which I will flush out again on sunday and replace with antifreeze.
I really can't tell if things are better. The temp gauge started to climb for a few seconds on my first dual carriageway run but then suddenly dropped to a normal level and didn't move from that at all after that. When driving relaxed and cruising at 60 it all seems to behave itself with the expansion tank and rad levels settling where I filled them. When driving a little harder and cruising at 70-75 I still seem to get a large amount of water collect in the expansion tank when checking at the end of the journey, which will then be empty when checking it again when cooler.
I didn't have much time when I flushed the Holts Speedflush out last night, so I didn't take the thermostat out, I did flush the rad through again though - bit pointless with it being brand new. Well the water came out fairly brown again, I've topped up with just water again to run a bit more and flush again soon.
Frustratingly this flushing has no effect on my problem. If I go out for a "Miss Daisy" drive everything seems happy and normal and the coolant levels stay fixed. Any hint of revvier driving and motorway speed and I get the expansion tank filling up (though not to the point of overflowing now). When checking later the tank is empty, so all the water forced into the tank and more has returned to the rad.
It must just be a coolant leak somewhere right? If the headgasket checks came back clear it must surely just be a hose leaking under pressure? It's so hard to tell as the back of my engine is fairly damp and oily anyway.
So a pressure test or one of those UV dye tests might be a good next move?
Frustratingly this flushing has no effect on my problem. If I go out for a "Miss Daisy" drive everything seems happy and normal and the coolant levels stay fixed. Any hint of revvier driving and motorway speed and I get the expansion tank filling up (though not to the point of overflowing now). When checking later the tank is empty, so all the water forced into the tank and more has returned to the rad.
It must just be a coolant leak somewhere right? If the headgasket checks came back clear it must surely just be a hose leaking under pressure? It's so hard to tell as the back of my engine is fairly damp and oily anyway.
So a pressure test or one of those UV dye tests might be a good next move?
Mazdamender said:
The problem you have points to a new rad,which you have done,plus you have change more bits, i would agree that a few more very good flush's should clear it, sounds like a lot of build up of crap in the cooling system still blocking somewhere giving her back pressure.
M-m
Doesn't explain the coolant loss though? M-m
NiceCupOfTea said:
I was losing a lot of coolant every time it boiled out of the expansion tank
Well yeah that is how I was losing it - but now after the flush it has improved in that it doesn't do its piss out the expansion overflow trick anymore. But it does go way past the "full mark" and when cooled after a run the expansion tank is empty. So I'm losing an expansion tanks, so maybe 1 litre roughly, worth of coolant every enthusiastic drive.Well it always used to be obvious that the area on the bulkhead around the expansion tank was wet after a drive, now it is dry after a drive. But I'm definitely getting an empty header tank after anything more than a gentle run round the block once cooled - it's doing my head in I just do not understand where the coolant is going and why there is such a lot of movement from rad to expansion tank in the first place.
On a brighter note absolutely rock solid temperature gauge levels throughout a 30 min drive today in warm sunshine.
Could someone with a healthy Mk1 comment on how much change there is in your expansion tank level during / after a drive.
On a brighter note absolutely rock solid temperature gauge levels throughout a 30 min drive today in warm sunshine.
Could someone with a healthy Mk1 comment on how much change there is in your expansion tank level during / after a drive.
No my overflow pipe is very short and it is very visible if coolant has been expelled. But that's a good idea maybe bodge in a small drinks bottle to the overflow and see if it catches anything.
And it's when it has all cooled down that the expansion tank is empty - it sucks it back to the rad as it cools BUT it sucks in what has moved into the tank under pressure AND the original contents of the tank. So it MUST be losing that volume of coolant during driving.
My next move is going to be a proper pressure test and/or coolant dye. It may be I need new hoses all round - I mean after that there is nothing else I can replace on the cooling system!!
And it's when it has all cooled down that the expansion tank is empty - it sucks it back to the rad as it cools BUT it sucks in what has moved into the tank under pressure AND the original contents of the tank. So it MUST be losing that volume of coolant during driving.
My next move is going to be a proper pressure test and/or coolant dye. It may be I need new hoses all round - I mean after that there is nothing else I can replace on the cooling system!!
Edited by vrsmxtb on Sunday 31st July 23:08
ks! 
No mayo under cap. I haven't had a compression test done yet, but I'm starting to think the colour of the coolant may have been oil related, as some of the sediment that as flushed out felt greasy once Id emptied the container I collected it into. Also I have noticed quite a few water droplets/vapour from the exhaust when started from cold.
It's about the only thing left to change! If I spend another £500 on it and it still does it I am selling up!!
It's about the only thing left to change! If I spend another £500 on it and it still does it I am selling up!!
Thanks for your input nicecupoftea 
Will report back once I have the compression test results and/or can afford the HG change. I'd love to be brave and do it myself but just don't have the tools / knowledge or working space.
If the car is not overheating and coolant is kept topped up it should be Ok to keep driving for a while, if maybe a bit more Miss Daisy-style!?
Will report back once I have the compression test results and/or can afford the HG change. I'd love to be brave and do it myself but just don't have the tools / knowledge or working space.
If the car is not overheating and coolant is kept topped up it should be Ok to keep driving for a while, if maybe a bit more Miss Daisy-style!?
