1999 MX5 roadster overheating?

Hi,
back again with another issue

My 1.8 s which has 67,000 miles on it and may have an overheating issue.

Sometimes it will seem to dump hot water into the overflow and then drips
the coolant away onto the drive after a 10mile or more journey.

The wter temp gaue will not go over the half way during a journey , the fan
comes on as it should, the garage tells me it might be the pump or the
radiator but tell me that although the symptoms are more likely to be the
radiator cannot believe it is as it was replaced 5/6 years ago (and anyway
its the NA or MK1 that suffers the blocked radiator I was informed)

last week I was answering the mobile so was sitting in the car at the end of
a journey (without the a/c) - didn't notice the fan cut in and when I got
out of the car it just smelt VERY hot so why did the fan not come on on its
own then? once again the water temp did't rise above the usual straight up

I'm avoiding the problem at the moment as its winter, Ive also started
putting the AC on for the last few minutes of a trip so that both fans come
on for the end of the journey.
Any ideas?

In article >,
"thomas" > wrote:

> Sometimes it will seem to dump hot water into the overflow and then drips
> the coolant away onto the drive after a 10mile or more journey.

Time for a new radiator cap.

--
Lanny Chambers
St. Louis, MO
'94C

> The wter temp gaue will not go over the half way during a journey , the fan
> comes on as it should, the garage tells me it might be the pump or the
> radiator but tell me that although the symptoms are more likely to be the
> radiator cannot believe it is as it was replaced 5/6 years ago (and anyway
> its the NA or MK1 that suffers the blocked radiator I was informed)
>

It's probably the radiator cap. There are testers available, if you
want to try testing it head down to autozone and rent a cooling system
pressure tester and get the adapter for testing import radiator caps.
Basically it's a little hand air compressor with a gauge, and you can
pump up the cap to see when the spring starts letting the excess
pressure divert into the overflow bottle. I'd bet your cap is weak and
isn't keeping the pressure in the system like it should.

> out of the car it just smelt VERY hot so why did the fan not come on on its
> own then? once again the water temp did't rise above the usual straight up
>

Pressurized coolant leaks will play tricks on you. Test the cap first,
and you'll probably find your problem. If it smelled hot, and the fan
wasn't on, then either it was overheating because the fan didn't turn
on, which you know isn't the case because the temp gauge reads normal,
OR you are bleeding out pressure from the cooling system creating all
those annoying, expensive-ish smells from the engine bay.

In your case, and at your mileage....I can say with almost certainty
that it's not the water pump or the radiator......basically, if the
gauge stays in the middle, then you are not overheating and the
thermostat, water pump, and radiator are doing their job. So you
either have a tiny pressure leak, or a bad cap. The afore-mentioned
tool lets you pump up the cooling system to operating pressure with
the engine off and cold...if you have a leak, the gauge will drop and
you'll see the leak dribbling out somewhere. It's a very handy tool to
have around...

If you're going to change the cap, do your car a favor if you have not
already done so, and flush the cooling system.

Good luck with it.

Chris

"Hal" > wrote in message
...
>> The wter temp gaue will not go over the half way during a journey , the
>> fan
>> comes on as it should, the garage tells me it might be the pump or the
>> radiator but tell me that although the symptoms are more likely to be the
>> radiator cannot believe it is as it was replaced 5/6 years ago (and
>> anyway
>> its the NA or MK1 that suffers the blocked radiator I was informed)
>>
>
> It's probably the radiator cap. There are testers available, if you
> want to try testing it head down to autozone and rent a cooling system
> pressure tester and get the adapter for testing import radiator caps.
> Basically it's a little hand air compressor with a gauge, and you can
> pump up the cap to see when the spring starts letting the excess
> pressure divert into the overflow bottle. I'd bet your cap is weak and
> isn't keeping the pressure in the system like it should.
>
>> out of the car it just smelt VERY hot so why did the fan not come on on
>> its
>> own then? once again the water temp did't rise above the usual straight
>> up
>>
>
> Pressurized coolant leaks will play tricks on you. Test the cap first,
> and you'll probably find your problem. If it smelled hot, and the fan
> wasn't on, then either it was overheating because the fan didn't turn
> on, which you know isn't the case because the temp gauge reads normal,
> OR you are bleeding out pressure from the cooling system creating all
> those annoying, expensive-ish smells from the engine bay.
>
> In your case, and at your mileage....I can say with almost certainty
> that it's not the water pump or the radiator......basically, if the
> gauge stays in the middle, then you are not overheating and the
> thermostat, water pump, and radiator are doing their job. So you
> either have a tiny pressure leak, or a bad cap. The afore-mentioned
> tool lets you pump up the cooling system to operating pressure with
> the engine off and cold...if you have a leak, the gauge will drop and
> you'll see the leak dribbling out somewhere. It's a very handy tool to
> have around...
>
> If you're going to change the cap, do your car a favor if you have not
> already done so, and flush the cooling system.
>
> Good luck with it.
>
> Chris

Thanks very much for your help guys - I was being advised (sort of) to go
down the new pump road which is £80 approx plus a few hours labour -
ordering a new cap is VERY good news for my wallet - £10 for a mazda one -
BUT still going in to have a flush and coolant change more as a precaution
than anything else.
As an aside - the last time I "did work" on a radiator over 40 years ago was
on my dads car - there were 2 lovely little taps I seem to recall - one at
the bottom of the radiator and one on the engine block somewhere - with the
roadster I couldn't even get my hand in to feel If the radiator was hot or
not.

And NO - I didn't have a little man walking in front of the car with a red
flag as a warning to the population ;-)

Finally got around to this thread!
If the cooling system is flushed, it's a very good idea to replace the
thermostat. (And cap, if it's been around for a few years.)
Seems that there is a significant chance that crud from the flushing can get
into the thermostat works, and cause it to stick.

