temperature sender and connector

[aleighs1990]

Does all this mean that whether I get a sender from O'Reilly or from the Chevy dealer it will not be correct? I have a 76 c10 350, haven't had a temp reading since I bought it, can't spend a lot of money for a sender. What will I experience with my temp guage if sender is not correct?

[Captkaos]

Consider starting a new thread instead of replying to one from a year ago.  The replacement should have a reading but in reference to what Rich posted it will probably read low.

In reference to this post: http://forum.73-87chevytrucks.com/smforum/index.php?topic=27971.0

[rich weyand]

As far as I know, for a 1973-1978, ANY sender you get other than the Autowire 01513321 (which is reasonably priced and has worked just fine in my truck for a while now) or a NOS GM 1513321 (which you can sometimes find for some serious coin) will be incorrect for the stock temperature gauge, including anything you get from OReillys or the GM dealer.  With the correct sender, the gauge reads half a needle width below straight up (two gauge ticks out of four) when the stock 195*F thermostat opens.  A cross-referenced replacement will read one gauge tick or a bit more at operating temperature, which basically sucks because you can be overheating and still be in the lower half of the gauge.

[76LongBox]

What temps do the ticks on the factory gauges represent? I've been running a temp sender from O'Reilly in mine for years, and wasn't aware that it wasn't correct.  During the hot summer time (95+ degrees), running the A/C, and driving on the interstate (65-70 MPH), my temp gauge will get up to almost the halfway mark.  Other times, not running the A/C, when it's not quite as hot out, etc., it will be just above the first mark.  It concerns me that I might have been running hotter than I should have been. 

[rich weyand]

I don't think they represent anything.  When I am idling, the gauge will go up to almost the second tick, the thermostat will open, and then the electric fan will cycle on and off to hold it there.  That's with stock 195* thermostat and about 195 set on the electric fan controller.

MOST aftermarket cross-reference senders read low, but some read high.  I would put the correct sender in there and see what you really have, compared to my setup above.

[76LongBox]

We had some unseasonably hot weather here in AR yesterday - temps in mid to upper 90's - so I got out and drove my truck.  Temp gauge was reading about halfway while running 70 MPH on the interstate with the A/C going.  At the time I got home and pulled into the shop, it was down to about 1/2 way between the first and second mark.  Checked the temp with my infrared digital thermometer at the inlet on the intake, the hoses, and the radiator, and it was about 160-degrees.  That several degrees cooler than I expected, but I guess that's a good thing.  I also noticed that the gauge was fluctuating quite a bit (very small amounts, but still fluctuating quickly), so I'll probably wind up getting one of the "correct" sending units for it and see what happens.

[rich weyand]

You sure your antifreeze is topped up?  I don't like the sound of that "fluctuating quickly".

If you just let the truck sit and idle, the temp will balance out pretty hot.  That's a pretty bad cooling scenario, with no ram air.  Let it sit and idle and see how high it goes, and you can use the infrared thermometer on the thermostat housing to see what the corresponding temp is.

[76LongBox]

Yesterday was the first time I had ever noticed the "twitch" in the needle...and that's basically what it was.  It would move about a needle's width back and forth while driving it - never going above the halfway mark on the gauge.

We had a front move through last night/this morning and the temp is about 20-25 degrees cooler today than yesterday.  I drove the truck into town a little while ago at lunch to have it cleaned up, and without the A/C running, driving up to 55 MPH, the needle sat at the first mark - which is typical under these weather conditions since I put this GM crate engine and new transmission combo in it about 2 years ago.  No difference when idling say at a red light or stop sign, etc.  I'll go out and move it into the driveway and just let it sit and idle for a while and see what it does.

[76LongBox]

Ok....so 2 things....

1. Truck idling for 15 minutes or so the needle stays at the first mark - no fluctuations, etc.
2. I now know that my infrared thermometer is JUNK!!  It's a Harbor Freight special, and it'll probably go in the trash later today. Holding it very steady on the hoses, intake, exhaust, radiator - even my wall thermostat in the shop - and it would fluctuate several degrees.  Upon further investigation, the thermometer would read hotter the closer I got to an object.  So while 3 feet away, it might read 150 on the radiator hose, right up close to it, it would read 180+.  So, I'll try this whole exercise again when I get my hands on a known GOOD infrared thermometer.

[rich weyand]

Normally at idle the engine will run at the thermostat temperature.  So I worry about the needle going so high when driving,

One thing you can do is replace the ATF with full-synthetic ATF.  It does not heat as much when compressed and released.  The result is reduced heating, which reduces the temps in the tranny as well as the heat carried to the radiator from the tranny.

[76LongBox]

Hey Rich...thanks for the suggestion.  I hadn't thought about the impact of the transmission fluid heat transferring to the radiator (duh!).  My transmission is a Streetrodder TH350 from TCI, and I did install an external cooler (one of TCI's "upgraded" models) in front of the A/C condenser behind the grill when I put all of this together a couple of years ago, but I guess running highway speeds could certainly be causing it to generate more heat.  I had been thinking that the forced air was going through both the external transmission cooler, plus the A/C condenser, before it gets to the radiator, and that could be what was causing it to heat up more. 

When I was messing with this cheap infrared thermometer this afternoon, I found that it appeared to read more correctly when held right close to the object I was trying to measure, and that was showing temps of about 180 (give or take 5 degrees) on the radiator hoses, which makes sense based on what you said, as I THINK I have a 180 thermostat in it.

I have a new Raytek MT6 infrared thermometer on the way from Amazon, which should (hopefully) be better quality than the Cen-Tech I have from Harbor Freight. When it comes in, I'll be able to do some more checking for what the real temps are.

[rich weyand]

You should be running a 195 thermostat.  You don't do yourself any favors running a lower temp thermostat.  The oil needs to be to temp to provide proper lubrication, so you are unnecessarily stressing parts.  And it will cost you gas mileage.

That said, that may explain the low gauge readings.  You really need to find out what the actual temp is when it is indicating straight up, though.

The synthetic ATF will help.  You have a double whammy there with the A/C.  You are drawing extra horsepower to run the A/C, but you are also drawing more horsepower because the A/C condenser coil is getting heated air from the trans cooler instead of cool air, and it's getting less air because of the trans cooler blocking it.  Triple whammy because both are also blocking air flow to part of the radiator.