A More Accurate Way Of Monitoring Engine Temps

If I stop in traffic etc the needle in the 944 will regularly creep up to the hot end of the gauge. Fan comes on and brings it back down. Just normal behavior. Most of the time cruising leaves it around the middle of the gauge (now that I've plopped a new thermostat in there anyway!)

The ECU has a different sensor to the gauge, but as you say you can't get the data out of them. You should be able to check it's resistance and calculate temp from that if you want a one off check.

I owned a Mazda Bongo for a good few years you have to keep a close eye on the temp and cooling system as by the time the gauge moves its too late.
So I bought this, now its not cheap but its ultra accurate and reliable and was for the 5 years I had it.
www.coolantalarm.co.uk/shop/index.php?_a=viewProd&productId=8
At the end of the day they fit these to very costly big earth movers so they are more up to the job than most, he also supplies low coolant alarms which are very good and saved me when I had a leak.
I got to know the company who market them and he wanted to do a test on some of these cheap Ebay ones and my van was one of the testers, whilst it worked and was accurate mine broke after 6 months, it was a mixed bag of performance about half the Chinese ones failed, but they are a lot cheaper.
www.ebay.co.uk/itm/STC-1000-DC-12V-All-Purpose-Thermostat-Digital-Temperature-Controller-Sensor2020/224020016376?_trkparms=ispr%3D1&hash=item3428a22cf8:g:xgYAAOSwtZFeyKRR&enc=AQAEAAACcIQvEcHUrT7nmUC3yY5qbPyaBN1nJEDYW8MyypsJPgXKetBSCbpa6EVEcxe8fAvGBNeE91R0HHbeweGTmRdqhgQKF%2FXbUVbZhoUnZaNoTGbmz2OhXxrxt9HMP8rsBdcg%2BJh6SIYAZqhXqDas0skwXBccHKYwSK6Nd%2F9oeB1ujm5WHnC4usjGJNLq8jXi%2FdIs%2Bjg%2FMl8KNHxbFHB5vSZnnw8MVDis41xDTdo0OfDuDa50wnATVyjxu7bRAhJIfFZz344nFadiFP9GTflByBorUSV4vaOJCXZRvQDDkMqgZxaUvu0Qbs93I8r2uDE9r1RpRdvRTwkNUfpODHWqUhuNwbb4zfqpttpLQgBEdGf%2FkU55rrKS6v3PBlVYzfcH68z3%2Fw%2FYz9OFSrV9Q%2BhuoBeXMNW%2BkFQ9MA8iRMcuuI6ol5TjROe6Y69IebYcEgAPqiBXcINdaQ8nzd1uYN7Y%2Fn3Duib1W%2FDxgF%2FJ%2Fq150sTAkpeviFME5ziPOOZe6fkOl1IFcMug4B7KCCn45y10HB2hjH3%2BPfI8eadwsZofCnZg8e0l8KhONDLbr1zotP9Dn1zCZg9WgG1ZTATy8I9l9NZFjlEKo4zZ%2B6CSaLvXDGa3iZ4fJfxukleGTGgEAO%2FKUg4rnTRSt%2Fq6cm5b7ZyJUlq4EubYnL22u0ZiPxOckHJffWNOrJWmo%2FmYFGARNsIIcAICav9yAzItloaX2E1cjg90j0XwjM3k8Ah6GYpdgfuvdN7yWAO8mP1k%2FihBdaF4vGPqC8Dn1ccFYT11HzPiWJyjpvRz8xhuv4VLr%2FDq%2BERI5Hi%2BLkKl61%2F7K%2BGLjtylJ51cyw%3D%3D&checksum=224020016376cc90a0f9a69d4508a02407f939e3dd6d

Are you talking about your 944?

If so, ensure the following is the case:
-The gauge movements are smooth and stable
-It doesn't randomly shoot up and pin itself to the top.

If that's the case I'd say the following. A 944 gauge isn't damped so it will move around like an older car would. Not many cars after that don't have damped gauges. it will go up to the last white mark before the red zone prior to the fans cutting in. It should come down quick however at this time of year and at this temperature. I'm surprised my M3 also has a semi-undamped gauge TBH! I will however say one thing.

If at this temperature in a 944, it takes more than 1 minute for your fan to go off and the fan operation seems fine, your problem will be one of two things
-Iffy Thermostat
-Poor radiator.

My rad in my 944 S2 seem fine visually. It wasn't massively corroded. However, the specialist who changed it noted the above and having raced many of them, knew the signs of it being bad. TBH I should have seen the signs then:
-Rad water was black ; it obviously had seen Radweld
-Fans would only cut out after 30 seconds in cold weather.
-Many of the heater hoses and other hoses were swollen.

There was a much much bigger clue. The engine was knocking like mental:



In short, due to an overheating problem, my 944 S2 saw 3 engines in its life. The last owner prior to me changed the engine. I then changed the engine after the 2nd engine went, and actually dealt with the root cause. The Long version?

-Heater matrix had been leaking, as had the rad at some point. Owner of 10 years put Radweld in.
-Rad's efficiency went down, I suspect it killed the engine (read on)
-Engine was knocking like above. A bad tappet can sound like that
-An idiot bought the car (me). £1.8k for an S2 back in 2010 seemed OK mind you, and low at the price point>
-I took the car to a couple of garages. Only one diagnosed the cause ; a Seized piston due to insuffient clearances. Cited cause either low oil or overheating. The bore was toast. That noise in that video is piston slap
-I drove the car until I found another engine. S2 engines then were between £800-1.5k depending on patience
-New engine fitted. Specialist noted and gave many notes on the car having a compromised cooling system as I advised. They advised I changed it prior to Spring arriving. Then it became apparent it was most likely a poor cooling system which had killed 2 engines prior to me buying the car.

On almost every car I have changed a rad on, even with regular coolant changes, I've always noticed a difference in the cooling temps. It's an item I now try not to go cheap on. I can appreciate 944 rads are not cheap anymore however.

But if your rad etc. is working OK as I've advised above, you're probably OK.