Engine Temperature


 Ask Dave / Posted 2 years ago / 779 views

Question: – I just had our failed radiator and charge air cooler replaced. Our coach is a 2004 Patriot, 505hp C12. The new units are steel and aluminum construction.

At the time of install, I asked the CAT dealer to replace the thermostat as I do not believe it had ever been changed. The new thermostat was rated at 195 degrees. During the first drive after the new thermostat was installed, engine temps were steady at 193-195 with a minor rise pulling small hills. Please note outside air temp was 54 degrees.

Now here is the difference from the “usual” temps we had been seeing. The intake air temps described here are shown on the Silverleaf. Prior to the change the air intake temps would rise until the coolant temps reached about 192 degrees, then the fan kicked in lowering coolant temps to 188-190 and air intake temps fell to about 15-20 degrees above ambient air temps and stayed there. Now, the air intake temps rise until the coolant temp reach 197+/- then will fall to about 90 degrees which was 40 degrees higher than the ambient air temp. Air intake temps then modulated around 80-100 degrees regardless of the outside air temp.

Also prior to the thermostat change, transmission temps were normally around 180-190 after the coolant had reached full operating temps. Now, the transmissions temps seem to be steady around 210-215.

The fan operation was checked by CAT and checked out OK. Hydraulic fluid levels were good. Coolant levels (Rotella ELC) were good. Engine oil and transmission fluids all OK.

Is the new thermostat changing the actual coolant temps inside the radiator so much that it is affecting fan operation (controlled by the thermal valve)? Are the new temps I have described the “new normal”. Although the new “normal” temps are within normal operating ranges, the cooling characteristics are certainly different now. Are there any things I need to watch for?

Thanks in advance for your reply.

Rod Ogle

Dave’s Answer:
The thermostat opens at 191 degrees F and is full open at 206 degrees F. At times there will be different readings, but if it falls in that window you are OK.
Question, did you replace CAC cooler or did CAT send out and repair the old cooler. My reason for asking is we used to repair old coolers, but stopped that practice when repairs lasted a short time.
The standard policy now is to replace the CAC with new one. When you were running with your old cracked cooler there would have been some variance in engine temp.


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