Press "Enter" to skip to content

Mazda MX5 NB, Coolant Change

Yet another part of the car that made me question who worked on it last. I needed to change the coolant as I did not trust what was in it.

When I first got the MX5 I did the usual check over, and checked all the fluid levels. One thing I noticed was that the coolant was a weird color. It wasn’t green, but sort of a yellow color, but smelt like anti-freeze.

The aftermarket aluminium radiator doesn’t appear to be too old, so I suspect the liquid in the cooling system isn’t old either, but I didn’t trust it. My coolant must be green (unless OEM is derp like VW).

After work today I grabbed some more of my favourite coolant. This is the stuff I run in the Rover, and its done me well. Its nice and easy to wipe off the floor when it inevitably leaks/spills out of the Rover too.

Being the little car it is, the radiator is right there and I didn’t have to jack the car up. My spill tray and catch pan fit perfectly under it. I used a 24mm spanner to remove the drain plug on the bottom.

This is what came out

Now normally I would be worried if my coolant came out this color, it could be what is termed “milky” and indicate a blown head gasket, but in this case I actually think it’s the type of coolant used. I suspect it’s something like Nulon One, which is a yellow brown color. There was no typical oily-ness to the coolant (or coolant in the oil), no frothing, no odd smell, no bubbling etc, so not a head gasket.

It kinda looked like banana milk, whilst still being watery and transparent

Being such a small car I used the radiator cap to regulate the flow of coolant into the pan, as my pan wasn’t big enough to contain all the fluid at once. I could have the cap in one hand creating a seal on the top of the radiator, and screw the drain plug in with the other hand. Small car ftw.

When nothing else came out, I plugged the radiator back up and filled it with plain water and ran the engine to cycle it through. I didn’t run it long as I didn’t want the coolant hot, so the thermostat didn’t open, but it seemed to get more of the stuff out, as this is the pan for round two

Once I was happy that I got as much out as I could, I mixed up some 50:50 coolant in another bottle, and using my new funnel, poured it in

I wrapped some insulation tape around the bottom of the funnel so it would create a seal with the neck of the radiator. This increases the coolant height to help remove trapped air bubbles, and gives a small amount of coolant to use when the radiator burps air.

I also needed to clamp off the overflow hose as it filled the overflow bottle from the neck of the radiator

I did take the opportunity when the radiator was draining to remove the overflow bottle and clean that out too

I bled the system by keeping it topped up with coolant, and running the engine until the thermostat opened and the top radiator hose was hot. This did take a while, so not sure if the thermostat is a bit slow, or if its normal. The gauge (which is apparently almost useless) was at operating temp for ages, well before the thermostat opened.

I also tested the fans activated, which they did. After a quick drive I was satisfied that it was keeping its coolant inside, the heater is hot as hell and the temps were good.

Another thing checked off the list. I have the oil and filter for the engine, and the oil for the trans, i’m just waiting on a delivery of parts for the gearbox before I change that oil.

5 1 vote
Article Rating

Discover more from Tastes Like Petrol

Subscribe to get the latest posts to your email.

Notify of

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Inline Feedbacks
View all comments