Datsun Roadster Forum-311s.org

I have read through the tech Wiki section and did not see info on just the temp gauge. I am currently using a 180 deg t-stat and when the engine is up to temp the temp gauge is pegged hot. Even after the t-stat opens the gauge reads hot.
A couple of questions,
Would the car have had a 160 deg t-stat for the climate and the gauge calibrated for that? The car was imported to southern California.
Is there an adjustment on the temp gauge to change between a 180 and 160 t-stat?

Thanks,
Dan

I have the same problem with my 68. I don't think someone would change the calibration on the gauge for a temp setting on the T-stat. Have you put a heat gun to the t-stat housing, head, block, etc. to see if your really running hot. Did you burp the cooling system? On my car, I have had it running perfectly cool, and pegged like yours, but seems that the engine temps are good with the heat gun, the last work I did to the car I wrapped teflon tape around the nut holding the temp sender and now it's pegged again. Go figure. I bought a new temp sender, but haven't installed it yet. Let me know what you figure out.

The 1500 uses a unique sender. Do you have the correct one?

bossbob, yes, after thinking about it, they would not be changing t-stats, too much hassle.
System is good, new 3 row radiator, fresh batch of 50/50 coolant. I have an IR heat gun and ran the engine from cold to hot. At about 145 the needle was in the mid range of the gauge. Gauge pegged at 180, t-stat opened and the engine ran about 175-185 at the temp sender. It didn't get any hotter. As far as I can tell, the engine is running normal.

spl310, from my research, I do have the correct sender. Which brings me back to the temp gauge.

As a positive ground gauge, the needle stays HOT when it it does not have a signal.

Try grounding out the gauge and confirming that the needle goes down to Cool.

By shear luck I found my answer, sometimes you gotta dig deep.
Thanks.
Dan

Please share what your sheer luck involved!

There was a short discussion on the subject back in Oct of 2017. I have an old temp sending unit, well I have an old car also. If there is an adjustment on the back of the gauge, I will adjust it. I just have to dig it out of the dash. I will let you know.
viewtopic.php?f=3&t=29003&sid=e519da745 ... 9d02cdc81f

I doubt it is the adjustment of the gauge.

IThe 1964 1500 was originally positive ground. Is you car still positive ground?

datsun65 wrote: Wed Aug 26, 2020 7:36 pm I doubt it is the adjustment of the gauge.

IThe 1964 1500 was originally positive ground. Is you car still positive ground?

The gauge can be adjusted. It doesn't matter if it is pos or neg ground.

Steve, you are. Correct.

In my experience it is rarely the adjustment that makes the gauge work, or not. If the gauge stays pegged to hot , it probably isn't an adjustment issue.

datsun65 wrote: Wed Aug 26, 2020 7:36 pm I doubt it is the adjustment of the gauge.

IThe 1964 1500 was originally positive ground. Is you car still positive ground?

Dan from Texas, the car is still pos ground. I have corrected many electrical issues not related to the temp gauge.
Engine cold, no ignition the needle reads hot as it should.
Engine cold, ignition on the needle goes to the cold position as it should.
Start engine, needle raises as it should, mid range the engine is at about 140 but the needle does not stop. When engine is at normal operating temp 180, needle is pegged hot, not as it should be. This leads me to believe there is an adjustment at the gauge itself. There must have been some factory calibration done to these gauges???

A couple of things,
I tried to remove the gauge cluster but the wiper motor bracket is in the way. Looking at the back I found two holes but was not able to get to them.
I could replace the sender ($150 unless someone knows a less expensive one), but reading the post from 2017 this may not solve the issue.
I have an aftermarket temp gauge but do not have the correct fittings to thread the sender into the block.

So, for now, I know the engine is running at normal temp despite what the gauge reads. Unless someone has personal experience calibrating these gauges or knows of a procedure for calibration, I really need to get the seats upholstered and work on the interior.

Thanks,
Dan from Spokane.

Hey Fetch, I'm no expert, but I don't think your gauge would just jump out of adjustment and show pegged at 180. As I mentioned, my car does the same thing, except, "with my engine cold, no ignition, the needle reads cold", and I am more prone to thinking it's the sending unit.

Can the sending unit be measured out to see if it is functioning correctly? I don't know, but if it has lost resistance somewhere, I would imagine it would send the wrong signal to the gauge.

Just my 2 cents, I'm interested to see what your fix is, so I can get mine more accurate.

Dan from Texas, the car is still pos ground. I have corrected many electrical issues not related to the temp gauge.
Engine cold, no ignition the needle reads hot as it should.
Engine cold, ignition on the needle goes to the cold position as it should.
Start engine, needle raises as it should, mid range the engine is at about 140 but the needle does not stop. When engine is at normal operating temp 180, needle is pegged hot, not as it should be. This leads me to believe there is an adjustment at the gauge itself. There must have been some factory calibration done to these gauges???

Great update. Thank you.

Here is a picture of the rear of the 1964 Gauge (temperature is on the left side).

Per the 1964 Owner's Manual the the pointer of the temp gauge at the middle is 175 Degree F.

Dan thanks, that was part of the information I was looking for. I read through the service manuals, I did not think to read the owners manual.
There is evidence the engine overheated at some point prior to 1979. That may have effected the temp gauge, to be 35 deg off?
I believe the sending unit is nos, never installed. It looks new with the part # stamped on it. However, it has been in a box of parts for 40 years.
Yes, that looks like the back of the gauge cluster. The screws still have the sealing paint on it.

bossbob, I don't think the gauge just jumped out adjustment, the car overheated at some point and has been sitting without power to it for 40 years. I don't know, I have to remove the wiper motor to get it out.

Thanks
Dan