JackCooper

The electrical prong on my temperature sending unit has brocken
off, and the unit is stripped (the casing that the wrench turns)
where I cannot get it out. It is not leaking or anything, but it is
useless.

So I pulled the plug out the other head and am going to put the new
sending unit in the passenger's side head. My question is, if I make the
wire longer so that it will reach the new location of the sending unit, will
this affect the calibration of the guage (by weakening the signal due to
an increased lengh of wire).

Thanx,
Jack

Smokehouse69

Jack,
The extra wire won't have much effect on the gauge, what will have an effect is trying to find a new sending unit that is very close to your old one. While looking for a sending unit to fit in my new heads I found a tremendous variation in sending units at parts stores. Some out of the same box gave me much different readings while checking them with an VOHM.
Good Luck!

R1234

Smokehouse69, I've been trying to get my temp guage to work for awhile now. Here are the symptoms : when guage hooked up the needle goes all the way over to the right. When I ground out the temp lead it does the same thing. I'm using a new sending unit from a local parts house and a new NOS temp guage. Could the new sending unit be the problem? What are the correct ohm readings for a sending unit?

Frankenvette

For six months I thought I had an overheat problem. I did everything to fix it. I finally found that someone had the wrong temp sending unit installed. What a pain in the a@*. Anyway, make sure you use an A/C Delco brand unit. Don't trust a cheap aftermarket unit made in China.

Another thing I did to make sure the gauge was accurate is install a mechanical temp gauge for a short period of time. This gave me a baseline from which to work.

69Rdstr,
sounds like you could have an inadvertant ground somewhere. Make sure the wire from the sending unit to gauge does not have any exposed wire. Also try to route it to avoid contact with metal. Maybe somewhere in your instrument cluster the gauge is grounding. If you touch the temp sending wire to metal, the needle should move to the right. Thats why I suspect a possible ground somewhere. I had to deal with a problem with my volt gauge for a month before I solved that mystery. Good luck!

Regards,

Jim

71DropTop

I had the same problem with temps all over the place until I went to the AC Delco. the foreign crap just doesn't cut it :rolleyes:

R1234

Jim73, I thought it might be a grounding problem. I took the guage out of the wiring harness and connected it with jumpers. It did the same thing! When I connect an after market guage it gives somewhat of a normal reading
of about 205 degrees although I don't know how accurate. The engine does not seem to be overheating while idling.
71droptop, I going to buy a AC/Delco unit to see what that does. Hopefully,
that might do the trick.

I'm trying to get my interior back together but it seems like one problem after another pops up.

killain

I'll third the vote to use only AC delco sending unit. It is just about the same price and it works perfectly. 69rdstr, I think you have a broke wire grounding out between the gaude and the sending unit.

glen242

Foreign Crap - I bought a new Delco oil pressure sending unit from the local Chevy dealer at twice the price as at the local auto parts store. Where was it made? CHINA!

Could not return it as it was a special order. Seems to work ok, but the one from the parts store was also made in China and was cheaper.

JackCooper

I told the fellow at carquest the year and model of my vette,
and he sold me a sending unit.

I installed it, and it says that my freshly built motor is running
at 280 degrees about 30 seconds after it is cranked up cold.

So it is apparently incorect.
I held the wire to the old sending unit with my thumb, and it works
correctly (too bad there is no way to fix the prong).

Anybody got the part number for the correct sending unit?

Frankenvette

Give your local a/c delco store a call. They will have the correct part # and hopefully have the part in stock.

Regards,

Jim

R1234

Jack, My new sending unit that seems not to be working correctly came from carquest too!
One other question. How much of a correction in temperature readings do the resistor strips that are mounted between the pos. and sending unit terminals give you? Are these designed to give slight corrections and/or major corrections?


[Modified by 68rdstr, 8:59 AM 2/17/2002]

Corellian Corvette

Hey guys -- There was a big string on this a couple of months ago.

Don't spend too much time here. *All* the sending units are bad -- doesn't matter who makes them. You're going to have a VERY hard time finding a guage that reads correctly. The AC Delco units are not built by AC Delco (can't remember the exact maker, but they OEM for a couple of other sending units as well) and they are off. Delco has admitted this.