- Sigh* the idea of the cheap second car that only needed a new set of boots and a geo set-up is long gone.
Well this is becoming a real saga now. Had yet another opinion from a very good mechanic who has touch wood pinpointed the problem to some kind of intermittent electrical fault with the coolant temp sensor which wasn't controlling the radiator fan correctly causing overheating and big build-up of pressure. I had seen the rad fan working but now I think of it I'd never heard it keep spinning after parking up and turning the ignition off.
There's still a mystery about the coolant gauge as that still showed a reading when he unplugged the sender socket on the back of the engine bay, and very rarely moved to show overheating. Apparently there's two electrical sockets but one seems to have a blank or broken plug in it.
At the moment I have a small removable bridge on the fan relay to keep the fan on permanently when driving, plus I'm running without the 'stat at the moment. Hopefully this should create a nice cool engine and solve the big pressure build-up causing the expansion tank overfilling, if so touch wood its a new £50 temp sensor and temp guage sender and job done!
Definitely no head gasket failure which is good news.
There's still a mystery about the coolant gauge as that still showed a reading when he unplugged the sender socket on the back of the engine bay, and very rarely moved to show overheating. Apparently there's two electrical sockets but one seems to have a blank or broken plug in it.
At the moment I have a small removable bridge on the fan relay to keep the fan on permanently when driving, plus I'm running without the 'stat at the moment. Hopefully this should create a nice cool engine and solve the big pressure build-up causing the expansion tank overfilling, if so touch wood its a new £50 temp sensor and temp guage sender and job done!
Definitely no head gasket failure which is good news.
Paul Dishman said:
Interesting thread.
We've had a similar problem with my wife's 10AE since shes owned it. We did the easy things last year- flush the system, new rad cap which appeared to help but didn't really solve the overheating in slow traffic or, for example, when putting the engine underload by climbing a hill.
In the end it went to the local Mazda dealer who have sorted it by installing a new radiator. The old radiator looked fine, but you can't tell by looking at it. The Mazda radiator was £128+Vat so no more expensive than buying from MX5 parts and the Mazda tech took the car home with him to drive it in heavy traffic to check that it wasn't still overheating. Sue drove it back across Exeter in really heavy traffic yesterday so problem (fingers crossed) solved
I've done a lot of trawling the internet on this and yes a new rad will fix 90% of MX5 overheating issues it seems. They are very sensitive to clogging up, which restricts the water flow. I've had all the cooling system replace excet for a full hose change and nothing worked, but it is really looking like the temp sensor was my fault all along! Still nice to have a new rad, pump etc for peace of mind I suppose. If your wife's still does it, check that the fan is kicking in correctly.We've had a similar problem with my wife's 10AE since shes owned it. We did the easy things last year- flush the system, new rad cap which appeared to help but didn't really solve the overheating in slow traffic or, for example, when putting the engine underload by climbing a hill.
In the end it went to the local Mazda dealer who have sorted it by installing a new radiator. The old radiator looked fine, but you can't tell by looking at it. The Mazda radiator was £128+Vat so no more expensive than buying from MX5 parts and the Mazda tech took the car home with him to drive it in heavy traffic to check that it wasn't still overheating. Sue drove it back across Exeter in really heavy traffic yesterday so problem (fingers crossed) solved
Bugger. After a drive on a warm day, including idling in traffic for 15-20mins I had still lost all coolant from the expansion tank when checking next day at cold. But at least the fan now comes on!
I think I'm getting a bit of white smoke out the exhaust and high dipstick oil level when checking from cold which makes me suspect head gasket again. Tempted to just bung k-seal in and see if it improves things and get gasket done when I can afford to
Seriously getting annoyed with this car now
I think I'm getting a bit of white smoke out the exhaust and high dipstick oil level when checking from cold which makes me suspect head gasket again. Tempted to just bung k-seal in and see if it improves things and get gasket done when I can afford to
Seriously getting annoyed with this car now
Hey Nicecupoftea! Welcome back 
The reservoir tank is fine, it doesn't leak. It's still either losing water within the system so sucking back all the overflow as it cools or expelling water out the overflow again, but not sure which it is now! The weird thing is it varies so much, some drives it will lose water, other times it is absolutely fine. I was running it without the 'stat for a while and it seemed to behave itself like that. But the stat definitely opens as the top rad hose gets very hot, so I don't think that is a problem.
Also I have had two sniff tests done which were negative but I'm worried it could be a gasket leak between a water/oil channel, rather than at the cylinder.
Aside from changing every single water hose to eliminate pinhole leaks, the only other thing I haven't done now is the head gasket
The reservoir tank is fine, it doesn't leak. It's still either losing water within the system so sucking back all the overflow as it cools or expelling water out the overflow again, but not sure which it is now! The weird thing is it varies so much, some drives it will lose water, other times it is absolutely fine. I was running it without the 'stat for a while and it seemed to behave itself like that. But the stat definitely opens as the top rad hose gets very hot, so I don't think that is a problem.Also I have had two sniff tests done which were negative but I'm worried it could be a gasket leak between a water/oil channel, rather than at the cylinder.
Aside from changing every single water hose to eliminate pinhole leaks, the only other thing I haven't done now is the head gasket
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