chlout

My '61 came with a different engine than stock and was pretty well shot. I bought and installed a new 355cid/375hp small block and everything has gone fine except with the temperature sending unit. The old one would not fit because the diameter of the sender was too large for the new engine. I went back to Jeg's (where I purchased the engine) and they sent me a sending unit to fit the new engine. Problem is, 5 minutes after running it, the temp gauge pegs over to 220. I made sure there was plenty of coolant and even though the gauge reads 220 the water is not even hot (I stuck my finger in the overflow tank. I pulled the water neck, coolant was there, and replaced the thermostat. No change in the reading. I called Jeg's and they said the sending unit they sent me would have been for an after market temp gauge, I am using original gauges. Their recommendation was to add an after market gauge. I really don't want to add an under dash gauge in my very nice stock interior. Anyone been here before? Any suggestions?

redred65cpe

Simplest thing to do is get an IR temp gun and record the temp at the base of the "snout" for the top radiator hose over the thermostat and record the temp gauge reading. It won't take you long to remember that a gauge reading of 220 is 170 degrees coolant temp, for example. Even calibrated, spring loaded gauges have a sweet spot of accuracy for some temp range. Also, if you do this, it's probably best to record the temps with the thermostat removed. This will make it easier to get an accurate temp of the coolant with the IR gun.

My temp gauge reads 220 or so and my coolant temp is at most 180.

larry

Donald #31176

One option is to contact Rick Stotler in Joppa, Md. He can calibrate a new sender to your gauges spec. His business is called Ricks Restoration. He used to do the gauge work for Corvette Specialists of Md. before going on his own.

420 Foster Branch Rd Joppa, MD 21085
(410) 538-4528

stafftech

I am having the same issue after doing a complete rewire with new harness from lectric.There are many posts on this issue as it is very common. Lots of ideas floating around from putting a cheap radio shack resister in line to keep trying different sending units until you get one that seems fairly accurate. Do a search and you will be surprised to find how many people have or are dealing with this.

ohiovet

I used a temp gun and then bought some resistors from Radio Shack.
Tried different ones in line on the wire from the sender until I got the right combination to match up with the temp gun reading.

jim lockwood

About adding a series resistor to "calibrate" the gauge: The gauge will be correct at only one temperature.

At all temperatures above its calibrated point, the gauge will read LOW.

This means your gauge could be telling you everything is fine while your engine is about to boil over. Never forget this.

Jim

65tripleblack

The gauge is nonlinear, and even if it's "properly calibrated" to the sender, it is only accurate at one temperature. In most cases, when adding a replacement or reproduction sender, the gauge reads too low, which means that its accurate temp reading might be as low as 120 degrees, and everything above and below that becomes increasingly inaccurate the further the needle moves away from the accurate spot. I have spent a lot of time measuring and documenting this with an apparatus, on the kitchen stove.

What I have found, is that by trimming the gauge with a series resistor, I tune so as to get the accurate spot of the gauge at the temperature where the engine operates in normally, which is 180 degrees. When I'm driving, normally, the gauge correctly reads "180", when the needle travels either way off of its normal location, then I know that I'd better pay closer attention to it. Anyone foolish enough to let the gauge travel up to or past the 240 degree mark deserves whatever happens next.

ohiovet

Jim,

Thanks for the information, I never realized that.

Bruce B

wraplock

I had this same problem with a few replacement sender I purchased for my 60. After talking to several people about it I called MaryJo Rohner and bought a used original sender from her. Gauge works perfectly now. I believe one way to I.D. an original is the originals have a small dimple on the center of the brass part that goes into the manifold.

stafftech

Do you happen to have her contact info?

Thanks,

Donald #31176

http://www.CorvetteGal.com

wraplock

Sorry it's not a dimple, more like a pimple that protrudes.

her direct link is: http://www.parts123.com/PartFrame.as...CORVETTE_PARTS

stafftech

Old post I know but....
After trying many different temp sendors I am going to go the resistor route. I stopped at Radio shack and saw they had many to choose from with ohms varying and different watt resistors, do you happen to remember if you got a 1/2 watt or 1 watt, or if it matters?

Also do you happen to have a picture of the resistor you used or one like it? I would like to make sure I am looking at the correct ones. The ones I saw look like typical resistors I used in electronics class. If these are correct, just curious how you installed them (just wrapped they wire around the end and tape it?)

Thanks,
Dan

jim lockwood

Dan, you might "get by" with a 1/2 Watt resistor but you'd be well served by selecting a 1 Watt resistor.

Keep in mind that if you "calibrate" the gauge with this technique that not only is the gauge accurate at only one temperature but also that if the gauge ever reads higher than that temp, the engine is MUCH hotter.

Jim

Frankie the Fink

My Sea Ray bowrider I/O boat has the same inaccurate temperature gauge problem. Their factory, under-warranty, fix is to install a compensating resistor behind the gauge.

It's 5 seasons later and it works fine....

The alternative is to buy 5-6 TU-5 Wells sending units from your FLAPS and swap them in until you get close (and you might never get close).

stafftech

Thanks for the response Frankie, I have tried 7 sending units, 5 tu5's one I got from ebay that looked like an original and the current one I got from corvette specialties of Maryland now located in Palm Desert, CA, and none have come close so I am resorting to a resistor.

My question is, how do I connect it to the green wire of the gauge? The resistors at Radio Shack look similar to the pic below.

5thvet

Corvette Central sells one ( more expensive than Radio Shack mind you) but it is made for this application and is adjustable with a screw. After you dial it in you just lock the screw.