Hey all, I just installed an aftermarket water temp gauge in my FD. After the reading I did, I decided to go the route of splicing into the TB coolant line with a tee.

I have read that the temperature readings in this location can sometimes have a tendency to read on the low side. I understand that the stock cooling fans come on the low speed mode at 226F (dependent on electrical load). Today after I shut my car off after the first drive with the new gauge, the temp was at about 180ish. It slowly crept up, and with the key still in accessory mode, I noticed my cooling fans come on at about 187 as indicated by my gauge. My parking lights were on at this time, if it’s worth mentioning.

I can’t imagine that the difference in location between the stock sensor and mine would account for THAT drastic of a temperature differential.

The car is also mostly stock, it has an aluminum rad, aluminum ast and a catless downpipe. To my knowledge, it is still on the stock FD thermo switch.

Can anyone offer any sort of insight on this? I suppose I could remove the probe, and heat some water, check it with a known good thermometer and compare the results to the gauge probe just to rule out that it’s not way off in terms of calibration.

Any input is greatly appreciated!

Thanks!

 

The thing about adding gauges to monitor things your weren't previously monitoring is this exact scenario here. If your car is not overheating or doing anything it shouldn't be doing then continue to live your life as you were before the gauge install.

Everyone starts to think there's something wrong now that they can see numbers. Ignore it. Its fine. With the car not running, water temp and what its doing is irrelevant anyway.

 

If the engine wasn’t running, coolant wasn’t circulating. I might just suspect heat-soak from the engine affecting the thermoswitch. The resolution and speed of both are probably different too.
Have you checked it from cold start?

Also, my gauge sensor is still mounted in that hose and has always been really close to what I see on my PFC commander. Actually sometimes the gauge seems to react just a little quicker.

 

Not necessarily that I think something is wrong with the car or how it’s running, I’m just trying to confirm the accuracy of my gauge. Having a reliable way to monitor temps in these cars is important in my opinion, it would be pointless to install a gauge if i’m just going to ignore it. But thanks for the input

 

That was my initial thought too, but I had basically just shut the car down, then the fan came on. I didn’t think that the location of the coolant the thermo switch is measuring would see a temp spike so quickly, but I suppose it’s possible, and since the coolant isn’t circulating, whatever is in the TB hose wouldn’t really heat soak much after shut down.

The lowest temperature the gauge indicates is 100F, so from dead cold i saw the temp slowly creep up, but I didn’t let the car idle long enough for the fans to kick on. That’ll be my next test.

While cruising and idling in traffic, I was seeing temperatures between 165 and 185F with 68F ambient temps

 

If it helps, your cruising/driving temps seem appropriate and what I’d expect.

Eventually, if you plan to stay on the stock ECU I would consider replacing the FD thermoswitch with the S5 FC version. It lowers the threshold for the fans from something like 105 C. to 96 C.
Its a little fiddly to get to on the back of the t-stat housing but worthwhile IMO.

 

Thanks for the advice. I plan to eventually upgrade the ecu, but I’m not sure when i’ll get around to that. Taking my time with modifying it. An FC thermo switch will most likely be one of the next things i do with the car in the meantime

 

FWIW I think it’s great that as a newer owner one of the first things you did was to add the temp gauge rather than some silly bling or ill-advised performance mods. And it sounds like you’ve been doing your reading.

But that said I get where cr-rex was coming from. Sometimes new owners get overly concerned with minutiae and forget to enjoy the car. It’s been about 20 years but speaking from experience.

 

That's definitely not untrue hahaha. I just want to make sure the car is running as well as it could be, and thankfully it's been pretty reliable. I would mainly like to be able to monitor temps during spirited driving, so I can let the car cool when it needs to and avoid accidentally pushing it too hard. If there is some sort of "calibration error" between the temp my gauge is displaying and the temp the stock sensor is reading, I'd like to figure out what it is so that I can mentally account for it. Thanks again for all the input, I'll update the thread when I run the car from idle until the fans kick on.

 

Yup, this is totally normally after shut off, heat soaking due to lack of coolant circulation. I can see up to 110°C on my commander after shut down and the fan will run, while my coolant temp gauge on the TB line still sit at 180°F. It's a small line and without flow it is not going to react as fast as the sensor at the water housing. Temperature will drop fast if you start the car back up to get coolant moving again.

 

This is pretty much exactly the answer I was looking for. I just wanted to validate that the readout on my gauge was accurate. Thanks again

 

This used to make me super nervous on the Cosmo. I used to sit around and run the fans till the temp came back down every time I shut the car off haha. I still do it from time to time, just because I don't think all the vacuum lines and plastics under the hood need to be baking in all that heat....but it's not something that I'm worried about, or **** about anymore.

@cr-rex is totally right. It was something I've never monitored in any of my rotary cars...so when I saw it the first time I got crazy nervous. But like he and the others have said, it's really irrelevant after the car shuts off

 

[QUOTE=REnaissance_Sle7in;12519893]This used to make me super nervous on the Cosmo. I used to sit around and run the fans till the temp came back down every time I shut the car off haha. I still do it from time to time, just because I don't think all the vacuum lines and plastics under the hood need to be baking in all that heat....but it's not something that I'm worried about, or **** about anymore./QUOTE]

i used to turn the car off, and then turn the key back on and let the turbo timer run the fan.

 

Thanks for the input! Yeah I totally get the concept of the car heat soaking after shut down. What I was trying to learn from the post was why the temp fan was coming on if my gauge only indicated 187F