After startup, the engine runs idle for 3-4 minutes then the coolant temp reading in my data logger jumps about 100 degrees. It will go from 124 F up to 240 F in less than a second, but the console gauge is still showing below 150-160. This has been constant for the last two days. I’m checking the sending unit and will replace it this week if needed but I wanted to throw this out to see if anyone has run across this before. Thanks in advance.

Well after replacing the Radiator, Thermostat, Coolant Temp Sensor, Coolant Temp Sender, and all of the hoses (upper, lower and heater). I still had the problem.

I flushed the system twice. I still had the problem.

I then removed all of the hoses, thermostat, throttle body, all sensors/senders and then started flushing each section one at a time.

Finally after I hit the section where the temp sensor was with water & compressed air whatever was blocking it broke free and water started flowing. Unfortunately, I could never see or find the material that caused the blockage but now I know if I every see this type of symptom again I know where to start.

I put everything back together and now it’s running better than before so I guess it was worth it. It also gave me a chance to clean up a few things while I was in there.

I just wanted to post a follow up for everyone.

Later.

Thanks for the follow up, definatly makes sense that there was some sort of blockage or air pocket.