Cooling issues following rad replacement

[Blip1]

Okay, let me start by saying say that I DID do my homework, searching here and elsewhere online prior to attempting to solve my cooling problem…but now I am stuck, so, any advice would be gratefully received…thank you!

1999 MK2 1.8i manual

Cooling system was in perfect order until my local garage cracked the old radiator upon removal (to allow access for an unrelated job). I supplied them with a new rad which they fitted. First thing I noticed upon driving the car, aux cooling fan cutting in unusually early, and, water temp needle closer to 11 'o’clock, rather than the usual 12noon. Other than that all seemed fine; however I soon noticed that there was a slow but steady leak of coolant. Got the car up on ramps, but couldn’t locate the leak. 

I removed the new radiator, checked it over thoroughly, no leaks or blockages. 

Thermostat removed, hosepipe in and a good flush until clear water flowing from bottom hose.

New OEM Mazda thermostat fitted.

Rad refitted.

Filled rad with coolant, topped up expansion tank (front of car still up on ramps). Leaving the rad cap off, engine started and allowed to idle for 15mins plus. 

As soon as the engine was running, coolant began gently overflowing from the rad, before settling down with the occasional large bubble. 

After a good ten minutes or so, the cooling fan cut in, and the level finally dropped in the rad - so I guess the thermostat opened?

Topped up the rad.

Plenty of heat from the heater, but temp needle still nearer 11 than 12. Top hose hot to touch - in fact too hot to hold onto; both heater hoses hot; but bottom hose stone cold. 

At this point I decided to increase the engine RPM from idle to around 2500rpm - at which point water spewed out of the radiator like a geyser!

Topped off again; water level in the rad continued to rise and fall, sometimes overflowing gently. Temp needle still steady at 11ish, heater still hot, top hose scorching, bottom hose stone cold.

Am I missing something?!! Or do I simply need to give it a good blast? I just feel that something is not quite right here, and don’t want to cook the engine!

Many thanks in advance.

 

 

[Drumtochty]

Sounds to me you have a head gasket fault.

Before going any further do the following as you have done before.

Fill system,
Have say three litres of coolant ready to put in the system.

Run the engine until the fan starts, keeping an eye on the coolant level all the time and topping up when required.

After the fan start carry on running the car for another 10 minutes to see if it settles down.

If there is still a problem get a cylinder leakdown test done to check for problems with the head gasket.

The head gasket is 20 years old. 10 years for a head gasket is a good innings.

[Blip1]

Thank you for your reply - (though not quite what I wanted to hear re. head gasket…)! I’ll give it a try. Thing is, there has been no sign of an issue prior to the rad swap… Hey ho.

[safetymatch]

You don’t say what the ‘unrelated’ job was.
Another possible fault could be the water pump, feel the hoses near to the pump for any discernible heat difference (i’m not over familiar with MX5 engine lay outs) but normally (i work on Nissan engines) i would remove the top hose or the thermostat housing and briefly start the engine, if the coolant/water spews out the water pump is ok.

[Mazda_mender]

As saftymatch says, don’t jump off the cliff yet, it could be a number of other issues just sat there testing you, it could be a dodgy pump, air lock, remember there are two rads…the heater matrix, it needs to flow through that also, a flaw in the new rad???could be a weak fan?, fan not workingcorreck? fan switch, relay,temp switch… there are a number of things it could be, but it sounds like it is a blockage be it air or what ever and it as not been done correct.

You say you had a leak? did you Find that leak as that is not helping and also sucking air, plus the system will not be getting up to pressure.

It sounds like a simple air lock…

 

Don’t go back to that garage…

M-m

[Blip1]

Thanks for your additional comments guys; much appreciated.

The unrelated job was to do with the front chassis rails, hence rad removal. Prior to this the water temp has always sat steady at 12 'o’clock, no coolant loss, no issues, cooling fan well behaved etc.

I suspect the leak from the new rad was simply from one of the hose connections. Once I had removed, checked and refitted it, all appeared watertight - though hard to tell for sure once coolant started overflowing upon engine start…

I’ll repeat the bleeding/top-up procedure as per previous post, then take it from there. Hopefully just a stubborn air lock… Any tips for checking the function of the waterpump - or should I simply follow safetymatch’s suggestion, start engine with top hose removed to check for a flow?

Cheers

[Mazda_mender]

Remove the rad cap (when cold) do not fill it right to the top… and start the engine you will see it flowing at some point …if not it is not pushing.

M-m

[ast]

When I converted to Waterless (new waterpump etc), it took 40 minutes to burp the system.

[Blip1]

Thanks - will do.

