Temp gauge/sensor reliability

[sam.pej]

In the hot weather last weekend my temperature gauge was reading about 105 degrees despite the fact I thought I had solved my cooling problems since fitting the V8! I thought I had better check out the accuracy of my gauge. As I had to order one or two other parts I sent off for a new temperature sensor from Rimmer Brothers. I thought I would test it before fitting so connected it to the gauge and dipped it into a cup of boiling water. The gauge shot up to 115 degrees. Brilliant I thought... my gauge over-reads and so the engine is not overheating. I fitted the new sensor to the engine and then thought I would test the old one. On dipping that in boiling water the gauge slowly crept up to just under 100 degrees. Now I am confused. Is the gauge accurate? Which sensor is accurate? Why did the old one react so slowly when the new sensor caused the needle to zoom up to temperature. Should the sender and gauge come as a matching pair or will any gauge work with any sender?

[dave_kitson]

Re: Temp gauge/sensor reliability

Hi Paul
You should always use the correct sender for the make of gauge, eg VDO sender with VDO gauge. The chances of matching say a Ford sender with a Smiths gauge are a bit slim. The same argument applies to most gauges.

I once had a Pinto engined car, with a temperature gauge in it with no makers identification (though possibly a Stewart Warner). The engine was clearly running at a sensible temperature but the gauge (attached to a Ford sender) showed 120 deg C. On enquiring with Burton, it appears that Pintos had 5 or 6 different senders fitted, depending on application, with different outputs, and distinguished only by a coloured band. There was no information to say what the outputs were. I tried another and the gauge read 60 deg C! Without going through them all at 10 pounds a time I'd never get a match, maybe not even then. Probably Rover V8s used different senders in different vehicles.

I doubt that the gauges (or the senders for that matter) are that accurate. In fact, a lot of gauges on production cars - if they even have one - just show cold-normal-hot. The other difficulty you may encounter if you fit a sender that is not the original for the engine, is the thread. Easy if everything is metric, but often they use tapered pipe threads on such things. Don't despair! If you can identify the thread, Europa can supply adaptors that cover pretty much all combinations.

Hope that sheds some light, and doesn't make you overheat!
Dave

[sam.pej]

Re: Temp gauge/sensor reliability

Hi Dave
I bit the bullet and bought a new gauge, sender and adaptor from Europa. Now the gauge says the engine is running at around 80 degrees C which seems rather low, especially as the elctric fan is coming on even though I have set the adjustable dial to 90 degrees! I wonder if my electrics are faulty given the charging problem I mentioned in a nother thread? At least the stainless windscreen surround looks good!

[chris_cussen]

Re: Temp gauge/sensor reliability

Most modern guages are internally voltage stablised, so if the rest of your electrics are working OK it is unlikely to be your charging problem.

Are the temp guage sensor and the fan sensor in close to each other in the water system? There could be some difference if they are far apart. Also how confident are you that the adjustable dial on the fan sensor is accurate?

I would expect the temperature gauge to read approximately the thermostat full open temperature under normal circumstances, i.e. driving along at a reasonable speed (50-70) to give adequate air flow and a relatively cool morning.

[dave_kitson]

Re: Temp gauge/sensor reliability

Hi Paul
Glad you've got the screen surround on ok, just don't scratch it!

As Chris says, the temp that the thermostat opens is probably the most accurate thing. It could be checked by putting in a pan of water with a thermometer and heating it up till it opens. The correct temp should be stamped on it.

As a further illustration of how these things can vary, on my car, if I turn the lights on, the temp gauge reads 10 degC higher! Had me worried first time. I guess that despite all new matched components, there is some sort of voltage leak, possibly from the gauge illumination. The other gauges are ok though. No idea where to start looking, so I live with it for now. Don't drive it at night much anyway. Unless anyone out there knows of course!
Cheers - Dave

[lizbillings]

Re: Temp gauge/sensor reliability

Hi Paul. Our temperature gauge on our Cabrio alters if we put the lights on and reads higher. Regards Liz

[CABRIOBOB]

Re: Temp gauge/sensor reliability

My Cabrio temp gauge reads about 10 degC higher to about 100 degC when the heater fans on max speed then drops back instantly to about 85/90 when switched off.

[chris_cussen]

Re: Temp gauge/sensor reliability

WoW!
I've got ETB gauges and they are rock steady under all electrial loads (except the fuel gauge which is all over the place anyway as the fuel surges in the tank).