Just purchased my first 1998 mx5 Mark 1, the previous owner spent a fortune on her but the basics seem to be poor.
i noticed on my second day of driving when I stopped, a light mist coming up from under the bonnet and when I checked, it was coolant coming from the top of the rad.
i decided to do a coolant flush, replace the thermostat and the grey probe ontop of the thermostat housing, the old parts hadn’t been changed in years and fell apart when I removed them.
Now that everything is in, and the new coolant is in, I still seem to have the same problem and also noticed that the fan isn’t coming on.
i read that there is another coolant temperature (green) sensor, but I don’t know where it is? The oil is clean including the dip stick, no milky mixture, temperature gauge doesn’t rise, but up here in Aberdeen the cold seems to keep it even.
if anyone has any idea what I need to do please help.
Stop this nonsence about up here, the temperature guage works exactly the same in Aberdeen than is does in Cornwall.
The other tempreture sendor is underneath the coil packs on the back end of the engine.
That temperature sender sends temperature information to the ecu. That information is sent to the temperature guage and also used to control the mixture when the engine is warming up.
I guess you may not have got all the air out of the cooling system when you changed the coolant.
Start the car with the radiator cap off and the engine cold with some premixed coolant handy let the engine come up to tempreture and you should find the water level falling as air is expelled from the system, you then add coolant up to the nearly the neck of the radiotor filler. It will take about 10 minutes to get the engine up to temperature. Then put the radiator cap back on and top up the expansion vessel if required. Over time the radiator cap may need changed as the spring gets a bit soft.
The temperature thermo switch you replaced on the front only switches on and off the radiatior fan.
You will need a multimeter to check if it is switching when the temperature gets up and does that voltage get to the fan motor. Maybe a fuse has blown or the fan motor is faulty.
The temp guage is part of the incar entertainment and the reading only goes above normal when the temperature is too high.
Let’s hope it is not a head gasket problem or the normal problem of the radiator tubes blocking and needing replaced. Typical of an older car with the antifreeze not being changed every two years.
I had a badly blocked radiator as Drum suggested but it took a long hard motorway run on a hot day to generate a problem and even them there was no mist from under the bonnet or coolant loss. The additional pressure of engine heat should just push displaced coolant through the rad cap pressure valve into the expansion bottle.
Mist from the radiator area suggests a failing radiator hose that is leaking slightly when under pressure. Either that or the top radiator gasket may be leaking under pressure.
I suggest that you let the engine idle for 15 mins or so to get it up to temperature and see what is happening under the bonnet.
Check the fan with direct feed from battery if you think that is not working.
Antifreeze lying around the top of the radiator; the plastic is cracking around the filler (common on original radiators); new radiator time. The pattern radiators are fine, and even the Mazda rad isn’t that expensive. The crack may not be obvious, and might only open up when the rad is hot. This crack was on the engine side, and only obvious with the radiator removed;
If the top hose has failed, besides looking or feeling fairly obviously failed, you won’t get coolant so much on the top of the radiator, but looking down, the front anti-rollbar, engine tray will be wet.
Crustiness around the radiator cap; may be indicative of a failed radiator cap, which can happen, but the overflow tank will be empty
Fan not working; as stated, make the checks. Fan motors can fail (bushes, and not serviceable). The temperature gauge has a dampner on it, to stop it waving about to every fluctuation in temperature. It will sit in the middle until ferociously hot, then suddenly sling to the right. If the car has been running hot for a while, it might be that the fan has been on most of the time. Possibly, more likely a wire broth when you replaced the sensor on top of the thermostat housing; its only a single wire.
I checked the coolant and ran the engine for 20 minutes, when the coolant heated up coolant vapour came from the radiator just under the plastic top section, so radiator required.
i’ll do a fan check when I take everything out, hopefully that will be ok.
Fitting power steering next, then I’ll be a happy man!
