Running hot or reading gauge wrong?

On my '68 standard, the gauge needle gets pretty close to H but when I check the radiator temp with an infrared it’s around 200deg. This doesn’t seem excessively hot, but I wanted to see what you guys think. I have replaced the sending unit, fan clutch and I’ve got the 3-row 24" radiator w/7-blade fan. Thermostat is next on my list, but I haven’t replaced it yet.

Here’s the gauge and infrared readings taken at the same time:

I always went by the gauge to determine the temp on the F100 and freaked out when my electric fan died and the gauge went way high. Then it dawned on me, the fan is kicking in at 205 and it is showing about where your gauge is showing when that happens, so it’s really not hot when the gauge says it is.

My vote would be to just keep an eye on it and see if you see any major changes in its behavior to indicate if there is a problem.

I’ve hear that the reproduction temp sending units have the wrong resistance & may cause the gauge to read high.

Can anyone confirm?

I have heard that too Chris - I think over on the SAAC Forum?

  • Phillip

That was the most recent place I’d heard it: got me wondering what sending unit I have in the R Code. It reads a tad over halfway in normal driving (40-50 mph back road cruising), and will spike to 3/4s if you sit in traffic or go like 80-90 (not that I ever do that), then drops right back down when normal driving is resumed.

The car shows no signs of overheating, never spits coolant, never pings, never hard to start.

That seems high. Granted I have a small block, but still I can hold mine at 100 forever and my temp gauge stays steady.

It took me 3 tries to get a sending unit for my 69 that read mid range. The first 2 read close to the red zone while driving although the temp was not over 210. The sending unit I got from West Coast Classic Cougars reads correctly at or just below middle most of the time except when in stop and go traffic on a hot day.


If normal operating temperature is ~190°F, gauge sligthly above mid-range at 200°F does not seem all that bad to me… and I beleive mine (original) is pretty similar. Will check tomorrow and post pictures as well.

I found this post where someone went through a bunch of senders that all read high:

He eventually settled on NAPA TS6628 being the one with the right calibration. NAPA says my local store carries it, so I may pick this one up and give it a shot.

YES The auto parts store senders read high. Sometimes they sell you one from a Ford that has an idiot light which is way different. Green Sales in Ohio usually has Ford NOS senders. Unless your original sender is electrically open I would not replace it, except to remove and clean the scale off the bottom of it.

In my opinion it should read less than half on a warm day. Here is a good sending unit.

I recently had to replace mine in a '69 428CJ. I would have bought from WCCC, but didn’t have enough time before hitting road to Dearborn show. Don put the ohm rating on his website… the 6628 has different rating. NAPA’s ECHTS6153 is what I bought and was correct when it told me I was overheating in stop & no go traffic. :unamused:

Here are pics of mine (1970), original temp sensor, at the end of stop & go traffic session + ± 10 minutes idling (sunny 79°F). In comparison, yours seems to read high.

The 351w is easier to cool than the 351c

Thanks guys, I just put the order in for the WCCC sender…which I should have done from the start :wall:

Awesome thanks for taking those pics, yeah looks like mine is definitely reading high. Your gauge is behaving exactly the way you’d expect, right in the middle at full operating temp. I’ll report back when I get the WCCC sending unit installed.

In theory, if the sender is working correctly, where should the needle be on average on a 302? lets say its 75 degrees out and doing city driving. Has anyone done a temperature reading and noted which temperature corresponds to a certain area on the temp gauge?

With my 289 with a 180 tstat, at a traffic light in average weather, mine stays between 1/4-maybe1/3. Even on a hot day here in Metro Atlanta with the long traffic lights I have never had it go any higher than that. When I checked my advance curve, which I did by myself, the car went as high as 1/2 as it was sitting and every 30 sec. going 500 rpms higher until I hit 3200 rpms. So I would safely say somewhere between 1/3 and 1/2, but I would also take a reading with a temp gun to verify what the ACTUAL temp is.

It was a cooler day so couldn’t hit 200, but you can see Don’s sender definitely helped. It still seems just a bit high, but the gauge itself has probably lost some accuracy over the years. Either way, the temp gauge is usable now so I’m happy.

For what it’s worth, I’ve had got luck with senders from Standard Motor Products. Many of their parts are reboxed OEM parts, many are stamped with the original Ford engineering numbers. Not always the case, but often so.