My 2 local vette shops confirmed this (and there was an article about this in VETTE, I believe as well) you really only have a couple of choices.

a. Go to your local parts store and hope they have a OLD sending unit lying around. You may get lucky and find one that works.
b. Go to the wrecking yard and pull a vintage one off another 350 of the same era.
c. Find a new one that reads wrong and at least you'll know how much it's off.

I had to go through 4 sending units before I found one that would even read below the red line. It had a plie of dust an inch high on the box, and it reads 40 deg too hot (had it checked at a radiator shop).

If anyone here FINDS one that works, go back to the same store and get another one to send to me :)

Just don't want anyone going on a wild goose chase.

theandies

If you can get an accruate reading from some sort of temprature probe on how hot your engine is running after warm up then any temp sending unit can be made to read correctly by placing resistior/resistors in series or parallel to the sending unit itself. All the older temp sensors/guages work off of resistance. You may be able to check the resistance of your old sensor and get to a close starting point. Thats what I did. If you don't know how to do this find one of your friends that know electronics and they can help you out. I used one of those RayTec Infrared temp guns when I installed my ZZ4 because my old temp sensor's connector was broken off. I played around with a new temp sensor and some resistors until I matched the reading on the guage to the reading on the RayTec. I check it every now and then just as a sanity check and it is always within 5 degrees of the RayTec. I tried 3 different sensors before I gave up and started playing with the resistance. One sensor would peg the temp needle another ouldn't even move the needle off of the low position and the last one I tried pegged the needle also. This is the one I used. I increased the resistance until it read correctly.
Good luck
John

Corellian Corvette

I believe that it was mentioned that, when adding a resistor, you are only correct at a certain temp. Since the resistance in the sending units is variable, you're going to be off on the cool and hot sides since the guage is linear. Since I'm not an electronics wiz, I'm not sure but I would think that would give you inaccurate readings, esp. if the car is overheating.

Just a thought...

Don Schuette

Yep, this subject comes up every few months. The old, outdated part number is 6400759. It has been superceded by another part #, which has the wrong ohms. Every once in awhile you see one on ebay for a "pretty penny." Mine was lost at the machine shop when I had my heads done, then I paid $33 with shipping for one. I then went back to the machine shop and they found it in their tank used for pressure testing heads.

So, I do have an extra one that I am going to cherish. When I was looking for the replacement, some other GM parts place wanted $80 for an NOS part.

I've been told to keep an eye out for them at the swap meets, they are pretty noticeable and most people don't realize what they have. And, it wouldn't hurt to check out the bone yards either, even non-corvette yards since the same part was used on different models, I believe.

If you find more than one, buy 'em all.


Don

Frankenvette

I replaced my temp sending unit with a Delco unit almost 2 years ago and have had no problems what so ever. Not sure when Delco changed their manufacturing, but I can't complain, and I only paid $12.00 for the sending unit.

Regards,

Jim

R1234

Looks like I'm going to the junk yards to see if I can get lucky and find an older sending unit.

Smokehouse69

Jim,
Which sending unit did you use with those Vortec Heads, or did you get them modified for the larger sending unit used on the older heads?


[Modified by Smokehouse69, 9:29 PM 2/17/2002]

Larry B.

Be careful looking for just ANY senders , Not everything with a V-8 chevy had gauges. One for an "idiot light" won't work. :nono:

Frankenvette

68rdstr,

The biggest problem with the vortec heads is the smaller diameter temp sending unit port. I went to the hardware store and found an adapter that fits the vortec stock opening and my temp sending unit. I found it in a box of misc stuff the hardware store had sitting in a box. The only problem was that the adapter had pipe thread. I just used some teflon tape and made a solid seal. No leaks yet! The best $.99 I spend in a while.

For those considering going to the junk yard to find a sending unit. The problem is that the sending unit has to be calibrated to the gauge. The resistance to ground is what gives you your temp. Not knowing if you have the exact sending unit could throw off your reading. Better to give the delco unit a try. If it does not work, then tack it back and try the junk yard. I would not really want to trust my engine temp to a 20-30 year old sending unit that may or may not be calibrated to my gauge. Just my .02 worth.

Regards,

Jim