Temperature Sender Options

[gtsmrt]

Hi,

What options are out there for replacing the temperature sender on a Tiger. I have recently replaced the standard intake manifold and carby, but the rest is stock 260. I have the stock temp gauge, so do I need to recalibrate the gauge?

Thanks, Robin.

[Tom and Joanne Ehrhart]

I was never able to find an alternate Temp sender unit in all the years I was in business. Yet I suspect there are some with the same electrical characterisitics with different thread sizes than what we use in a Beam. These would be Brit cars in the mid 60’s with gauges that used the instrument voltage stablizer (regulator) that supplied the bi-metal thermal gauges like we have in our Beams. These were popular gauges used in many Brit cars. The faces may be different but the internals are the same.

Some of the sender units I had seen had smaller diameter threads
than what we use on our Beams. If that is your mssion, keep looking. Bet you will find one.
Merry Christmas………………..TT

[gtsmrt]

Hi,

Thanks for the reply. I did some running around to a few auto parts stores today and I have ordered a temperature sender which is not Rootes, but may suit. I will measure my current sender and compare it with the new sender once in my hot little hand (early new year). The only other issue is that the thread is 1/8 BSP where my current sender is 3/8 BSP (that is not an issue).
I will let you know if it works out OK.

Merry Christmas, Robin.

[Tom and Joanne Ehrhart]

Many years ago when I ran a development laboratory, I did a statistical study on dozens of sender units and gauges to determine resistance values of sender units at various temperatures and equivalent voltage levels required for gauges.

I can’t find the resistance data for senders but I still use the voltage levels to calibrate gauges. With respect to the sender unit, I do remember that I could not substitute a resistance device of the same resistance as obtained from the sender unit and get similar results with the gauge. I suspect that with the gauges approximate 100MA current through the temp sender that there is internal sender unit heating occurring which in turns affects the actual resistance.

In your case, since you are comparing old and new units, a basic temperature/resistance test should correlate for same temperatures. The main reference I’d use is boiling water.

The following info applies to all thermal type small gauges used in the mid-sixties, whether its a fuel or temp gauge. Each gauge has tiny marks at the minimum, midpoint and maximum on the face above the numbers. The marks are either two dots or a dash line. The following voltages are required for Min, Mid and Max points. 1.89, 4.95, 8.00. A constant current/voltage power supply capable of at least 100MA is required to test. The voltage must be measured at the meter terminal.

[stu]

Tiger Tom provided much useful information for the article I prepared for the TigersUnited web site. If you are interested in learning more about what you are up against when trying to replace a temperature sender, take a look at:

http://www.tigersunited.com/techtips/Br … Gauge1.asp

Stu Brennan

[Tom and Joanne Ehrhart]

Stu, thanks for referring me to the early info. I had it buried somewhere and didn’t want to dig it up when responding. You’ll notice that my recommended voltages are slightly higher than those calculated from resistance.

I found that the voltages calculated from resistance measurements were providing lower than normal gauge readings. I have some theories about why. But none the less, I reversed the procedure. I measured the actual voltage required to get repeatable measurements on a a bunch of used gauges. It was amazing how consistent the gauges were with the same voltage inputs….despite how ugly they looked. The gauges really are quite rugged. I use an HP voltage and current regulated power supply. When measuring voltage to two decimal places it is important to note where the actual voltage is measured. It certainly isn’t measured at the source. I measured on the threaded round nuts of the gauges to eliminate lead and termination voltage drop.

[gtsmrt]

Hi,

Where is the best place to mount the temperature sender when using an aluminium intake manifold? I have mine mounted at about the centre of the water cross over, but I find that it is reading high. Is it better mounted closer to the thermostat?

Thank you, Robin.

[Tom and Joanne Ehrhart]

You are correct. The water passage associated with the output of the intake water to the T-sat will give the best average eng. temp. In the scheme of things, you really shouldn’t see any significant temp difference of water anywhere in the intake. Water temp in the intake is a product of head output temp so the temp should be relative uniform unless you have head or gasket registration issues.

If you have what appears to be too high a temp, validate the actual reading. I use an IR Temp gun to measure and validate what I think I see on the cars gauge. I look for possible causes of temp measurement error once actual temp is verified. If reading high, its most likely an incorrect temp sender unit or instrument voltage regulator. I don’t ever remember finding a temp sender that will cause high temp readings. Maybe low, but not high.

[gtsmrt]

Hi,

Thank you for the reply. I have been thinking about the sender side of things and was wondering about the earthing of the intake manifold. I do have an earth connected to the intake, but I might try a different position. I also sealed the sender with some teflon type paste sealant which may also be effecting the earth. If the regulator was playing up, the fuel gauge would also be wrong.

Regards, Robin.

[Tom and Joanne Ehrhart]

Poor or insufficient grounding of intake or sender unit is not a cause since you stated gauge reads high. Poor grounds will cause gauge to read low. You are correct that a improperly functioning instrument voltage regular will also affect the fuel gauge. Good point. But how do you know for sure the fuel gauge has not been affected as much as the temp gauge? Since it is near impossible for an owner to validate fuel gauge accuracy without removing the fuel sender unit, I wouldn’t try to validate the fuel gauge at this time. So it’s back to validating the IVR. The falure modes for this device are that it typically cause the gauges to read too high or not at all. A simple test you could do is to get one of those cheap 12 test light probes and touch the point on each regulator terminals. One side the light should be on constantly. The other terminal it should have a very erratic flashing light. On for a fraction of a second to several seconds and constantly flashing. The case of the IVR MUST be securely grounded. Make sure the mounting screw is really tight and the IVR is secured.

TT

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