[i4abuygto]

I need some help with the operating temperature of my 79 403.
I just had the stock 403 heads done installed all with new hoses, belts, thermostat and temp sending unit - all new
Sounds like a brand new motor- runs strong. Filled with coolant and all air is out of the system and (with the opening and closing of the new thermostat) the operating temperature floats between approx. 224-234 on the stock gage. See attached photo
Is there any suggestions as to how to calibrate the stock gage or is the thermostat and sending units that I was sold, incorrect?
The old thermostat and sending unit would hardly move the needle on the gage at all (maybe 2 needle widths above the 100 mark on the gage).

[i4abuygto]

More information is that the 409 has an aftermarket fan setup and the previous owner has a fan installed in front of the radiator that is not hooked up but does work. When I ran the fan it did not seem to change the operating temperature at all.
It concerns me that a fan was installed which leads me to believe there were operating temperature issues.
I just don't want to overheat.
There is no redline on the temp gage- what is considered overheating if the gage is known to be reading properly (yet to be known).

[78w72]

factory t-stat is 195f, the engine/gauge could easily read 200-220 on these cars in hot temps. 220 is at the beginning of being too hot but wont damage the engine.

i would remove that elect fan on the front of the rad, it restricts air flow through the radiator. get a stock clutch type fan with a factory shroud, make sure the fan is spaced right, about half way in the shroud. also use a 180 t-stat & make sure the radiator is not clogged, a stock 4 core radiator should cool these cars easily. or look into an aluminum radiator if all else fails but the stock fan/shroud is best for these cars & hard to beat with electric fans.

also depending on your location/climate you can reduce the concentration of anti freeze to about 25-30% if it diesnt get too far below freezing, water cools better than anti freeze, also try some of the water wetter or hyper-cool products, they will reduce the temps a little & provide anti corrosion.

& to confirm the gauge temps, buy a cheap $20 infrared temp gauge & point it at the t-stat housing or upper radiator tank/hose & see what the actual temp is... could just be the new sender thats off.

[i4abuygto]

Thank you 78w72 for your help, comments and advice.
A did get a chance today to check temp at the radiator and I must have the wrong sending unit. The temp at the radiator is 160-165 degrees steady at an idle while the factory temp gage reads over 220 degrees as pictured in my first post. I tried 3 different probe thermometers at the radiator tank while running at an idle and let run for over 20 minutes thru several cycles of the thermostat.
I have an infrared gun thermometer on order and when that comes I will point and shoot the temperature at the upper radiator hose at the thermostat housing.
The sending unit they sent me was Standard brand #TS71
The thermostat is Murray brand #MU55359
If I am running at 165 degrees max at the radiator tank I would assume I am good to go and I can just use the gage in the car at operating temp as pictured above knowing that when the gage shows 230 degrees I am really at 165 at the radiator. The main thing is I want a reference point to start to gage overheating.
Any advice or comments are much appreciated
Thanks

[78w72]

Originally Posted by i4abuygto

Thank you 78w72 for your help, comments and advice.
A did get a chance today to check temp at the radiator and I must have the wrong sending unit. The temp at the radiator is 160-165 degrees steady at an idle while the factory temp gage reads over 220 degrees as pictured in my first post. I tried 3 different probe thermometers at the radiator tank while running at an idle and let run for over 20 minutes thru several cycles of the thermostat.
I have an infrared gun thermometer on order and when that comes I will point and shoot the temperature at the upper radiator hose at the thermostat housing.
The sending unit they sent me was Standard brand #TS71
The thermostat is Murray brand #MU55359
If I am running at 165 degrees max at the radiator tank I would assume I am good to go and I can just use the gage in the car at operating temp as pictured above knowing that when the gage shows 230 degrees I am really at 165 at the radiator. The main thing is I want a reference point to start to gage overheating.
Any advice or comments are much appreciated
Thanks

id try to find the right sender or reuse the one you had if its still available. the gauge could still be off/bad. check all the wiring & grounds too.

your idea on reading the gauge should work better than nothing but not accurate at all since you dont know how much the gauge moves above the 225 being 165 at the radiator, you want to know the engine temp at the sender or T-stat housing. should be able to get the right sender for your year car/gauge.

also idling for 20 minutes is not what the engine will do when driving, especially on a hot summer day. but at least you know the gauge reading isnt correct.

