Hey gang, got an odd one for you.

My car used to sit rock solid at 170 (has a 170 degree thermostat) but within the past year that's become more variable depending on if I'm sitting idle or driving.  If sitting idle in 95 degree weather, it will go a little past half which I know isn't bad but the fact that it used to sit rock-solid at 170 regardless of weather tells me there's something wrong and even though its not severe it's annoying lol.

I've changed the fan clutch, thermostat, water pump, checked fanbelt tightness, changed coolant, used a flushing chemical, and even got a brand new radiator but while the temperature isn't moving as much, the needle still moves depending on if idling or driving.  There is definitely rust in the system because the PO used tap water and ever since I got it years ago, its been a game of 'how much rust will come out with this flush' (its always less but there nevertheless).

I've also cleaned the temp gauge harness connector/sensor outlet and nothing has changed.  I'd have thought it was the temp gauge if the car didn't go back to 170 like it used to while driving - but since it does, it tells me the temp gauge hasn't lost calibration and the coolant temperature really is changing.

Any ideas?

I had issues reading temperatures when I first started working on my Z. Sometimes the gauge would work (but give bad readings) and other times it wouldn't move at all. My issue was that my connection to ground wasn't good (due to a cracked thermostat housing). You could run through 50 different temp sensors but if the grounding is bad the readings will never be reliable. 

6 hours ago, Zed Head said:

Take it out and run it and see if temperature keeps climbing or if it just rises and levels out.  Fill up the reservoir first so you can see if the level changes.

Here's a question though - how can you be so precise on the temperature?

Alright, I'll give that a shot.  Again, it's not about being precise or 'that's a fine temperature.'  The car is running differently than it was before which is indicating there is an issue.  The fact that it is not bad yet doesn't mean the issue should be ignored.

The difference isn't only the temperature it's getting to - the main difference is the temperature flux between idling at a stop light and driving with air through the radiator.  Before this issue started in 2020, the needle got to 170 and never moved regardless of idling at a stoplight or not.

Edited December 19, 20222 yr by chaseincats

With all respect friend, these gauges are far from precise. New gauges are of course NLA. It would be interesting if you could try another gauge or better yet install a temporary or just take readings from the radiator itself. You might be just chasing a ghost. From what I’ve read in this thread you’re relying on a reading from a 40 plus year old gauge. My 2 cents 

8 minutes ago, Yarb said:

With all respect friend, these gauges are far from precise. New gauges are of course NLA. It would be interesting if you could try another gauge or better yet install a temporary or just take readings from the radiator itself. You might be just chasing a ghost. From what I’ve read in this thread you’re relying on a reading from a 40 plus year old gauge. My 2 cents 

Definitely a fair point but I grabbed an IR temp gun and verified that the engine temp was fluctuating and not a goofy gauge 😞

On 12/18/2022 at 11:28 PM, Yarb said:

With all respect friend, these gauges are far from precise. New gauges are of course NLA. It would be interesting if you could try another gauge or better yet install a temporary or just take readings from the radiator itself. You might be just chasing a ghost. From what I’ve read in this thread you’re relying on a reading from a 40 plus year old gauge. My 2 cents 

Ran the car without a thermostat and it got up to the temp it gets with the thermostat in it (albeit took a lot longer to get there of course).  I also had the block/radiator power flushed and not much rust came out which either means its REALLY clumped up in there or I got it all out flushing it a few times.

Update: After getting the car back from the radiator shop they are recommending a stronger fan clutch since the Aisin one I have doesn't move ALL THAT MUCH air (it is brand new and replaced one that moved just as much air).  Are there fan clutches out there for our cars that grip harder and move more air?

It might be running hotter since I run the car at a stoichiometric air/fuel ratio instead of the richer configuration they come with.  The car was set that way by me using an air/fuel gauge.

 As I understand it, 14.7:1 is the ideal ratio but everything I've seen and heard says a gas engine runs much stronger and COOLER with the mixture somewhere in the 12.5:1 to 13.2:1 area.

1 minute ago, Mark Maras said:

 As I understand it, 14.7:1 is the ideal ratio but everything I've seen and heard says a gas engine runs much stronger and COOLER with the mixture somewhere in the 12.5:1 to 13.2:1 area.

That's absolutely true and that's why the TPS drops the ratio to around 12.5 when you floor it but 14.7 is the ideal ratio for highway driving

No ideas on a grippier fan clutch?

5 minutes ago, chaseincats said:

No ideas on a grippier fan clutch?

If you are using the OEM setup, there isn’t any option, it is what it is.

What is the condition of the one on your engine now?

 

6 minutes ago, Racer X said:

If you are using the OEM setup, there isn’t any option, it is what it is.

What is the condition of the one on your engine now?

 

I heard that the american-made ones make more fan noise because they grip harder.  The aisin one is brand new, so it should be good but its just not moving as much air as it should I feel.  While the car is running it wont even blow a rag if you put it behind the fan

The clutch gets stiffer as it heats up.  The fan doesn't need to push much air on a cold engine.