I just finished putting in a crate motor in my 69 and was wondering the best way to solve the temp sending unit problem. My preference is to stay with the original gauge, but will the late model sending unit work with it?

 

No other sending units from later years will work with your gauge, and the later ones that fit the heads won't work with your gauge either.

On Curt's engine, with Vortec heads, I drilled out the bore and tapped it for the larger stock sender. It worked great so long as you get the proper drill bit, tap, and are very careful with shavings. I sealed up all the cooling passage ports and used compressed air on one of the drain plugs to constantly shoot air out of the bore I was drilling and tapping.

 

Could I put the sending unit in the intake manifold and expect some level of accuracy?

 

Yes, usually the heads are preffered location,
but everything feeds up to the manifold and out the thermostat.
I would think the temp at the stat, would be more averaged,
and you would not see any immediate temp changes.

 

Great....thank!

 

I have a question on this matter. The guage on my 69 reads about 220 most of the time, but the car does not seem to be running hot. The guage was supposedly recalibrated by "Clocks by Roger", but I am not sure I trust it since about half of the other guage work they did for me is no good. What is the best way to determine the actual operating temperature? Is the radiator temp comparable to the temp at the sensor? Thanks.

 

You can use the smaller more modern temp sender for your new heads but you'll have to find the one that works for you. I'm on my third one and it is "dead on". The temp sender and the guage are calibrated to each other.The temp sender has an ohm rating that needs to be the same as the one you are replacing.

 

Use an IR gun, pointed to various points on the engine. Get the beam right on the sender for a close to accurate indication of what temp the sender is seeing and then compare that reading to the gauge inside.

 

Remove sender and put it in a pot of water on the stove. Connect ohmeter leads to the threaded body of the sender and to the signal 'out' pin connector. Record resistance measurement at room temp (approx. 70F). Heat water to boiling, then turn off heat. Read resistance measurement and assume that it is near 212F. Now, put the sender back in the car and run it till warm. Connect ohmeter to signal 'out' pin and to block ground [same as sender body]. Take resistance measurement and record it. If the "in-car" resistance is between the "boiling" resistance and the "room temp." resistance, you know that the engine is NOT running hot. You can mathematically estimate the engine temp or you can plot the 70F and 212F resistance values on some graph paper, draw a line between them, and then you can work off that chart to find the [proportional] resistance for any temperature in its working range.

Now, if your engine is operating at about 180F and the gauge says that you are running at 220F, you can re-calibrate the gauge by adding {the correct size} a resistor in parallel with the sender unit. If you want to follow the above procedure and PM me with the results, I will provide you with a recommended resistor to install so that your gauge reads nearly correct.

 

Sending units may even read the correct ohms, you think you need,
However .... if they are not linear with the gauge,
your temp could be incorrect at either end of the Gauge scale.
Everyone keeps saying use an IR gun, But unless these are calibrated correctly these too can be off by quite a bit.

If I had any doubts about my gauge/ sending unit.

I would pull them out and test them with Hot water on the stove,
throw your thermostat in the pan with the gauge, to check it also.
with a good thermometer.
If you do not want to rip out your gauge, use a long ext cord to run over to the stove, and connect your singal and gnd. wires up.
69VETT

 

Once you know the sending unit's calibration and the ohms it registers at the engine's normal operating temp, you can calibrate ANY gauge. I didn't say the whole gauge range would be accurate...or even linear. But, if the gauge is correct at its normal op temp, why do you care? The gauge will still be approximately correct on either side of that temp and will definitely indicate when you have an overheating problem. Isn't that all we need the gauge for, anyway????

 

Lots of great suggestions here. I decided to pull out my temperature gauge and sent it to Clocks by Roger. He calibrated it to a smaller late model sending unit.

 

This thread is full of really good info. My temp gage in my '79 reads really low so I know it is not correct. I want to replace the sending unit but I'm not sure on how to get the correct one for the gage. I'm going to order this unit and hopefully it will work.

Thanks everyone for all the great tips and tricks.



Part #
303160 Description
TEMPERATURE SENDER - COOLANT

Year
1979-1980 Price
20.95

Package
EACH

 

Will do. Many thanks. I have an IR gun, but due to a recent move, I don't have a clue where it is! I guess it's time to pick up a new one. Thanks so much for all your help on the forum DB. Especially the car wash pics!

 

I used this sender & got good results more accurate than the original

 

Corvette Central makes the proper replacement sending unit for pre 72 cars so the guage works properly.

 

I just went and looked through the Corvette Central Website and I didn't see the "proper replacement" sending unit? thx

 

check with lectric limited, they make them, sell for $25

 

Lectric Limited unit worked perfectly with my original stock gauge.

 

It's right here for a '68.

303570 Description
TEMPERATURE SENDING UNIT

Year
1968-1971 Price
22.00

Package
EACH