[i4abuygto]

What is the correct sender or a cross reference part # for the correct temp sender for the stock 79 gauge. It was hard for me to find out for sure but my research tells me that the TS71 is the right part # for the Standard brand sending unit and should be correct for the 79 TA stock gauge. However, I know on my GTO there was only one brand and one part number that would truly give the correct reading for my stock 67 GTO gauge. All of the others I tried would give a reading but not an accurate reading for the stock gauge.

[burd]

Run a 160° Thermo. I do.

[78w72]

Originally Posted by i4abuygto

What is the correct sender or a cross reference part # for the correct temp sender for the stock 79 gauge. It was hard for me to find out for sure but my research tells me that the TS71 is the right part # for the Standard brand sending unit and should be correct for the 79 TA stock gauge. However, I know on my GTO there was only one brand and one part number that would truly give the correct reading for my stock 67 GTO gauge. All of the others I tried would give a reading but not an accurate reading for the stock gauge.

looks like the TS71 is listed for your car/engine, but they also list a few other options like the TS71T, whatever that means as well as other brands like ac delco. i would assume what you have should work if your gauge is correct for 1979, many times gauges are swapped out. if the sender is correct & working right, maybe the gauge itself is bad or there is a wiring/ground issue. hard to diagnose these things over the internet. senders are cheap enough it might be worth trying out another brand. & definitely check out your wiring & make sure all grounds are good including the little metal strap from the headlight switch to the gauge housing behind the dash bezel. heres a list of senders at R/A.

https://www.rockauto.com/en/catalog/...+/+sensor,4748

& since you confirmed ~160 at the radiator & know the gauge reading is wrong & its not really overheating... do not use a 160 T-stat, that wont help or fix anything related to your issue. unless you're trying to cure an overheat issue or live in the desert, there is no reason to use a 160, 180 is ideal as you want some heat in the engine to burn off condensation & many say that too cool of an engine will increase wear.

keep checking things out & you should be able to fix the issue.

[Old Goat 67]

Originally Posted by 78w72

& since you confirmed ~160 at the radiator & know the gauge reading is wrong & its not really overheating... do not use a 160 T-stat, that wont help or fix anything related to your issue. unless you're trying to cure an overheat issue or live in the desert, there is no reason to use a 160, 180 is ideal as you want some heat in the engine to burn off condensation & many say that too cool of an engine will increase wear.

This is correct.

Did you check Lectric Limited for correct sending unit? They are the best for that sort of thing.

https://www.lectriclimited.com/vehic...del/58?cat=734

[i4abuygto]

Thanks guys for the info and the links.
Charles, it is nice to hear from you - as you know I am knowledgeable in the GTOs just getting going on this TA I picked up.
It is interesting that the links you guys sent with rock auto it shows the same sender will work with the 403 Olds and the 400 / 301 Pontiac. However, Charles the link you sent from lectriclimited shows two different senders for the 400 or 301 Pontiac and the 403. Seems like the Pontiac motors took one sender and the Olds takes a different one according to lectriclimited.
I know my 67 GTO stock temp gauge and oil pressure gauge would only read correctly with the one sender that I ended up getting. All of the others made the gauges work but not calibrated correctly to the sender.
I know the only way I could confirm calibration on the temp gauge for the GTO was to bench test heating water to a boil and had the sender next to a known calibrated thermometer. Only one of the temp senders was spot on to the stock gauge calibration.
There is a pretty good chance that the gauge cluster on this car came out of a different year vehicle because my research tells me the 79 shouldn't have the "Radial Tuned Suspension" plaque under the temp gauge.
There is a chance this gauge cluster is for the 400 or 301 and not the 403.
I'll pick up the sender for the Pontiac 400 and see if that works better.
I'll let you know what I find out.
Thanks for the advice and help.

[78w72]

the RTS badge is definitely correct for 79. the gauges aren't engine specific, i think at a certain year they may have changed. maybe the lectriclimited senders are more accurate than the cheap aftermarket ones? give them a call & see what they say.

do you have another gauge you could swap out or another cluster?

[i4abuygto]

Thanks for all of your help
Charles - thank you for reminding me about the lecriclimited sending units. This appears to be the same case as the GTOs - rally gauges. I happen to have a second lectriclimited sender (the only one that would accurately calibrate to the stock temp gauge) and I bench tested it this morning.
I disconnected the sending lead in the car and jumpered that to the lectriclimited sender I have part #06402383. I grounded the sender to the car ground and boiled a pot of water on the stove. I hung the sender from the side of the pan of water and a probe thermometer to measure the temp in the pan of water. The lectriclimited sender was spot on to the stock gauge in the car.
1st mark on the gauge is a needle over 175 degrees.
200 degrees is half way between the 1st mark and the 220 degree mark which should be operating temperature with a 195 degree thermostat.
Thanks guys for your help.
I will install the lectric limited sender and all should be good.
Advice to all - dont buy an over the counter sender.

