Boiling or not?

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Boiling or not?

Postby Rostra » Fri Apr 21, 2017 6:28 pm

When I come home and park up there is the noise of boiling from my engine (Mk1 MX5) although the temp gauge on the dashboard shows normal. The radiator reservoir frequently needs refilling, so I assume I have a leak somewhere. How can I tell what the problem is? My garage doesn't know. I am in Lanzarote.
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Re: Boiling or not?

Postby drumtochty » Fri Apr 21, 2017 8:15 pm

How are things out there Rostra.

Try a new genuine Mazda radiator cap others can give problems, but just before you fit it run the car at a tickover with the cap off and slowly add coolant to fill the radiator take around 10 minutes to get rid of any air.

Assume either a hose or cylinderhead gasket those cars are getting on.

Even out there you must use say 25% antifreeze changed every few years to stop corrosion.

Non genuine radiator caps can give problems.
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Re: Boiling or not?

Postby drumtochty » Sat Apr 22, 2017 12:19 pm

Radiators at that age can cause problems different unit for manual and automatic cars.

The radiator cap first to see if that stops the leakage.
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Re: Boiling or not?

Postby mic » Tue Apr 25, 2017 6:53 am

mine does the same, but only if I drive it hard. its not actually leaking coolant, it boils in reservoir bottle and splutters out of the overflow(and all down the inside front of engine and all down the driveway!). I have had this 4 times now although only lost fluid twice. have since changed my engine thermostat(check all hoses heat up!) and hope this has helped but haven't as yet had a chance to really put it to the test.
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Re: Boiling or not?

Postby OldSpice » Tue Apr 25, 2017 9:59 am

mic wrote:mine does the same, but only if I drive it hard. its not actually leaking coolant, it boils in reservoir bottle and splutters out of the overflow(and all down the inside front of engine and all down the driveway!). I have had this 4 times now although only lost fluid twice. have since changed my engine thermostat(check all hoses heat up!) and hope this has helped but haven't as yet had a chance to really put it to the test.


It should not do that. Ought to be able to cane it senseless and only see header tank level rise.
Might be a radiator blockage, or it needs flushed. Might as well pop on an OEM rad cap for starters.
Check for mayo on the dipstick & oil cap too. Just a precaution..no panic measures implied.
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Re: Boiling or not?

Postby drumtochty » Tue Apr 25, 2017 1:00 pm

Yes in Mic's case.

1 Check for oil contamination that is the cheapest check and would suggest a cylinderhead gasket / head skim problems if there is contamination.
2 Double check for leaks equal cheapest check.
3 Mazda Genuine radiator cap and maybe again Mazda Genuine Thermostat second cheapest job did you use a Mazda Genuine thermostat other unknown makes of thermostat can be iffy.
4 Replace radiator as they have a tendancy to block up and that shows after the car has been working hard and tends not to be a problem in town.
5 Also take the cambelt covers off to check for water pump leakage.
6 Long shot here, the sensor in the thermostat housing turns off and on the cooling fan. if that is iffy when you come back home and you are only doing say 15 mph as you park up, if the sensor does not work, you will have that problem for the first 5 minutes or so and possibly loose water from the system. This can be checked with a thermometer in a pan of hot water on the cooker and a multimeter on the resistance setting.
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Re: Boiling or not?

Postby mic » Tue Apr 25, 2017 8:50 pm

thanks to those taking the trouble to comment, I will try and work my way through all your suggestions, but for now I can add that it is a genuine new thermostat, I have recently flushed the radiator and changed all the hoses and refilled the coolant. car is garaged so I know there are no leaks(not while stationery anyway) and I have not had to top up the fluid other than the twice it spluttered out.
as I said in my earlier post, I haven't had a chance to really test it out since, although I did around 150miles last week in one steady journey with no problems.
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Re: Boiling or not?

Postby mic » Tue Apr 25, 2017 8:57 pm

p.s. no oil contamination on dipstick or cap, no leaks, not the model with housing sensor. really hope I've fixed it with my flush and new stat. will hopefully give it a blast at weekend and report back! 8)
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Re: Boiling or not?

Postby drumtochty » Tue Apr 25, 2017 10:04 pm

Yes on the 1.8 Mk1 cars, the sensor is under the coil pack at the back of the engine. It is the 1.6 Mk1 cars that have that sensor at the front on the Mk1.

I believe it also feeds the ecu on the 1.8 which will switch on a relay that feeds the fan, therefore a good few items to check if the fan does not come on.

Picture here on the fifth message it has the grey head. There is a further single wire sensor there that only does the temperature guage.

If it is faulty this is it on mx5parts but there are other vendors out there who sell these grey coloured units.

http://www.mx5parts.co.uk/sensor-water- ... p-703.html
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Re: Boiling or not?

Postby mic » Thu Apr 27, 2017 6:19 am

brief update; hammered it last night for an hour(still grinning) with no adverse effects this time. happy that my flush and new thermostat have at least helped. possibly all that ROSTRA needs in the first instance??? still don't appear to have my fan running(fuses and relays and cable continuity all ok and fan itself does work with a direct power supply) so might try a replacement heat sensor. thanks for that DRUMTOCHTY
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Re: Boiling or not?

Postby drumtochty » Thu Apr 27, 2017 10:50 am

Remember to half drain the radiator before you remove the sensor. I did not when I replaced my first one.
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