Bob's right -- the gauge must be read with respect to what's "normal". I've checked my gauge against the temp read by a thermocouple inserted in the block side of the top radiator hose, so I know what the lines represent in terms of absolute coolant temp. It wouldn't be useful to share those numbers because on another car the absolute temp is likely going to be different for the same gauge position.

 

AFAIK, thermostats vs. gauge:

Just below the second line, 83C, 92810612917

Just above the first line, 75C, 92810612916 (Behr 1162000015)

 

Heres the deal. I JUST completed a TB and WP change on this car. Also added Kens tensioner and a 75C thermostat. Obviously I drained the radiator to do all this. Added one gallon of antifreeze and a bottle of water wetter and topped of with distilled water. ( I did not drain the bottom of the block ) added about 2 to 3 gallons of water.
After doing all this I didn't want to just assume what I saw was normal for this car. Honestly I don't remember what the dash read before the maintenance started.

 

Dean--

The one-fan-running symptom could easily be a loose plug on the fan console. You had that out and disconected for the TB project so that's where I'd start first on this part of the diagnosis.

On the cooler thermo install, folks often change to the cooler thermostat and expect the car to run cooler as a result. It's not a good expectation. The thermostat determines the --minimum-- temperature that the engine will run at by blocking coolant flow to the radiator until the set temperaure is reached. Once that temp is achieved, the thermostat open over the course of a few more degrees until all the coolant goes to the radiator and none is recirced/bypassed back through the block. From that point on, air circulation and radiator heat transfer capability decides what the actual temps will be. When you are sitting still, cooling fans determine airflow. Since the fans only start working a little north of 190ºF, the engine temp will sail up to that point. If you happen to have plenty of airflow as you are driving, the engine may settle at thermostat temp. As soon as you slow down and need more airflow from the fans, you get to wait for coolant temp to rise a bit before they come on. Ultimately the temp gauge will likely go lower at speed, and go up when slogging through traffic and depending on the fans.

 

got ya Bob....what about changing switch in fan relay to come on earlier at a cooler temp??? Would that help? Is there one available? Is it a good idea for someone like myself who lives in the hot south east?

 

The fan speed and operation are managed based on temps measured at the bottom front driver's side of the radiator. Measured by a thermistor-type sensor rather than a switch.

If your cooling system components are in reasonable shape, there's no need to change anything. If the radiator is tired/fouled/partially plugged (most common problem) then no amount of earlier fan operation will help.

 

One more thing..turn the defroster **** insert 45 degrees clock wise until it sits level.

 

Hi Aryan.
What means turn the defroster ****?

 

The Thermostat switch center is askew, that's all.

 

I HAVE NOT UNDERSTOOD?????????

 

He is telling me the **** is not square.

 

You wrote, "... air circulation and radiator heat transfer capability decides what the actual temps will be."

Dr. B, I hate to differ, and I've been wrong before, but ...

The thermostat will determine the temperature at which the coolant runs within a small window if a car has adequate designed-in cooling capacity . The thermostat cycles constantly from (usually partially) open to (usually partially) closed. So, assuming everything's in proper running order and there's enough designed-in cooling capacity to handle the heat, a 75º thermo wil have a car running around 75º and a 90º around 90º, whether you're at 5000rpm in fifth, 2500rpm on the interstate or idling in traffic, all three regardless of the outside temp. This is also the reason our members in Sweden and Norway can use their cars in January. In a properly functioning system with an adequate heat-shedding capacity, a lower temp thermo will result in a lower operating temp and vice versa. Low temp thermos are not necessarily a good thing, as the factory designs the engine to run at a specific temperature, though I'd expect a 5-10% variance between 2500rpm on the interstate and the high heat loads of 5k in fifth and idling in 100º ambient. (The Tech Spec book says the thermo opens at 81-85ºC. OTOH, six lines later it gives oil pressure specs at 80ºC )

The big points are:
the guage is just an indicator,
the needle position is not necessarily a reason to panic unless/until you have independently verified the coolant temp,
and because the factory engineers an operating temp (which might be 75º or 98º) it can actually be a bad idea to run a lower thermostat than stock.

Of course, all this goes out the window when you start adding heat - by supercharging, by a stuck thermostat, by a clogged radiator that sheds heat slower than it should, maybe by racing.

And all that said, in my air/oil cooled 911 (which had a gauge with actual numbers) iirc there was a 15º variance between a sustained 70mph and a sustained 120mph in 100º west Texas. The needle actually moved up and down pretty quick, one could watch it change as sustained speed rose or fell. Even so there appeared to be a max temp, ten minutes at 120mph wasn't different than thirty minutes.

will

 

Yes.

Pure ***** retentive* cosmetics. Has noting to do with engine cooling.