GT's 78

I have a question about a sending unit for after market heads. I have a 78 corvette with 383, the temp sending unit for stock heads is 1/2" pipe thread. The hole on my new heads is 3/8". What temp sending unit can I use for my stock gauge in these heads. Also while were talking about gauges too I have a question about those as well. The gauges I took out had a ceramic back with what looks like a connector that bridges between two contacts on the back of the gauge. The new ones I bought had a plastic back with no connector between the two terminals. Will this make a difference?

REELAV8R

Wilcox , You guys are awesome! I never even considered taking a temp sender apart.
Mine works good for now, but this will be saved in my favorites.

For guys without a lathe (most), I think you could chuck the sensor in a drill that is gripped in a vise and use a file to take down the retaining lip on the sensor to get the cap off.
It's worth a shot vs just throwing it away.

0Willcox Corvette

If you purchased new gauges, the resistor is inside the gauge instead of externally mounted. Do not use the ceramic resistor with the new gauges.

I know they are pricey, but they are made one at a time. http://willcoxcorvette.com/advanced_...eywords=sender

FireballXL5

Update:

Cleaned the terminals on the two temp gauges that run my water temp and aux fan... Took a mini wire wheel I had for my dremmel and brushed em clean... Tightened the connectors a little bit after cleaning them too... Tested ohms on the temp plug at cold and it's around the 600 ohms range. Was hoping this may do the trick...

Started the car and drove to work ... No temp still at the water temp gauge... Oddly enough, when I shut the car down and switched the key to the auxiliary position to listen to music before work the temp gauge raised slightly above the 100' mark... ???.. Turn the key back to the run position and the gauge drops back below the 100 position where it's ALWAYS been. Dunno what this is telling me besides I'm not getting enough input through the wiring, or the temp sending unit needs more TLC, or replacement... I didn't pull it out of the block yet, just cleaned the terminals...

Don't think I got any reaction from the aux fan either...

Lastly... Found the wire for the oil temp gauge ... Grounded it and it pegs the oil temp gauge! Hooray, they all WORK! Now I just need to get em proper signal. Downside... There is no oil temp sending unit installed above the oil filter... Perhaps the PO didn't get it reinstalled with the motor swap.. Will look for suggestions on what to get and where to put a new one in later...

I had an odd thought... What if I don't have enough, or proper grounds running to the block? Could THAT be why none of these engine mounted sending units are not working properly? I do have a ground wire running from the block to the Frame on the A-arm it looks like. .. The one that's tucked up behind the starter on the pass side... But it runs dangerously close to the headers and I'm pretty sure the wire coating is burnt through... Will look into grounding the motor with new straps before I go too much further... Just to eliminate the possibility... Any new thoughts? ;-) thanks

PGPierce

Get your self a catalog Volunteer Vette Products catalog, no #139,go to page 101 You will find Temp Gagues from 63 to82..This isn't complicated Guys.

FireballXL5

I'm beginning to become very familiar with the system ! Lol. And all signs are pointing towards my sending units... Or a slim chance of poor ground to the block...

When I first posted about this I had no idea what I was doing with these gauges ... And sending units... Through all the great expert help here it's becoming increasingly simple! I concur with your statement... It's just a little daunting for the newbie or novice... I appreciate it greatly, all the helpful tips and patience with my 'Learning curve' in this matter ... It does seem to be a often brought up topic, and every post about successes and failures in the diagnostic process could very well help the next guy in a similar situation... So... My troubleshooting continues, and I thank all of you for your help! ;-) Carry on.

0Willcox Corvette

***

0Willcox Corvette

You keep posting, we'll figure this out..

FireballXL5

Oh, and that little jump up in the water temp gauge that I was hoping was some kind of signal making it through... Was not... It's still sitting just above the 100 mark after being in the parking lot all day, and will jump back below 100 once the key is in the run position...

I don't know if I will get ANY better results after removing the temp sending unit and 'cleaning' the outside of it anymore ... I really think my two options are verify a solid ground wire going from the frame to block, and then purchasing a new sending unit.

I have no obvious signs of overheating of anything... Just want my gauges to function so I can keep an eye on the engine... ;-)

As for my oil temp sending unit not being present... Not sure what I'm going to do there yet... The wire appears to have a single female spade terminal on it if that helps at all... Perhaps the original one I bought and thought was wrong could have been correct... But at this point , if I buy anything, it'll be through Wilcox... You've earned my respect and business!

0Willcox Corvette

Have you watched this?

If the dash unit is stuck on 100, then it is not getting signal... Ground that wire out and see if the gauge goes to full hot.... If it does and you cleaned and re-installed the sender then you have a bad sender.

Testing a 68-82 Temperature Gauge -or- What your non working gauge can tell you!

FireballXL5

Yea, grounding the input wire makes the gauge go full hot... As far as cleaning goes, I took a dremmel with a small wire wheel to the posts, and wire contacts... I have not taken the sending unit out of the block yet... Would pulling it out of the block and shining it up potentially offer any help? Would trying to ground out the base with a wire help to eliminate a possible grounding issue? I don't necessarily think I have a grounding issue... Just trying to eliminate possibilities... But I'll probly end up picking up some new sending units at this point. ;-) I'll be in touch later to get the ones I need from you... Thanks for all your help...

0Willcox Corvette

I would pull it out, clean the threads and then take an ohms reading... If you don't get a reading, then I would take the sender apart as defined above, clean it and epoxy the cap back on.. it'll work then. If you purchase a new sender, it will not read correctly.. but I do have a fix for that coming real soon.. btw.. The gauge is not getting ohms.

Willcox

AirBusPilot

I installed the new sensor from Zip, and it works perfectly. Highway reading was the middle mark, which would indicate about 160*F (thermostat). Saw as high as 210 when the electric fans kicked in. I'll take an ohms reading of the old sensor (which admittedly had teflon tape remains on it).

AirBusPilot

Old sensor reads about 1000 ohms, at least according to my old ohm meter, which doesn't appear to be working right.

0Willcox Corvette

From time to time we'll find a sender that is working near correctly.. except under higher temperatures.

For instance, look at the required inputs for the 68-74 gauge. The sender may work perfect from 0-190 degrees.. or so... But when the thermister is not capable of going down to the required 79 or 65 ohms.. you may over-heat..

The other issue is they will reach lower ohms faster than the actual temperature. Or showing a "hot" condition when one does not exist. The best friend for anyone is the IR gun..

If you sender is cold and reading 1000 ohms heat it and see what it does. If you heat the sender, the ohms should fall. A lighter will work just fine for doing this and you should see movement pretty much instantly.

Or are you showing 1 for infinite indicating an open circuit? Use the 200 setting and see what it reads.

Mark_Milner

Thanks for all the information on this. That was great.

These bad senders is a reason I bought several old ones long ago. I find it a terrible mark on GM that they can't build something today so simple as a sending unit and keep it as an accurate match to what they made 40 years ago. It isn't brain surgery after all.

0Willcox Corvette

My pleasure Mark... I stashed a few of those old senders too.

0Willcox Corvette

ttt

AirBusPilot

Mr. Wilcox, I see on your web page you sell a water temp sender. Are these modified to work correctly?

I ask because the sender I bought over a year ago appears to be failing. I did the gauge test, and that works. I'm now getting erratic readings with the 'new" sensor I bought awhile back from another vendor.

Thanks.

0Willcox Corvette

You don't need a sender, you need this to correct the issue:

https://willcoxcorvette.com/catalogs...table+Resistor

There isn't a perfectly working sender but with this adjustable resistor you'll be able to dial in the gauge to match the sender.

Willcox