What's up with my cooling system?
Discussion
For at least the last couple of summers, when it is very hot outside and I am stuck in traffic, when I get to my destination I can hear (what I assume is) coolant in the top up reservoir boiling 
It's had a water pump and a couple of new hoses and a (genuine Mazda) radiator cap, but always the same when it gets hot.
I will stress now, the temp guage never goes above just left on centre in the guage. Under bonnet temps seem very high, can't touch bonnet or bonnet stay (touches top hose) - but the bonnet is black which doesn't help...
I can often (even when cool out) smell coolant when the car is running.
I've had the system checked for leaks - none found - and it doesn't seem to leak. I can't recall ever having had to top up the system.
Today it was hot again, had a crap crawling drive across London, either stationary or moving slowly. Whilst in the Blackwall tunnel the temp guage started creeping up. Fortunately the traffic start moving, in combination with the heater on full blast, the temp dropped and it was OK for the rest of the journey.
Now what the hell is going on?
I am guessing that the cooling system is over-pressurising and forcing hot coolant back into the top up reservoir, which I can smell. I suppose it's possible that it's a duff radiator cap, but I replaced it a while back with no improvement. Could it be that the rad is blocked and needs reverse-flushing? It's the original.
Any other thoughts?
It's had a water pump and a couple of new hoses and a (genuine Mazda) radiator cap, but always the same when it gets hot.
I will stress now, the temp guage never goes above just left on centre in the guage. Under bonnet temps seem very high, can't touch bonnet or bonnet stay (touches top hose) - but the bonnet is black which doesn't help...
I can often (even when cool out) smell coolant when the car is running.
I've had the system checked for leaks - none found - and it doesn't seem to leak. I can't recall ever having had to top up the system.
Today it was hot again, had a crap crawling drive across London, either stationary or moving slowly. Whilst in the Blackwall tunnel the temp guage started creeping up. Fortunately the traffic start moving, in combination with the heater on full blast, the temp dropped and it was OK for the rest of the journey.
Now what the hell is going on?
I am guessing that the cooling system is over-pressurising and forcing hot coolant back into the top up reservoir, which I can smell. I suppose it's possible that it's a duff radiator cap, but I replaced it a while back with no improvement. Could it be that the rad is blocked and needs reverse-flushing? It's the original.
Any other thoughts?
If a rad cap doesn't cure it, it could be a dodgy stat but usually its the rad thats duff.
I'm changing loads these days it seems their life is around 15 years.
Lots of cars are fine in normal use but a thrash on a hot day will send the needle soaring.
If it only overheats in traffic wiring the AC fan to come on as well might cure it.
I'm changing loads these days it seems their life is around 15 years.
Lots of cars are fine in normal use but a thrash on a hot day will send the needle soaring.
If it only overheats in traffic wiring the AC fan to come on as well might cure it.
grumbledoak said:
If you can smell coolant, then you definitely have a leak.
There's an overflow pipe on the reservoir, could I not smell it from that if hot coolant is being forced back into it?Think I will change the rad, it's 16 years old. Another rad cap while I'm at it and maybe a stat if it hasn't been done recently.
I wouldn't rely too much on your nose for location. And I wouldn't recommend changing bits experimentally; that'll get expensive fast.
Circulation- do the two radiator hoses get warm at about the same rate? If they do, the water is circulating.
Fan- does it come on? And then go off? If so, that bit is working too.
Hopefully someone can give you an easy 'tell' for the thermostat.
If none of these, you probably have a small leak. Hoses could be porous by now, or a hole in the radiator, or a mis-placed cap. If any of these happen you'll have an air/water coolant system. And that won't work. It'll bugger up the circulation and allow it to boil, and then it'll come out somewhere, possibly just through the vented cap. Then, you'll smell it.
I'm no motor mechanic. The only time my MX did this to me, a top-up fixed it permanently. I suspect a badly re-fitted cap at the service.
Best of luck.
Circulation- do the two radiator hoses get warm at about the same rate? If they do, the water is circulating.
Fan- does it come on? And then go off? If so, that bit is working too.
Hopefully someone can give you an easy 'tell' for the thermostat.
If none of these, you probably have a small leak. Hoses could be porous by now, or a hole in the radiator, or a mis-placed cap. If any of these happen you'll have an air/water coolant system. And that won't work. It'll bugger up the circulation and allow it to boil, and then it'll come out somewhere, possibly just through the vented cap. Then, you'll smell it.
I'm no motor mechanic. The only time my MX did this to me, a top-up fixed it permanently. I suspect a badly re-fitted cap at the service.
Best of luck.
Got the car up on ramps at the moment.
I ran it up to temp with the cap off to make sure the fan was coming on, which it did (101 degress - Rod Grainger book reckons 97, but close enough I suppose).
The car temp guage came up quickly enough as usual (sensor is at the back of the engine IIRC, or is that the fan sensor?), but the temp in the radiator just sat at 40 degress until I revved the engine, where it shot up immediately.
is that normal? It had a water pump recently so I'm just assuming that idle speed wasn't enough to get it circulating properly... but then what if the car's stuck in traffic, no good if the coolant isn't circulating...
