Overheating Problem

[COramprat]

98 Cobra with a 96 motor. After coming up to operating temp it will be fine for about 10 minutes and then gets hot. On the datalog it got as high as 240. Doing between 60 and 65 at the time. As I came down to city speeds and stop and go it goes between 228 and 234. After about 25 minutes total driving it drops to around 218 for just a few minutes then comes back up to 235ish. Has a new thermostat, high and low fans seem to come on when they are supposed to.

 

[wmburns]

Can you explain HOW the air was purged from the cooling system?

 

[COramprat]

Kind of working on that now. I removed the crossover fitting and poured water/coolant in with the reservoir cap removed as well. Filled it up then started the car to allow it to get to temp. Low speed fan comes on as well as high speed during the wait. Hoses got hot so I'm pretty sure the thermostat opened. I made sure fill through the inlet as I gently bumped the throttle to push out air. Once it got to the point where coolant was forcing it's way out of the inlet, I closed it and took a drive. Reading from the datalogger it got up to 238 during a steady 60 mph run. Once I slowed to 45ish it would drop between 228 and 232. I let it cool overnight and filled it through the inlet this morning with about 1/4 gallon but didn't run it until he left for school. He took surface streets and said the temp never got over 235 but still kind of high. I'm going to try some more burping today.

 

[wmburns]

FWIIW, the DOHC motor is notorious difficult to bleed the air from the coolant crossover. The DHOC motor will not normally self purge over multiple heat/cool cycles like the SOHC will. The DOHC is so difficult to purge that often people resort to using vacuum filling systems.

Have you crossed checked the accuracy of the ECT sensor with anything else? For example an external temperature scanner?

Is the radiator clean (inside and out)? Are all air dams and fan shrouds in place?

FWIIW2, I believe the high speed fan turn on point is 220 degrees F. So being a few degrees above the HS fan kick on point should be considered within normal ranges.

What is the temperature that you think the motor is "hot"? I ask this because the coolant boiling point at 14 PSI should be around 260 degrees F.

https://durathermfluids.com/pdf/techpapers/pressure-boiling-point.pdf

 

[COramprat]

No external temp check other that the Predator. All shrouds in place. The radiator should be OK but I'm basing that on the function before we swapped the engine. The temps before the swap were fine so I'm assuming the temp sensors are OK as well.

The hottest point was 240 degrees read on the datalog. This put the gauge at the edge of "L" on "NORMAL".