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hi guys has anyone got a after market temp water gauge on the mx5 picking up temp at back of head in the standed spot

i do and it is reading around 98C when warmed up i have not done a cooling reroute on my car as yet
is this temp at the back there normal

on the standed gauge it was reading half way

also i brought a new thermostat as i was thinking it may help cool it down
but dont think its the right one can any one confirm
the one in the car looks ok to me is there any way of testing them


this the one that was in it







this is the new one from auto barn ??????????????

They will register quite warm back there pre-reroute. I take it that is the temp you are seeing out on the track? That is actually pretty good if that is the case.

As for the thermostat, yep the aftermarket ones look different, but as long as the temp is correct and the diameter is right, you should be fine.

My sensor is in a Maruha sandwich plate above the thermostat so readings may be different than yours. My car sits between 71c and 74c on the road and the track, and never gets any higher than about 84c when the cars got no airflow through the radiator. I have an aftermarket 42mm alloy radiator and the AC has been removed so there's nothing in front of the radiator.

I am guessing you want to know if the thermostat is opening at the right temp. I also guess that you test this in water of a known temp to see if it opens at that temp- need thermometer. The other thing to do is replace with an OE thermostat. Perhaps the local radiator guys can test it. The higher temps you are reporting may be giving a false reading?

rossint wrote:My sensor is in a Maruha sandwich plate above the thermostat so readings may be different than yours. My car sits between 71c and 74c on the road and the track, and never gets any higher than about 84c when the cars got no airflow through the radiator. I have an aftermarket 42mm alloy radiator and the AC has been removed so there's nothing in front of the radiator.

This makes sense - this is the practical consequence of an un-rerouted cooling system. #4 gets cooked

Thanks guys

Have to do a reroute

I'll test this one I have taken the other back
Was not the right one as it was a by pass

The autobarn one should be OK. Make sure you fit it with the big copper bit and spring facing in towards the head. Otherwise the little cold running by-pass jiggly thing will be pushed shut instead of held open when the main thermostat is closed. If it's jammed shut then you may not get enough flow of hot water to actuate the main thermostat part early enough.

zossy1 wrote:

rossint wrote:My sensor is in a Maruha sandwich plate above the thermostat so readings may be different than yours. My car sits between 71c and 74c on the road and the track, and never gets any higher than about 84c when the cars got no airflow through the radiator. I have an aftermarket 42mm alloy radiator and the AC has been removed so there's nothing in front of the radiator.

This makes sense - this is the practical consequence of an un-rerouted cooling system. #4 gets cooked

Really? 71-74 degrees? Even on the track? I am betting you have a calibration issue there (or some other problem). What thermostat have you got (what temperature is it set for)? Hmm, you do have one don't you?

With a functioning pressure cap, you can go well over 100 degrees, but No4 is the weak link, you don't want it boiling there (or anywhere else ...). But you should have something like 95-105 at the front, if it is not into the 90s at least there is something funny happening, and it would be worth checking out.

I believe standard Mx5 thermostat is 80C (or 175F). could be wrong there but I don't think so. 160-165F thermos were also popular in the US, especially those installed in hotter climates like Arizona and Florida.

The vent holes would allow seepage at all temps through the thermo. If it has a cooler thermo installed, these temps wouldn't be that far off, would they?

On the later cars (NB) the thermostat and fan activation temps are higher... just out of interest.

Last time I checked I had a thermostat It's possible the gauge is not calibrated properly and the numbers aren't 100% accurate.
I was under the impression that the thermostat was more progressive rather than open/closed, the gauge would indicate that the thermostat is fully opening around the 80deg mark. I was also under the impression that lower engine temps (around 65-75deg) were more desirable for optimum HP and is still well within normal operating temps.

rossint wrote:Last time I checked I had a thermostat It's possible the gauge is not calibrated properly and the numbers aren't 100% accurate.
I was under the impression that the thermostat was more progressive rather than open/closed, the gauge would indicate that the thermostat is fully opening around the 80deg mark. I was also under the impression that lower engine temps (around 65-75deg) were more desirable for optimum HP and is still well within normal operating temps.

Yes and no. I think the temps indicated at that location are not outrageous, but lower running temps can cause issues with the OEM ECU fuel map. I believe the leaner "warm" fuel map kicks in around 70-75C...? if you run too cold, you will burn much fuel and make much carbon (and less power).

zossy1 wrote:

rossint wrote:Last time I checked I had a thermostat It's possible the gauge is not calibrated properly and the numbers aren't 100% accurate.
I was under the impression that the thermostat was more progressive rather than open/closed, the gauge would indicate that the thermostat is fully opening around the 80deg mark. I was also under the impression that lower engine temps (around 65-75deg) were more desirable for optimum HP and is still well within normal operating temps.

Yes and no. I think the temps indicated at that location are not outrageous, but lower running temps can cause issues with the OEM ECU fuel map. I believe the leaner "warm" fuel map kicks in around 70-75C...? if you run too cold, you will burn much fuel and make much carbon (and less power).

I'm using a 70deg thermostat in mine. I suspect that Zossy is right about the OEM ECU feeding too much fuel at that temp in mine. It's mainly having an effect on closed loop running, so touring fuel consumption is up. Currently contemplating going back to 80 deg (stock) or modifying the ECT to ECU signal.

Makes cense that if the you're running too cold then the ECU will think the cars not warmed up yet. The dummy temp gauge on the dash gets to just under half way where it normally would sit at around 60deg on my water temp gauge, you'd think the car is warmed up at this point?
Am I wrong to assume that since the water pump is constantly pumping then there is always some flow through the engine, the thermostat just controls how much flow? I'm far from an expert in these things. It's an interesting discussion, I hope the OP doesn't mind the semi hijack

rossint wrote:Makes cense that if the you're running too cold then the ECU will think the cars not warmed up yet. The dummy temp gauge on the dash gets to just under half way where it normally would sit at around 60deg on my water temp gauge, you'd think the car is warmed up at this point?
Am I wrong to assume that since the water pump is constantly pumping then there is always some flow through the engine, the thermostat just controls how much flow? I'm far from an expert in these things. It's an interesting discussion, I hope the OP doesn't mind the semi hijack

The OEM temp gauge is progressive. I have a 180F thermo in mine (82 C) and the thermo opens just short of 1/2 on the OEM gauge.

I have to apologise though, as I think I think I'm wrong about the OEM thermostat. It opens around 90C, not 80C.

Sounds like you have a cooler thermo in there.