[i4abuygto]

Just an FYI to all
Bench testing showed me that half way between the 100 degree mark and the next mark is 160 degrees.
150 degrees is about 3 needle widths off the 100 degree mark.
175 degrees is about a needle shy of the 1st mark.
200 degrees is about half way between the 1st mark and the 220 degree mark.
I didnt test above the boiling point of water but I believe that with the sender from lectric limited you can trust that it will properly show the rise in temp.to the stock gauge.

[Old Goat 67]

Originally Posted by i4abuygto

Thanks for all of your help
Charles - thank you for reminding me about the lecriclimited sending units. This appears to be the same case as the GTOs - rally gauges. I happen to have a second lectriclimited sender (the only one that would accurately calibrate to the stock temp gauge) and I bench tested it this morning.
I disconnected the sending lead in the car and jumpered that to the lectriclimited sender I have part #06402383. I grounded the sender to the car ground and boiled a pot of water on the stove. I hung the sender from the side of the pan of water and a probe thermometer to measure the temp in the pan of water. The lectriclimited sender was spot on to the stock gauge in the car.
1st mark on the gauge is a needle over 175 degrees.
200 degrees is half way between the 1st mark and the 220 degree mark which should be operating temperature with a 195 degree thermostat.
Thanks guys for your help.
I will install the lectric limited sender and all should be good.
Advice to all - dont buy an over the counter sender.

Originally Posted by i4abuygto

Just an FYI to all
Bench testing showed me that half way between the 100 degree mark and the next mark is 160 degrees.
150 degrees is about 3 needle widths off the 100 degree mark.
175 degrees is about a needle shy of the 1st mark.
200 degrees is about half way between the 1st mark and the 220 degree mark.
I didnt test above the boiling point of water but I believe that with the sender from lectric limited you can trust that it will properly show the rise in temp.to the stock gauge.

Now, THAT'S the way to do it!!
Good Job.

[bhill86]

I know this thread is like 6 months old but your bench testing of the factory gauge caught my attention. I’ve always wondered about my factory temp gauge so I installed a mechanical gauge I had around. The pic below are of each and that’s about as hot as my car gets. Curious as to your, or others’ opinions, as to whether or not both gauges are accurate/reading correctly. And whether or not the factory one is representing 170ish where it sits in the picture. .

[Aus78Formula]

The RTS emblem is only on the dash fascia, could have any gauges swapped about and not affect that. It's correct for '79, was there since roughly '75, and roughly '74 when introduced had it on glovebox door instead. Swapping thermostats are specific to engine and mods, location, use etc. It can help to make things slightly better or slightly worse. but is not a fix, it only hides the problem until it gets worse.

Brian, would think those 2 gauges matching is a good indication that it's fairly close to accurate, without checking with another source like a laser temp gun, but then how do you confirm it's correct...!

[77 Canamman]

The 1979 speedo used yellow numbering for the kilometers per hour, and had a quartz clock in the tach.

[bhill86]

Originally Posted by Aus78Formula

Brian, would think those 2 gauges matching is a good indication that it's fairly close to accurate, without checking with another source like a laser temp gun, but then how do you confirm it's correct...!

Thanks, I actually did check the intake crossover, which is where both gauge senders are, after I shut down the engine and the mechanical had climbed to around 180°. The infrared thermometer showed 172° I believe so I suppose it’s not out of the realm of possibility for the coolant to be 8-10° warmer inside the intake than the outside of the crossover. I think I measured a head at the same temp to from what I remember.

I thought my factory gauge seemed a little high compared to what the OP posted on his findings.

[Warren Seale]

Originally Posted by 77 Canamman

The 1979 speedo used yellow numbering for the kilometers per hour, and had a quartz clock in the tach.

The quartz clock was a mid year production change in 79.

[padgett]

Just a note but over the last 50 odd years I have found GM oil and water temp senders to be wildly inaccurate. My CTS coolant reads 210F but at the water neck and at the sensor it is 170-180. Some difference sure but not 30F.