old87iroc

Just replaced the radiator, radiator hoses, fan switch (now set at 220 degrees), and coolant gauge sending unit (wasn't working). Using my laser thermometer all looks good. Thermostat opens when the temperature of the metal hose connector coming out of the water pump when it shows about 180. Metal connector at top where the top radiator hose connects comes right up to 195 moments after the thermostat opens. Fan turns on when the temp at the top shows right around 220 so all looks good except for one thing. The temperature gauge is showing about 25 to 30 degrees higher than what everything else shows. As I said the sensor was replace with part that both Rock Auto and NAPA say is the correct part. Is it possible that the drivers side of the engine really is running hotter than the rest or is it most likely something in the temp gauge sensing?

sofakingdom

iTrader: (1)

Probably just an inaccurate gauge.

Now you know what it reads when everything is working right. If it changes, that's really all you need to know.

i88aGT

This sensor you're referring to, is it the fan switch, or sender for gauge? Out of curiousity, what PN?

old87iroc

Thanks for the response sofakingdom.
i88agt, for the gauge TS6641.

sofakingdom

iTrader: (1)

Of course, you can shoot the area around the sensor with your IR, and see what its temp REALLY is, to double-check the gauge.

They've used the exact same temp gauge sending unit since the 50s, except for changing the pipe thread size sometime in the mid 70s, and changing the connector from a slide to that "mushroom" thing the factory used but you can't buy anywhere sometime in the 60s. The basic guts though, and their response to the actual temp, is the same for all of them. I don't think there's any chance that the sending unit is "wrong". Defective, maybe, of course; "new" is no guarantee of "perfect" unfortunately, as we all know; but there's not a compatibility type of issue.

old87iroc

I do plan on snooping around a bit more. I hope to get my laser thermometer underneath but that is difficult to do without burning my hands. Since the spec says 220 degrees should give 147 ohms I plan on replacing the sensor with a 147 ohm resistor to see what the gauge reads. I may follow that up with a clip lead on the sensor so that I can measure the resistance of the sensor when the coolant coming out of the top of the engine is at 220 degrees. Of course the sensor spec also quotes 15% tolerance at 220 which makes it seem kind of worthless. The Enginenerd in me would like all the numbers to match up. Given that this is the first time I have done anything like this on a car I just want to make sure I don't damage anything.

ironwill

I wouldn't rely on a 3rd gen temp gauge for an absolute reading; they're just too inaccurate. The best you can expect is for it to be useful for relative readings; IOW, if it shows "higher" than what you've come to expect over time to be normal, something may be amiss with the cooling system.

Vader

Good luck finding that 147Ω resistor. Just pick something close and see if it is reasonable.

i88aGT

I'll piggyback on what Ironwill commented about if it's suddenly higher, or gage seems suddenly inaccurate something is probably up. I think you mentioned changing a fan switch to a 220 degree? I dunno if you have 1 or 2 fans, or how your switches are, but I'll throw a word of caution here about mislabeled switches. NAPA sold me multiple fs111 fan switches (in pass. head for 2nd fan) that were way higher than their reported spec. So uncomfortably high I always shut car off before reaching turn on. Changed brands and all was good. My gage was suddenly "off". And yeah gage was like 15-20 degrees hotter than what I could read at t-stat.
It would be nice if you could read the CTS on a scan tool, or like Sofakingdom said, actually measure at the switches/senders. Good luck.

sofakingdom

iTrader: (1)

https://www.digikey.com/en/products/...C150FET/678912

Should make the gauge read about 218 or so. Or, if you REALLY want to come up with 147 ohms on the nose, buy a handful like maybe 10 (be careful, they're EXTREMELY $$$$$), and pick the one closest to 150 ohms ( I hope you have a good accurate ohmmeter, most aren't too much better than 1% anyway), and parallel it with a 4.5k such as this https://www.digikey.com/en/products/...00FHEB/1554069 which will give you within a tenth of a percent of the "ideal" value you want.

Or, just acknowledge whatever your gauge reads as it is, accept it as "normal", and when it starts showing something really different, worry about it then.

Personally I think it would be a waste of time and money. Measure with micrometer, mark with spray paint, cut with cruise missile. Butt hay, you do you.

NoEmissions84TA

iTrader: (1)

Really? Common values - 100 ohm + 47 ohm.

Brown Black Brown plus Yellow Violet Black

And yeah, I had to Google it as a double check. I'm old too.

OrangeBird

iTrader: (1)

Yep.....




The standard disclaimer applies, I do not have any affiliation whatsoever with the resistors I have posted links to, they were the first hits on a search of 47 and 100 ohm resistors

old87iroc

Laser thermometer on the coolant coming out of the top of the engine says the fans switch is correct. Fortunately, my employer had a 147 ohm 1% resistor I could use. Have just been living with it driving over the weekend but when I get some free time I will run it into the ground. Everything is remaining consistent and working well.