The Stovebolt Site Forums The Shop Area The Electrical Bay coolant temp sensor

Hi Fellas,
I am working on our 1959 Chevy apache 3100. It has a 283 with an aluminum edelbrock intake. When I bought the truck, it already had that manifold installed. The P.O. had a set of aftermarket gauges that were working ok. We purchased a new gauge cluster due to the fact that nothing was working on the old cluster anyway. I got the fuel gauge working and the oil pressure and the amp gauge all working, but the temp sensor is giving me a fit. The gauge goes full hot when you touch the sensor wire to ground. I've tried two different sensors one from parts store and one from Summit racing. They were marked on the box as for a gauge not a light. Using a volt/ohm meter I get zero ohms when touching probes to top and bottom on the sensors. I also used a heat gun set to 220 deg. while holding the sensor over the heat gun and still Zero ohms. Doing this same process with the sensor attached to the wire and holding the sensor on the engine to ground it the temp gauge pegs out hot.

I need the piece of the puzzle I am missing. At first I thot the aluminum intake wasnt providing a good ground, so I attached a wire from the eng block to the sensor and wrapped bare wire around the brass neck of the sensor and pinched it with a steel spacer which should have been a good ground. NADA. Even ran the engine until my hand held temp reader shows 180 deg and NADA on the gauge.

Is there a 30 ohm temp sensor I need like the fuel sending unit? Anyone have a part number? Maybe LMC trucks?

The wires are all new. The P.O. replaced the entire wire harness and I ran new 16ga wire to the gauges.

Sounds like they keep giving you a temp sendor. Look at Autometer, VDO or Stewart Warner for one of their sensors that match the gauge you have. Most of the time they post their specs at their respective web sites.

The speedo can be a worn sender gear. That’s my bet. If cable is new. Then it should not be broken you see that on broken ones work at low speed. Also could be a worn end female side on either gauge or sender. Ther is a good tech tip I think that has how to service and lubricate the gauge correctly.

Thank you for the recommendations I will look into those temp sensors, and I need to get another gear for the transmission end.

Roadking53, On your question concerning the speedometer issue, please post a new thread in the Driveline forum as that is the correct forum for that topic. Just trying to keep topics in the best places for helping you out.

This is your sender. The green wire goes to that and the gauge. Power to gauge comes from ACC at the switch. Pink wire.
I don`t know of a ground

It's grounded by virtue of being screwed into the engine.

The manifold and brass threads are providing a great ground, no need to add anything. I would say it is the wrong sensor also.

Do you guys think the aluminum intake will still provide a good ground? The engine has 2 new ground straps to the firewall, one on each side.

Roadking53 lets start with some testing.

here is a write up i found a while back.
To your question yes the aluminum intake will provide plenty of ground (completed circuit) with the straps. Do not use any tape or pipe dope on sender.

see below for other items.

Power on the driver side of the gauge and wire to sender/sensor in engine on passenger side pin.

The temperature sender changes resistance as it warms up. When it's cold it has 500 Ohms resistance. When hot it has 50 ohms.
Gauge testing; When the sender/sensor wire is disconnected the needle should be below C. When sender/sensor shorted to ground the needle will go above H. if it always stays hot no matter what then there may be a chafe somewhere or the gauge is bad.

If you have an ohmmeter you can check the sender. Measure resistance with the engine cold and the gauge disconnected. Should be 500 ohms or greater. Start the engine and idle until warm. Resistance should go down to around 50 ohms or less.

If you have some resistors you could connect them between the gauge wire and ground to see how the gauge responds. Again, 500 ohms for cold and 50 for hot.
Measuring your gauge will also tell you how it scales for future adjustment.

Also try moving the wire harness with the key on to see if the gauge goes to H. Short testing

IMPORTANT: The original gauge calibration puts the temp gauge near the center of the range around 170 to 180 degrees. Running a 190 thermostat usually causes the needle to rest much closer to "hot." If your engine is averaging 195-205 that's going to put the needle at "Hot." Aka the LS guys get burned on this one because they think its hot when its not.
You can add a resister in line to scale it appropriately for your setup.

hcb3200

Thank you very much for the response. One thing I failed to mention is the entire wiring harness has been replaced before I bought her. Also I made up a harness for the cluster with 16ga wires all correct colors ect. Used a plug kit and the wire from the sensor to the gauge is new. Only driven the truck about 5 miles since rewire of dash.

When sitting with key off the gauge is at the far left ( only has 3 dots ). When I touch the wire, with the key on, to the engine at the sensor (ground), it deflects to the far right almost out of sight.

when I turn my fluke VOM meter to Ohms and touch top spade and bottom of sensor I get OL (open). I have not tried with sensor installed from top spade to engine.

I have a 180 Thermostat installed and at warm idle she reads 177 degrees F. using a hand held laser temp gun.

