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Temp drops when thermostat opens?
2002 F350 7.3, 145k. Running CAT ELC and a 203* tstat.
Its starting to get cold around here, and the truck sat overnight and all day without being started. This is the coldest its been that I've used the truck since I've owned it (only owned it for 3000 miles).
I plugged the block heater in about 2 hours before starting it this evening, and I fire it up and it starts right up (probably 20* out). After running for 3-5 minutes, I get outside and in the truck and the stock temp gauge is at full operating temperature. I thought this was weird, because its been taking forever for this thing to get up to temp since its been getting colder out - usually at least 5 minutes of idling and then 5 miles of driving.
I could hear the EBPV still closed while idling. I hopped in and started driving, and I can still hear the EBPV closed at light-to-no throttle - as soon as it gets over a little bit of throttle, it opens up, but as soon as I go back to light-to-no throttle, it closes and I can hear the hissing again - all while the temp gauge is still up to full operating temp.
After driving maybe ~5 miles (the usual time to get it warmed up fully), I look down at the temp gauge and it has moved DOWN to about 1/2 temp. It wasn't until after the engine started to reach full operating temp again that the EBPV hiss went away completely.
What's the deal, any thoughts? This is the first time I've used the block heater, so my theory is that the block heater was very effective in warming up the coolant in the block, so it showed full temp right away... then the thermostat opened, and all that coooold coolant rushed from the radiator and into the block, causing it to register less than full temp? Not sure if that makes sense though. Also, is the EBPV operation based on the EOT or the ECT (or both)? I thought it was weird that the EBPV stayed closed when the stock ECT gauge was at full temp, unless the block heater only heats the coolant in the block and not the oil in the pan, and the EBPV operates based on the EOT?