Coolant expanded out of the rad and overflowed a bit without the cap but I guess that's normal - reservoir always looks fuller when the car's hot after a run.
Does all this sound normal? I am happy to change the radiator but I can't afford to spunk £80 if there's nothing wrong with it.
There's defintely something up - smell of coolant, boiling in reservoir, temp gauge creeping up on Saturday - but at least I know that the fan/fan sensor work now...
if the stat was jammed open it would take forever to heat up but would then stay cool, if it was jammed closed then it would just plain overheat irrespective of ambient temp and whether I was in traffic, so I assume this is right.
Could be the rad cap but it was a genuine replacement a couple of years ago.
Prudent to order rad & cap and just swap them over now? Or am I wasting my money without knowing what the problem is?
Help, I have nobody here to bounce ideas off
I ran it up to temp with the cap off to make sure the fan was coming on, which it did (101 degress - Rod Grainger book reckons 97, but close enough I suppose).
The car temp guage came up quickly enough as usual (sensor is at the back of the engine IIRC, or is that the fan sensor?), but the temp in the radiator just sat at 40 degress until I revved the engine, where it shot up immediately.
is that normal? It had a water pump recently so I'm just assuming that idle speed wasn't enough to get it circulating properly... but then what if the car's stuck in traffic, no good if the coolant isn't circulating...Coolant expanded out of the rad and overflowed a bit without the cap but I guess that's normal - reservoir always looks fuller when the car's hot after a run.
Does all this sound normal? I am happy to change the radiator but I can't afford to spunk £80 if there's nothing wrong with it.
There's defintely something up - smell of coolant, boiling in reservoir, temp gauge creeping up on Saturday - but at least I know that the fan/fan sensor work now...
if the stat was jammed open it would take forever to heat up but would then stay cool, if it was jammed closed then it would just plain overheat irrespective of ambient temp and whether I was in traffic, so I assume this is right.
Could be the rad cap but it was a genuine replacement a couple of years ago.
Prudent to order rad & cap and just swap them over now? Or am I wasting my money without knowing what the problem is?
Help, I have nobody here to bounce ideas off
Edited by NiceCupOfTea on Thursday 8th July 17:17
Well, mine has just done the exact same thing and a rad cap sorted it.I'm not saying that is 100% your problem, but it's a cheap way to find out.Someone also pointed out that if your car has air con, turning it on enables the second fan on the rad, so I guess that is handy for those 'temp gauge creeping stuck in traffic' moments
I got one of these..
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&am...
I got one of these..
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&am...
Digby said:
Well, mine has just done the exact same thing and a rad cap sorted it.I'm not saying that is 100% your problem, but it's a cheap way to find out.Someone also pointed out that if your car has air con, turning it on enables the second fan on the rad, so I guess that is handy for those 'temp gauge creeping stuck in traffic' moments
I got one of these..
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&am...
A/C was already on - which is why I think there's something wrong.I got one of these..
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&am...
I'll order a new radiator cap anyway and see if that fixes it.
I too have the faint smell of coolant in mine, but its not going down at all. It has been like it for months now and I cannot see any signs of any leaks anywhere and its driving me mad looking for them as the smell must be coming from somewhere.
It has been pressure tested too with no loss. Have also changed the rad cap as I thought it might be that. It has had new pipes all over.
It has been pressure tested too with no loss. Have also changed the rad cap as I thought it might be that. It has had new pipes all over.
Could it be down to a duff thermostat? Not opening fully, when you rev it, the pump creats enough pressure to push the hotter coolant through- giving you your increased temps.
A radiator cap will only be a couple of quid- worth the peace of mind IMO. Thermostat, again a couple of quid. You could always try & purchase a lower temp range thermostat- i.e. it'll open/close earlier.
If it's still playing up, then it could either possibly be air trapped- this would manifest itself in air escaping from the expansion tank with the cap off.
Or, extremely unlikely, but possible, a damaged waterpump.
Check for flow in the radiator- not very scientific, but, put a hose pipe in the top feed of the rad, then monitor the flow- if it comes out of the neck quicker than it can escape from the bottom & if it looks phisically knackered, then that could also be a cause of your restriction.
When you do put it back together, put the correct mixture of antifreeze/coolant in as this will affect the boiling point.
This isn't MX5 specific, but it's what I'd check on any of my cars.
A radiator cap will only be a couple of quid- worth the peace of mind IMO. Thermostat, again a couple of quid. You could always try & purchase a lower temp range thermostat- i.e. it'll open/close earlier.
If it's still playing up, then it could either possibly be air trapped- this would manifest itself in air escaping from the expansion tank with the cap off.
Or, extremely unlikely, but possible, a damaged waterpump.
Check for flow in the radiator- not very scientific, but, put a hose pipe in the top feed of the rad, then monitor the flow- if it comes out of the neck quicker than it can escape from the bottom & if it looks phisically knackered, then that could also be a cause of your restriction.
When you do put it back together, put the correct mixture of antifreeze/coolant in as this will affect the boiling point.
This isn't MX5 specific, but it's what I'd check on any of my cars.
Edited by Vidal Baboon on Thursday 8th July 22:15
Edited by Vidal Baboon on Thursday 8th July 22:16
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