mx5cartalk.com

hi team,
now, be gentle I am not technaically minded

so recently the water temp gauge (factory) has been moving around too much. once car getting warm, the temp gauge moves up normally. after a bit of a drive, the gauge then flutters between cold, and just below middle - normally always sits just under the middle even after a race/session at track.

at wakefield last sunday the gauge seemed to do it a lot more, more so sitting on cold!
after each race I noticed the thermo fan wasnt come on. one mate said it came on once that he remembers.

so the fuel also, plugs are black, seems to run through a lot more fuel than usual.

this leads me to believe...is the car constantly running in "cold mode" and dumping more fuel in - which could be a brokern thermostat?
if so, fairly simple process to fix?

or could it be a broken gauge sensor? if so, where is the water temp sensor?

what else potentially could it be?

to give you an idea, I have a 42mm a/m radiator and MX5mania type coolant reroute. coolant and spark plugs were only changed in august 2011 and have done 2 track days since.
and be gentle on me haha

Cheers,
Chris

thermostat is stuck open.

If it is the thermostat, replacements are not expensive and not a difficult job to replace. They are also easy to test on the stove with a high temp thermometer.

so I was kinda right? haha

If thermostat is stuck open, what causes that? jsut a broken thermostat?

now with the mania coolant reroute, Im going to take a stab in the dark here...do I have two thermostats?
the mania one with the reroute and the standard one?

I actually beg to differ. The car would still get up to normal operating temperature if the thermostat was stuck open, but it would just take forever. It would be up to normal temperature, or higher, during a race that's for sure. I think what might be going on in your case is as you said; the ECU thinks the coolant is cold, so it is running in cold mode. As a result I would be inspecting the coolant temperature sensor at the back of the engine beneath the coil packs. Feel free to correct me if I am wrong.

Thermostat getting stuck open happens by the wax inside the thermostat leaking out over time, which is just basic wear and tear.

I think any re-route basically just puts the thermostat at the back of the engine, so just the one thermostat. Not sure if it is entirely necessary unless you have a turbo; my car has never overheated on the track, and I have raced on some very hot days.

the gauge then flutters between cold, and just below middle

"Flutter" indicates rapid movement which would indicate an electrical issue, or doe's it fluctuate gradually up & down?

Yo Mitch!

how did you go with your temp issue?

Ok cool, will check that.
So what would I exactly be looking for with this sensor? How would you tell its fubared?

Eskimo,
good question - from what I have noticed its both, I know that doesnt help but one time it'll be looking normal temp, then POW next thing I know its down the cooler end. then might move up slightly, back down slightly fairly quickly.

check the thermostat/s first. don't go on wild goose chases until the easy stuff has been checked first.

it will not hold operating temp or go higher than normal as previously mentioned if it is stuck open.

the reason it is running in cold mode, is because the thermostat is open and the coolent is not getting up to temp.

I agree with the above. Check the thermostat first. If it is an electrical fault, so be it but at least you know the engine will be ok

The purpose of the thermostat is to bring the engine up to operating temp quickly, not keep it cool. I would assume this would be vital if you have a bigger radiator and a coolant re-route. You would want to achieve operating temp asap as the other bits are doing their job in removing the heat.

A couple of things you could try would firstly, If you are close to a workshop that has an EFI system scanner that they might
be willing to attach, if they can bring up the current data you shoud be able to check efi systems temp sensor reading against
the gauge reading as they use different sensors and the chances of both being stuffed are unlikely.
Or you could remove the thermostat altogether, this is generally not recommended (it will run too cold) but if your temp stabilises at least you'll at least
be on the way to diagnosing the issue.
Oh, and make sure you have no air locks/pockets in the cooling system as they can cause strange/bad things to happen.

Temp issue seems to have been result of an airlock, which was cleared by properly bleeding the coolant system. If you want to check the functioning of the sensor you would need to remove it(access gained by removing coil pack), hook it up to one of those things that measures current (name has slipped me right now), and put it in a pot of water and bring it to the boil and watch what the current does. If it jumps around you have a problem, if it is a linear increase it's all good. But I do agree with the previous suggestions of trying the thermostat first, as it is the cheapest and easiest option.

evil_weevil wrote:So what would I exactly be looking for with this sensor? How would you tell its fubared?

If it turns out not to be the thermostat, then this might be of interest from two angles:
viewtopic.php?f=29&t=48498

2 coolant temp sensors on NA8 - one at rear of head is coolant temp for ECU & one at rear hotside of block is temp gauge. Btw, with the above NA8 Clubman it seemed to be a loose TPS connector.

OK!
so finally got some spare time with the car this evening. got to look at both thermostats.

now my questions...

1. the aftermarket thermostat has a 5mm hole? yet the factory one has like mini thermo plus the normal one! why is this? is it a by-pass of some sort? am I dribbling sh*t?
(again, I'll remind you all I am not technically minded!!!)

2. the factory thermostat has
"BP05 NTC 85-88degrees"

so I assuming thats the part number + temp range?

when I tested the a/m one, I honestly could not see it it move at all. it should be opening yes? when I did take it out of the bucket water coming out of it from the thermostat.

Didnt test the factory one at the front of the engine, however how do you remove the thermostat out of its position?

Im thinking just taking it to my local bloke as you can kinda see - Im hopeless with this sh*t and would jusr rather it fixed! haha

One last thing, how do you get rid of an air pocket?

Cheers,
I have no idea on cars and should pay someone to do it Chris

evil_weevil wrote:2. the factory thermostat has "BP05 NTC 85-88degrees" so I assuming thats the part number + temp range?

BP05 is the identifier for the MX5 NA8 head. BP05 was also the head identifier on other Mazda models of a similar vintage using the BP (1.8 ) motor.

right!
see? Im waaay off