[Blip1]

Re. 40mins to burp…will keep that in mind as well - thanks!

[F12NK_R]

Hi, one thing I do when refilling a system is to squeeze the hoses, so as mentioned, refill then with the cap off running, I go round squeezing the hoses to ease things along. It might help. 

[Scottishfiver]

Back in the day…many moons ago…it was advised to actually jack the front up about a foot or 18" or so to help induce the air to expel from the top of the radiator.

You’ve nowt to lose by trying. 

 

[Blip1]

Well I allowed the engine to idle for half an hour today, rad cap off, front of car raised. Very little happened to the coolant level; the heater became toasty hot, as did the top hose; bottom hose remained cold. At no point did the cooling fan kick in, even though the engine cam cover became too hot to touch. Engine temp needle remained steady at 11ish, just as before. No leaks evident.
Unconvinced, I took the car out for a 40min drive. Heater very hot, temp needle steady.
However when I pulled up at the end of the run, there was steam coming off the rad. - not a leak, but evaporation of excess fluid from the previous overflows etc - I was surprised that the rad was hot enough to create steam on it’s surface - and still no cooling fan. Bottom hose now hot though.
With the front of the car back up on ramps, I let it cool down for half an hour, then took off the rad cap and allowed it to idle again. There were a few bubbles and I was able to add perhaps 100ml extra coolant. Within 15mins the cooling fan finally began kicking in and out as you would expect. Each time the water level would just creep up to the filler neck, dropping when the fan kicked in. I let it do this for a further 15mins before shutting down. Temp needle steady throughout.
So, although there are no obvious issues, and the temp gauge is completely steady, the radiator is getting pretty hot. I ran the car again later on, this time with cap in place, and once again it became hot enough to create steam off the wet surface.

Am I simply being paranoid, or should this be of concern? Hmm.

Guess I’ll just keep a close eye on everything and report back in due course…

[safetymatch]

Just a thought, but i have seen thermostats fitted upside down…could this be a possibility?

[ast]

@Blip1

Well I allowed the engine to idle for half an hour today, rad cap off, front of car raised. Very little happened to the coolant level; the heater became toasty hot, as did the top hose; bottom hose remained cold. At no point did the cooling fan kick in, even though the engine cam cover became too hot to touch. Engine temp needle remained steady at 11ish, just as before. No leaks evident.
Unconvinced, I took the car out for a 40min drive. Heater very hot, temp needle steady.
However when I pulled up at the end of the run, there was steam coming off the rad. - not a leak, but evaporation of excess fluid from the previous overflows etc - I was surprised that the rad was hot enough to create steam on it’s surface - and still no cooling fan. Bottom hose now hot though.
With the front of the car back up on ramps, I let it cool down for half an hour, then took off the rad cap and allowed it to idle again. There were a few bubbles and I was able to add perhaps 100ml extra coolant. Within 15mins the cooling fan finally began kicking in and out as you would expect. Each time the water level would just creep up to the filler neck, dropping when the fan kicked in. I let it do this for a further 15mins before shutting down. Temp needle steady throughout.
So, although there are no obvious issues, and the temp gauge is completely steady, the radiator is getting pretty hot. I ran the car again later on, this time with cap in place, and once again it became hot enough to create steam off the wet surface.

Am I simply being paranoid, or should this be of concern? Hmm.

Guess I’ll just keep a close eye on everything and report back in due course…

 

You can test if the fan works

 

https://www.mx5oc.co.uk/forum/yaf_postst75699_Testing-the-radiator-fan.aspx

https://www.miata.net/garage/CoolingSystemProblems.html

 

[Roadster_Robbie]

@Blip1

Well I allowed the engine to idle for half an hour today, rad cap off, front of car raised. Very little happened to the coolant level; the heater became toasty hot, as did the top hose; bottom hose remained cold. At no point did the cooling fan kick in, even though the engine cam cover became too hot to touch. Engine temp needle remained steady at 11ish, just as before. No leaks evident.
Unconvinced, I took the car out for a 40min drive. Heater very hot, temp needle steady.
However when I pulled up at the end of the run, there was steam coming off the rad. - not a leak, but evaporation of excess fluid from the previous overflows etc - I was surprised that the rad was hot enough to create steam on it’s surface - and still no cooling fan. Bottom hose now hot though.
With the front of the car back up on ramps, I let it cool down for half an hour, then took off the rad cap and allowed it to idle again. There were a few bubbles and I was able to add perhaps 100ml extra coolant. Within 15mins the cooling fan finally began kicking in and out as you would expect. Each time the water level would just creep up to the filler neck, dropping when the fan kicked in. I let it do this for a further 15mins before shutting down. Temp needle steady throughout.
So, although there are no obvious issues, and the temp gauge is completely steady, the radiator is getting pretty hot. I ran the car again later on, this time with cap in place, and once again it became hot enough to create steam off the wet surface.

