engine heating up way too fast after thermostat housing replacement

[mikealex]

Hi, Been away from here for a long while! I have a suspicious engine temp problem. Looking for advice. The therostate housing was apparently cracked and just replaced by Midas along with a new thermostat. (yes, didn't do it myself) For 21 years, on first start of the day it takes about 4 minutes maybe for the engine temp to reach normal operating temp (about mid-dial). But now after repair, it's going the mid-dial in about 20 seconds. Way to fast to be believable. But it's staying there. It's not overheating. I have some supicions - (1) could the electrical connectors for the two temp sensors have been swapped maybe, and the gague is getting from the wrong sensor? or (2) could the thermostat have been put in backwards? or (3) could the rotation of the thermostat be wrong? or (4) could it be air in the system, or (5) just bad thermostat and it's not opening? Or something else that could account for this? Unfortunately I just left it overnight for them to look at it again, so I can't experiment with it just yet. But I'm not optimistic they'll believe there's anything wrong with it, so I got to plan on doing it.

 

[Uncle Gump]

Doubtful on connectors crossed... the temp sender is a single wire... ECT is a two wire.

Best to hook up a scan tool and monitor ECT to confirm what's on the gauge.

 

[Curious Hound]

Did they "fix" or change anything else? Do you have a heater bypass valve? Flow of coolant will change how the engine heats up and how the sensors see it. A pocket of stagnant water at the sensors will take longer to heat up. Water moving through the engine and past the sensors may show heating effects quicker. A stuck open thermostat would send coolant through the radiator all the time, thus slowing down the heating process, but making the sensors report more accurately due to the flow. Allowing flow through the heater core would cool coolant and allow slower engine warmup. But bypassing the heater does the opposite. A thermostat with a vent hole and "jiggle pin" allows a tiny bit of radiator flow and changes the dynamics a little bit. Of course, air pockets are also an issue. There are a lot of dynamics in play.

20 seconds to operating temp sounds abnormally fast.

 

[85_Ranger4x4]

Does it do get up to temp by just turning on the key without even starting the engine?
- If so you may have an electrical issue either with the sensor or wiring