bleeding/venting the cooling system

[nize]

now you got me all curious so i had to google it. here's a good diagram of the coolant flow path from clark's garage:
https://www.clarks-garage.com/shop-manual/cool-10.htm

[soxnail]

Yah I have the PET and the flow diagram.
My question is rather simple:
If the vent hole is the highest point in the cooling system, and I fill the system via the reservoir till a steady stream comes out of the vent. At this point I close the vent, there should be coolant on and above the temperature sender. So if I remove the sender coolant should come out of the hole as there is coolant all the way up to the vent hole....
I understand if the car is warm and the system is pressurized it will come out of the sender hole, but it should come out regardless as it is lower in the gravity well then the vent hole.
So how can it come out of the vent but not the sender hole ?
Sox

[nize]

in order for the coolant to come out, there needs to be a hole higher up for air to displace the coolant. does it come out if you open the vent? i'm not sure if the coolant reservoir cap is higher than the temp sensor hole.

[soxnail]

The coolant reservoir is higher at the top then the vent hole, hence the coolant coming out of the vent hole when you top of the reservoir. Thus the reservoir would be higher then the temp sender hole.
The hole of the sender is big enough to let air in and coolant out at the same time. Like punching a hole in a can even if the top is not open liquid comes out as air goes in at the same time.

I feel I am missing something or not quite understanding something.....
Sox

[700ltr]

Go to AutoZone, sign out the coolant pressure bleeder.
You'll be done in 15 minutes. Works every time.

[soxnail]

found the issue with no coolant at the sender...there was an air bubble the size of Alaska sitting on top of it.
Further chasing the running hotter then normal, I finally bit the bullet and got the thermostat out. What a pain in the A$%...any way the thermostat in there was a new one purchased from 944 online. It said made in Brazil, put the old one and the new one in a pot of hot water, at 80 C the old one had started to open. The new one was firmly closed. At 83 C the old one was fully open good 10 plus mm, the new one had just cracked. At 90 the new one finally fully opened but it was maybe 5 or 6 mm only.
On cool down the new one closed fully at 82 C while the old one closed at 78 C.
Moral of the story always test component if possible, especially when it is getting put in a place where the sun doesn't shine.
Sox

[soxnail]

Well follow up...
Did not fix the over heat issue.
What I think is happening is that:
-Car acts like it is staying in bypass mode. The inlet to the top of the radiator does not heat up with the car. The outlet (bottom of radiator) is actually a few degrees hotter, probably due to proximity of the headers etc. The slow fans do not come on( to be expected as the coolant in the radiator does not get to 80 Deg +). The fans do come on when the car goes over the 100 deg C mark, but I think this is just general heating up of the whole engine bay.
Things I have done (again) tried the old thermostat and then again back to the new one, no change. Made sure the radiator was not blocked.
Retested the temperature gauge and sendor, both function correctly.
I have been venting/bleeding, emptied the radiator used vacuum method to refill, emptied it used pressure tester to refill.
Venting done with car level, tail high, front high. Not getting any air out of the vent, BUT when I use pressure to test the system the level in the expansion tank drops about 2 inches, it comes back up when pressure is released. This makes me think that there is still air in there as the coolant should not compress but an air pocket will. (No leaks under 15psi test).
Not sure how else to get the damn thing out.
Any insight/advice would be welcome.
Thanks Sox

[soxnail]

Further testing..
I have set up a rig to vent the system, but it also works for testing coolant temp versus what the sensor is telling the car temp gauge. I have tested the gauge in the car multiple times. It is accurate as per the test in Clark's. (Tad off at 115 deg C).
The system has a clear tube attached to the vent hole. (Tapped aluminum tube with the clear tube attached). When the car is up to operating temp, using the fan coming on as opposed to the gauge in the car. The pump is turned on, it is immersed in coolant in a cup. The coolant is pumped to the expansion tank and comes out of the clear tube into the immersion cup. The temp sensor is also immersed into the coolant cup to measure the temp. It should be the hottest point as it is coming from the vent hole just before it goes to the radiator.
Looks like the car sensor is reading too high.
-Slow fan on is aprox 82 deg C.
-Dip sensor shows 89 deg C.
-Ir temp measure at the engine block next to the water temp sensor is aprox 92 deg C. (this is kind of variable as moving the red dot even a little bit changes the reading. So I used the highest reading.
-Car gauge shows 100 plus deg C.



A closer look at the cup arrangement.



Sensor temp reading from the dip sensor in the cup 192.9 deg F or 89 deg C.



Car temp gauge reading.

[soxnail]

So after all that it was the the new sensor the car was never running hot. I had purchased from Summit racing fwiw...
To trouble shoot I tore open the old sensor and put a new sensor element in it. This gives an actual reading in Deg F out. Took the car for a long hard drive temperature never went over 183 F. (83.8 C). Which would be right at the first mark on the gauge.
Will send the sensor back.
For those who like to know the process:
First I took the old sensor apart, I used a dremel with a cutoff wheel to remove the brass retaining ring.





Then I cleaned out the old sensor housing, just used a drill press. With the housing cleaned and ready for reuse, I filled it with thermal compound (for better heat conductivity to the new sensor element).






Finally the finished unit.



temperature readings when the slow Fans came on.




The issue is that the car's gauge reads a very narrow band. The resistance of the sensor only has to be off by a couple of Ohms and it will read wrong.
If any one would like more details let me know.
Sox

[soxnail]

sitting at a traffic light with AC on, temp only went up to 187 F (86 C). Ambient was low for here about 78 F.
So waiting on the new VDO sensor to get here.
Sox

[soxnail]

Since I could not find any transfer equation or data on the water temp sensor, here is an empirical derivative for inquiring minds out there. R ohms on the X axis and Deg C on the Y axis.
Sox

[soxnail]

Better graph, also shows the read error in Deg C at battery voltage of 12.5v. With the car running and battery at 13.75v (because of alternator charging). The T diff is the difference about 1.82 Deg C at 0 Deg C to 3.69 Deg C at 115 Deg C.
Sox