So for a while I’ve noticed it’s running way too cool and I’ve drawn the conclusion that the thermostat is likely seized open.
Not only does it take a lifetime to warm up to the point of putting heat into the cabin, but if its cooler outside and you’re cruising at motorway speeds without the motor being under any real load, the temperature gauge goes no higher that 1/4, where as I’m sure it should stick pretty rigidly around the half way mark.
I’ve changed a thermostat before on these, it’s a pig of a job but I reckon I can do it again, however if I remember correctly, bleeding the system (I’ll be changing the coolant too) was a bit of an issue.
Any advice on how to make this as simple and quick as possible?
I’m obviously going to drain the radiator via the drain plug, and I’m also going to disconnect the lines from the heater matrix to remove as much coolant as possible.
After that, refill the rad and expansion tank and go from there.
Any suggestions on a better way?
Lastly, I was thinking of changing the water temp sensor at the same time just to rule it out as a weak link, a good idea or overkill?
If you’ve done the job before then I won’t bore you with the procedure although there is info out there on the web on what’s involved just search.
Buy this one for the job…
The stat above is the long neck one, the NC engines apparently have two types of stat to fit, see MX5parts stats, one has a shorter neck too. It doesn’t really matter as the long neck one can be fitted and you just trim the large hose to fit this on the car, trim off the around 30mm.
To burp the system all I did was, once the system was filled I run the car for a few minutes then put the nose of the car up on the ramps, run the engine again and out popped the air after a while. I manipulated the hoses (squeeze) particularly the heater hoses and it helped.
Obviously I didn’t manipulate the large hose down by the aux belt whilst the engine was running, I like to keep my fingers Do turn the heater on to full whilst carrying out this procedure and you’ll soon get the heat blasting out.
I didn’t change anything else, not even the coolant I saved that and returned it to the system filtering out any tiny bits through a gauge as I had the coolant changed the year before.
I was going to buy an OEM thermostat from MX5 parts for nearly £80… Is the Mahle one just as good? £11.95 is much more favourable!
Yeah I’ve heard of the length differences for the T-Stats before too, so there’ll be absolutely no issue aside from shaving 30mm off the hose? 30mm is such a small amount, I wouldn’t have thought it would be even necessary really, or is 30mm enough to make the hose foul something?
Quite a few have used that stat from Opie, it was also on ebay maybe from the same supplier.
Probably get the hose on without trimming it but it may push it out of alignment a tad. If you have the shorter neck version fitted offer it up to the new (Opie) long neck version when off and just cut that difference in size off the hose, job done and it will sit perfectly. Use the same hose clips, they are strong.
Just make sure you take care removing the bolts holding the stat in, don’t drop any or it’s a search and rescue operation. If I remember I just about managed to grab hold of them with my fingers to withdraw and one was a pig to get back in (the one you can’t see) but got there in the end.
Just to add I fitted mine over two years ago the gauge sits bang in the middle never fluctuates, it’s a stat made by Mahle, I’ve used various filters etc of that brand before all ok.
I changed the stat in mine last year. Not too bad a job once you’ve got the airbox out of the way just a bit fiddly. The worst part for me was bleeding the system. Shortly after I bought myself a vacuum bleeder. This simply creates a vacuum in the system using an airline, then it’s a case of turning the tap and the engine literally sucks the coolant into all it’s cavities leaving no air. I’ve not had a chance to use it on the 5 yet but I used it on my motorbike the other day and was amazed how easy it made the job. No funnels, no messing trying to pour coolant into the engine, no half an hour revving the engine up or sticking the front up in the air to get rid of the air.
Just on this point @MickAP, am I correct in thinking that all the caps should be removed while trying to burp/bleed the system, I.e the radiator and expansion tank caps?
Similarly, how will I know when it is completely and successfully bled?
I filled up the system and put the caps on. Run the engine to warm and switch off. As I said earlier I gave the hoses a squeeze, and remove the caps, you’ll probably notice the level drop in the tank, top up. Repeat the process a couple more times topping up as you go return caps switch on engine. I literally heard the system give a loud burp and finally topped up and that was it. Btw I had the nose half way up a set of ramps, I think it helped.
Okay cool, I was also going to flush as much of the system as possible with a hose… I.e the radiator, and also the heater matrix by disconnecting at the bulkhead and putting the hose to it until the water come out of the other side.
Have a read here below I’ve come across my own contribution. I didn’t flush as my system coolant got done the year before when it was in for other work. You need to use distilled water to flush apparently not tap water. Other stuff too like what coolant (FL22) and tools needed.
ChrisMK3 don’t flush it with a hose. Depending on your water hardness and purity you probably don’t want standard tap water in your cooling system. When you fill up with coolant there will be some normal tap water left inside, the old coolant you flushed out is probably better. Flush with deionized water if you really think it needs it. Regardless of what you flush with you will be reducing the antifreeze concentration levels in the FL22, unless you flush with FL22 of course but whos got the money for that type of escapade!
edit: That first bit was not supposed to sound like an order! just a recommendation
Yeah I’ve since bought 10L of de-ionised water to flush it, but it got me thinking, how can I be sure that as much of it is out before I do the final flush?
I don’t think you can get all of it out unless you can suck it out with some special equipment. Just flush with what you have, you’ll be fine.
I’ve fitted this recently below and just topped up with deionised water, about half cup full of coolant spilt.
I would not worry too much about getting every last drop out. Empty the radiator and change the stat, refill with deionised. Run engine till warm. Empty radiator and then refill with whatever coolant is the right one for your car and then burp it. If you use fl22 it will be diluted a bit so you could do the empty refill process once more with fl22 instead if you have enough but I’m sure that even slightly diluted the antifreeze properties of fl22 are good enough for the uk. When i first got my mx5 I gave it a proper flushing. It took few tries with deionized water to get the original fl22 out
Do turn the heater on to full whilst carrying out this procedure and you’ll soon get the heat blasting out.