Am I simply being paranoid, or should this be of concern? Hmm.

Guess I’ll just keep a close eye on everything and report back in due course…

Nothing sounds out of the ordinary there…

 

[Blip1]

Thank you RR, that’s reassuring to know.

'Stat fitted the correct way up.

Fan appears to be behaving itself.

It would seem that the initial problems after collecting the car from the local garage (cooling fan kicking in very quickly and frequently, coolant leaks) were the result of a poor/rushed job.

Fingers crossed all okay now…!

Thank you for all the input - it makes MX5 ownership all the better!

[Hilux]

@Blip1

Okay, let me start by saying say that I DID do my homework, searching here and elsewhere online prior to attempting to solve my cooling problem…but now I am stuck, so, any advice would be gratefully received…thank you!

1999 MK2 1.8i manual

Cooling system was in perfect order until my local garage cracked the old radiator upon removal (to allow access for an unrelated job). I supplied them with a new rad which they fitted. First thing I noticed upon driving the car, aux cooling fan cutting in unusually early, and, water temp needle closer to 11 'o’clock, rather than the usual 12noon. Other than that all seemed fine; however I soon noticed that there was a slow but steady leak of coolant. Got the car up on ramps, but couldn’t locate the leak. 

I removed the new radiator, checked it over thoroughly, no leaks or blockages. 

Thermostat removed, hosepipe in and a good flush until clear water flowing from bottom hose.

New OEM Mazda thermostat fitted.

Topped up the rad.

Plenty of heat from the heater, but temp needle still nearer 11 than 12. Top hose hot to touch - in fact too hot to hold onto; both heater hoses hot; but bottom hose stone cold. 

At this point I decided to increase the engine RPM from idle to around 2500rpm - at which point water spewed out of the radiator like a geyser!

Topped off again; water level in the rad continued to rise and fall, sometimes overflowing gently. Temp needle still steady at 11ish, heater still hot, top hose scorching, bottom hose stone cold.

Am I missing something?!! Or do I simply need to give it a good blast? I just feel that something is not quite right here, and don’t want to cook the engine!

Many thanks in advance.

 

 

 

My money is on that the thermostat has failed - its not opening if the bottom hose is cold

 

Not sure if these thermostats can be put in the wrong way up?

 

[Hilux]

@Blip1

Well I allowed the engine to idle for half an hour today, rad cap off, front of car raised. Very little happened to the coolant level; the heater became toasty hot, as did the top hose; bottom hose remained cold. At no point did the cooling fan kick in, even though the engine cam cover became too hot to touch. Engine temp needle remained steady at 11ish, just as before. No leaks evident.
Unconvinced, I took the car out for a 40min drive. Heater very hot, temp needle steady.
However when I pulled up at the end of the run, there was steam coming off the rad. - not a leak, but evaporation of excess fluid from the previous overflows etc - I was surprised that the rad was hot enough to create steam on it’s surface - and still no cooling fan. Bottom hose now hot though.
With the front of the car back up on ramps, I let it cool down for half an hour, then took off the rad cap and allowed it to idle again. There were a few bubbles and I was able to add perhaps 100ml extra coolant. Within 15mins the cooling fan finally began kicking in and out as you would expect. Each time the water level would just creep up to the filler neck, dropping when the fan kicked in. I let it do this for a further 15mins before shutting down. Temp needle steady throughout.
So, although there are no obvious issues, and the temp gauge is completely steady, the radiator is getting pretty hot. I ran the car again later on, this time with cap in place, and once again it became hot enough to create steam off the wet surface.

Am I simply being paranoid, or should this be of concern? Hmm.

Guess I’ll just keep a close eye on everything and report back in due course…

 

Just seen this update.

The water shouldn’t pulse in the rad when running with fan on or off. The fan has no effect upon the water flow however it draws current and the engine auto corrects the idle so a slight increase in engine revs would make the pump work harder.

Note that the alternator and pump are driven by the same belt.    Unlikley but…Is the belt old and slipping without squealing?

The plastic rad surface shouldn’t be so hot to boil off water/create steam however if the ambient temperature is low it might be seen as steam.

Based on the above I would suggest the pump efficiency is a possibility. Has it been changed? Either that or review the belt tension/condition. Review the alternator also, check if its running freely.