Will a TS-76 be the correct sensor I need?

interesting. if its open then you may have a switch type like used for fan on and off and not a sensor for a gauge that uses resistance.
put it in a pot of boiling water take it out with tongs and touch tip to spade if you get closed that will be your answer to that question.

I think the TS-76 is too modern

try Part # 53-811 temp sender its the 57-70s range for trucks.

Since you are in a 1959 unless someone has put in a different cluster from 55.2 (mechanical) or 56 (different resistance) you should be using the 1957 and up sender.

The stock one is not a spade. (but some new reproduction flavors with correct resistance have spades)
The real headache is GM was all over the map during the tri-five and 55-59 trucks with the gauges. So half the internet sites don't have the right information on compatibility.

If one of the parts books guys wants to look it up they can be a lot more accurate to the 1959 truck you have.

As HCB has said THIS is the correct sender if you have stock gauges.

Buy that, Put in on/wire per original method and try it. No testing with meters or wires touching this and that or heat guns or wrapping wires around sender turret.... start the motor and observe where pointer is and what it does after warm up. Then report exactly what the pointer does before doing anything.

We do not need a discussion about thermostats or anything else. With 3 dots, this is an approximation gauge.
These are the alleged specs:
220 degrees 88-72 ohms

Alledged specs are all over the place, you don't care what they are if you buy/have stock 59 gauge and stock sender and wire it correctly and don't burn out one by "testing". When we hear what the result of a new set/CONFIRMED correct set, we will advise next steps. One step at a time. So if you are at a point where you need help, wait for responses AND questions for you.

FYI: Aluminum is one of the best conductors known to man.
The brass neck on sender is not supposed to be grounded with a wire.
Use Permatex High Temp Thread Sealant.

This works with my 235 and 327`s. ACDelco GM Original Equipment 213-4792 Engine Coolant Temperature Indicator Switch.
I did not know of a ground wire to be clear. Yeah ,its ground to the engine, not by a wire.
This the other style sender

If you are going to install ANY temperature sensor lets follow manufacturers instructions.

DO NOT use Teflon tape on the threads. These threads are slightly tapered and designed to be self-sealing.

The sender uses the threads for its ground connection and sealant may cause a poor ground causing inaccurate readings.

If supplemental sealant is needed, we recommend using Loctite C5-A anti-seize. This is a copper based anti-seize which will allow a good electrical connection for the sender ground.

The threads I see are 1/2-18 UNEF. Not NPT. The word tapered is not used on the 53-811 senders I see.... or in the thread designation of a 1/2-18 UNEF. I believe that is a parallel thread.

By the way Van, there is a 53-811A sender. I find no difference in your case. It would be impossible not to get good ground when using permatex, threads have to touch. Teflon is, as said several times, not recommended.

Install dry if you wish and see if no leaks.
I have a feeling you will need an adapter bushing but I don't know what the Edelbrock thread is.

Bartomos you are correct sir. I was looking at a incorrect sender instructions. way to many tabs open.
and after doing more digging there are all kinds of ways. even crush washers on some versions of senders.
Devil in those details. But in the end it is knowing exactly what you actually have in hand and applying the appropriate methods.

I do have C5 in my shop. I was going to order that 53-811 or the 53-811A. I sent them an email asking about the thread size of the 53-811A. And inquired about a possible adapter if available. Mine has 3/8 NPT

Didn't orig sbc have the temp sensor mounted on the driverside directly on the head? Maybe I can install a pipe plug in the intake and see if I can get a plug out of the head. I'll bet that 1/2-18 fits there.
That sensor sounds like the very exact one I need.

Thank you fellas very much for the responses! Much appriciated. I know it seems like a simple problem but I was getting stuck.

Chevy heads and Edelbrock manifold are pipe threads, if you find a factory installed plug in the head I doubt you will be able to remove it. My original '57 sbc heads have no threaded ports, my sender is in the original cast iron 2 bbl. manifold.

This how I saw a 283 that looked stock had its temp sender location. Thermostat housing.

Wherever it ends up just make sure it has good flow over the tip. not tucked in a corner or pulled back into some adapter that does not allow the tip into the flowing fluid.
or in a location where it could have air trapped around it.

I can not figure out why a so called original replacement sender has 1/2-18 threads and no bushing found for that to NPT? VERY odd. It almost seems like the cast iron intake had 1/2-18?
Buckshot should be able to give us an idea of thread size in cast iron and sender PN from his 57...... or a pic or two. i know that is a bit moot with Van's Edelbrock but we need some history on this weird thread or a bushing PN.

Also Van, what is the part numbers of senders you tried and what thread is on them and what size is in the aluminum manifold ?

Problem with that placement of a temp sensor is that if the thermostat sticks closed you'll never know it until the engine boils over.

