Factory temp gauge problem

[briank]

I have a problem with my 70 jimmy 350 4bbl factory temp gauge problem. Gauge reads high after driving awhile....it basically pegs hot but it is not running hot. Engine is not original and has been replaced in 85 or so . Guy I got from recently said gauge was reading fine until he had a edelbrock intake...1806 carb with electric choke and a msd hei distributor. He said since all that was installed it reads high but he checked with a thermal gun and said its fine. Any ideas what to check? I have shop manuals but since the engine isnt original and wiring has been messed with Im at a loss. Temp sending unit is new and the same one he said worked prior to all the other work. On pass side I did notice a green wire and a black wire cut that may have been the original temp sending unit wires. Now the temp sending unit is on the drives side with a single wire running towards the firewall.

[briank]

Heres a picture that hopefully doesnt flip.

[demian5]

Originally Posted by briank

Heres a picture that hopefully doesnt flip.

If gauge slowly creeps up, it wouldn't be a disconnected wire issue.

Also, confirm the engine is NOT running hot yourself, don't take a sellers word. He may have installed the intake without a t-stat. Could be one of many possibilities.

[briank]

I need to find my laser temp gauge to check but when I do drive it and its pegged there is no steam or other signs its hot. When I popped the hood things aren't extremely hot to the touch. I may check to see if there is a thermostat in there since I have some coolant drained out now after replacing the heat control valve.

[dmjlambert]

Sorry, all I have is a bunch of questions, no answers. But stuff to think about. Where is the temperature sender screwed into the engine? Into the head between a couple of the spark plugs, or on the intake manifold? Have you traced the wire from it to verify it is the wire going to your gauge and the wire is in good condition? Do you have a stock gauge on stock instrument cluster, or something else, and is the sender the proper one that matches the gauge? What is your radiator situation, is it filled with 50/50 coolant/water and do you have an overflow tank on it or does it keep some air in the radiator, and how full is the radiator? Do you have a clutch fan and is the clutch working ok?

If your coolant system is OK and temperature as read by another device is OK, then you could simply have a sender that does not made to match your gauge or wire is burned or frayed.

[GASoline71]

I'm guessing the new location for the temp sending unit is in the intake manifold. Worst place for it, if that's where it is. The green wire might be it, if the PO ran a longer wire over to the passenger side. The stock location is the forward port in the drivers side head between #1 and #3 cylinders.

Gary

[briank]

Factory gauge with factory cluster. The sending unit is on the drivers side as Gasoline71 describes. The sending unit is a vdo 118 6-24 v and I think it also had 8/10 on it. Havent been able to check the temp yet...does have an overflow tank added..I did notice coolant level was low..has the stock 7 blade clutch fan and it had a broken shroud which I just replaced to today with a nice factory one. Wonder if the sending unit is wrong...any suggestions on one to try?

[Boog]

There are several sending units available. The gauge uses a different sender than a temp light. I was sold the wrong one for my application and will have to buy the other one.

[dmjlambert]

I think that is the wrong sending unit for the factory gauge. It has been discussed before on other threads you can only use the stock 1/2" threaded sender. If you have a 3/8" threaded hole you can get a 1/2" sender and have a machinist turn and thread it. I had forum member A1971Blazer turn and thread mine. Other people had it done by brian mac. I used GM part number 12334869, AC Delco number G1852.
More discussion here:
http://67-72chevytrucks.com/vboard/s...d.php?t=703388
http://67-72chevytrucks.com/vboard/s...d.php?t=627880

['68OrangeSunshine]

It was about 18 years ago that I put in another crate 350 in my '71 GMC, so my details might be fuzzy: I was told the elec water temp gauge on the ''new'' engine was different than the 1971 stock unit, and needed a couple of resistors [forgot the value] in-line to the gauge, but that was supposed to make the gauge read right. I tried the shadetree solution and it wouldn't work at all. Since I live in Arizona full time, not having a precise water temp indicator has cost me a couple of engines, so I gave up on the redneck avionics solution and went with an AutoMeter mechanical gauge. Very happy ever since.
I still have an elec temp sensor in my t-stat housing but voracious packrats love that green wire. Mech temp probe is in middle of Cyls 1 and 3.

[briank]

I think the sending unit I took out was 1/2 but Im wondering (after googling and reading up on these) if the ohms werent correct for the factory gauges. I may pickup a different one tomorrow to try. If that doesn't work Ill try everything else.

[briank]

Ok...pulled it out again and it is a 3/8. I guess Ill get the right one turned down by Brianmac.

[demian5]

Originally Posted by briank

Ok...pulled it out again and it is a 3/8. I guess Ill get the right one turned down by Brianmac.

Please return with the results and post what was next. These posts help others using the "search' function.

[rockyrivermark]

Originally Posted by demian5

If gauge slowly creeps up, it wouldn't be a disconnected wire issue.

Also, confirm the engine is NOT running hot yourself, don't take a sellers word. He may have installed the intake without a t-stat. Could be one of many possibilities.

Exactly. That is step one.
Posted via Mobile Device

[ElKotze]

Napa # TS6469 is the sender I always use. Works great with factory gauges and has the right thread.

[briank]

Isnt the napa one 1/2"?

[demian5]

Did you confirm that disconnecting the sender (with the ignition on) takes the gauge back to C?
Did you ground the wire (with the ignition on) and confirm the gauge goes to H?

Looking at your picture I would say your sending unit is not the correct resistance range for the gauge.

You can look for resistance values for the factory sender in relation to temperature and verify the readings with a DVOM.

Your solution is somewhere in the link below, let us know what part you had to replace.

http://forum.73-87chevytrucks.com/sm...?topic=25339.0

[briank]

Ok...got a turned down unit from brianmac (thanks dmjlambert for the links of previous threads mentioning him.) Problem was the stock gauge and use of the newer 3/8 units that aren't designed to be used with our factory gauges. Since my engine had been replaced with a newer (circa 1983 goodwrench engine) it had the newer heads which uses 3/8 unit. The original used 1/2 which has a much larger probe that sticks in the coolant. I replaced the temp sending unit , replaced and used the correct connector for the original temp sending unit, refilled the system, took it for a drive and it seems to be reading correct now. If it does read high again, Ill post to advise that the temp sending unit wasnt the problem, otherwise it's fixed. Thanks again.

[demian5]

Rad. Thanks for the results. What was the part number and manufacturer that worked?

Did you measure resistance just for kicks to see the differences between the two?

[briank]

Box shows it to be a BWD wt203 that has been turned down from1/2" to 3/8". I never checked ohms......took it out again tonight and still going good. I recommend BRIANMAC for this fix to anyone having problems.