"thomas" > wrote in message
...
>
> "Hal" > wrote in message
> ...
>>> The wter temp gaue will not go over the half way during a journey , the
>>> fan
>>> comes on as it should, the garage tells me it might be the pump or the
>>> radiator but tell me that although the symptoms are more likely to be
>>> the
>>> radiator cannot believe it is as it was replaced 5/6 years ago (and
>>> anyway
>>> its the NA or MK1 that suffers the blocked radiator I was informed)
>>>
>>
>> It's probably the radiator cap. There are testers available, if you
>> want to try testing it head down to autozone and rent a cooling system
>> pressure tester and get the adapter for testing import radiator caps.
>> Basically it's a little hand air compressor with a gauge, and you can
>> pump up the cap to see when the spring starts letting the excess
>> pressure divert into the overflow bottle. I'd bet your cap is weak and
>> isn't keeping the pressure in the system like it should.
>>
>>> out of the car it just smelt VERY hot so why did the fan not come on on
>>> its
>>> own then? once again the water temp did't rise above the usual straight
>>> up
>>>
>>
>> Pressurized coolant leaks will play tricks on you. Test the cap first,
>> and you'll probably find your problem. If it smelled hot, and the fan
>> wasn't on, then either it was overheating because the fan didn't turn
>> on, which you know isn't the case because the temp gauge reads normal,
>> OR you are bleeding out pressure from the cooling system creating all
>> those annoying, expensive-ish smells from the engine bay.
>>
>> In your case, and at your mileage....I can say with almost certainty
>> that it's not the water pump or the radiator......basically, if the
>> gauge stays in the middle, then you are not overheating and the
>> thermostat, water pump, and radiator are doing their job. So you
>> either have a tiny pressure leak, or a bad cap. The afore-mentioned
>> tool lets you pump up the cooling system to operating pressure with
>> the engine off and cold...if you have a leak, the gauge will drop and
>> you'll see the leak dribbling out somewhere. It's a very handy tool to
>> have around...
>>
>> If you're going to change the cap, do your car a favor if you have not
>> already done so, and flush the cooling system.
>>
>> Good luck with it.
>>
>> Chris
>
> Thanks very much for your help guys - I was being advised (sort of) to go
> down the new pump road which is £80 approx plus a few hours labour -
> ordering a new cap is VERY good news for my wallet - £10 for a mazda one -
> BUT still going in to have a flush and coolant change more as a precaution
> than anything else.
> As an aside - the last time I "did work" on a radiator over 40 years ago
> was on my dads car - there were 2 lovely little taps I seem to recall -
> one at the bottom of the radiator and one on the engine block somewhere -
> with the roadster I couldn't even get my hand in to feel If the radiator
> was hot or not.
>
> And NO - I didn't have a little man walking in front of the car with a red
> flag as a warning to the population ;-)

On Mar 2, 2:11*pm, "Chuck" > wrote:
> Finally got around to this thread!
> If the cooling system is flushed, it's a very good idea to replace the
> thermostat. (And cap, if it's been around for a few years.)
> Seems that there is a significant chance that crud from the flushing can get
> into the thermostat works, and cause it to stick.
>

I don't ever replace a thermostat unless it has failed. And having
done regular coolant changes on every vehicle I've owned, I've yet to
replace a thermostat. I've put over 100,000 miles on an OE thermostat
with nary a complaint. Temp gauge always sits in the exact same spot
no matter how hot it is outside and it gets to that point on the gauge
relatively quickly.

My truck on the other hand was never maintained well, and the
thermostat on that one stuck closed. The replacements I've been
getting from the local parts place have been crap, I've changed it
several times in the past few years and it never holds up. This
despite a new engine, radiator, hoses, water pump, and so on. So I am
convinced that if you have to replace a thermostat you should try to
get the replacement from the dealer. The aftermarket stuff is crap.
But in the case of my truck, when your vehicle is 25 years old the
dealer doesn't want to see you unless you're coming to buy a new
truck. You can forget about parts support at that age....

Chris

First, the local Mazda dealer does not carry factory thermostats for the
older Miatas.
Next-- I've had several problems over the years with both factory and
aftermarket thermostats. Usually, its sticking partially open,
then if really pushed, or tapped, the thermostat will usually fully open. On
the Miata temp gauge, you may not see this happen.
It's obvious with a ScanGage II.

"Hal" > wrote in message
...
On Mar 2, 2:11 pm, "Chuck" > wrote:
> Finally got around to this thread!
> If the cooling system is flushed, it's a very good idea to replace the
> thermostat. (And cap, if it's been around for a few years.)
> Seems that there is a significant chance that crud from the flushing can
> get
> into the thermostat works, and cause it to stick.
>

I don't ever replace a thermostat unless it has failed. And having
done regular coolant changes on every vehicle I've owned, I've yet to
replace a thermostat. I've put over 100,000 miles on an OE thermostat
with nary a complaint. Temp gauge always sits in the exact same spot
no matter how hot it is outside and it gets to that point on the gauge
relatively quickly.

My truck on the other hand was never maintained well, and the
thermostat on that one stuck closed. The replacements I've been
getting from the local parts place have been crap, I've changed it
several times in the past few years and it never holds up. This
despite a new engine, radiator, hoses, water pump, and so on. So I am
convinced that if you have to replace a thermostat you should try to
get the replacement from the dealer. The aftermarket stuff is crap.
But in the case of my truck, when your vehicle is 25 years old the
dealer doesn't want to see you unless you're coming to buy a new
truck. You can forget about parts support at that age....

Chris