78Buckshot Our truck came with the aluminum intake. I wish I had the original cast iron 2BBL manifold. The P.O. had a dual line 650 cfm on it and it was way too much for it. The heads are original single hump I think they are 220 hp, but I have not looked for a plug yet.
The P.O. told me to add lead additive bc the valve seats are not hardened. Anyway we put a 450cfm with a square bore adapter plate. She likes that much better. I dont mean to ramble and this isnt the category for engine talk just electrical. (I got sort of warned).

Bartamos its a performer spreadbore intake is all I know. I don't have the part numbers for the sensors handy (im at work Tues am). I do have the boxes they came in on my workbench still, I can post them later. Anyone need a spare :-)

Thank you all for the help and suggestions. I will keep this thread updated when I find a solution.

From memory I think the stock Chevy manifold and later heads have a 3/8" NPT, I'll try to confirm that and also post a picture of mine. I do have some '70's sbc heads and Q-Jet manifolds I can look at for comparison. The thermostat housing with the threaded port is not used for the temperature gauge, that is a later housing and the port would be used for a temperature switch used in some spark/emissions equipment.

I'm waiting for the pictures to get to my email. From what I can see on my '57, the threads are probably 1/2" pipe. The heads from the '70's have 1/2" pipe threads and that is the time the factory moved the sender from the manifold to the drivers side head. I also have a late '70's factory aluminum Q-Jet manifold on a 383, it has the 1/2" port for the heater hose and a 3/8" port for temperature, probably a temperature switch for emissions. My best guess for the temperature sending unit for a gauge in 1959 would be 1/2" pipe thread.

Edelbrock aluminum and tape. Works perfect.

OK so no confirmation about odd 1/2-18 thread, so I am forced to use logic because I have reached the end of the internet. The 53-811 is 1/2-14 MNPT and the vendors errored and have all copied each other or their supplier gave them the wrong thread designation.

1/4 NPT(F) is APPROXIMATELY 1/2" OD, and has 18 threads per inch. But it's NOT designated 1/2-18 NPT. I think the confusion was trying to designate it based on APPROXIMATE OD.
First pic is NPTF (National Pipe Taper Fuel) dimensions, which is a dry seal thread pattern.
Second pic is NPT (National Pipe Taper) dimensions, slightly different than NPTF in that it requires a sealant.

There's also 1/4" NPSM that's roughly 1/2" OD (0.54") with 18 TPI, but normally has an internal 30 deg chamfer for sealing with a female fitting that has the matching chamfer inside.
Third pic is NPSM (National Pipe Straight Mechanical)

Elkers lists it as 1/2-14 NPTF. A variation of 1/2 NPT for, as said, "fuel". The "F"ers should seal without sealant. NPTF will thread into NPT but may or may not have quite the same seal. May be good enough for Government work or GM. Guessing Edelbrock has just 1/2-14 NPT. (when I've sealed up unused manifold ports, I used hardware store NPT pipe plugs.)

Top of the thread will measure about .800 for either. Same taper. Same pitch.

So to reiterate my logic post, consider the 53-811 as 1/2 NPT....and note that the thread has been mis identified in some places. No big deal it just bugged me no end.

I think a female unshrouded spade terminal works on a turret top/nail top sender if you don't have a connector. Can't remember if it's the 3/16 or 1/4. Probably 3/16.

ok I went by summit and bought a stewert warner that boasted 100-230 degrees. The gauge is now at least reading about 3/8 on the gauge. Still not the correct one but I'm closer. Maybe if I install some resistors parallel in the circuit I can reduce the reisitance of the circuit.
I'll have to research that a little deeper. Hopefully these pictures load ok.

Here is the latest pic of Baby

Very nice looking truck.

Roadking53, if it helps ease the concern of being mis-matched, my original 1957 gauge registers very close to what yours does. I have also installed a secondary mechanical dial gauge because I was concerned of the running temperature. With the AutoMeter gauge reading 180 degrees, the factory gauge is between the first and second marks.

Thanks bartamos :-)

78buckshot: Thank you for that information ! I think Im going to let it ride for a while then. All we are worried about is for the truck to let us know if She is getting hot.

If I find some info for resistors in parallel I will post it. I had a friend who is an engineer tell me about that idea ( I aint smart nuff to figure that out)!

The correct gauge and sender need no resistors.

"Problem with that placement of a temp sensor is that if the thermostat sticks closed you'll never know it until the engine boils over."

Probably right. I found a pic of the housing before I cleaned it up.
Definite TEMP sender there. Thats a 1958-60 283

The 283 block might be 1958 - 1960 but the intake manifold is a Q-jet manifold, Q-Jet wasn't brought on board until1965, the water neck could be from any year as they are all interchangeable. It certainly is a temperature gauge sending unit but that port was used for emissions/spark/heat riser control.

Yes , good spot. It was upgraded with the manifold. Most were?